Hervé Bricout

Théodore Vanbésien

Muh-Mei Wei

Muriel Billamboz

Christophe Len

Eric Monflier

Frédéric Hapiot

Rh Catalyzed Hydroformylation of Divinylglycol: an Effective Way to Access 2,7-dioxadecalin-3,8-diol

Keywords: hydroformylation, biomass, homogeneous catalysis, ligand effects, regioselectivity

Obtained from glycerol, divinylglycol (DVG) is a promising bio-based building block. Upon hydroformylation of DVG, a very complex mixture of different products is obtained. Unexpectedly, addition of chloroform at 0°C on this mixture provokes the selective precipitation of 2,7-dioxadecalin-3,8-diol, an interesting bicyclic bishemiacetal.

Introduction

The development of bio-based platform chemicals has become a challenging task that has received considerable attention from the research community over the past decades. Countless publications and reviews have been recently published on the subject and describe the conversion of biomass into value-added platform molecules. [START_REF] Climent | [END_REF] From the four basic biomass components (cellulose, hemi-cellulose, lignin and triglycerides), a wide range of bio-based molecules is now accessible. Cellulose and hemicellulose [START_REF] Delidovich | [END_REF][3][4] produce bioethanol, [5][6][7] sugars, [8,9] HMF [10][11][12] and furfural derivatives [13,14] that can be further converted into levulinic acid [15] and -valerolactone. [16,17] Lignin offers phenols, eugenols and guaiacols. [18][19][20] Plant oils find application in polymer synthesis. [21] Triglycerides are of particular interest as they are usually converted into liquid alkanes, biodiesel, glycerol and fatty acids. [22,23,24] Designing a new class of bio-based platform molecules that have unique properties and support different functionalities within a single system is appealing. Recently, some of us developed an eco-friendly synthesis of hexa-1,5-diene-3,4-diol (divinylglycol = DVG) from glycerol. [25] Such bifunctional molecule opens up new perspectives as bio-based platform. As such, DVG already proved effective as building block in the synthesis of natural products [26][27][28][29][30][31] and polyenes. [32][33][34] DVG and derivatives are also actually used as a cross-linking agent and monomers for the production of polymers. [START_REF] Bader | Hydroxy alkylene ethers of divinyl glycol[END_REF][START_REF] Skochdopole | Process for the production of foamed cross-linked polymers[END_REF][START_REF] Michelin | Improvements in or relating to the production of polyurethane elastomers[END_REF][START_REF] Stogryn | Divinyl ethylene oxide[END_REF] The conversion of the biomassderived products is usually achieved either by classical organic reactions or under catalytic conditions. [39] Although heterogeneous catalysis is the most widespread technique to convert bio-based chemicals, [START_REF] Suib | New and Future Developments in Catalysis, 1st Edition, Catalytic biomass Conversion[END_REF][START_REF] Verma | [END_REF] homogeneous catalysts have emerged as a promising alternative. [43] For example, hydroformylation appears as one the most effective catalysed reaction as it is atom economic and provides aldehydes as useful intermediates. [44,45] Our team recently showed that triglycerides can be directly functionalized at their carbon-carbon double bonds to form valuable compounds through hydrohydroxymethylation (HHM) [46] or hydroaminomethylation (HAM). [47][48] The present study sought to address the use of a rhodium-catalyst to convert DVG into a series of DVG derivatives under hydroformylation conditions. Hydroformylation of C4 and C5 substrates comprising terminal hydroxyl group has already been described in the literature. [49] The C=C bond undergoes hydroformylation and subsequently cyclizes into five-or six-atoms rings. However, to our knowledge, nothing has been described so far on the hydroformylation of bifunctional DVG. Here, we especially focus our attention on the catalytic hydroformylation of DVG, which significantly extends the scope of renewables as platform chemicals.

Results and Discussion

Let us first focus on the theoretical reactivity of DVG under hydroformylation conditions. As hydroformylation can take place either at the terminal and internal positions of the carbon-carbon double bonds, a wide range of products can be formed (Scheme 1). Upon hydroformylation, both linear (L) and branched (B) aldehydes are accessible if only one of the two carbon-carbon double bond of DVG reacts. The studied DVG consists of a 50/50 mixture of dl and meso (also denoted m in the following study) diastereoisomers because of the presence of two identically substituted stereocenters. Hence, the L aldehyde can exist as a mixture of two couples of enantiomers and the B aldehyde comprises four couples of enantiomers. Each aldehyde can then undergo cyclisation reactions resulting from the nucleophilic addition of the hydroxyl group. Cyclisation of B can give the hemiacetal B5 (cycle derived from B consisting of five atoms, mixture of eight couples of enantiomers). Note that the hydroxyl group at position 3 with respect to the formyl group cannot react as a too unstable four-atoms ring would be formed. Conversely, L can lead to two cyclic hemiacetals L5 and L6 consisting of five and six atoms, respectively. Each product is a mixture of four couples of enantiomers. Concurrently to cyclisation reactions, L and B can also be subjected to hydroformylation of the remaining C=C bond. As hydroformylation produces branched and linear aldehydes, three different dialdehydes can be formed. B leads to BB (mixture of two m stereoisomers + four couples of enantiomers) and BL (= LB, four couples of enantiomers). BL can also be formed upon hydroformylation of L concurrently to LL (mixture of one m + one dl). Further cyclisation of BB, BL and LL can produce ten cyclic hemiacetals consisting of one or two cycles comprising five or six atoms. Each of them exists as a mixture of m stereoisomers and/or enantiomers. For example, B5B5 consists of six stereocenters and potentially possesses 2 6 stereoisomers. However, the symmetry of the molecule greatly reduces the number of possible stereoisomers to thirty-six (four m stereoisomers + sixteen couples of enantiomers). The detailed procedure to calculate the number of possible stereoisomers is given in SI considering B5B5 as an example (Table S1). In our study, hydroformylation of DVG is carried out using Rh(CO)2(acac) (acac = acetylacetonate) as a catalyst precursor (C=C double bonds/Rh = 250) under CO/H2 pressure (25 bar) at 80 °C in diethyl ether over a period of 18 h. The reaction conditions have been chosen to ensure total conversion of the carbon-carbon double bonds and facilitate the identification of the products. Note that full conversion of alkenes into aldehydes could also be obtained by reducing the CO/H2 pressure to 5 bar or using a substrate/Rh molar ratio of 7500. To limit the formation of branched aldehyde and selectively orient the reaction towards linear aldehydes, Xantphos is selected as a ligand. In its presence, hydroformylation of DVG should mainly furnish the LL dialdehyde and small proportions of BL. The absence of signal in the 9-10 ppm region on the 1 H NMR spectrum of the crude reaction products clearly indicates that no aldehyde is present in the mixture (Fig. 1a). Thus, in solution, the equilibriums are shifted from the open LL and LB forms to the corresponding bicyclic structures B5L6, L5L5, and L6L6. As explained previously, these bicyclic structures exist as mixtures of meso stereoisomers (except for B5L6) and couples of enantiomers. All the possible stereoisomers for B5L6 and L5L5 are gathered in SI (Fig. S1 and S2, respectively). We focused our attention on L6L6 (two meso stereoisomers + four couples of enantiomers but sixteen possible spatial structures because of ring-flipping). The junction between the two fused cycles of L6L6 is either cis or trans, similarly to what is observed for decalin (3 out of 16 possible structures of L6L6 are displayed as examples in Fig. 1). As hydroxyl groups can be either in equatorial or axial position, there are four different stereoisomers for R,S-L6L6 (resulting from R,S-DVG, i.e. meso-DVG) and twelve different possibilities for R,R-L6L6 and S,S-L6L6 (L6L6 resulting from dl-DVG) (SI, Fig. S3-S6). The mechanism by which all these stereoisomers are formed is detailed in SI (Fig. S6). At this stage, the attribution of all the signals of the intricate 1 H spectrum displayed in Fig. 1a is a very delicate task. Unexpectedly, addition of CHCl3 (5 mL for 3.5 mmol (0.4 g) of initially added DVG) at 0 °C on the resulting oil (crude product) obtained after evaporation of diethyl ether provokes the selective precipitation of the diastereoisomer 1 of L6L6 resulting from the meso-DVG (Fig. 1). [START_REF] Gerber-Lemaire | In Anomeric effects in pyranosides and related acetals[END_REF]51] Its NMR spectrum allows attribution of all protons of this isomer (Fig. 1b) by comparison with previous data from Burton [52] and Pomin. [START_REF] Pomin | Unravelling Glycobiology by NMR Spectroscopy[END_REF] Both teams show preferential formation of six-membered ring derivatives over five-membered ring ones. Hydroxyl protons a1 are detected at 6.09 ppm (d, J=3.9 Hz) while the signal at 5.01 ppm is attributed to anomeric protons b1. Protons e1 attached to bridgehead carbons are also clearly identified at 3.54 ppm and the remaining alkyl protons c1 and d1 resonate at 1.64 ppm and 1.49 ppm. Interestingly, subsequent addition of CHCl3 (5 mL) causes the precipitation of a mixture of diastereoisomer 1 of L6L6 and another product (Fig. 1c). The latter can be identified by Rh-catalyzed hydroformylation of a sample of pure R,R-DVG (SI, Fig. S17) which was selectively obtained from chiral D-mannitol using a protection/deprotection sequence. [START_REF] Schmidt | [END_REF] The only possible products resulting from hydroformylation of R,R-DVG before the equilibriums take place are 6 chiral structures of L6L6 (SI Fig. S6), among which four structures are characterized by a C2 symmetry. The new peaks detected in Fig 1c were attributed to stereosiomers dl-2 of L6L6 featuring their OH groups in axial positions (protons a2-e2). The reason why these stereoisomers precipitated selectively while other isomers remained in solution probably lies in their lower syn 1,3-diaxial interactions, as explained in SI (Fig. S7). Other signals are also detected in Fig. 1a. The attribution of some of them is deduced from an aging test carried out with a solution containing diastereoisomer 1, which rapidly epimerizes into diastereosiomer dl-1' (protons a1'-e1' and a1'*-e1'*, Fig. 2). Further epimerization affords the more thermodynamically stable 1" via dl-1' (protons a1"-e1", Fig. 2) (55% of axial hydroxyls became equatorial within 48 h). The remaining signals of Fig. 1a are relative to L5L5 and B5L6 (SI, Fig. S8). The presence of B5L6 is especially revealed by the signals at 1.0-0.8 ppm attributed to methyl groups. Hence, although Xantphos is used as a ligand, a small fraction of branched isomer is formed during the course of the hydroformylation reaction. Integration of the signal attributed to the methyl of B5L6 and comparison with L5L5 and L6L6 protons lead to a 92:8 linear/branched derivatives ratio. Yields are determined from the gathered fractions of L6L6 resulting from the precipitation procedure (SI). Note that high proportions of branched derivatives in the mixture prevents precipitation of L6L6, thus highlighting the need to achieve high selectivity in linear derivatives. Note that the 13 C spectrum of L6L6 (SI Fig. S28) confirmed the presence of two carbons at the junction of two six-membered rings characterized by chemical shifts <76 ppm, as exemplified by Burton et al. [52] Carbons at the junction of two five-membered rings would have been more deshielded.

To further increase the proportion of linear aldehyde derivative L6L6, a series of experiments have been implemented using other ligands (see SI, Fig. S18 for ligand structures). The selectivity in linear and branched derivatives is not significantly influenced by monophosphines with different Tolman's cone angle  (Table 1, runs 1 and 2). Indeed, utilization of PPh3 (=145°) or P(OPh)3 (=128°) give similar results. [55] Conversely, the selectivity in linear and branched derivatives strongly depends upon the bite angle of diphosphines. [56,57] Generally speaking, bidentate ligands featuring bite angle around 120° are predestinated to adopt an equatorial-equatorial configuration upon coordination on rhodium, resulting in the predominant formation of linear aldehydes. Oppositely, bidentate ligands with bite angle close to 90° adopt an apical-equatorial configuration upon coordination on rhodium, resulting in the preferred formation of branched aldehydes. Accordingly, diphosphines featuring high bite angles such as Xantphos (=112°), 56 Nixantphos (=114°), [58] BISBI (=123°), [56] and Biphephos (=123°) [59] provide the best linear/branched ratios (up to 96:4) (runs 5-8). Note that DBFphos (=131°) presents a poor selectivity for linear aldehyde derivatives (l/b = 67:33) because its too high bite angle prevents the formation of chelates (run 9). [60] The best yield in L6L6 is obtained using Biphephos as ligand (run 8). Hence, Biphephos is the most effective ligand in terms of both selectivity and yield in the hydroformylation of DVG.

Table 1. Rh-catalyzed hydroformylation of DVG. [a] Run Ligand Bite angle/° Conv. C=C/% l/b [b] L6L6 Yield (%) [c] 1 TPP [d] -100 72:28 42 2 P(OPh)3 [d] -

Conclusions

In conclusion, this study provides compelling evidence that DVG can be easily hydroformylated into the bis-hemiacetal L6L6 consisting of two fused cycles (2,7-dioxadecalin-3,8-diol). The selectivity of the Rh-catalyzed hydroformylation reaction is mainly controlled by the nature of the metal-stabilizing phosphine. Diphosphines featuring high bite angle such as Biphephos prove to be appropriate to orient the reaction towards the expected bicyclic hemiacetal L6L6 displaying less strained six-membered rings. Interestingly, selective precipitation of L6L6 in chloroform displaces the equilibriums and improves the L6L6 yield.

Experimental Section

General procedure for hydroformylation

In a typical catalytic hydroformylation, Rh(CO)2(acac) (0.014 mmol, 1 equiv.) was degassed three times by vacuum-N2 cycles and dissolved in a degassed solution of ligand (0.07 or 0.14 mmol, 5 and 10 equiv. for bidentate and monodentate ligands, respectively) in diethyl ether (15 mL).

Scheme 1 .

 1 Scheme 1. Possible products resulting from Rh-catalyzed hydroformylation of DVG.

Figure 1 .

 1 Figure 1. 1 H spectra of a) the crude mixture, b) diastereoisomer 1, and c) a mixture of diastereoisomers 1 and dl-2 of L6L6 in DMSO-d6 at 25 °C (300 MHz).

Figure 2 .

 2 Figure 2. Aging test carried out with a solution of with a solution of diastereoisomer 1 in DMSO-d6 at 25 °C a) initial 1 H NMR spectrum, b) after 2.5 h at 25°C c) after 24 h at 25 °C (300 MHz).

  The resulting solution was stirred at room temperature for 2 h. A mixture of R,R-DVG, S,S-DVG and R,S-DVG (25/25/50, 3.5 mmol, 250 equiv.) was poured into the 25 mL autoclave equipped with a mechanical stirrer and N2-purged. The catalytic solution was then cannulated under nitrogen into the autoclave. Once the desired temperature was reached, the autoclave was pressurized under CO/H2 (1:1) pressure (typically 25 bar) and the solution was vigorously stirred (2500 rpm) at 80 °C. After 18 h, the apparatus was cooled down to room temperature and depressurized. The solvent was evaporated giving an orange oil. L6L6 was isolated by successive addition of CHCl3 at 0 °C, precipitation and filtration (SI). The products were analyzed by 1 H and 13 C NMR experiments. All runs were performed at least twice in order to ensure reproducibility.

Acknowledgments

This work was performed, in partnership with the SAS PIVERT, within the frame of the French Institute for the Energy Transition (Institut pour la Transition Energétique (ITE) P.I.V.E.R.T. (www.institut-pivert.com) selected as an Investment for the Future ("Investissements d'Avenir"). This work was supported, as part of the Investments for the Future, by the French Government under the reference ANR-001-01.


Laurianne Paris

Mathilde Dutaut

Sylvain Coly

David Foltier

Benoît Gire

Marianne Coulon

Antoine Thouvenot

Delphine Latour

Benjamin Legrand

Effect of water temperature on a phycocyanin probe for monitoring cyanobacteria and its effectiveness on biomass estimation of three cyanobacteria morphotypes

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Effect of water temperature on a phycocyanin probe for monitoring cyanobacteria and its effectiveness on biomass estimation of three cyanobacteria morphotypes

Laurianne Paris 1 , Mathilde Dutaut 2 , Sylvain Coly 2,3 , David Foltier 2 , Benoît Gire 2 , Marianne Coulon In a context of global warming and high anthropization of freshwater systems, cyanobacteria monitoring becomes a key priority. Thus, water companies have recently deployed large-scale submersible fluorescence sensors, capable of measuring diagnostic pigments and estimating cyanobacteria biomass in near-real time. However, these tools have several limitations, such as the detection limit of phycocyanin or the impact of temperature, one of the most important factors generating a bias on the measurement of phycocyanin probes. In an attempt to address these shortcomings, we compared the efficiency of a phycocyanin probe at different temperatures, first on three cyanobacteria cultures (Microcystis, Dolichospermum and Synechocystis) and secondly on a small eutrophic lake in continuous recording.

The in vitro results showed a high correlation between cyanobacterial biomasses, estimated by flow cytometry (Microcystis and Synechocystis) or by microscopic counting (Dolichospermum), and phycocyanin probe measurement, with R² higher than 0.96, even for biomasses lower than hundreds of mm 3 .L -1 . A saturation effect was demonstrated only between 350 and 550 mm 3 .L-1 depending on the strains, corresponding to very high concentrations, far from the limit value for the use of water.

However, laboratory tests on temperature highlighted the limitations of the sensor with a strong overestimation and underestimation at low (< 15 °C) and high (> 25 °C) temperatures, respectively.

Given this discrepancy, a temperature correction factor was determined and applied over the three years of field data, which significantly improved the signal quality. The strong relationship found between the corrected signal and the cyanobacteria biovolume obtained by microscopic enumeration allowed us to validate this temperature correction factor, offering the possibility of using it for monitoring other lakes and to better understand the short-term dynamics of cyanobacteria. Keywords: Cyanobacteria; Probe sensor monitoring; Phycocyanin; Temperature; Picocyanobacteria


Sofiane Amziane

Chafika Djelal

K El-Cheikh

Faber Fabbris

Shirin Fataei

Dimitri Feys
email: feysd@mst.edu

Markus Greim

Irina Ivanova

Helena Keller

Kamal Khayat

Mohammed Sonebi

Khadija Elcheikh

Laurent Libessart

Viktor Mechcherine

Ivan Navarrete

Arnaud Perrot

Egor Secrieru

Yannick Vanhove

May 2018

Keywords: Concrete, flow curve, interface, rheology, structural build-up

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Research on rheology of cement-based materials has been ongoing for over half a century [1], but it has known a more recent boom with the introduction of self-consolidating concrete (SCC) and other highly flowable mixtures, and more recently 3D printing. Concrete rheometers before roughly the year 2000 were instruments with complicated flow patterns where particle sedimentation and shear-induced particle migration constituted major artefacts that can affect the assessment of rheological properties [1]. Since the introduction of SCC, rheometer design has been simplified with "simple geometries" used in new instruments, inspired from conventional rheometry. In the early 2000s, two experimental campaigns were undertaken to compare different concrete rheometers: the first in Nantes, France and the other in Cleveland, OH, United States [START_REF] Ferraris | Comparison of concrete rheometers: international test at LCPC[END_REF][START_REF] Ferraris | Comparison of concrete rheometers: International tests at MB[END_REF]. These campaigns focused on different concrete types, including a limited number of SCC mixtures, evaluated in commonly used rheometers at that time. However, since then, many new devices have been developed and refined. In addition, knowledge and awareness of measurement errors, such as structural breakdown, plug flow and shearinduced particle migration, has increased. The RILEM TC MRP (Measuring Rheological Properties of Cement-based Materials) organized a new campaign in Bethune, France in May 2018 to evaluate the rheological properties of different mortar and concrete mixtures. This paper describes the various rheometers employed during the testing, the mixtures, the testing procedures and the data analysis.

Rheometers

The various devices employed during the Round-Robin tests are shown in Figure 1. A short description of each rheometer is provided below.

ICAR

The ICAR rheometer is a portable device, composed of a container, a driver, a four-blade vane and a frame [4]. The container is equipped with vertically protruding ribs to prevent slippage. Two types of tests can be performed: a stress growth test and a flow curve test. In the stress growth test, the vane is rotated at a constant slow speed and the maximum torque measured during this test is used to calculate the static yield stress. For flow curves, the torque is plotted versus rotational velocity of the vane, allowing the calculation of the Bingham parameters (dynamic yield stress and plastic viscosity).

Viskomat XL

The Viskomat XL rheometer is designed for stationary measurements of fresh mortar and concrete with maximum particle size of up to 16 mm. It is based on the Couette principle and can be operated with probes with different geometries. The measurement profiles can be freely defined using the wide dynamic speed range from 0.0001 to 80 rpm. Due to the high resolution and a broad torque range from 0 to 10 Nm, fresh concrete with different rheological properties can be characterized. For the investigation of other materials properties, such as visco-elastic properties of the material, Shear Stress Control mode and an Oscillation Mode can be used [START_REF] Greim | Oscillation Shear Measurements of SCC with a Couette Type Rheometer. 3 rd Iberoamerican conference on self-compacting concrete[END_REF][START_REF] Greim | Measurement of concrete rheology (in Spanish)[END_REF]. For the round-robin test measurements, a six-bladed vane probe was used.

eBT-V

The mobile rheometer eBT-V from Schleibinger Geraete GmbH is a compact battery driven rheometer specially designed to determine the rheological properties of fresh mortar and concretes with maximum particle size of up to 32 mm [START_REF] Greim | Measurement of concrete rheology (in Spanish)[END_REF][START_REF] Greim | eBT-V -A new rheometer for fresh concrete[END_REF][START_REF] Keller | A portable rheometer for fresh concrete -Concrete requirements[END_REF]. The eBT-V has two builtin sensors and can be operated in two different methods: V-mode for modern concretes such as SCC, or ultrahigh performance concrete (UHPC); and P-mode for conventional vibrated and very stiff or no-slump concrete. The measurement profiles are freely programmable and can be adjusted to the rheometer configuration used and the mixture to be measured. For the measurements, the eBT-V in V-mode with the six-bladed vane geometry was used. The vane probe is attached to the drive shaft of the rheometer and was immersed into the concrete together with the device holder containing rods to prevent the wall slippage during the measurement.

Rheocad

The RheoCAD500 device imposes a rotation speed to an inner cylinder tool, submerged into a container with the sample, and measures the resulting torque. During this study, two tools were used: the helical screw and the vane. The concrete is placed in a cylindrical container of 300 mm of diameter and 350 mm of height. This container contains a cage to prevent any slipping. The torque sensor has a capacity of 1000 Ncm and the speed can reach 250 rpm. For the vane tool, the Reiner-Riwlin equations allow to determine yield stress and plastic viscosity in Pa and Pas (assuming Bingham behaviour), respectively. For the helical tool, the device gives the variation of the torque (in N.cm) according to the rotational velocity.

BML Rheometer 4SCC

The Rheometer-4SCC is a portable rheometer for SCC developed by OH Wallevik at the Icelandic Building Research Institute (IBRI) [START_REF] Wallevik | Rheometer-4SCC, a Portable Rheometer for Self Compacting Concrete[END_REF][START_REF] Wallevik | Rheometer-4SCC used as a stability meter for SCC[END_REF]. It is capable of determining the yield stress and plastic viscosity of concrete mixtures with yield stresses ranging from 5 Pa to 120 Pa, plastic viscosities ranging from 5 Pas to 120 Pas, and maximum aggregate sizes of up to 22 mm. The Rheometer-4SCC consists of a control box and measurement unit. The control box and measurement unit are each less than 25 kg, which makes the device suitable for quality-control measurements at both building sites and in laboratories [START_REF]Report on Measurements of workability and rheology of fresh concrete[END_REF]. Two geometries were employed: a mixer-type of device and a cylinder inspired by the Tattersall Mk-II rheometer. Due to the lack of equations to obtain fundamental units, the ConTec Rheometer 4SCC software provides flow resistance results (driver electric intensity that can be linked to the torque) in mA.

Plate test

The plate test consists of measuring the mass variation of a rough tool (plate or cylinder) immersed in a fresh cement-based material with time [START_REF] Amziane | A novel settling and structural build-up measurement method[END_REF] and was adapted for SCC [START_REF] Perrot | SCC formwork pressure: influence of steel rebars[END_REF][START_REF] Amziane | The plate test carried out on fresh cement-based materials: How and why?[END_REF]. This device was initially developed to enable a simple measurement of the evolution of yield stress with time or the structuration rate. The apparent mass of the immersed tool or the apparent mass of the sample is continuously monitored (recorded every 5 seconds during one hour). During the tests, the mortar or concrete was placed in a 1.5 m high and 200 mm in diameter column. The tool was a steel rebar (d = 150 mm, l = 130 mm) for the concrete mixtures and a screw (d = 14 mm, l = 80 mm) for the mortar mixtures, in order to adjust the tool's roughness to the size of the largest particles [START_REF] Amziane | The plate test carried out on fresh cement-based materials: How and why?[END_REF].

Sliper (Sliding Pipe Rheometer)

The Sliper was developed by Kasten [START_REF] Kasten | Sliding Pipe Rheometer -A method to establish the flow properties of high viscous media in pipelines[END_REF] and is produced by Schleibinger Geräte GmbH. It allows a quick assessment of the pumping characteristics of concrete and other materials in the laboratory and on-site. The device enables to establish a relationship between pressure (P) and flow rate (Q) results. Although the formation of the lubrication layer is not measured directly, it influences the P-Q results and hence can be indirectly measured by the Sliper. The Sliper was successfully applied for both stiff and highly flowable concretes [START_REF] Mechtcherine | Testing pumpability of concrete using Sliding Pipe Rheometer[END_REF][START_REF] Secrieru | Pumping behaviour of modern concretes -Characterisation and prediction[END_REF]. Further details on the measuring procedure and limitations are available in [START_REF] Secrieru | Pumping behaviour of modern concretes -Characterisation and prediction[END_REF]. In the study at hand, the prediction of P-Q relation was compared with the analytical approach based on the tribometer measurements according to [START_REF] Kaplan | Design of concrete pumping circuit[END_REF].

Interface rheometer on ICAR

To evaluate the interface properties of concrete near a smooth surface, the vane of the ICAR rheometer was replaced by a smooth cylinder, 125 mm in diameter and 200 mm in height. The bottom has a conical shape to facilitate insertion in the concrete. This interface device enables the calculation of the lubrication layer properties yield stress and viscous constant, according to the procedure described in [START_REF] Feys | Development of a tribometer to characterize lubrication layer properties of self-consolidating concrete[END_REF], which can be used to analytically predict pressure with the equations in [START_REF] Kaplan | Design of concrete pumping circuit[END_REF].

Tribometer

The tribometer aims to mimic the friction between concrete and formwork. The principle is as follows [20]: an auger coupled to a motor moves, at various speeds, an interchangeable plate between two concrete samples. The concrete samples are pressurized between 50 kPa and 1000 kPa. The sample holders are cylinders fitted with a hatch for introducing the concrete. A tension sensor tied to the plate measures the tangential friction stresses [START_REF] Djelal | Analysis of friction and lubrification conditions of concrete/formwork interfaces[END_REF]. Tests were conducted on a plate cut from a formwork wall with roughness value Ra = 1.07 µm. The plate displacement speed of 3 m/h (0.84 mm/s) corresponds to the casting speed of concrete in a formwork. The contact pressure of the selected jack corresponds to the concrete pressures exerted at the formwork base for a given height. Pressure values between 50 kPa to 150 kPa have been evaluated, corresponding to concrete heights between 2 m and 6 m.

Mixtures

Over the two-day testing campaign, eight mixtures were evaluated. All mixtures were prepared in a nearby concrete batching plant. In the case of some mortar mixtures, admixture dosages were adjusted on-site to ensure that the workability of the mixture was within the requested target range. Five wheelbarrows were sampled for rheological and workability testing.

Concrete mixtures

The first day consisted of measuring the properties of three SCC mixtures and two highly flowable concrete mixtures intended for foundation construction. Concrete 1 was a reference SCC mixture containing a Type III/A cement (EN 197) and limestone filler as powder materials, and a maximum aggregate size of 12 mm. The target slump flow of SCC 1 was 550-650 mm. Concrete 2 had the same mixture proportioning as concrete 1, except for a higher HRWRA content to increase the target slump flow to 650-750 mm. Concrete 3 was a highly viscous SCC, containing 50 l/m 3 less water than concrete 1, with a target slump flow of 550-650 mm. The cement content in the powder was increased, and the maximum aggregate size was 20 mm for concrete 3. Concretes 4 and 5 are typical mixtures for concrete foundations that have lower powder contents compared to the three SCC mixtures. These were produced with a maximum aggregate size of 12 mm. The admixture combinations were altered between mixtures 4 and 5 to create a less flowable and more cohesive nature for the latter mixture. It should be noted that the team chose not to evaluate any conventional concrete mixtures to avoid the issue of extensive plug flow.

Mortar mixtures

On the second day of the campaign, three mortar mixtures were evaluated. The idea behind testing mortar mixtures in concrete rheometers is to reduce the influence of shear-induced particle migration. However, the mixtures had to be sufficiently stiff or sticky to ensure adequate response of the load cells in the rheometers. The mortars were produced with a Type I 52.5 cement and a limestone filler. Mortar 1 was a reference mixture, mortar 2 was a mixture with high viscosity and low yield stress, while mortar 3 was intended to have a (relatively) high yield stress and low viscosity. None of the mixtures were air-entrained.

Reference material

During the course of the testing campaign, the ICAR rheometers, BML with modified Mk-II configuration and the Viskomat XL were used to evaluate the rheological properties of the NIST reference material. This material consists of a mixture of corn syrup, limestone filler and water to mimic a Bingham-like paste. Glass beads with 1 mm diameter were used as fine aggregate to simulate mortar, and other beads with 10 mm diameter were added to create an artificial concrete. The reference material was only used to evaluate flow curves.

Testing methodology

In contrast to the previous comparison campaigns, different properties were evaluated with different devices. Flow curves, static yield stress values and interface properties were evaluated at each time. The following sections describe how each of these properties were determined.

Flow curves

Flow curves were determined by decreasing the rotational velocity, stepwise, from the maximum to the minimum imposed rotational velocities. Each flow curve contained seven or eight steps of 5 s duration each (except for one ICAR rheometer). Each flow curve was preceded by a 20 s (concrete) or 30 s (mortar) preshear period at the highest rotational velocity (except for one ICAR, where the pre-shear was 60 s). However, the rotational velocities were different for each rheometer. Although this sounds counter-intuitive for a comparison, one of the reasons why different rheometers may give different results is the applied shear rate. As geometries are different, the shear rate in each rheometer will be different if the same rotational velocity is imposed. Instead, the rotational velocities were adjusted theoretically to ensure that an approximately constant shear rate was imposed across the different rheometers in use.

Static yield stress

Static yield stress values were determined by evaluating the peak torque at a low rotational velocity in each rheometer. Static yield stress tests were executed with a 30-min interval to determine and compare the structural build-up of each mixture. The computed values of structural build-up are compared with the results obtained using the plate test.

Interface properties

The interface properties were calculated according to the procedures developed for each device. No procedure could be standardized, as all three rheometers have different modus operandi. The comparison between the devices can be made by predicting the pressureflow rate relationship in a pipe with the results from each equipment separately.

Fresh concrete tests

The fresh concrete mixtures were evaluated for temperature, slump or slump flow, T50 (if possible), air content, density, L-box, J-Ring and V-Funnel flow time. In addition to the standard slump cone, several smaller cones were utilized for the mortar flow testing.

Timeline

Table 1 shows the timeline of tests for each mixture. All times are relative to the first tests executed. All rheometer tests were started at exactly the same moment. In between tests, the rheometers were emptied, cleaned and prepared for the next tests. When static yield stress tests were executed, the sample was left undisturbed until after the 40 min test.

Analysis steps and challenges

At the writing of this paper, data analysis and comparison of the results of the different rheometers are still underway. However, to ensure that all data can be compared, the following analysis steps were enforced, as described below.

Flow curves

The flow curves are perhaps the most critical to evaluate, as many measurement errors need to be taken into consideration. For each test, the following procedure was followed: Zero measurement to evaluate the residual torque before the introduction of the test material.

Determination of equilibrium at each rotational velocity step. Steps with decreasing torque trends during the measurement interval or extreme fluctuations of data are not considered in the analysis. Preliminary calculation of yield stress and plastic viscosity by means of the Reiner-Riwlin equation, if the rheometer configuration can be approached as concentric cylinders (vane geometry). Verification of plug flow, and iterative calculation of yield stress and viscosity by taking reductions in the sheared domain into consideration. Estimation of the thickness of the sheared zone: if this zone is smaller than the maximum aggregate size, the measurement is certainly invalid. This analysis procedure ensures that measurements errors caused by structural breakdown and plug flow are eliminated from the measurements. Shear-induced particle migration is more difficult to assess, but mixtures with very small sheared zones have probably undergone shear-induced particle migration. However, it is uncertain whether no shearinduced particle migration is present in each of the tests. The expected outcome of this analysis step are the yield stress and viscosity values for each rheometer tests. Ongoing analysis evaluates the correlation between each rheometer and the average, as well as an identification of outliers and any reason why certain points could be outliers.

Static yield stress tests

For the static yield stress tests, the analysis is somewhat less complicated. The zeromeasurement remains important to correct measured torque values. The static yield stress values are determined by dividing the peak torque value by 2 π Ri 2 h, in which Ri and h are the radius and height of the inner cylinder in the rheometer, respectively, in case of a rotational rheometer. It can be noted that the shear surface located underneath the vane tool is neglected. Based on the 10 and 40 min data, thixotropic indices can be calculated, according to different strategies in literature [e.g . 22]. The analysis will be focused on the calculated indices, rather than the individual static yield stresses.

Interface tests

Each interface rheometer has its own procedure to analyze the data, so no uniform strategy was established. However, each device enables the calculation of a pressure-flow rate relationship for flow inside a pipe. This strategy will be employed to compare the different interface devices.

Concluding remarks and outlook

A new testing campaign compared the output of different concrete rheometers, being several ICAR rheometers, Viskomat XL, eBT-V, Rheocad, BML 4SCC, Sliper, plate test, and tribology tests. The tests were carried out on three SCC mixtures, two highly flowable concrete mixtures for foundation construction, and three mortars. Significant variations in yield stress, viscosity and thixotropy were induced by variations in the mix designs. The testing procedures were adjusted to ensure that each rheometer imposed approximately the same shear rate on the materials. Flow curves, structural build-up, and interface properties were evaluated. Attention was paid to potential sources of errors in the analysis. With the results, the research team will draw comparisons between rheometers, analyze outliers, investigate the validity of the measurements and potentially identify critical combinations of mix design parameters and rheological properties that can compromise the correct assessment of the characteristics of the materials.

1 .

 1 a) ICAR Rheometer b) Viskomat XL Rheometer c) eBT-V Rheometer d) Rheocad Rheometer e) BML Rheometer 4SCC f) Plate Test Method g) SLIPER Rheometer h) Interface tool for ICAR i) Plane/Plane Tribometer Figure Rheometers evaluated during the round-robin testing program.

Table 1 .

 1 Timeline of tests. FC = flow curve, YS = static yield stress, IF = interface properties.

	0

min 10 min 20 min 40 min 50 min 60 min 80 min ICAR 1

	Plate test		Continuous structural build-up measurement
	Fresh concrete tests	Yes			Yes	Yes
		Vane	FC	YS	YS	FC	FC
	ICAR 2	Vane	FC	YS	YS	FC	FC
	ICAR 3	Vane	FC	YS	YS	FC	FC
	ICAR 4	Vane	FC			FC	FC
		Cylinder		IF		IF
	eBT-V	Vane	FC	YS	YS	FC	FC
	Viskomat XL	Vane	FC	YS	YS	FC	FC
	Sliper			IF		IF
	Rheocad	Vane	FC	YS	YS		FC
		Helix				FC
	BML 4SCC	Mod. MK-II				FC
		Mixer	FC				FC
	Tribometer			IF

Acknowledgments

The authors would like to acknowledge EQIOM for the production and delivery of the desired concrete mixtures, as well as the technical staff and undergraduate students at the Université d'Artois for their valuable assistance. Special appreciation goes to Drs. Yannick Vanhove and Chafika Djelal for the organization and dealing with all logistic demands going into this testing campaign.


M Chevry

S Menuel

B Léger

S Noël

E Monflier

F Hapiot

Hydrogenation of hydrophobic substrates catalyzed by gold nanoparticles embedded in Tetronics/cyclodextrin-based hydrogels

Hydrogenation of alkenes, alkynes and aldehydes was investigated under biphasic conditions using Au nanoparticles (AuNP) embedded into combinations of -cyclodextrin (-CD) and poloxamines (Tetronics®90R4). Thermo-responsive AuNPcontaining -CD/Tetronics®90R4 hydrogels are formed under well-defined conditions of concentration. AuNP displayed an average size of ca. 7 nm and a narrow distribution, as determined by TEM. The AuNP/-CD/Tetronics®90R4 system proved to be stable over time. Upon heating above the gel-to-sol transition temperature, the studied catalytic system allowed hydrogenation of a wide range of substrates such as alkenes, alkynes and aldehydes under biphasic conditions. Upon repeated heating/cooling cycles, the Au NP/-CD/Tetronics®90R4 catalytic system could be recycled several times without significant decline in catalytic activity.

Introduction

Since the emergence of synthetic catalysts during the 19 th century, the search for effective catalytic systems have been receiving great attention. Although significant progresses have been made in terms of catalytic activity and selectivities, efforts should still be made to both recover and recycle the catalyst once the reaction is complete. During the past twenty years, we have been developing catalytic systems capable of ensuring high catalytic performance and reusability of organometallic or metallic catalysts. [1][2][3] Most of our strategies rely on cyclodextrins (CDs) which are cyclic oligosaccharides consisting of glucopyranose units linked by -D-1,4glycosidic bonds (Fig. 1). 4 Among the latest developments, one of our idea is to benefit from the ability of -CD (6 glucopyranose units) to form thermoresponsive hydrogels by inclusion of organic molecules or polymer chain within their hydrophobic cavity. 5 At room temperature, such hydrogels are in the gel phase wherein they can efficiently stabilize organometallic and nanoparticle catalysts. When they are heated beyond their gel-to-sol transition temperature, the catalyst-containing gel phase turn into a sol phase. Upon stirring of the resulting catalyst-containing sol phase and a liquid organic substrate, the latter is converted into the corresponding product. Once the reaction is complete, the system is cooled down below the gel-to-sol transition temperature. The hydrogel returns to the gel phase and the catalyst and the product are easily recovered separately in two different phases.

The concept has been developed for several applications. For example, Rh-catalysts embedded within -CD/PEO (polyethylene oxide) hydrogels proved to be effective in the hydroformylation of very hydrophobic alkenes (>C12). 6,7 Ruthenium nanoparticles (RuNP) dispersed in a supramolecular CD-based hydrogel matrix showed great catalytic activity in hydrogenation of alkenes. 8 Interesting results were also obtained with -CD and poloxamines (also known as Tetronics® macromolecules). The latter consist of block copolymers based on hydrophilic PEO and hydrophobic polypropylene oxide (PPO) attached on an ethylene diamine spacer. 9 . Their X-shaped structure differs from the linear chains of poloxamers (Pluronics® macromolecules). Conventional sequential Tetronics® consist of PEO blocks at the outer sphere and PPO blocks attached to the diaminoethylene core, while reverse-sequential poloxamines show PPO blocks at the periphery and PEO attached to the central diamino moiety (Fig. 1). -CDs slide along the PPO/PEO copolymer blocks and selectively accommodate the PEO blocks. The threaded -CDs form stacked nanocylinders that further aggregate into nanosized columnar -CD domains through non-covalent interactions (Fig. 2). 10,11 Using Rh-catalyst embedded within -CD/Tetronics® hydrogels, hydrophobic alkenes were efficiently converted into their corresponding aldehydes. 12 The catalytic performance remains unchanged upon recycling as the -CD/Tetronics® hydrogel matrix prevents the oxidation of the phosphane (ligand stabilizing the Rh catalytic species). In the light of the previous results, we have sought to extend the use of -CD/Tetronics® hydrogels to nanoparticle catalysts, especially gold nanoparticles (AuNP). Although combination of AuNP, hydrogels and CDs has already been reported in the literature, [13][14][15][16][17][18] few has been devoted so far to the application of the resulting system in catalysis. 19 Reported herein is the AuNP-catalyzed hydrogenation of alkenes. Emphasis is especially on the reusability of the catalytic system.

Materials and methods

Reagents

Gold (III) chloride (99.9% -Au) was purchased from Strem Chemicals. Styrene, 1-heptyne, 1-octyne, 1-nonyne, 1-octene, 1-decene, 1dodecene, trans-2-octene,  and  -pinenes were purchased from Acros. Cinnamaldehyde and benzaldehyde were purchased from Fischer. Tetronics®90R4, allylbenzene, phenylacetylene, methyl oleate, methyl linoleate and citronellal were purchased from Sigma Aldrich. -CD was purchased from Wacker. All the chemicals and solvents were used as received without further purification.

Characterization techniques

A Brookfield Model LVDVII+Pro viscometer with the SC4-25 spindle at 20 rpm was used in this study. Viscosity was measured for temperatures ranging from 4 to 85 °C into a SC4-13RPY sample chamber with embedded RTD temperature probe. The temperature was controlled with a TC502 circulating bath refrigerated using a programmable controller. The sample volume was slightly adapted to the volume of the sample chamber. The program parameters and results analysis were controlled with the Rheocalc@ PC Software. The UV-vis spectrophotometry analysis was carried out with a Perkin Elmer Lambda 19 UV-Vis spectrophotometer. 0.25 mL of the reaction mixture (with or without -CD) are diluted in 2 mL of deionized water in order to get a transparent pink-purple solution. Transmission Electron Microscopy (TEM) was performed on a Tecnai microscope (200 kV). A drop of the colloidal suspension was deposited onto a carbon coated copper grid. Metal particle size distributions have been determined from the measurement of around 400 particles found in arbitrarily chosen area of the images using the program SCION Image.

Colloidal suspension synthesis

A Tetronics®90R4 solution (1250 mg in 2.5 mL of deionized water, 0.17 mmol) was stirred at 40 °C during 30 minutes at 1000 rpm. Then, 2.5 mL of an AuCl3 solution ([Au] ranging from 0.1 to 2 mM) were added and the resulting solution was stirred at 40 °C during 1h at 1000 rpm. Finally, 725 mg (0.75 mmol) of -CD were added and the mixture was stirred at 40 °C during 30 min at 1000 rpm. The flask was put in the fridge overnight to facilitate the sol-to-gel transition.

Catalytic experiment

All hydrogenation experiments have been performed using a Parker-Autoclave Engineers stainless steel autoclave containing the AuNP@-CD/Tetronics®90R4 colloidal suspension in a glass vessel. The mixture was heated up to 50 °C with a thermostated oil bath in order to work beyond the gel-to-sol transition temperature. The substrate was added, the reactor was purged three times with nitrogen and hydrogen was fed to the system at constant pressure up to 40 bar. The reaction composition was determined after taking 0.25 mL of the reaction mixture which was diluted in 1 mL of water. The organic products were extracted with 0.5 mL of chloroform and analyzed by gas chromatography with a Varian 3900 gas chromatograph, equipped with a CP-Sil-5B (30 m × 0.25 mm x 0.25 µm) and a flame ionization detector, using decane or dodecane as external standard.

For the recycling experiments, after the first run, all the reaction compounds (styrene and ethylbenzene) were extracted several times with chloroform (5mL) until complete elimination of the organic products. Then, the organic phase was separated from the colloidal suspension after cooling down below the gel-to-sol transition temperature and the traces of chloroform were removed by purging the hydrogel phase with nitrogen during 10 minutes. Finally, after heating up to 50 °C, AuNP@-CD/Tetronics®90R4 colloidal suspension was reloaded with styrene and dihydrogen and reused in the autoclave under the same experimental conditions (40 bar H2, 50 °C).

Results and discussion

Synthesis of hydrogel-embedded AuNP

Given our previous results on the use of Tetronics® in hydroformylation, 12 the reverse-sequential Tetronic®90R4 (Mw 7200, 16 EO and 18 PO units per arm) was considered as poloxamine in the present study. Contrary to procedures described in the literature for which HAuCl4 was used as Au precursor, 20 we used AuCl3 whose fast reduction in an aqueous solution of Tetronics®90R4 (0.17 mmol in 5 mL water) led to AuNP at 40 °C. A small sacrificial quantity of Tetronics® acted as reductive agent thanks to terminal hydroxyl groups of Tetronics® 21 and imparted a pink color characteristic of the presence of AuNP to the solution (Supporting Information, Fig. S1). The AuNP embedded in the hydrogel matrix (AuNP@Tetronics®90R4) were characterized by UV spectrometry ([Au]=0.5 mM). UV spectra displayed in Fig. 3 confirmed the reduction of gold salts by the terminal hydroxyl groups of Tetronics® as a strong absorption band appeared at 532 nm due to the surface plasmon resonance of AuNP. 22 Interestingly, a red shift was observed from 532 to 547 nm after 90 min, which could be explained by an increase in the nanoparticle size. 23 AuNP@Tetronics®90R4 were further characterized by transmission electronic microscopy (TEM). The bimodal distribution of AuNP observed after 30 min reaction time (two populations respectively centered at a mean diameter of 3.9 and 8.1 nm) suggested that the growth of AuNP was incomplete (Supporting Information, Fig. S2). Conversely, small size and narrow Gaussian distribution characterized AuNP with a mean diameter of 7.7 nm after 60 min. Longer reaction time had deleterious effect on both the AuNP size and their distribution. Indeed, increase in the AuNP size and loss of the Gaussian shape of the size distribution were noticed after 90 min, indicative of the relative poor stability of the system over time in the absence of -CD. To prevent the formation of larger AuNP, another AuNP synthesis was carried out by addition of -CD (0.75 mmol) in the Au/Tetronics® solution after 60 min. Upon heating at 40 °C, -CD slided along the copolymer chain. Upon cooling down the system to room temperature, the sol phase turned into a AuNP-containing hydrogel (AuNP@-CD/Tetronics®90R4). UV analysis revealed that addition of -CD provoked a blue shift of max from 532 to 527 nm (Fig. 4), indicative of a change in the environment around the AuNP. 22,24 no further variation of max was noticed for longer reaction time after addition of -CD, suggesting that the -CD/Tetronics® combination led to a better AuNP stabilization over time than Tetronics® used alone. The ability of the -CD/Tetronics® matrix to protect efficiently the Au NPs from aggregation results from the additional effects of steric stabilization due to PEO/PPO polymer chains, [25][26][27] nitrogen atoms from ethylene diamine spacer 28 and the presence of -CD. [29][30][31][32][33][34] Further evidence of the increased stability of AuNP@-CD/Tetronics®90R4 regarding the system without -CD was given by repeated heating/cooling cycles. We first determined the sol/gel transition temperature, which was established at 25 °C by viscosity measurements (Supporting Information, Fig. S3). While the viscosity of the gel was slightly influenced by the presence of AuNP, no variation of the viscosity was noticed in the sol phase.

Secondly, upon heating and cooling down the system repeatedly, no modification of the AuNP shape or size was detected by TEM, indicative of the robustness of the AuNP@-CD/Tetronics®90R4 system (Supporting Information, Fig. S4). Crystalline domains are shown on TEM image at a magnification of 490K with the presence of distinct lattice planes, which can be further analyzed using reduced Fast Fourier Transform (FFT)-derived diffraction patterns (Supporting Information, Fig. S5). The FFT-derived diffraction pattern indicates that the diffraction spot could be identified as Au nanocrystals with a face-centered-cubic (fcc) structure, based on the reflection from the (111) planes having a typical d-spacing of 0.23 nm. Various concentrations of AuCl3 ranging from 0.1 mM to 2 mM were also considered to assess the variation of the AuNP shape, size and distribution (Fig. 5). Transmission electron micrographs revealed that the spherical shape of AuNP was not altered upon increasing [Au]. The observation is in line with literature data that establish that the AuNP size is dependent upon the nature of the stabilizer (anionic, cationic…) or reducing agent concentration. 35,36 In fact, both -CD and Tetronics®90R4 participate in the controlled growth of the AuNP through a "soft template" effect. [37][38][39] The presence of Tetronics®constitutive nitrogens probably reinforce the stabilization of AuNP in the hydrogel matrix because of interactions between nitrogen atoms and the AuNP surface. [40][41][42] The average AuNP size only slightly affected by variation in Au concentration, with mean diameter ranging from 7.4 to 7.7 nm. Conversely, the distribution was more influenced by the initial AuCl3 concentration. From [Au] ranging from 0.5 to 1.5 mM, the distribution resembled a Gaussian curve while it was more polydisperse at [Au] = 2.0 mM.

AuNP-catalyzed hydrogenation of styrene

The catalytic performance of AuNP@-CD/Tetronics®90R4 was assessed in hydrogenation of alkenes under 40 bar of H2 at 50 °C (sol for 30 min. Styrene was first chosen as a model substrate (Table 1). No trace of ethylcyclohexane could be detected once the reaction was complete. Ethylbenzene was exclusively formed, indicative of the high chemoselectivity of the reduction. Increasing the concentrations of AuCl3 led to a regular decrease in conversion. We first thought that increasing the amount of AuCl3 would lead to larger AuNP that would be responsible for the drop in conversion. However, as no significant variation of the AuNP size was noticed by TEM within the considered concentration range (Fig. 5), the reason of the drop in conversion probably lies in the increasing amount of chloride that limited the diffusion of the substrate at the aqueous/organic interface (salting-out effect). [43][44][45] Acidification of the medium by increasing amounts of chloride could also be a valid reason. Moreover, previous DFT studies clearly show that a strong interaction between chloride and Au(111) surface has been calculated 46,47 and could explain these catalytic results. Note that the viscosity of the -CD/Tetronics®90R4 hydrogel could not be incriminated in the sol phase as it did not vary upon addition of AuNP, irrespective of the Au concentration (Supporting Information, Fig. S3). It should be noticed that to have a better understanding of the catalytic process, control experiments have been carried out. First, AuCl3 was solubilized in water without any additive and the resulting yellow solution was stirred under standard experimental conditions. After 1 h, the color of the solution remained unchanged. No reduction of the gold precursor was detected under hydrogen pressure. Moreover, in the case of styrene hydrogenation, no catalytic activity was obtained with AuCl3 alone. Another control experiment consisted in solubilizing of AuCl3 int water in the presence of Tetronics®. After addition of styrene and considering the same experimental conditions described above, the color of the solution changed after 1 h of reaction from yellow to deep purple with metal sedimentation. Indeed, because of the presence of Tetronics®, it was possible to reduce the metallic precursor during the catalytic test. Nevertheless, the Au NPs sedimentation resulted in reproducibility issues and the catalytic result was not relevant. These control experiments clearly show Au NPs are the active catalyst and the addition of -CD is mandatory to avoid any aggregation of Au NPs during the catalytic process in sol state.

Recyclability of the catalytic system

The reusability of the nanoparticle catalytic system was assessed using styrene as substrate under 40 bar of H2 at 50 °C (Fig. 6). After each run, the organic phase was removed and fresh styrene was added on the hydrogel mixture. The catalytic system displayed good reusability as the conversion remained roughly the same around 40% upon recycling. To explain the decrease in catalytic activity observed after the first run, additional experiments were carried out. The organic phase from the first run was reused at 50 °C under 40 bar of H2 with fresh styrene in -CD/Tetronics®90R4 hydrogel without AuNPs (Fig. 7). As shown by the orange line in Fig. 7, the organic phase recovered after the first run was catalytically active. The increase in conversion suggested that a small proportion of AuNP was not properly immobilized within the hydrogel matrix just after the reduction of gold salts, and migrated into the organic phase during the first run (leaching). However, the remaining AuNPs in the hydrogel matrix were well stabilized, as the conversion no longer varied using the organic phase resulting from the second run. This was confirmed by TEM images of AuNPs embedded in hydrogels resulting from runs 1, 2 and 3 (Fig. 8). The distribution remained roughly constant throughout the catalytic process, thus demonstrating the robustness of the AuNP@-CD/Tetronics®90R4 system. Fig. 7 Variation of the conversion over time.  organic phase control (carried out without catalyst),  organic phase after run 1,  organic phase after run 2. Conditions: See Fig. 6.

Other substrates

Given the promising results obtained in the AuNP-catalyzed hydrogenation of styrene, the substrate scope of AuNP@was evaluated using different alkenes under 40 bar of H2 at 50 °C for 1h. It should be noticed that the comparison with previous reported works is not so obvious. Indeed, most of the catalytic systems reported in the literature using gold nanoparticles for hydrogenation reaction in gas phase or liquid phase are heterogeneous catalysts where influence of the support on the catalytic activity and selectivity is not negligible. [48][49][50][51][52][53] Only one publication is reporting the use of solvent dispersed gold NPs into aqueous phase containing surfactants such as SDS or CATB for the hydrogenation of anthracene. 54 The so-obtained conversions of unsaturated compounds are low and could be explained by the fact that gold is known to have i) a high energy barrier for hydrogen dissociation and ii) the least stable chemisorption state in comparison with metal such as Ni or Pt. 55 Styrene was rapidly converted (39%) to yield exclusively ethylbenzene (Table 2, entry 1). Addition of NaCl significantly affected the conversion (31%, entry 2) as already described for styrene (vide supra). Linear alkenes were equally converted into their corresponding alkanes, irrespective of the length of the alkyl chain (entries 3-5). Trans-2-octene gave similar conversion, suggesting that AuNP also reacted with its less accessible carbon-carbon double bond (entry 6). While allylbenzene gave 34% conversion (entry conjugated C=C of cinnamaldehyde was not hydrogenated at all within 1h (entry 8). Interestingly, benzaldehyde gave a low 5% conversion with excellent selectivity in benzyl alcohol, indicative of the ability of the catalytic system to reduce C=O as well (entry 9). The versatility of the AuNP@-CD/Tetronics®90R4 was also demonstrated in hydrogenation of alkynes. Mixtures of alkenes and alkanes were obtained, alkenes being logically intermediates before conversion into alkanes (entries 10-12). Phenylacetylene was selectively hydrogenated into styrene and ethylbenzene, with a styrene/ethylbenzene selectivity ratio of 74/26, without alteration of the phenyl group (entry 13). This catalytic result is in line with previous published works because gold NPs are known to be interesting in the semi-hydrogenation of alkynes into their corresponding alkenes. [56][57][58][59] The substrate scope was further extended to biosourced substrates. The best results were obtained for citronellal (54% conversion; almost exclusively 3,7-dimethyloctanal, entry 14). This selectivity is not surprising because the isolated C=C double bond can be hydrogenated more easily than C=O double bond. [START_REF] Rylander | Catalytic Hydrogenation in Organic Synthesis[END_REF] Hydrogenation of -pinene and -pinene yielded mixtures of cis and trans isomers in 2/1 proportion (entries 15 and 16). Methyl oleate and methyl linoleate showed no conversion probably because of the lower diffusion of such very hydrophobic substrates within the viscous liquid-liquid biphasic system (entries 17 and 18). Note that the activities obtained in olefins hydrogenation are lower in comparison to aromatics and alkynes. This difference could be explained by a better adsorption of aromatic compounds [START_REF] Wetterer | [END_REF] and alkynes 50,56 onto Au(111) surface compared to alkenes.

Conclusions

With the aim of recycling nanoparticle catalysts, we developed a catalytic system consisting of AuNP embedded in -CD/Tetronics®90R4 hydrogels. AuNP displayed an average size of ca. 7 nm and a narrow distribution, as determined by TEM. The AuNP/-CD/Tetronics®90R4 proved to be stable over time. Upon heating above the gel-to-sol transition temperature, the studied catalytic system proved versatile, as a wide range of substrates such as alkenes, alkynes and aldehydes could be converted under biphasic conditions. The best results were obtained in AuNP-catalyzed hydrogenation of citronellal (54% conversion within 1h, 99% selectivity in 3,7-dimethyloctanal). Interestingly, upon repeated heating/cooling cycles, the AuNP@-CD/Tetronics®90R4 catalytic system could be recycled several times without significant decline in activity.

Fig. 1

 1 Fig. 1 Structure of a) cyclodextrins (CDs) and b) conventional sequential poloxamines and c) reverse-sequential poloxamines

Fig. 2

 2 Fig. 2 Polypseudorotaxane aggregates of -CD / reverse-sequential poloxamines (Tetronic®90R4).

Fig. 3

 3 Fig. 3 Liquid UV spectra of hydrogel embedded AuNPs. [Au] = 0.5 mM, and Tetronics®90R4 (1250 mg) in water (5 mL) at 40°C at different reaction times, considering the start time t0 as the instant where -CD was added to the reaction medium.  t0; ̵ ̵ ̵ t0 + 15 min;  t0 + 30 min; ̶ ̶ t0 + 60 min; ̶ ̶ t0 + 90 min; ̶ ̶ t0 + 18 h.

Fig. 4

 4 Fig.4Liquid UV spectra of hydrogel embedded AuNPs. [Au] = 0.5 mM, Tetronics®90R4 (1250 mg) and -CD (750 mg) in water (5 mL) at 40°C at different reaction times, considering the start time t0 as the instant where -CD was added to the reaction medium. ̶ ̶ t0 ; ̶ ̶ t0 + 1 h ; ̵ ̵ ̵ t0 + 3 h ; ̶ ̶ t0 + 5 h ; ̶ ̶ t0 + 18 h ;  after 10 consecutive sol/gel transitions.

Fig. 5

 5 Fig. 5 TEM images and corresponding size distributions of AuNPs embedded in -CD/Tetronics®90R4 hydrogel at (a) [Au] = 0.1 mM ; (b) [Au] = 0.5 mM ; (c) [Au] = 1 mM ; (d) [Au] = 1.5 mM and (e) [Au] = 2 mM.

a

  Conditions: styrene (50 equiv/Au), -CD (0.75 mmol, 1250 mg), Tetronics®90R4 (0.17 mmol, 725 mg), water (5 mL), 40 bar H2, 50 °C, 30 min, 1000 rpm. b determined by GC analysis.

Fig. 6

 6 Fig.6Recyclability of AuNP@-CD/Tetronics®90R4 in hydrogenation of styrene over 5 consecutive runs. a Conditions: styrene (0.125 mmol, 13 mg), AuNP@-

Fig. 8

 8 Fig. 8 TEM images and size distributions of AuNPs embedded in -CD/Tetronics®90R4 hydrogel a) before catalysis and b) after run 1, c) after run 2 (b), and d) after run 3 for hydrogenation of styrene. Conditions: see Fig 6.

Table 1

 1 AuNP-catalyzed hydrogenation of styrene in α-CD/Tetronic®90R4 hydrogel. a

Table 2

 2 AuNP-catalyzed hydrogenation of terminal and internal alkenes in α-CD/Tetronic®90R4 hydrogel. a determined by 1 H NMR. c with NaCl (17 mg added during the synthesis of the colloidal suspension). d AuNPs at the interface (colorless aqueous phase). e no isomerization. f no citronellol.

	Entry	Substrate	Conv. (%) b	Sel. b
	1	styrene	39	100% ethylbenzene
	2 c	styrene	31 d	100% ethylbenzene
	3	1-octene	21	100% octane e
	4	1-decene	22	100% decane e
	5	1-dodecene	19	100% dodecane e
	6	trans-2-octene	20	100% octane
	7	allylbenzene	34	100% propylbenzene
	8	cinnamaldehyde	0	-
	9	benzaldehyde	5	100% benzyl alcohol
	10	1-heptyne	8	61% 1-heptene 39% heptane
	11	1-octyne	18	53% 1-octene 47% octane
	12	1-nonyne	14	58% 1-nonene 42% nonane
	13	phenylacetylene	15	74% styrene 26% ethylbenzene
	14	citronellal	54	99% 3,7-dimethyloctanal 1% 3,7 dimethyloctanol f
	15	-pinene	15	66% cis-pinane 34% trans-pinane
	16	-pinene	9	64% cis-pinane 36% trans-pinane
	17	methyl oleate	0	-
	18	methyl linoleate	0	-
	a Conditions: alkene/Au = 100, AuNP@-CD/Tetronics®90R4 ([Au]= 0.5 mM in 0.75 mmol
	-CD + 0.17 mmol Tetronics®90R4), water (5 mL), 40 bar H2, 50 °C, 1 h, 1000 rpm.

b

Acknowledgements

Chevreul Institute (FR 2638), Ministère de l'Enseignement Supérieur et de la Recherche, Région Nord -Pas de Calais and FEDER are acknowledged for supporting and funding partially this work. The TEM facility in Lille (France) is supported by the Conseil Regional du Nord Pas de Calais and the European Regional Development Fund (ERDF). We are grateful to Dr. A. Addad for his contribution in setting up the TEM measurements. We also thank Dr. Nicolas and D. Prevost for technical assistance. The authors gratefully acknowledge the financial support from the Major Domain of Interest (DIM) "Eco-Energy Efficiency" of Artois University.

Conflicts of interest

There are no conflicts to declare.


Laurent Libessart

Amine Lahlou

Chafika Djelal

Yannick Vanhove

Sandrine Mateo

Yannick Vanhoveis

Influence of the emulsions to the interface formwork/concrete

Keywords: Emulsion, concrete, formwork, interface, adhesion energy, facing aspect, image analysis

The concrete is the ultimate building materials today and answers all the requirements of the modern architecture. The emulsion or the release agents are used to facilitate the concrete demoulding and to protect the formwork surfaces against corrosion. The final quality of the facings depends on the physicochemical characteristics of the demoulding products used. They must be selected according to the nature of the formwork and their compatibility with the casing skins. They must be consistently applied to the unit of the formwork, to a clean surface, in thin layers, uniform thickness. This agent must allow a placement of the more effective concrete while adhering perfectly to the formwork. The adherence of oil with the support is thus very important. It is studied by the determination of the adhesion energy Solid/Liquid on a formwork surface. This study is interested more particularly in the emulsions. Two forms are distinguished: Mineral reverses emulsion with the dispersed phase is water and Vegetable direct emulsion with the dispersed phase is oil. The first physicochemical results show an influence of the temperature on the adhesion energy. The quality of the concrete facings demoulded with emulsions appears better qualities that those carried out with oils demoulding.

INTRODUCTION

Owing to its flexible setting conditions, concrete remains the most widely used material in the construction industry. The appearance of new concretes, coupled with the more demanding specifications imposed by project managers, has led to the marketing of increasingly efficient products (admixtures, demolding agents, etc.). However, the formwork removal step may give rise to certain problems, typically caused by an insufficient understanding of the mechanisms occurring at the concrete/formwork interface. In an effort to satisfy industry requirements as well as environmental protection and user safety conditions, many such products are plantbased. Among the array of demolding agents available on the market, emulsions meet the criteria for successful material placement due to their formwork removal attributes, in conjunction with cladding quality, which often raises conflict between project partners when works are submitted for acceptance. Over the past few years, this requirement has become a major economic challenge for the industry, yet emulsion use still tends to be limited. Moreover, the behavior of emulsions, whether plant-or mineral-based, has only received scant attention, especially as regards stability over time. This lack of investigation is in sharp contrast with the case of demolding oils, which have been extensively studied [START_REF] Djelal | Comprehension of demoulding mechanics at the formwork/oil/concrete interface[END_REF][START_REF] Hermann | Produits de décoffrage[END_REF], as evidenced in the bibliography. The emulsions make it possible to apply less oil to the formwork surface and thus to reduce the total quantity of product. It is important to control this application to ensure a good demolding. The suppliers advise the pulverization followed or not of a scraping or a brushing. After the application, latency is advised of approximately 15min to ensure a total evaporation of the absorbent phase. As regards demolding agent classification, the SYNAD (French Association for Concrete and Mortar Admixtures) created an abacus [START_REF]Syndicat national des adjuvants pour bétons et mortiers (SYNAD), Classification Synad des agents de démoulage[END_REF] based on product composition as well as a set of criteria related to its use (fire safety, health, environmental considerations). Concrete cladding is generally visible once the structure has been built; it forms the structural skin, which must resist the range of stresses acting on the structure throughout its service life and blend in with its environment as naturally as possible. Achieving high-quality cladding necessitates considerable attention in: designing the concrete mix, establishing component homogeneity, and laying out the various setting steps. The quality of formwork and demolding product, plus the casting sequence and use of vibration, all contribute to ensuring a satisfactory final result. The goal of this study is to correlate the physicochemical properties of mineral-and plant-based emulsions with cladding appearance after formwork removal, as a means of improving understanding of the concrete/formwork interface. The main parameters analyzed are: type of emulsion and influence of both temperature and wait time prior to concrete casting.

EXPERIMENTAL INVESTIGATION

This section discusses the materials and physicochemical characterization techniques used to study emulsions. Also detailed here in will be the procedure for analyzing concrete cladding images.

Materials

Release agents

The demolding agents selected for this study are both mineral and plant emulsions.

Two emulsion forms are distinguished (Fig. 1) [START_REF] Zolfaghari | Demulsification techniques of water-in-oil and oil-in-water emulsions in petroleum industry[END_REF]: a mineral-based inverse emulsion with water as the dispersed phase; and a direct plant-based emulsion with oil as the dispersed phase. From a practical perspective, the majority of emulsions are composed of an aqueous liquid phase and a phase with limited water solubility. In oily emulsions, the hydrophobic part of the emulsifier molecule is found in the dispersant phase (oil) and, conversely, in the other type of emulsion (as shown in Fig. 1). Emulsion formation relies heavily on a stable environment. To prepare an emulsion, the oily and aqueous phases need to be assembled and stirred together, along with the addition of one or more emulsifying agents. The efficiency of this emulsification process depends on both the stirring mode and intensity. The emulsifier must also be introduced under appropriate conditions; it must feature a structure capable of strengthening interphase linkage to the greatest extent possible. Such is a key element in ensuring mix stability [START_REF] Fingas | Studies of the formation process of water-in-oil emulsions[END_REF]. Table 1 lists the various characteristics provided by the manufacturer. At construction project sites, the demolding agent is most often sprayed onto the formwork or spread after spraying with a rubber scraper in order to remove excess product relative to each single layer. For this experimental campaign, only the spray-on application will be studied. Concrete A CEMI 52.5 CP2type of Portland cement was used for this investigation, while the concrete employed to study cladding aesthetics was of a conventional variety containing 28% cement paste. The workability, as measured by the Abrams cone test, must lie between 12 and 14 cm. The specific mix design is given in Table 2. Formwork Metal formwork is extensively introduced in the building trades; it serves to streamline concrete setting and enhances worksite productivity. Formwork reuse possibilities are substantial for structural elements repeated throughout a project, i.e.: vertical shear walls, floors, and columns. The use of stiffeners enables extending elements over large surface areas. Before characterizing the wettability and determining the bonding energy of the various mix designs, the surface roughness was first measured. This new formwork surface used [START_REF] Libessart | Influence of the type of release oil on steel formwork corrosion and facing aesthetics[END_REF] was homogeneous and devoid of any defects or particularities regarding its lamination. Its roughness was measured at 1.27 µm [START_REF] Libessart | Correlation between adhesion energy of release agents on the formwork and demoulding performances[END_REF].

Mixing protocol

Mixing was carried out in accordance with Standard NF P 18-404, entitled "Concretes: Mix design, suitability and inspection tests -Casting and storage of test specimens", which specifies the following operating procedure: Tests were conducted in the laboratory at room temperature (around 20°C). The cladding analysis relies on molds measuring 30*30*30 cm 3 . The concrete is cast in three layers and then vibrated at 5 points for 10 seconds per layer using a 40-mm diameter vibrating needle. The vibration step is carried out in five 10-second sequences per layer with the 40-mm needle. All emulsions studied were applied by spraying, with a wait time of 15 min prior to concrete casting. This application was completed without experiencing any leakage or overload.

Methods for characterizing the physical chemistry of emulsions

Rheological properties

The rheological properties of demolding oils exert a powerful influence on the behavior of the concrete/oil/formwork interface. This influence is directly felt on: wettability, friction stresses at the concrete/formwork interface, and ultimate cladding quality [START_REF] Hart | Concrete release agent, associated materials and surface finishes[END_REF][START_REF] Caro | Influence of the nature of demoulding agent on the properties of the formwork/concrete interface[END_REF]. The viscosity of the two oils is determined using a HAAKE VT550 single-speed viscometer, fitted with a 1° (PK5) cone. A constant volume of oil (v = 0.6 cm 3 ) is deposited on the plate with a pipette, and the cone is then lowered toward the plate. To obtain an accurate measurement, a 5-to 10-min wait time (depending on measurement temperature and after depositing the oil on the plate) is required for the oil to reach the desired temperature. During the testing phase, temperature must be held constant so as not to bias the reading. Viscosity measurements were conducted at three constant temperatures (10°C, 20°C and 40°C). Surface tension The liquid/vapor surface tension of a liquid is correlated with the value of the contact angle formed by a drop on a support [START_REF] Chappuis | Contribution to Study of Wetting -Analysis of a Measuring[END_REF]. Contact angles are a readily observable physical manifestation of the more fundamental concepts of energy and surface tension. This insight serves to determine the properties of wettability and adhesion of a film, which in turn makes it possible to predict the properties of a lining or detect the traces of surface pollutants. As part of a theoretical approach, adhesion energy values are calculated based on contact angle data. It may be considered that the liquid/solid adhesion energy value is representative of the adhesive strength between the liquid and the support. Young [START_REF] Gennes | Wetting: statics and dynamics[END_REF] was the first researcher to derive an equation for the equilibrium of a drop of liquid placed on a given solid. This equation is expressed in the following form:

( ) SL SV LV g g q g - = cos ( ) q g g g cos LV SV SL - = Û (1)
where θ is the contact angle formed by the surface and the plane tangent to the meniscus, SV g the solid surface energy, LV g the liquid/vapor surface tension et LS g the liquid/solid interfacial tension.

The liquid/solid adhesion energy value is also representative of the adhesive force between a liquid and its support. Adhesion energies are calculated according to Zisman's Equation [START_REF] Zisman | Relation of the Equilibrium Contact angle to Liquid and Solid Constitution[END_REF]:

) cos 1 ( q g w + = LV LS (2)
In order to determine the solid/liquid adhesion energy, it is necessary to measure both the contact angle of the oil and the liquid/vapor surface tension. The liquid/vapor surface tension was measured using Wilhelmy's plate method at 20°C. The device employed is a tension meter manufactured by the CAD firm (Fig. 2) fitted with a platinum blade. According to this method, a thin platinum plate is hooked to a Kahn scale and then immersed into a liquid contained in a tank. The surface tension is indicated by the meniscus formed along the plate boundary. The material contact angle was determined using a PGX type of mobile goniometer. This device measures the contact angle at the interface between a liquid drop and the substrate surface where it has been deposited.

EXPERIMENTAL RESULTS AND DISCUSSION

Dynamics viscosities

Table 3 presents the dynamic viscosities obtained by averaging the results from 3 tests. Given its low viscosity value, the EDV2 reference could not be measured. Results show that the demolding agents display a linear behavior without any yield point: the behavior of emulsions is thus Newtonian [START_REF] Caro | Influence of the nature of demoulding agent on the properties of the formwork/concrete interface[END_REF]. Viscosity decreases as a function of temperature, hence making it important to control the film application after spraying.

Liquid/vapor surface tension

The L/V surface tension values, derived at 10°, 20° and 40°C, are given in Figure 3. These findings suggest that increasing the temperature causes the surface tension to drop. Since the molecules are becoming more thermally excited, they are more likely to leave the surface and move toward the interior. The force attracting molecules toward the interior should therefore decrease as temperature rises. This analysis demonstrates that film adhesion may be modified depending on temperature. Nonetheless, values remain in the vicinity of 30 mN/m, as recommended during previous studies [START_REF] Libessart | Correlation between adhesion energy of release agents on the formwork and demoulding performances[END_REF]. For the remainder of this study, results will be exclusively analyzed at 20°C.

Wettability Instantaneously

The drop angles, provided in Table 4, all lie between 20° and 35°, with the inverse emulsions yielding the smallest angles. Emulsions must therefore stabilize over time, and it is preferable to track the evolution in wettability over time as well.

Over time

Measurements spanning a time period were carried out in order to study the variation in demolding agent wettability. Figure 4 shows the evolution in wettability vs. time for the four tested emulsions. Wettability stabilizes after some 7 min for EDV1 and at 5 min for EDV2 and EIM1. These values all lie between 10° and 20°. It is also observed that prior to stabilizing the drop, a significant slope suddenly appears for both emulsions. This variation may be due to many parameters (e.g. type of emulsion, emulsion mix design, water evaporation). The surface tension balance becomes modified at the formwork surface. The plate roughness parameter might also serve to influence this variation. Water evaporation leads to greater emulsion wettability on the support as the drop spreads more readily. Adhesion energy Instantaneously Figure 5 summarizes the various adhesion energy values at t = 0 min and at 20°C. Emulsions EDV1, EIM1 and EIM2 all display a satisfactory adhesion energy level of at least 70 mN/m. Only the EDV2 value lies below this threshold. It can thus be concluded that demolding agents must exhibit the highest possible surface tension and the lowest drop angle.

Over time

This change in wettability thus implies a change in adhesion energy between t = 0 and t = 20 min. Figure 6 depicts such an evolution over time. The rise in adhesion energy values reveals the benefit of allowing the water contained in the emulsion to evaporate as a means of generating the best possible adhesion. It is preferable to let the evaporation step last at least 5min after emulsion application in order to ensure that all the water has evaporated and a homogeneous oil film has been obtained.

Analysis of concrete cladding images

The most significant cladding defect is a color variation, which produces a visual differentiation between large adjacent surface zones [START_REF]Bétons et ouvrages d'art -La maîtrise esthétique des parements en béton[END_REF][START_REF] Lemaire | Evaluating concrete surfaces using an image analysis process[END_REF]. This kind of alteration typically affects concrete over several millimeters of thickness. Two types of color variation exist, namely those between different concrete mixes on a single cladding, and those on the same mix. A rating scale with 7 shades of gray has been developed by CIB [START_REF] Cib | Tolérances sur les défauts d'aspect du béton[END_REF] (Fig. 7). French Standard P18-503 also offers a guideline for evaluating the surface appearance of concrete cladding [START_REF] St P | Concrete surfaces and facing. Identification elements[END_REF]. This standard is based on three characterization criteria: flatness, texture (bubbling), and hue. To analyze cladding and formwork surfaces, the rating criteria selected were those used by our team when testing for the influence of mix designs on cladding quality. For this cladding, a rating is determined 24hours nafter formwork removal. The cladding appearance, microbubbling, dusting, fouling, shading and snag points are all parameters capable of characterizing formwork removal quality [START_REF] Libessart | Influence of the type of release oil on steel formwork corrosion and facing aesthetics[END_REF]. The color variation analysis entails an image analysis. The cladding obtained was photographed on days 1, 3 and 7 following formwork removal. The concrete blocks were released 12hours after casting and then stored indoors at a temperature of 20° +/-2°C and at a constant humidity of 60% +/-5%. The first measurement stage consists of a general assessment of the cladding, complete with snapshots of its overall appearance. To perform this assessment, the following procedures are required: -Specify the average color through use of the color chart [START_REF] Cib | Tolérances sur les défauts d'aspect du béton[END_REF].

-Eliminate any artifacts attached to surface edges. -Calculate the total cladding surface area.

-Determine the rate of color variation. Two freeware applications are available for this step: GIMP 2.8, and ImageJ 1.48. The types of cladding obtained with EDV1 and EIM1 are shown in Figure 8. At first, the photograph is adjusted to yield an image without any background capable of influencing the image analysis. Next, the color, brightness and saturation are all improved, followed by a binarization operation involving threes holding. For the color variation, it is critical to select shade-of-gray 1 or 2 from Figure 3 as the reference. This scale is then compared with the photograph taken of the concrete cladding. To determine the color variation rate value, an appropriate measurement scale needs to be defined. As a final step, the "black" zones are calculated. Table 5 lists the full set of color variation results for the demolding agents studied herein. No notable differences appear between the direct and inverse emulsions, nor in the selection of mineral-based vs. plant-based products, with very good cladding quality measured at 7 days.

The visual analysis reveals little fouling and few snag points; moreover, no dusting was detected on the cladding. Microbubbling was found to be relatively sparse (approx. 0.25%), which indicates that the emulsion composition does not prevent air bubbles from rising to the surface. Figures 9 and 10 present the color variation for cladding obtained with emulsions EDV1 and EIM1. The black zones show the variation in color created with respect to the reference color chosen on the CIB scale. No shade of gray is identified, as all zones with a higher color value have been darkened. For purposes of this study, level 1 was selected. Since bubbling may slightly alter the values, it needed to be removed from the calculation. CONCLUSIONS The emulsions studied as part of this research have demonstrated strong physicochemical performances. Their viscosity values are lower due to the presence of water in their composition, hence making it possible to apply these emulsions using an adapted spraying protocol between 10°C and 40°C. The drop angles lie near 25° (especially for plant-based emulsions), while their liquid/vapor surface tension is close to 30 mN/m, thus providing for a good level of adhesion energy. The change in wettability over time serves to homogenize the surface of the film being applied; resulting in a greater bond with the surface, which further increases the adhesion energy value. It is thus essential to wait 5 -10 minutes before setting the concrete into the formwork. Cladding quality improves over time; consequently, it is preferable to wait at least 7 days to derive an evaluation. While the color does visibly evolve, a homogeneous color pattern can be achieved after 7 days. It is also necessary to develop the images analysis on a microscopic scale (porosity analyses) and by spectrocolorimetry measurements. A complementary study can be realized to know the emulsion influence on the concrete friction on the formwork by tests with a plane/plane tribometer. The analysis of anti-corrosive protection can be given by Electrochemical Impedance Spectroscopy (EIS).

FURTHER RESEARCH

The continuation for the study will be to analyze the various types of application and to carry out an experimental campaign on a plane/plane tribometer in order to release the coefficients of friction of the concrete on the various formulations and thus to supplement the physicochemical study.

TABLES AND FIGURES

Fig. 1 -Fig. 5 - 6 - 8 -Fig. 9 -

 15689 Fig. 1-Emulsion forms[START_REF] Doumeix | Opérations unitaires en génie biologique -Tome 1 -Les émulsions[END_REF]

Table 1 -

 1 Release

	agents properties
		EDV1	EDV2	EIM1	EIM2
	Color	White	White	White	White
	Nature	Mineral	Mineral	Vegetable	Vegetable
	Flash point, °C	> 100	> 100		85	96
	Density	< 1	0.985 ± 0.02	< 1	< 1
	Table 2-Concrete formulation
		Concrete			B28
		Paste volume (%)		28
	Cement CEM I 52,5 CP2 (kg/m3)	232
		Fillers (kg/m3)		77
		Sand 0/4 (kg/m3)		838
		Gravel 4/8 (kg/m3)		287
		Gravel 6/20 (kg/m3)		778
		Water (l)			176
		W/B			0.57
	Table 3-Dynamic viscosity of emulsions
		Viscosity at	Viscosity at		Viscosity at
		10°C (mPa.s)	20°C (mPa.s)	40°C (mPa.s)
	EDV1	43.5 ±0.7%	38.9 ±7.1%		27.9 ±1%
	EDV2	-		-		-
	EIM1	62.8 ±0.63 %	53.4±7%		31.8 ± 6.7%
	EIM2	79.1 ± 8.9%	60.6 ±2.9 %		34.9 ±2%
	-=not measured items.
	Table 4-Instantaneous contact angle of emulsions at 20°C
			Contact angle (°)
		EDV1		33.3
		EDV2		35.1
		EIM1		28.2
		EIM2		23.1

Table 5 -

 5 Percentage of color variation on days 1, 3 and 7

		1 day	3 days	7 days
	EDV1	9.75	4.25	3.5
	EDV2	13.45	5.11	2.65
	EIM1	13.71	3.64	2.94
	EIM2	7.23	5.43	3.31

ACKNOWLEDGMENTS

The authors wish to express their gratitude and sincere appreciation to the CHRYSO SA industry for financing this research work.