Mark G Allen
email: mark.allen@astro.unistra.fr

Patrick Dowler

Janet D Evans

Chenzhou Cui

Tim Jenness

The International Virtual Observatory Alliance in 2018

Interoperability Meeting held in College Park.

An alliance for the global vision of the Virtual Observatory

The Virtual Observatory (VO) is a collection of interoperating data archives and software tools that facilitate astronomical research. The overall goal is to support innovative research in astronomy by exploiting the full power of growing and emerging datasets and interoperable services. Many projects and data centres worldwide are working to make data and other resources work as a seamless whole. The International Virtual Observatory Alliance1 (IVOA) is an organisation that debates and agrees on the technical standards that are needed to make the VO possible. Constituted in 2002 (see for example [START_REF] Quinn | Optimizing Scientific Return for Astronomy through Information Technologies[END_REF]), the IVOA has now been joined by 21 national and international VO projects that meet bi-annually. Major IVOA accomplishments include standards for data and metadata (Data Models), data exchange methods (Data Access Layer; Query Language), and a registry that lists available services and identifies what can be done with them. Organisations have implemented VO-enabled tools and services that can interface seamlessly with VO-enabled archives worldwide, and some projects have built new data systems with VO services at their core. The IVOA acts as a focus for VO objectives, a framework for discussing and sharing VO ideas and technology, and a body for promoting and publicizing the VO.

Recent IVOA activities have focused on the engagement with future large data producing projects, and priorities have most recently focused on multi-dimensional data, and time domain astronomy. IVOA is also evolving as an organisation in a rapidly changing landscape, with the emergence of new large initiatives for research data sharing such as the Research Data Alliance [START_REF] Treloar | [END_REF] with strong support of the Findable, Accessible, Interoperable, and Reusable (FAIR; Williamson et al. 2016) principles. Astronomy is also changing as we enter an era of very large data, and multi-wavelength and multi-messenger astrophysics where there is an essential need for high level interoperability of data, simulations, tools and services. The bi-annual Interoperability Meetings are working meetings for making progress on and facing the challenges [START_REF] Arviset | Astronomical Data Analysis Software and Systems[END_REF]) of coordinating the global effort for interoperability in Astronomy.

The IVOA work is pursued by Working Groups (WG) and Interest Groups (IG) (see table 1), coordinated by the Technical Coordination Group (TCG), guided by a scientific priorities committee (CSP), with the overall direction provided by the IVOA Executive Committee. Participation in the IVOA working and interest groups is open, as is the participation in the bi-annual Interoperability meetings.

IVOA November 2018

The November 2018 Interoperability meeting2 was held in College Park, MD, USA, preceding ADASS XXVIII. One hundred and nine participants gathered for two and a half days of productive discussions. Sessions were held by most of the WGs and IGs, running in two parallel streams, and with a number of joint WG-IG sessions.

Applications

In the Applications (Apps) sessions the themes were: Python and its increasing importance in astronomy software and services; the VOTable format including its use in mapping of data models; HEALPix (Górski et al. 2005) and its use in coverage maps (MOC) and the Hierarchical Progressive Survey (HiPS; [START_REF] Fernique | [END_REF]; also the use of Authentication in applications and services. The relationship between Python and the VO was widely discussed and questions were raised about where best to contribute VO tools, how to raise the visibility of Python VO code, and how to avoid duplication. The discussions recognised a need for reference implementations of IVOA standards in Python, and potential follow-up activities such as IVOA hack-a-thons were identified. This is discussed further in [START_REF] Donaldson | ADASS XXVIII[END_REF].

Data Access Layer. The Data Access Layer (DAL) WG sessions included discussions on the current minor version updates being prepared for the Table Access Protocol (TAP), Astronomical Data Query Language (ADQL) and DataLink standards that allow linking of datasets with various resources such as related datasets, metadata, or other services. New proposals were put forward for standards in support of multimessenger astrophysics. These standards are intended to describe the sky visibility of observatories and missions as is needed for the follow-up of events such as gravitational Data Curation and Preservation. The Data Curation and Preservation (DCP) session focused on the role of Digital Object Identifiers (DOIs), including examples of current practice and different approaches being taken throughout the astronomy and data sharing communities. Vizier presented a proposal for how they were considering using DOIs for their holdings and how this might work for datasets where they were not the primary data source. LSST discussed different ways in which DOIs for queries of large datasets could be issued and how to distinguish between the query itself, for a specific data release, and the results of the query, along with the possibility of allowing curated subsets of query results. Finally it was agreed to look into issuing DOIs for VO standards. A summary of the discussion was presented at ADASS [START_REF] Muench | ADASS XXVIII[END_REF]).

Solar System. The Solar System IG sessions included reports from projects such as EuroPlanet VESPA, and there was discussion on bridging VESPA and PDS4. The use of the EPN-TAP protocol, a specialised version of TAP used in the planetary science context in the VESPA project, was discussed. A preliminary discussion was held about Space Reference Frames.

Theory. The discussion in the Theory IG session highlighted the need to raise the visibility of Theory IVOA standards in upcoming projects that will make heavy use of simulations (EUCLID, LSST, SKA etc.), and to make stronger links between observations and theory.

Knowledge Discovery and Education. While the Knowledge Discovery IG and Education IGs did not have sessions at this meeting, the members highlighted the various relevant current topics from across the various WGs and IGs. KDIG emphasised the need for Science Platforms for using and sharing scientific workflows and batch processing using the concept of "code to the data", and the use of DOIs. Education IG made plans for exploring connections to Education and Public Outreach activities of the IAU for VO-enabled data driven astronomical education.

IVOA next steps

The work of the IVOA is all aimed at enabling new and innovative science. The IVOA standards, defined by the community, for the community, form an important part of the astronomy data infrastructure. Realising the vision of the VO of course relies on widespread implementation of the infrastructure via the adoption of the standards in data archives, services and tools. A recent visible success is the publication of the ESA Gaia mission DR2 via VO technologies, proving VO capabilities for handling the peak load challenges of a very large data release (see e.g., [START_REF] Baines | IVOA Newletter[END_REF][START_REF] Salgado | ADASS XXVIII[END_REF].

The continued growth of the VO system requires that future and current data producing projects and missions are fully engaged with IVOA to ensure that the standards address the changing scientific needs of the community. The IVOA CSP, which has recently expanded with new members has the role of fostering these engagements and identifying the most important scientific priorities to guide IVOA developments.

Astronomy is rapidly entering into a new era of Big Data, and interoperability is increasingly important for multi-wavelength, multi-messenger and time domain astronomy. The participation of projects such as SKA, CTA, LSST, EUCLID etc., and the astronomy community in general, is essential to help define the scientific priorities that guide the IVOA activities in these areas. One of the common themes that is being driven by the needs of these big data projects is the concept of science analysis platforms that will enable analysis of the data with capabilities for providing computational resources close to the data. Access to VO resources via these platforms will be essential, and the role of standardisation for interoperability of these platforms is a strongly emerging topic being discussed within IVOA. The user-centric focus of the science platforms presents many opportunities to enable a greater level of programmatic access to VO resources, with popular languages and systems used by scientists (e.g., Python notebooks). Other strong themes for future development include the use of machine learning, new visualisation capabilities, and use of VO data in education and outreach.

IVOA seeks to welcome new projects and their scientific and technical input. The IVOA web pages and wiki are being updated with information to facilitate the use of VO systems for data providers and astronomers, highlighting the many scientific and practical benefits to publishing data in the VO -that the data becomes interoperable with other worldwide resources and that the data becomes visible in many widely used tools. For developers there is information on libraries, clients and tools that can be used to interact with the data when they are available through VO protocols. The revised web pages are also being updated with information on a number of well-tested frameworks available for publishing data.

Following this short-format interoperability meeting in College Park, the IVOA work continues via various email and slack communication channels, using the IVOA wiki for organisation of all the activities. The IVOA Newsletters [START_REF] Baines | IVOA Newletter[END_REF] provide latest news and results, and a calendar of events. The recently appointed IVOA Media Group continues to enhance the IVOA social media presence, and is making plans for a revised IVOA information web portal. A major 5-day Interoperability Meeting is planned for May 2019 in Paris.

Table 1 .

 1 IVOA Working Groups and Interest GroupsData Modelling Framework for the description of metadata attached to observed or simulated data, and logical relationships between metadata.Grid & Web ServicesGrid technologies and web services within the VO context.SemanticsExplore technology in the area of semantics with the aim of producing new standards that aid the interoperability of VO systems. UCDs, Standard Vocabulary, exploration of Ontologies. Resource Registry Registry provides the mechanism with which users and applications discover and select resources -typically, data and services.Data Modelling. The Data Modelling WG sessions reviewed the preparation of the major new version of the Space Time Coordinates (STC) standard. Progress was reported on the STC component models: coordinates, measurements, and transformations. A revision of the Simple Spectral Line standard was discussed. The concepts and purposes for the mapping of data models were reviewed. The Provenance data model standards document was in the "Request For Comments" (RFC) phase during the meeting, and presentations on the topic of provenance highlighted the reference im-plementations using the new model including one being used in the preparation of the Cherenkov Telescope Array (CTA).Grid and Web Services. The Grid and Web Services (GWS) sessions covered the topic of Authentication and Authorization, in particular the use of OAuth (Open Authorization) an open standard based on tokens. The application of Big Data technologies was discussed, including an example of Apache Spark for simulated Euclid data. Feedback was provided on the use of the VOSpace 2.1 standard. The use of the VO Service Interface (VOSI) for managing versioning of services was discussed, and a new IVOA note is in preparation to outline best practices for its practical use.Registry. The Registry WG activities were largely combined into joint sessions with other WGs namely DAL, GWS and Apps. The role of the Registry in providing Authenticated Endpoints for resources was discussed, and a TAP prototype was shown. In the context of the VODataService standard, the use of spatial coverage maps (MOCs) in the registry was discussed. A plan was made to clean up the Registry-of-Registries (RofR) to improve operations by removing invalid records. This level of monitoring is very valuable for the operation of the overall system, and also for highlighting areas of the standards that need improvement, indeed some issues may be most appropriately resolved by updating standards. Another topic was HTTPS, reporting that most VO protocols are compatible with HTTPS but challenges remain for WebSAMP (Web enabled Simple Application Messaging Protocol). Domain Astronomy. Time Domain astronomy is a current priority area for the IVOA. The Time Domain IG session addressed the status of the Time Series Data Model, and various ways of expressing time related data in the VO. Following the publication of an IVOA note, a proposal was presented for a TIMESYS element in VOTable, as a basic component for interoperability of time based data expressed in VOTable documents. The driving use case is the combination of two time-series, requiring two time coordinates to be put into a common frame of time scales with a reference position and a time origin of the time scale. Consistency with future STC2 data model is taken into account.

	Working Group Description
	Applications	Tools that Astronomers use to access VO data and services. Standards spe-
			cific to VO Astronomy-user-Applications.
	Data	Access	Define and formulate VO standards for remote data access.
	Layer
	Interest Group	Description
	Time Domain	Representation of the emerging time domain community, specific time do-
			main issues in a VO context.
	Solar System	IVOA standards in the scope of Solar System sciences.
	Theory		Ensuring that theoretical data and services are taken into account in the
			IVOA standards.
	Education	VO tools, data and practices in support of astronomy teaching in schools and
			universities.
	Data Curation	Share best practices and engage IVOA member projects in the long-term
	& Preservation	curation and preservation of astronomical data.
	Knowledge	Knowledge discovery is the task of processing and analyzing data-sets with
	Discovery	the aim of extracting new knowledge. This area spans visualization, remote
			data exploration, machine learning techniques, statistical methods, workflow
			orchestration, and polymorphic data access in the context of the VO.
	Operations	Coordinate and publicize activities of individuals, institutions and groups
			interested in facilitating robust operations of distributed astronomy applica-
			tions, particularly those based upon implementations of IVOA protocols.
	wave detections. The DAL sessions also included feedback on implementation of VO
	standards by NED and All-Sky Virtual Observatory (ASVO; O'Toole 2019) groups.

Semantics. The Semantics WG reviewed the organisation of the various Vocabularies, and discussed the needs expressed by the Theory IG, Data Model WG (for coordinate frame semantics), and Solar System IG. The nomenclature for describing instruments and facilities was also discussed.

Operations. The Operations IG sessions included presentations on service monitoring and "weather reports" of VO services. VO service up-times are shown to be 98-99% overall. VOParis and the European Space Agency (ESA) monitoring systems show that Cone Search services are now generally fully compliant with VO standards. Simple Image Access (SIA version 1) services have some common minor issues, as do the more complex Table Access Protocol (TAP) and and Simple Spectral Access (SSA) services.

http://www.ivoa.net 1

https://wiki.ivoa.net/twiki/bin/view/IVOA/InterOpNov2018MeetingPage

Acknowledgments. The IVOA would like to thank the local organisers of both the IVOA Interoperability Meeting, and the ADASS XVIII conference.


Marion Bruneau

Jocelyne Brendle
email: jocelyne.brendle@uha.fr

Simona Bennici

Lionel Limousy

Patrick Dutournie

Sylvain Pluchon

Talc-like hybrids: influence of the synthesis parameters on the polycondensation degree, crystallinity and thermal stability

Keywords:

This study aims to understand how the synthesis parameters influence the formation of organicinorganic hybrids having a talc like structure synthetized using N-[3-(trimethoxysilyl))propyl]ethylenediamine as silicon source. The hybrids have been analysed mainly by 29 Si solid-state NMR in order to access the condensation degree of the silicon species. The results have shown that the solvent and the synthesis duration have no influence on the condensation. The addition of water in the synthesis medium induce a strong decrease of the degree of polycondensation of the silicon species. A basic pH of the synthesis medium can also further decrease this parameter. Additional information has been provided by X-Ray Diffraction and Thermogravimetric analyses which allow to highlight a correlation between the Full Width at Half Maximum and the thermal stability of the hybrids synthetized in presence of different amount of water. This opens the possibility to modulate the polycondensation degree of the silicic species, the crystallinity and the thermal stability changing only one parameter.

Introduction

Talc is a 2:1 phyllosilicate composed of one magnesian octahedral sheet sandwiched between by two silicic tetrahedral sheet. Organic-inorganic talc-like hybrids derive from this structure with organic moieties covalently bonded to one silicon of each tetrahedron of the tetrahedral sheet. These organic moieties are pending in the interlayer space and at the surface of the hybrid (Figure 1). The general chemical formula for these hybrids is Mg 3 (RSi) 4 O 10 (OH) 2 were R stands for an organic moiety. Synthesis of organic-inorganic hybrids with talc-like structure have been first performed by Fukushima and Tani in 1995 [START_REF] Fukushima | An organic/inorganic hybrid layered polymer: methacrylatemagnesium (nickel) phyllosilicate[END_REF] using a sol-gel process. This synthesis have been subsequently developed by other teams [START_REF] Burkett | Synthesis, Characterization, and Reactivity of Layered Inorganic-Organic Nanocomposites Based on 2: 1 Trioctahedral Phyllosilicates[END_REF][START_REF] Whilton | Hybrid lamellar nanocomposites based on organically functionalized magnesium phyllosilicate clays with interlayer reactivity[END_REF][START_REF] Fonseca | Aminated Phyllosilicates Synthesized via a Sol-Gel Process[END_REF][START_REF] Gallégo | Synthesis of new lamellar inorganic-organic talc-like hybrids[END_REF][START_REF] Yang | 3-aminopropyl functionalized magnesium phyllosilicate as an organoclay based drug carrier for improving the bioavailability of flurbiprofen[END_REF] as well as for the preparation of other phyllosilicate-like hybrids such as for example saponite-like [START_REF] Ukrainczyk | Template Synthesis and Characterization of Layered Al-and Mg-Silsesquioxanes[END_REF][START_REF] Jaber | A new Al,Mgorganoclay[END_REF][START_REF] Chaillot | Insights on the influence of the precursors on the sol-gel synthesis of hybrid organic-inorganic saponite-like materials[END_REF] or hectorite-like materials [START_REF] Carrado | Preparation of hectorite clays utilizing organic and organometallic complexes during hydrothermal crystallization[END_REF][START_REF] Carrado | Synthetic organo-and polymer-clays: preparation, characterization, and materials applications[END_REF]. Sol-gel synthesis is a simple way to obtain organic-inorganic hybrids with talc-like structure, it consists to dissolving a magnesium salt in a solvent before adding an organoalcoxysilane (RSi(CH 3 ) 3 ), the silicon source, and increasing the pH with an alkaline solution in order to promote the condensation of the silicon species [START_REF] Schaefer | Fractal Aspects of Ceramic Synthesis[END_REF]. Then, the solution is aged under stirring, generally at room temperature during several hours. The advantages of this procedure are the low energy consumption, the duration of the synthesis and the high purity of the obtained materials [START_REF] Jaber | A new Al,Mgorganoclay[END_REF]. The aim of this study is to understand the influence of the key parameters governing the formation of organic-inorganic talc-like hybrids synthetized using N- [3-(trimethoxysilyl))propyl]ethylenediamine as silicon source.

Several parameters have been tested such as the solvent of the synthesis, the synthesis duration, the presence and the type of the base in the synthesis medium or the presence of water during the synthesis. The polycondensation degree, the crystallinity and the thermal stability of these materials have been determined by solid-state Nuclear Magnetic Resonance (NMR) of 29 Si, X-Ray Diffraction (XRD) and thermogravimetric analysis.

Material and Methods

Reactants

Magnesium nitrate hexahydrate Mg(NO 3 ) 2 6H 2 O (Fluka, 99 wt%), N-[3- (trimethoxysilyl)
)propyl]ethylenediamine, N2TMS (Sigma-Aldrich, 97 wt%), absolute ethanol (Carlo Erba, 99.9 wt%), phenoxy-2-propanol (Sigma-Aldrich, >93 wt%), sodium hydroxide NaOH (Fluka, 99 wt%), tetrapropylammonium hydroxide TPAOH (Sigma-Aldrich, 1 M) and distilled water were used without further purification.

Synthesis

Talc-like hybrid materials were prepared by mixing 1.73 g of nitrate of magnesium in 20 mL of solvent. Then, 2 g the organotrialcoxysilane N2TMS have been added in order to obtain a Si/Mg molar ratio equal to 1.33. At this step, a base can possibly be added under stirring in order to enhance the condensation process [START_REF] Schaefer | Fractal Aspects of Ceramic Synthesis[END_REF]. After 24h or more of stirring at room temperature, the solgel solution is centrifuged at 11000 rpm for 10 min and dried at 60 °C for 24 h in an oven.

Using this general protocol, several parameters have been changed.

To test the influence of the solvent, two different solvents have been used, absolute ethanol and phenoxy-2-propanol. This last solvent is non miscible to water and the two syntheses have been carried out without the addition of a base. The synthesis duration was five days for this study.

For the study of the influence of the synthesis duration, two syntheses of talc-like hybrids have been prepared in ethanol, without addition of a base. One beaker has been let under stirring for one day while the other has been let under stirring during five days.

In order to see the influence of the addition of a base in the synthesis medium, two syntheses have been performed in ethanol. In one of them, 8 mL of an aqueous solution of sodium hydroxide 1M has been added to obtain a pH of 10. This addition, in organic-inorganic hybrids syntheses, theoretically allow to enhanced the condensation process [START_REF] Schaefer | Fractal Aspects of Ceramic Synthesis[END_REF].

To know the influence of the base type, two syntheses have been performed where sodium hydroxide NaOH or tetrapropylammonium hydroxide TPAOH at the same concentration (1 M) and volume (8 mL) have been added to obtain a pH of 10.

To test the effect of the water on the polycondensation degree of silicic species of the talc-like hybrids, three syntheses where water was added in the synthesis medium have been done. To compare with the previous study, the same amount of water (8 mL) that the sodium hydroxide was used in one of them. For the two others, 4 mL and 12 mL of water was added in the synthesis medium.

Finally, in order to study the influence of the pH on the polycondensation degree of the silicon species, four hybrids have been synthetized adding sodium hydroxide at different concentration and volume. Two synthesis have been performed at pH = 9, the first one adding 4 mL of NaOH at 1 M and the second one adding 8 mL of NaOH at 0.5 M. One synthesis has been done at pH = 10 adding 8 mL of a solution of NaOH at 1 m and the last one has been carried out at pH = 13 adding 8 mL of NaOH at 2 M.

Characterization

Solid-state NMR spectra were recorded on a Bruker Avance II 300 MHz spectrometer. Samples were packed in a 7 mm diameter cylindrical zirconia rotor and spun at a spinning frequency of 4 kHz. For 29 Si CPMAS NMR, a π/2 proton pulse duration of 7.7 µs with a contact time of 10 ms and a recycle delay of 6 s were used. For 29 Si MAS+DEC NMR, a π/4 pulse duration of 3.85 µs and a recycle delay of 80 s were used. The reference sample for 29 Si analysis is Octakis(trimethylsiloxy)silsesquioxane(Q8M8).

X-Ray diffraction (XRD) patterns of the hybrid materials were recorded using a Panalytical X-pert Pro MPD diffractometer operating with Cu-Ka radiation (λ=0.15418 nm), between 3 and 70 °2ϴ with a step size of 0.02 °2ϴ per 2 s on randomly oriented powder samples.

The thermogravimetric analysis (TGA) of the synthesized samples were realized with a TG-DTA apparatus (Mettler-Toledo TGA/DSC1 LF1100) under air, with a flow rate of about 100mL.min -1 from 30 to 800 °C and a heating rate of 5 °C min -1 in alumina sample holders. A reference experiment was recorded to correct base line deviation with an empty sample holder. This technic permitted also to calculate the ratio of organic moieties in the hybrids obtained in the different conditions.

Results and discussion

The first part of this work is dedicated to the study of the condensation state of the silicon species. This parameter has been followed by 29 Si solid-state NMR as it it possible by this way to gather information on the local environment of the silicon atoms. In talc-like hybrids, the different T sites of silicon are named with the conventional Tn notation, n corresponding to the number of OM bonds (M = Si or Mg) of a silicon atom. T3 sites correspond to silicon bonded to three Si or Mg via an oxygen in order to form RSi(OM) 3 groups whereas T1 and T2 sites correspond to RSi(OM) 2 OH groups and RSi(OM)(OH) 2 groups respectively and indicate the presence of defects in the structure and the border sites. The higher the proportion of T3 sites is, the higher the condensation degree is. All the presented spectra in this paper are CPMAS spectra. Deconvolution of the NMR spectra were performed on MAS+DEC spectra, using the dmfit software [START_REF] Massiot | Modelling one-and two-dimensional solid-state NMR spectra: Modelling 1D and 2D solid-state NMR spectra[END_REF] which gives the relative proportion of each component with an error of 5 %. In all this study, only the T3 sites proportion will be observed to compare the condensation degree of the silicic species of the hybrids.

Influence of the solvent

Two different organic-inorganic hybrids have been synthetized by using absolute ethanol in one case and phenoxy-2-propanol in the other one. Figure 3 displays the 29 Si CPMAS NMR spectra of the synthetized hybrids. Three resonances can be observed in each spectrum with chemical shifts at -49, -56 and -68 ppm, corresponding to T1, T2 and T3 sites respectively. The integration of each resonance give the proportion of the T sites [START_REF] Massiot | Modelling one-and two-dimensional solid-state NMR spectra: Modelling 1D and 2D solid-state NMR spectra[END_REF] (Table 1). It is worthy to note that the proportion of T3 sites is high in both case indicating a high degree of condensation of the silicic species. The proportion of T1 site is similar and there is a slight difference in the proposition of T2 sites, nevertheless and taking into account the accuracy of the deconvolution, one may assume that there is almost no influence of the solvent in the formation of the hybrids. All the following synthesis have therefore been carried out in absolute ethanol.

R

Influence of the synthesis duration

The effect of the synthesis duration on the condensation degree of the silicic species has been tested. Few differences can be observed between the two NMR spectra of the hybrids synthetized during one and five days. (Figure 4). The deconvolution of the peaks gives the proportion of each T site (Table 2). These results showed that the longer the synthesis duration is, the higher condensation degree of the silicic species is. This phenomenon can be explained by the lengthening of the hydrolysiscondensation process time which enhanced the formation of talc-like hybrids. A synthesis time of one day was chosen for the next experiments.

Influence of the addition of Sodium Hydroxide

Then, the effect on the polycondensation degree of the addition of sodium hydroxide in the synthesis medium have been studied. The solid-state NMR spectra of the two synthetized hybrids and the relative proportion of each T site are presented in Figure 5 and in Table 3. The condensation state of the silicic species is quite low for the sample prepared with sodium hydroxide, with only 15% of T3 sites compared to 59% of T3 sites for the sample prepared without. The addition of this base have thus a strong influence on the polycondensation degree. Whilton et al. in 1998 [3] have also observed such difference between hybrids synthetized with the same organoalcoxysilane in presence or absence of sodium hydroxide with a T3 sites proportion of 0 % in the first case. This difference was attributed by the author to the high pH of the synthesis, allowing the self-assembly of the brucite layer and constraining sterically the covalently bonded moieties whereas at neutral pH, the self-assembly of organoalcoxysilane act as a template for brucite assembly [START_REF] Carrado | Preparation of hectorite clays utilizing organic and organometallic complexes during hydrothermal crystallization[END_REF]. Another hybrid synthetized with N2TMS was also done by the team of Fonseca et al. [START_REF] Fonseca | Aminated Phyllosilicates Synthesized via a Sol-Gel Process[END_REF] one year later. They have found a proportion of T3 sites of 12 %. The difference with the previous study was attributed to the synthesis temperature and duration (50 °C and five days respectively). This last affirmation can be rejected in view of our previous study. The following of this work aims to complete these two studies in order to understand the key parameter of the polycondensation degree of such a hybrid. The current results of our study allows to ask if the decrease of the condensation of the silicon species is due to the base type, to the presence of water or to the pH. The influence of the base type has been tested performing two syntheses with two different bases (NaOH and TPAOH). The 29 Si solid-state NMR spectra and their deconvolution (Figure 6 and Table 4) indicate that the type of base (sodium hydroxide or tetrapropylammonium hydroxide) has no influence of the condensation degree of the silicic species.

Influence of the base

Influence of the addition of water

The difference between the addition of NaOH or water in the synthesis medium on the condensation degree of the silicon species have been investigated. The solid state NMR spectra and T sites proportion in Figure 7 and Table 5 did not show a huge difference between the two hybrids. The proportion of the different T sites are very similar between the hybrids synthetized in presence of NaOH or water indicating a low condensation degree of silicon species for these hybrids. These results are very different to that of the hybrid synthetized in absence of NaOH and water which has shown a very high degree of condensation. This result allows to conclude that this is the water present in the aqueous solution of sodium hydroxide that induces the important decrease of the polycondensation degree of the silicic species in the hybrids. To go further, several hybrids have been synthetized with different amount of water in the synthesis medium (Figure 8 and Table 6). All the NMR spectra presented in Figure 8 show three resonances at the same positions but at different relative intensities. The hybrid synthetized without any addition of water show an intense resonance corresponding to the T3 sites which indicate a high degree of condensation of the silicon species. With the increase of the amount of water in the synthesis medium, the resonance corresponding to T3 sites tends to decrease in favour of the resonance corresponding to T1 and T2 sites. A relationship between the amount of water in the synthesis medium and the condensation degree of the silicic species is underlined. Showing that it is possible to modulate the polycondensation degree of this type of hybrid by changing only the proportion of water in the synthesis medium.

Influence of the pH

Finally, the study of the influence of the pH on the condensation of the silicon species have been done. The results of the solid-state NMR analyses of these hybrids are presented in Figure 9 and Table 7. 9a and Figure 9b are related to samples prepared at the same pH value (i.e. 9) but with different concentration of NaOH solution. Here also, the influence of the water content is emphasizing as the more water is in the medium, the less T3 environments are present. Changing the pH values up to 10 or 13 lead to a slight decrease of the proportion of T3 sites. This parameter has thus a small influence on the condensation degree of the silicic species, the proportion of water in the synthesis medium remaining the key parameter. This results are not in agreements with the one obtained by Whilton et al. [START_REF] Whilton | Hybrid lamellar nanocomposites based on organically functionalized magnesium phyllosilicate clays with interlayer reactivity[END_REF] and Fonseca et al. [START_REF] Fonseca | Aminated Phyllosilicates Synthesized via a Sol-Gel Process[END_REF] for an hybrid synthetized with the same organoalcoxysilane. The relative rate between hydrolysis and condensation process is affected by an addition of water in the synthesis medium and consequently, by an addition of an aqueous alkaline solution. Contrary to our study where the maximum water proportion tested was 40 %, in the studies of Whilton et al. [START_REF] Whilton | Hybrid lamellar nanocomposites based on organically functionalized magnesium phyllosilicate clays with interlayer reactivity[END_REF] and Fonseca et al. [START_REF] Fonseca | Aminated Phyllosilicates Synthesized via a Sol-Gel Process[END_REF], the water proportions in the synthesis medium was 80 % and 61 % respectively. This gap between the two study can explain the difference of 12 % of T3 sites proportion in their hybrids.

Relationship between crystallinity and thermal stability

In order to go deeper in the characterization of the samples, all the four hybrids synthesized in the presence of different proportions of water in the synthesis medium this study were analyzed by XRD and TGA.

All the diffractograms recorded show five large reflections at 4.84°, 9.69°, 21.93°, 35,02° and 59.17° 2ϴ. Applying the Bragg law: where d hkl is the distance of the plane (hkl), ϴ in the angle of diffraction, n is the periodicity index and λ is the used Kα radiation, interlayer distances of 18.24 (d 001 ), 9.1 (d 002 ), 4.05 (d 020,110 ), 2.58 (d 130,220 ) and 1.55 Å (d 060 ), respectively, could be calculated. The obtained values are in agreement with the expected reflections for talc-like hybrids [START_REF] Fukushima | An organic/inorganic hybrid layered polymer: methacrylatemagnesium (nickel) phyllosilicate[END_REF][START_REF] Whilton | Hybrid lamellar nanocomposites based on organically functionalized magnesium phyllosilicate clays with interlayer reactivity[END_REF].

The position of the ( 001) and (060) reflection are typical of a trioctahedral 2:1 phyllosilicate, but the broadness of the peaks indicates a low crystallinity (organization), probably due to the presence of organic moieties in the structure.

Many XRD patterns of this study are presented in the Supplementary Information File (Figure A to F). The four hybrids synthesized in the presence of different proportions of water in the synthesis medium were analyzed by XRD and the results XRD patterns are presented in Figure 10. where d hkl is the distance of the plane (hkl), ϴ in the angle of diffraction, n is the periodicity index and λ is the used Kα radiation. The position of the (001) and (060) reflection are typical from a trioctahedral 2:1 phyllosilicate but the broadness of the peaks indicates a low crystallinity (organization) because of the presence of organic moieties in the structure.

Using these patterns, the Full Width at Half Maximum (FWHM) of the (001) reflection can be determined (Table 8). This criterion is an indicator of the crystallinity [START_REF] Warr | Interlaboratory standardization and calibration of day mineral crystallinity and crystallite size data[END_REF][START_REF] Dellisanti | Changes of the main physical and technological properties of talc due to mechanical strain[END_REF]. Lower is the value, higher is the crystallinity. Thermogravimetric analysis were performed for all the hybrids synthetized in this study. This technic allows to verify the thermal stability of the materials and to estimate the content of organic moieties in the hybrids obtained under different synthesis conditions. Indeed, the organic fraction degradation corresponds to the weight loss between 100 and 550 °C. The results are presented in the Supporting Information file, table A. According to the structural formula, the theoretical content of organic moieties in the hybrids is 49.0 %. After the TG analysis, the residue presented a grey color, indication of carbonaceous residues and of the uncompleted volatilization of the organic fraction. The organic content of our hybrids is therefore slightly underestimated, which explains the small differences between the theoretical and experimental values in terms of organic moieties content.

Thermogravimetric analysis were also performed in order to study the thermal stability of our the hybrids. The derivative curves (DTG) of the samples synthetized in presence of different proportion of water in the synthesis medium are presented in Figure 11. In these curves, the first peak below 100 °C corresponds to the water loss of the hybrids. The peaks between 100 °C and 530 °C correspond to the degradation of the organic moiety of the hybrid and the peaks visible below 550 °C correspond to the phenomenon of dehydroxylation of OH groups [START_REF] Jaber | A new Al,Mgorganoclay[END_REF]. Except for the hybrid prepared without water, the profiles are almost similar. Nevertheless, and without taking into account the first peak, corresponding to the water loss, it can be noticed that the peak at around 200 °C shifts toward higher temperatures, when the proportion of water added in the synthesis medium increases. This indicates a better thermal stability for hybrids synthetized in presence of water.

An inverse linear correlation between the FWHM and the temperature of the decomposition first peak of the hybrids have been found (Figure 12) and indicate a dependence between crystallinity and thermal stability. Indeed, the crystallinity is inversely linearly correlated to the thermal stability [START_REF] Burgaz | Prediction of thermal stability, crystallinity and thermomechanical properties of poly(ethylene oxide)/clay nanocomposites with artificial neural networks[END_REF], because lower is the FWHM, higher is the crystallinity. The good crystallinity of a lamellar material is related to a stronger chemical stability, and to the presence of stronger bonds between atoms, which results in an improved thermal stability. On the contrary, a material that present a low crystallinity is generally characterized by the presence of defects that weaken the structure stability thus decreasing the material thermal stability.

All these results help to say that higher is the proportion of water in the synthesis medium, higher is the crystallinity and the thermal stability, but lower is the condensation degree of the silicic species and the thermal stability.

Conclusion

Several organic-inorganic talc-like hybrids have been synthetized synthesized using N- [3-(trimethoxysilyl))propyl]ethylenediamine as the silicon source, changing different synthesis parameters, and have shown multiple polycondensation degree crystallinity and thermal stability. A detailed study of these parameters has highlighted that the proportion of water in the synthesis medium is the key parameters of in the hybrid formation. This result opens the possibility to modulate the polycondensation degree of the silicic species, the crystallinity and the thermal stability just changing only one synthesis parameter.

Figure 1 :

 1 Figure 1: Schematic representation of the structure of an organic-inorganic talc-like hybrid

Figure 2 :

 2 Figure 2: T sites of silicon, with R being an organic moiety pending in the interlayer space and a the surface of the hybrid.

Figure 3 :

 3 Figure 3: 29 Si CPMAS Solid-state RMN spectra of the talc-like hybrids synthetized in absolute ethanol (a) and phenoxy-2propanol (b)

  Scale: 3.67 ppm/cm, 218.8 Hz/cm

Figure 4 :

 4 Figure 4: 29 Si CPMAS Solid-state RMN spectra of the talc-like hybrids synthetized during 1 day (a) and 5 days (b)

Scale: 3 .

 3 67 ppm/cm, 218.8 Hz/cm

Figure 5 :

 5 Figure 5: 29 Si CPMAS Solid-state RMN spectra of the talc-like hybrids synthetized in presence of NaOH (a) and in absence of NaOH (b)

Scale: 3 .

 3 67 ppm/cm, 218.8 Hz/cm

Figure 6 :

 6 Figure 6: 29 Si CPMAS Solid-state RMN spectra of the talc-like hybrids synthetized in presence of NaOH (a) or TPAOH (b)

Scale: 3 .

 3 67 ppm/cm, 218.8 Hz/cm

Figure 7 :

 7 Figure 7: 29 Si CPMAS Solid-state RMN spectra of the talc-like hybrids synthetized in presence of NaOH (a) or water (b)

Scale: 3 .

 3 67 ppm/cm, 218.8 Hz/cm

Figure 8 :

 8 Figure 8: 29 Si CPMAS Solid-state RMN spectra of the talc-like hybrids synthetized in presence of different amount of water in the synthesis medium : 0 mL -0 % (a), 4 mL -17 % (b), 8 mL -29 % (c) and 12 mL -38 % (d)

Scale: 3 .

 3 67 ppm/cm, 218.8 Hz/cm

Figure 9 :

 9 Figure 9: 29 Si CPMAS Solid-state RMN spectra of the talc-like hybrids synthetized at different pH : pH=9, 4 mL of NaOH 1 M (a); pH=9, 8 mL of NaOH 0.5 M (b), pH=10, 8 mL of NaOH 1 M (c) and pH=13, 8 mL of NaOH 2 M (d)

Scale: 3 .

 3 67 ppm/cm, 218.8 Hz/cm

Figure 10 :

 10 Figure 10: XRD patterns of the hybrids synthetized in presence of different amount of water in the synthesis medium : 0 mL -0 % (a), 4 mL -17 % (b), 8 mL -29 % (c) and 12 mL -38 % (d)

Figure 11 :

 11 Figure 11: DTG of the hybrids synthetized in presence of different proportion of water in the synthesis medium

Figure 12 :

 12 Figure 12: Linear correlation between FWHM and thermal stability

Table 1 :

 1 Proportions of each T site for hybrids synthetized in absolute ethanol and phenoxy-2-propanol

	Sites In ethanol In phenoxy-2-propanol
	T1	10 %	12 %
	T2	23 %	14 %
	T3	67 %	74 %

Table 2 :

 2 Proportions of each T site for hybrids synthetized during 1 or 5 days

	Sites	1 day	5 days
	T1	13 %	10 %
	T2	28 %	23 %
	T3	59 %	67 %

Table 3 :

 3 Proportions of each T site for hybrids synthetized in presence or absence of sodium hydroxide

	Sites	With NaOH	Without NaOH
	T1	49 %	13 %
	T2	36 %	28 %
	T3	15 %	59 %

Table 4 :

 4 Proportions of each T site for hybrids synthetized in presence of NaOH or TPAOH

	Sites	With NaOH	With TPAOH
	T1	49 %	50 %
	T2	36 %	39 %
	T3	15 %	11 %

Table 5 :

 5 Proportions of each T site for hybrids synthetized in presence of NaOH or water in comparison with the hybrid synthetized without any addition of NaOH and water

	Sites	With NaOH	With water	Without addition of NaOH and water
	T1	49 %	51 %	13 %
	T2	36 %	29 %	28 %
	T3	15 %	20 %	59 %

Table 6 :

 6 Proportions of each T site for hybrids synthetized with different proportion of water in the synthesis medium

	Sites 0 % of water	17 % of water 29 % of water 38 % of water
	T1	13 %	35 %	51 %	51 %
	T2	28 %	34 %	29 %	34 %
	T3	59 %	31 %	20 %	15 %

Table 7 :

 7 Proportions of each T site for hybrids synthetized at different pH

	Sites	pH=9 (4 mL NaOH 1 M)	pH=9 (8 mL NaOH 0.5 M)	pH=10 (8 mL NaOH 1 M)	pH=13 (8 mL NaOH 2 M)
	T1	35 %	50 %	49 %	45 %
	T2	34 %	30 %	36 %	41 %
	T3	31 %	20 %	15 %	14 %
	Figure

Table 8 :

 8 FWHM of the hybrids synthetized in presence of different proportion of water in the synthesis medium

	Proportion of water	FWHM
	0 %	2,48
	17 %	1,46
	29 %	1,19
	38 %	1,13

Acknowledgments

This work was supported by Agro Innovation International and ANRT (Association Nationale de la Recherche et de la Technologie).

XRD, TGA, and NMR measurements were performed on the technical platforms of IS2M. The authors are very grateful to Laure Michelin, Habiba Nouali, and Séverinne Rigolet for their contributions.