Rachelle Abou Jaoude

Ilango Thiagalingam

Roch El Khoury

Gabriel Crehan

Berkeley thermal comfort models: Comparison to people votes and indications for user-centric HVAC strategies in car cabins

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

trends about thermal preferences are brought to light for each body part. It is observed that body parts have, depending on the global thermal ambiance, different expectations in terms of thermal preferences. For instance, one can mention that the pelvis should only be cooled slightly even in extreme hot environments, otherwise the comfort is strongly deteriorated. Based on this investigation body parts that have to be focused in priority have been identified for different global thermal ambiances (very cold So = -4, cold So = -2, neutral So = 0, warm So = 2 and very hot So = 4) and suggestions for comfort-oriented and energy saving-oriented strategies have been proposed.

Introduction

The automotive industry is today at the beginning of a historic turning point as the mobility concept is going through a paradigm shift. The political pressure to reduce local pollution led automotive manufacturers to replace the fleet composed of vehicles with an internal combustion engine by electric vehicles [START_REF] Hildermeier | Shaping an emerging market for electric cars: How politics in france and germany transform the european automotive industry[END_REF]. In this respect, today's strategies to bring thermal comfort have to be fully reviewed as the power used to bring thermal comfort directly impacts the autonomy of electric vehicles [START_REF] Kambly | Geographical and temporal differences in electric vehicle range due to cabin conditioning energy consumption[END_REF]. Thermal comfort research has been recently reactivated to find technological solutions in order to bring the highest quality of thermal comfort inside cabins with the lowest level of energy use [START_REF] Oi | Effects of heated seats in vehicles on thermal comfort during the initial warm-up period[END_REF][START_REF] Oi | Effects of heated seat and foot heater on thermal comfort and heater energy consumption in vehicle[END_REF][START_REF] Zhang | The influence of heated or cooled seats on the acceptable ambiant temperature range[END_REF][START_REF] Brooks | An ergonomics investigation into human thermal comfort using an automobile seat heated with encapsulated carbonized fabric (ecf)[END_REF][START_REF] Pasut | Energy-efficient comfort with a heated/cooled chair: Results from human subjects tests[END_REF][START_REF] Vesely | Personalized conditioning and its impact on thermal comfort and energy performance -a review[END_REF].

The European EN ISO 14505 [START_REF] Iso | Ergonomics of the thermal environment -Evaluation of thermal environnements in vehicles Part 1: Principles and methods for assessment of thermal stress[END_REF][START_REF] Iso | Ergonomics of the thermal environment -Evaluation of thermal environnements in vehicles Part 2: Determination of equivalent temperature[END_REF][START_REF] Iso | Ergonomics of the thermal environment -Evaluation of thermal environnements in vehicles Part 3: Evaluation of thermal comfort using human subjects[END_REF] and the American ASHRAE-55 [START_REF] Ashrae | Thermal environmental conditions for human occupancy[END_REF] are the current standards proposing methods for the thermal comfort evaluation in car cabin environments. In these standards, thermal comfort indices employ the equivalent temperature concept which can be used in heterogeneous but steady environments [START_REF] Nilsson | Comfort climate evaluation with thermal manikin methods and computer simulation models[END_REF][START_REF] Nilsson | Thermal comfort evaluation with virtual manikin methods[END_REF][START_REF] Han | A sensitivity study of occupant thermal comfort in a cabin using virtual thermal comfort engineering[END_REF] and the PMV (Predicted Mean Vote)-PPD (Predicted Percentage of Dissatisfied) approach introduced by Fanger [START_REF] Fanger | Thermal comfort-analysis and applications in environmental engineering[END_REF] which unfortunately has been intended particularly for homogeneous and steady environments inside buildings.

Automotive environments set apart from building environments by the tight and confined space in which passengers are constrained to stay seated for a relatively long period of time. And contrary to building environments, cabin environments mainly evidence high transient and non-homogeneous thermal conditions [START_REF] Alahmer | Design for thermal sensation and comfort states in vehicles cabins[END_REF][START_REF] Ruzic | Thermal interaction between a human body and a vehicle cabin[END_REF][START_REF] Simon | Factors which influence the thermal comfort inside of vehicles[END_REF]. This specificity is explained principally by the use of air conditioners and the impact of solar radiation. Effectively, the level of the convective heat transfer between the human body and its surroundings is driven by air velocities and temperature differences. In automotive environments, due to the orientation of aerators, their relative closeness to the driver and passengers and heterogeneous speed and temperature setpoints of the blown air at the aerators' outlet (for instance in actual vehicles and in winter conditions, the air blown in feet compartments is warmer than the air blown from aerators located on the upper side of the dashboard) the operating air conditioning system generates heterogeneous air temperature around the body. Besides, certain body parts experience large radiative heat exchanges under summer outdoor conditions because of the directionality of the direct short-wave solar radiation. In addition, the non-uniformity of interior wall temperatures (use of radiating panels for instance) could lead to a non-uniform long-wave radiation field around the human body. Conductive heat exchange with the seat (heating or ventilated active seats) could be another source of non-uniformity in automotive environment. Furthermore, unlike air-conditioned buildings, the in-cabin climate is dominated by transient thermal conditions as more than 85% of trips involve an average distance fewer than 18 km, with a duration of 15 to 30 min [START_REF] Cisternino | Thermal climate in cabs and measurement problems[END_REF]. Thus, it was shown in [START_REF] Zhou | Experimental investigation of thermal comfort in a passenger car under driving conditions[END_REF] that thermal comfort study should be conducted under transient conditions in car cabins as thermal conditions remain transient in most of the situations.

As the PMV indices were established based on a steady-state heat transfer between the human body and the homogeneous surrounding environment, it does not provide accurate predictions for automotive environments. Effectively, it was pointed out for instance that the overall percentage of dissatisfied was higher than the PPD obtained with the Fanger's model for the same overall thermal sensation vote when the thermal non-uniformity exceeded a certain level. It implies that a non-uniform thermal environment increases the occupants' overall percentage of dissatisfied [START_REF] Wang | A thermal comfort model for the non-uniform environments[END_REF]. Moreover, the European EN ISO 14505 and the American ASHRAE-55 standards are based on environmental parameters and do not request a thermophysiological model describing the thermal response of the human body to external thermal solicitations. Thus, they may provide acceptable predictions in steady state conditions but they are not intended to model the comfort perception in unsteady environmental conditions [START_REF] Koelblen | Thermalsensation models: Validation and sensitivity towards thermophysiological parameters[END_REF]. The inertia effect, active and passive thermo-regulation mechanisms of the human body to restore the thermal equilibrium between the body and the environment have a significant impact in the transient perception of thermal sensation [START_REF] Fiala | Dynamic SImulation of Human Heat and Thermal Comfort[END_REF][START_REF] Joris | Experimental validation of a multi-solver heat transfer simulation methodology including occupant thermo-physiology[END_REF]. The need to include these transient effect is highlighted for instance by the DTS (Dynamic Thermal Sensation) model [START_REF] Thiagalingam | Confrontation of thermal sensation and comfort models to votes in a transient thermal exposure[END_REF]. In order to capture accurately transient physiological and psychological effects on the thermal comfort perception, a fine modelling of the interaction between the unsteady thermal environment and the human thermal system is required. In this respect, a refined multi-node model for thermal comfort which fits to the current imperatives can be seen as a substitute to the PMV indices [START_REF] Katic | Thermophysiological models and their applications: a review[END_REF][START_REF] Enescu | A review of thermal comfort models and indicators for indoor environments[END_REF][START_REF] Fu | Review on modeling heat transfer and thermoregulatory responses in human body[END_REF][START_REF] Cheng | Thermal comfort models: A review and numerical investigation[END_REF]. Comfort models proposed by Zhang [START_REF] Zhang | Human thermal sensation and comfort in transient and nonuniform thermal environments[END_REF][START_REF] Zhang | Thermal sensation and comfort models for non-uniform and transient environments: Part I: local sensation of individual body parts[END_REF][START_REF] Zhang | Thermal sensation and comfort models for non-uniform and transient environments: Part II: local comfort of individual body parts[END_REF][START_REF] Zhang | Thermal sensation and comfort models for non-uniform and transient environments: Part III: wholebody sensation and comfort[END_REF] and based on thermophysiological parameters are shown to be convenient to predict human perception of comfort in heterogeneous and unsteady environmental conditions. With such models, the local impact of transient and heterogeneous thermal stress can be fully accounted and used to spot local discomfort so that the HVAC system could be intended to bring satisfaction on those particular body parts. In this paper, it is proposed to investigate experimentally the applicability of the local thermal comfort model of Zhang in transient and quasi-homogeneous automotive environment and suggest indications to properly set the HVAC system. The present experimental investigation will mainly focus on the evaluation of the Zhang model to predict the perception of local and global comforts in unsteady environmental conditions.

In the following sections, the experimental set up is first presented. Cool and warm transient scenarios are investigated and thermal sensation and comfort votes of a panel of human subjects are recorded. Those votes are then compared to the UCB Zhang thermal comfort model predictions. Finally a parametric study is carried out with the UCB Zhang thermal comfort model to draw main qualitative trends between local and global sensations and comforts in order to come up with indications to set an user-centric HVAC system that either satisfy the occupants thermal needs at best or either bring the minimum comfort while reducing the energy use.

Experimental set up 2.1 Description of the test bench

A thermal test bench that represents a B-segment car cabin is used for the experimental investigation (Fig. 1). The cabin interior volume is 2.9 m 3 . The internal walls of the test cell are covered with 42 independent flat stainless steel heat exchangers reproducing the car cabin geometry. Their temperatures can be controlled from 5 to 45 • C using ten independent water-glycol circulation circuits. An air handling unit provides control over the mass flow rate, temperature, and humidity of the air that is injected into the cabin. Several temperature probes monitor surface as well as air temperatures throughout the test (see Fig. 2). Other environmental parameters such as black globe temperature, air humidity, and airflow velocities are also measured around the tester. The human test subjects that underwent thermal exposures are provided with identical and thermally characterized clothes (T-shirt+legging+shoes resulting in a clo of 0.38) for the experiments. Each tester went through the following exposure: Throughout the test, airflow and humidity from the air handling unit are fixed to 250m 3 /h and 50% respectively. Air is injected into the cabin through aerators. There are three aerators at the center of the dashboard, one on left and right side corners, two others are below the wind shield (Fig. 1) and two below the dashboard near the driver and front passenger feet. All temperature sensors are calibrated using a standard Pt100 thermometer with an accuracy of 0.2 • C. During tests, the environmental conditions are continuously recorded at an interval of 10 seconds. Thermal sensation and comfort votes are collected at a five-minute interval and the Zhang nine-point scale is used for the votes.

Test scenarios 2.2.1 Description

Scenarios have been designed to bring the human body from the comfort zone (preconditioning at 25 • C before entering in the test bench or walls and air temperature setpoint maintained at 25 • C) to a discomfort zone (cool or warm) and then bring it back to the comfort zone. The investigated scenarios are the followings:

• Test A: injected air and panel temperatures set at 45 • C for 30 minutes and afterwards switched abruptly to 25 A number of at least eight human subjects by scenario is recommended [START_REF] Iso | Ergonomics of the thermal environment -Evaluation of thermal environnements in vehicles Part 3: Evaluation of thermal comfort using human subjects[END_REF] in thermal comfort experimental investigation. We observed that this number could be reduced to a minimum of five human subjects to capture the qualitative mean trend of sensation and comfort votes as most individual signals are dampened making the mean vote curve and the standard deviation band noiseless.

Validation

To make sure that human subjects are experiencing nearly the same thermal environment, it is checked that measured temperatures on the panels or at the aerator nozzles are effectively the given temperature instructions. Fig. 3 shows for instance that for the test scenario C, there is a very good agreement between the temperature of the fifth water-glycol circulation circuit (B5 for loop or Buckle number 5) regulating among others the panel number five and the temperature on the panel number five (P5 for Panel number 5). A very good agreement between the six tests is found as well. Likewise, during the test scenario B for instance, it is observed a good match between the temperature at the central aerator nozzle (TC0 in Fig. 2) and the air handling unit loop (Fig. 4). The temperature on thermocouple 13 (see Fig. 2) located at the midpoint between the driver and the passenger seats at 40 cm from the roof shows that the general thermal environment is comparable for all testers. However discrepancies of around 1 • C can be found in the stationary part whereas they can reach 2 • C to 4 • C in the very transient part (see Fig. 7). UCB Zhang local comfort models prediction ability in transient situations is investigated in this study. Thus, the thermal environment is intended to keep homogeneous by setting all panels and blown air temperature setpoints identical and by blowing through aerators an air at a high flow rate (250m 3 /h). Despite this, the thermal stress experienced by testers is neither homogeneous nor very heterogeneous (high thermal asymmetry). Effectively, as can be seen in Fig. 8, for the test scenario B, there are noticeable differences between temperatures measured by the probe TC30 which is located at the midpoint between the driver and the passenger at 12 cm from the roof and the one located driver side below the dashboard and above the foot pedals (TC2 in Fig. 2). For instance at t = 120 min, the probe TC2 reaches 16 • C whereas the probe TC30 measures a temperature around 18.5 • C. Thus, the thermal environment experienced by human subjects is considered to be transient and quasi-homogeneous.

Zhang overall sensation model

The Zhang global sensation model So as proposed in [START_REF] Zhang | Human thermal sensation and comfort in transient and nonuniform thermal environments[END_REF] is the weighted average of local sensations on 19 body parts. It stipulates that some body parts have larger weight than others and that weighting for each body part can be different depending whether it is warmer or cooler than the mean sensation. The importance of local asymmetry is emphasized suggesting a weight factor for each body part as a function of difference between the local and the average sensation. The global sensation is measured on a 9-point ASHRAE-scale ranging from -4 (very cold) to 4 (very hot).

So = 19 i=1 w i S i 19
i=1 w i (1)
where S i is the local sensation on the body part i obtained from people votes and w i is the weighting factor,

w i = a i (S i -Sm) (2)
with a i parameters of the individual body parts (numerical values are given in Table 6.4 in [START_REF] Zhang | Human thermal sensation and comfort in transient and nonuniform thermal environments[END_REF]) and Sm the area weighted average sensation,

Sm = 19 i=1 A i S i 19 i=1 A i (3)
In [START_REF] Zhang | Thermal sensation and comfort models for non-uniform and transient environments: Part III: wholebody sensation and comfort[END_REF], Zhang proposed to reconsider the way of evaluating the overall sensation. Two different conditions are addressed separately:

• there are body parts feeling a strong opposite sensation (Sl < 0 for instance) compared to the sensation felt by the others (Sl ≥ 0) which represent the majority of the body parts;

• There are no body parts feeling an opposite sensation regarding the other body parts (Sl ≥ 0 or Sl ≤ 0 for all body parts).

In the first case, body parts feeling opposite sensations act to pull the overall sensation of the rest of the body parts towards them. Each body part feeling opposite sensation can be viewed as creating an individual force in order to modify the overall sensation of the rest of the body. In the second case, the overall sensation is driven by the most extreme sensations (|Sl| ≥ 2) creating a sort of complaint in the mind. When there are no extreme local sensations, the complaint-driven process becomes less obvious and the overall sensation approaches the average of all the local sensations.

The overall sensation model is compared to the people votes collected during the experimental campaign. For different test scenarios in hot and cool thermal stress (A, B and C presented in the previous section), people local sensation votes are recorded and given as inputs to the Zhang overall sensation model. The output is averaged regarding to the number of human subjects and compared to the averaged actual people votes. In Fig. 9, the average people vote is depicted with a plain line and the standard deviation by a solid stripping around the mean vote. Both Zhang models (the original one dating from 2003 and the revised one dating from 2010) are also represented. A good match between the experimental data and the models is found. The revised version is performing better than the original one as for the most of the time the model is close to the mean vote and almost always under the standard deviation. The formula for the local thermal comfort index derived by Zhang [START_REF] Zhang | Human thermal sensation and comfort in transient and nonuniform thermal environments[END_REF] is based on effects seen in the literature and in the experimental data collected during her own tests. It is observed that the hotter or colder people are, the more uncomfortable they feel [START_REF] Wang | Observation of upper-extremity skin temperature and corresponding thermal sensations[END_REF]. Moreover, based on the overall sensation the local sensation at which the maximum comfort occurs is shifted to the cooler or the warmer side. For instance, when the whole body is warm, local cold or cool stimuli are perceived as pleasant [START_REF] Hensel | Thermal sensation and thermoreceptors in man[END_REF][START_REF] Cabanac | Plaisir ou deplaisir dela sensation thermique et homeothermie[END_REF]. It is also observed that when thermal stimuli remove the heat stress or relieve the discomfort, sensation of pleasure is created and the magnitude of the comfort is increased.

Compared to the magnitude of maximum comfort in neutral overall thermal state, its value is shifted and increased asymmetrically when the overall thermal state is warm or cold [START_REF] Dm | Perceived intensity of peripheral thermal stimuli is independant of internal body temperature[END_REF][START_REF] Attia | Thermal pleasantness and temperature regulation in maan[END_REF][START_REF] Kuno | Comfort and pleasantness[END_REF][START_REF] Cabanac | Pleasure: the common currency[END_REF]. The comfort is measured on a 9-point ASHRAE-scale ranging from -4 (very uncomfortable) to 4 (very comfortable).

Lc = le slope -ri slope exp(5(Sl + of f set)) + 1 + ri slope • f + Lc max (4)
with

So < 0 = { of f set = C 8 + C 31 • |So| Lc max = C 6 + C 71 • |So| (5)
So ≥ 0 = { of f set = C 8 + C 32 • |So| Lc max = C 6 + C 72 • |So| (6)
and

le slope = 4 + LC max | -4 + of f set| N , ri slope = -4 -LC max |4 + of f set| N (7)
and

Sl + of f set < 0 → f = -|Sl + of f set| N Sl + of f set ≥ 0 → f = |Sl + of f set| N (8)
In the revised version, the framework of the model and the assumptions are kept identical to the original model but a number of the model coefficients have been modified (see [START_REF] Zhang | Thermal sensation and comfort models for non-uniform and transient environments: Part II: local comfort of individual body parts[END_REF]).

It has been noticed that for some body parts the revised model of Zhang [START_REF] Zhang | Thermal sensation and comfort models for non-uniform and transient environments: Part II: local comfort of individual body parts[END_REF] is not matching the trend of people votes when the sensation indices are negative (see Fig. 10a). It is then recommended to use the original version of the Zhang [START_REF] Zhang | Human thermal sensation and comfort in transient and nonuniform thermal environments[END_REF] model for local comfort predictions.

As presented in Fig. 10, local comfort can differ from one body part to another even if they are experiencing the same quasi-homogeneous cool thermal stress. Local comfort on hands (see Fig. 10c) is not very sensitive to thermal strain (at t = 60 min) or relief (at t = 120 min). Belly (see Fig. 10d), thighs, upper arms and back are body parts resisting to comfort deterioration as the comfort level decreases slowly. However, they react promptly to a thermal solicitation that pull them from a discomfort zone (as it can be seen at t = 120 min Fig. 10d when the temperature setpoint is switched to 25C). Lower legs (see Fig. 10a), neck, head and face are moderately sensitive to comfort deterioration or recovery. And conversely, feet (see Fig. 10b) and forearms are very sensitive body parts. When experiencing quasi-homogeneous warm thermal stress(see Fig. 11), sensitivity of body parts differs from the trend that has been observed during cool thermal solicitations. Effectively, only head and face evidence a high deterioration of the local comfort (see Figs. 11b and11d) whereas the deterioration remains moderate on the other body parts (see Figs. 11a and11c).

Regarding test A, for body parts such as chest, head (see Fig. 11b) or feet the model is close to the mean vote. As for the rest of the body parts (lower arms, belly, lower legs, upper arms, upper back, lower back, thighs, neck and hands (see Fig. 11a)), there is a good qualitative accordance between the model and the vote although the quantitative differences between the model and the mean vote can be higher and reach 2 points on a 9-point ASHRAE-scale. The worst case is presented in Fig. 11a. One can notice that the original Zhang model predicts on the left hand a comfort which is 2.5 points lower than the mean vote at t = 0 min. Despite the fact that the model prediction is quite far from the mean vote, it still remains close to the range ±σ where σ is the root mean square deviation. It is also worth noting that the standard deviation can be quite large and the ±σ interval range can cover 3 to 4 points on a 9-point ASHRAE-scale. This high deviations are mainly due to the variability of the thermal environment people experienced during the test (see Fig. 7) and the effect of testers inter-variability in terms of psychology, physiology and physical morphology on the sensation and comfort perceptions.

Likewise, people local comfort votes during the test scenario B are compared to Zhang models. Despite the high discrepancies observed on body parts such as hands (see Fig. 10c), upper arms, back, belly (see Fig. 10d), neck, chest, head or thighs, fair agreements are found between the people votes and the Zhang model on the other body parts (forearms, lower legs (Fig. 10a),feet (Fig. 10b)). As for the test scenario C, if for body parts such as head and face (see Fig. 11d) feet, neck, belly, chest, thighs, lower back, lower legs, forearms or upper arms, there is a good matching between the model and the mean people vote, discrepancies are found on other body parts such as hands (see Fig. 11c) and upper back. Fig. 12 summarizes the deviation distribution between predictions computed with the both Zhang models and peoples vote on all the body parts. It can be observed that on the whole, Zhang models are more likely to predict a low level of comfort than the vote of peoples. Moreover, it is observed that the revised version is less accurate than the original one, supporting our recommendation to use the original version of the Zhang model to predict local comfort.

Zhang overall comfort model

Zhang observed that the overall comfort follows a complaint pattern. In other words, the most uncomfortable body parts have crucial impacts on the overall comfort perception.

When the thermal conditions are transient or when the subject is allowed to control his/her thermal environment, the overall comfort is evaluated as the average of the two minimum and the maximum local comfort votes. Otherwise, the overall comfort is the average of the two minimum local comfort votes. In conclusion, based on the experimental observations it seems that the revised Zhang model [START_REF] Zhang | Thermal sensation and comfort models for non-uniform and transient environments: Part II: local comfort of individual body parts[END_REF] better predicts global sensation and comfort whereas the original one [START_REF] Zhang | Human thermal sensation and comfort in transient and nonuniform thermal environments[END_REF] shows greater performances in predicting local comforts. Moreover, it is worthwhile to notice as evidenced with tests B that Zhang local comfort models predict poorly the experimental trend in cool/cold environments.

Parametric study and suggestions

The Zhang comfort model was compared to people votes in an automobile environment and a good qualitative accordance was found particularly in warm environment supporting hence the following parametric study. The aim of this investigation is to represent graphically noticeable trends of the local comfort regarding to body zones local sensation and the global sensation with a view to deduce usable strategies for heating and cooling system inside of an automobile cabin (Fig. 14). It is noticed that based on the previous comparison of the two models of Zhang [START_REF] Zhang | Human thermal sensation and comfort in transient and nonuniform thermal environments[END_REF][START_REF] Zhang | Thermal sensation and comfort models for non-uniform and transient environments: Part II: local comfort of individual body parts[END_REF] with people votes in warm and cold environments, the original version of the Zhang [START_REF] Zhang | Human thermal sensation and comfort in transient and nonuniform thermal environments[END_REF] model seems to better represent the local comfort. Therefore, we have decided to take into consideration the coefficients of the original version and do the interpretation accordingly. When a thermal stress is applied on a body part, it is seen that the local comfort felt on that body part depends on the global thermal stress of the entire body. Moreover, its response to the thermal stress in terms of local sensation of pleasure can have a very different trend to the one observed on another sector of the body. Understanding the evolution of the local body parts comfort preferences in various local and global thermal stresses enables to better set the HVAC system instructions.

The equation 4 has been plotted for each body part as a function of local sensation in different thermal ambiances represented by the global sensation parameter. The local comfort perception on the neck and thighs are independent of the overall thermal sensation. The maximum local comfort is centred on the thermal neutrality (So = 0 and Sl = 0) for the thighs and slightly shifted to the warm side for the neck. The local comfort decreases linearly when local sensation moves away from the thermal neutrality state irrespective of the global sensation (Figure 14c, Figure 14j). Neck and thighs need then to be kept around thermal neutrality.

Maximum local comfort is reached on the face body part when it is slightly refreshed from thermal neutrality and compared to the neck or thighs, the comfort zone (range of the local sensations for which the local comfort is positive, Cl ≥ 0) is wider suggesting a greater tolerance regarding to the thermal stress. Moreover, the asymmetrical shift of the maximum local comfort when moving from the global thermal neutrality (So = 0) shows that the face body part should be kept in a cool environment. Effectively, when the overall sensation is getting hotter and hotter the face is feeling more and more comfortable when it is kept cool. However, when the global sensation is getting colder and colder the face requires thermal neutrality to feel the maximum comfort (Figure 14b).

The head needs to be cooled in environments leading to warm global sensations, and kept around thermal neutrality in cold environments. It is worthwhile to notice that the comfort zones are wide and the comfort feelings are not symmetrical when moving from the global thermal neutrality (So = 0). It should be noticed that local comfort predictions of Zhang in hot environments are unrealistic as the local comfort model fails to drop when the local sensation becomes very cold (Figure 14a).

Hands have a narrow comfort zone at the thermal neutrality state of the body (So = 0). It widens when the overall sensation moves away from the neutral thermal sensation. The maximum comfort is also shifted away symmetrically from the thermal neutrality state with the enlarging distance between the overall sensation and the neutral overall thermal sensation. For instance when the overall sensation is cold, heating the hands will raise its local comfort to a great comfort but when the heating exceeds a certain threshold the felt comfort drops very abruptly (Figure 14g).

The comfort zone is wide for the feet suggesting that they can tolerate a wide range of thermal stress. People seem to be more comfortable with warm feet than with cold ones. Therefore, a local solution for enhancing thermal comfort inside a cabin would be to locally heat the feet in cold global conditions whereas the feet in warm global condition must be cooled with caution (feet prefer to be refreshed than cooled). Otherwise, the comfort may drop abruptly (Figure 14l). It should be also noticed that local comfort predictions of the Zhang model are unrealistic in cold environments as the feet local comfort do not drop when the local sensation becomes extreme.

When the overall sensation is cold, warming the pelvis region increases the local comfort but only up to a certain level. For instance, for a cold global sensation of So=-2, a warm local sensation of (Sl = 2.5) is perceived with a comfort level higher than 4 on the 9-point scale but when the heat applied is too hot (Sl > 2.5), the comfort drops sharply. On the other side, cooling the pelvis when the global sensation becomes warmer do not improve the local comfort. It suggests that there is no need for instance to equip an active seat with cooling devices in order to refresh the pelvis area in hot thermal conditions (Figure 14i).

The chest behaviour is similar to the pelvis but has a slightly wider comfort zone. Local warming of the chest does increase significantly thermal comfort when the body is cold. However, local cooling of the chest does not improve the thermal comfort when the body is warm (Figure 14d).

Upper arms seem to be body parts with a secondary importance for an HVAC as whatever the effort put to heat this body part, it would only result on moderate satisfaction level in cold environment. Moreover, no improvement can be expected in cooling this body part in hot environments (Figure 14e).

The back is an excellent candidate to warm in priority cold environments as great comfort can be reached by slightly warming this zone. It also means that the comfort can degrade if the heating is felt too hot. In hot environments, it must be refreshed cautiously as it seems to tolerate only cool thermal stress (Figure 14h).

In cold environments heating lower arms enables to improve the local comfort even if local comfort predictions are unrealistic in extreme cold conditions. In warm environments, only slight cooling can be applied in order to prevent a comfort degradation on this zone (Figure 14f).

Lower legs behaves similarly to the hands except that there is no symmetry in the shift of the maximum comfort when the global sensation moves away from the neutral sensation (Figure 14k).

From examining the different patterns for each body part, one sees that the thermal local or global sensations are not very meaningful to give instructions in order to optimize comfort whereas the local thermal preferences for each body part are much more relevant. For instance, under global neutral conditions (So = 0), the face and lower legs show a preference for a slightly cool local sensation whereas the pelvis and arms show a preference for a warm local sensation. The chest, the back, thighs and hands do not show any preference in neutral conditions. Therefore, to achieve a maximum comfort at neutral conditions heating of the pelvis is recommended while slightly cooling the face. However, it is worthwhile to notice that these directives are linked only to the temperature of the HVAC system as the speed of the air or the humidity, which are also sources of comfort and discomfort, are not considered in the Zhang model. Depending on the objective one is looking for, the HVAC system can be set accordingly. Optimizing comfort requires for each body part a focus on the level of local sensation that corresponds to the maximum of its local comfort. However, optimizing the energy use requires that the HVAC system maintains local sensations level so that local comforts 1. Thus, we can see that for a cold global sensation chest, feet, lower arms and the pelvis have a preference to be vigorously heated whereas the back, hands, lower legs and upper arms need to be slightly heated (max Sl = 2). Head, face, neck and thighs rather prefer a sensation near the thermal neutrality. The HVAC strategy can then be set accordingly with a maximum and minimum thermal power applied respectively on the feet and the face. An energy saving strategy would be to keep the head cold (Sl = -2) while maintaining arms, hands, feet and the pelvis around thermal neutrality and other body parts cool (Sl = -1). For a warm global thermal sensation of So = 2 (Table 2), cooling lower legs and the head vigorously, cooling hands and the back moderately and refreshing slightly the face while maintaining the other body parts such as the neck, chest, thighs, pelvis, arms and feet around the thermal neutrality will be the best possible scenario for optimizing comfort in this situation. An energy saving strategy would be to maintain face, chest and feet hot while keeping the rest of the body parts slightly warm leading to large improvements in local thermal comfort with a moderate thermal effort. In a very cold environment, (So = -4) feet, chest, pelvis, arms, lower legs and hands have to be vigorously heated whereas the back side need to be only moderately heated. Moreover, the head, face, neck and thighs have to be maintained around thermal neutrality. An energy saving strategy would be heating moderately the feet and leaving relatively cold the head (Sl = -2) while keeping arms, hands, pelvis and lower legs around the thermal neutrality and the other body parts relatively cool (Sl = -1). In a very hot environment (So = 4), the head, hands, lower legs and the back have to be vigorously cooled whereas the other body parts need to be maintained around thermal neutrality. An energy saving strategy would be to keep refreshed the pelvis while head, hands and the back are maintained around thermal neutrality. Feet, chest and the face have a large resiliency zone so that they can be kept warm (Sl = 2) whereas other body parts can be maintained slightly warm (Sl = 1).

From the above analysis, it is showed that smart and local thermal solicitations on specific body parts can be set to prevent from comfort deterioration when the whole body is placed in a discomfort zone. Such an investigation would not be possible to consider using the PMV-PPD model as it has been derived to compute the physiological response of the body in terms of sensation (heat balance between the body and environment) and thus ignores the influence of the psychological effect in the prediction of people comfort (concept of pleasure when leaving the discomfort zone for instance).

Conclusion

In this study, it is proposed to confront Zhang models prediction to people votes in car cabin situations in transient and quasi-homogeneous cool and warm environments. The original Zhang model is suggested for estimating the local comfort. It is observed that for the most of the body parts, quite good qualitative agreements are found between predictions and actual votes in warm and cool environments. However, the Zhang local comfort model has to be improved for a number of body parts. The revised Zhang model is recommended for the global sensation prediction from local sensations and for the model giving the global comfort from local comforts. The global sensation and comfort models showed very satisfying performances regarding the experimentally obtained votes. As can be noticed, the present study targeted mainly transients scenarios and the next steps would be to confront experimentally the Zhang model in very asymmetric environments (sun load on the upper body parts for instance).

Based on this initial results, a parametric study has been carried out. Thermal preferences seem to be impacted by the thermal state of the entire body and are very different from one body part to another. For different thermal ambiances experienced by the human body and measured by means of the overall sensation, body parts that need to be handled in priority are identified enabling to set adequate strategies to bring them back to comfort. Comfort-oriented and energy saving-oriented (downgraded mode) strategies are suggested and it is noticed that depending on the strategy, body parts that need to be focused and the resulting HVAC settings can be very different.

The PMV-PPD approach is not the appropriate model to investigate customized solutions with localized strategies on body parts mainly in transient phases (very common in automotive environments) as the concept of pleasure or comfort is not included in this model. The Zhang model appears to be a good candidate for this kind of approaches. Thanks to refined comfort models such as Zhang models, frugal and effective solutions can be conceived to bring comfort to occupants inside car cabins in order to reduce the impact of auxiliaries on EVs range.

•

  30 minutes of sedentary preconditioning at 25 • C in a separate room • 90 or 180 minutes of test with the tester seated in the driver seat inside the test bench experiencing a transient quasi-homogeneous scenario (a) external sight (b) internal sight

Figure 1 :Figure 2 :

 12 Figure 1: The test bench

  (a) Water-glycol circulation circuit temperature (b) Panel temperature

Figure 3 :

 3 Figure 3: Temperature profiles on the panel 5 and on its corresponding water-glycol circulation circuit for the test scenario C

Figure 4 :

 4 Figure 4: Temperature profiles recorded on TC0 and in the air handling unit loop

Figure 5 :

 5 Figure 5: Box plots of panels temperature RMSD for test scenario A, B and C. The diamond represents the mean value.

Figure 6 :

 6 Figure 6: Box plots of aerators temperature RMSD for test scenario A, B and C. The diamond represents the mean value.

Figure 7 :

 7 Figure 7: Temperature profiles measured by the sensor TC13 during the test scenario C

Figure 8 :

 8 Figure 8: Temperature profiles measured by TC2 and TC30 during the test scenario B

Figure 9 :

 9 Figure 9: Comparison of the Zhang overall sensation model with people votes

Figure 10 :

 10 Figure 10: Examples of local comfort on body parts when experiencing cool thermal stress

Figure 11 :

 11 Figure 11: Examples of local comfort on body parts when experiencing warm thermal stress

  (a) Discrepancies between the original model of Zhang and the mean vote (b) Discrepancies between the revised model of Zhang and the mean vote

Figure 12 :

 12 Figure 12: Box plots illustrating the distribution of discrepancies between models prediction and the mean vote.

Figure 13 :

 13 Figure 13: Comparison of the Zhang overall comfort model with people votes

Figure 14 :

 14 Figure 14: Local thermal comfort for different local and global thermal sensations

Figure 14 :

 14 Figure 14: Local thermal comfort for different local and global thermal sensations (cont.) 23

Figure 14 :

 14 Figure 14: Local thermal comfort for different local and global thermal sensations (cont.)

  Test C: injected air and panel temperatures set at 25 • C for 60 minutes, switched abruptly to 35 • C for 60 minutes and reset to 25 • C for another 60 minutes. Number of human subjects: 6.

	• C for an additional 60 minutes.
	Number of human subjects: 10.
	• Test B: injected air and panel temperatures set at 25 • C for 60 minutes,
	switched to 15 • C abruptly for an additional 60 minutes and reset to
	25

• C for another 60 minutes. Number of human subjects: 5.

•

Table 1 :

 1 Maximum local thermal comfort and its corresponding local sensation for a cold global thermal sensation So = -2

	Body Element Maximum C loc Corresponding S loc
	Head	1.9	-0.5
	Face	2	-0.24
	Neck	1.9	0.24
	Chest	3.7	2
	Upper Arms	2.2	1
	Lower Arms	4	3.2
	Hands	2.97	1.55
	Back	3.6	1
	Pelvis	4	2.5
	Thighs	1.95	0
	Lower Legs	2	1.5
	Feet	2.6	4

Table 2 :

 2 Maximum local thermal comfort and its corresponding local sensation for a warm global thermal sensation So = 2

	Body Element Maximum Cl Corresponding Sl
	Head	2.25	-2.85
	Face	2.82	-0.57
	Neck	1.9	0.24
	Chest	1.8	0
	Upper Arms	2.1	0.24
	Lower Arms	3	-0.24
	Hands	3	-1.5
	Back	2.1	-1.1
	Pelvis	1.4	0
	Thighs	1.95	0
	Lower Legs	4	-3
	Feet	2.2	-0.2
	remain positive. Let's consider a cold global thermal sensation of So = -2.
	The maximum level of comfort and the local thermal sensation for which this

Table 3 :

 3 Maximum local thermal comfort and its corresponding local sensation for a very cold global thermal sensation So = -4

	Body Element Maximum Cl Corresponding Sl
	Head	2.4	-0.5
	Face	2.0	0
		1.94	0.24
	Chest	4	2.7
	Upper Arms	2.16	1.9
	Lower Arms	4	3.9
	Hands	4	3
	Back	4	1.8
	Pelvis	4	3.5
	Thighs	1.96	0
	Lower Legs	3.8	3.4
	Feet	2.3	4
	comfort is reached are displayed in Table

Table 4 :

 4 Maximum local thermal comfort and its corresponding local sensation for a very hot global thermal sensation So = 4

	Body Element Maximum C loc Corresponding S loc
	Head	2.6	-4
	Face	3.62	-0.73
	Neck	1.94	0.24
	Chest	1.9	0
	Upper Arms	2.1	0.3
	Lower Arms	3.5	-0.95
	Hands	4	-3
	Back	2.2	-2.2
	Pelvis	0.1	-0.7
	Thighs	1.96	0
	Lower Legs	4	-4
	Feet	2.9	-0.5


Dora Garduño-Jiménez

Alejandra Nuñez-Pineda

Melina Tapia-Tapia

Gerardo Salinas
email: gerardo.salinassanchez@enscbp.fr

Bernardo A Frontana-Uribe

Quantification of MWCNTs incorporated into PBTh matrix composite obtained by electrochemical polymerization and their effect on the conductive properties and structure

Keywords: MWCNT, Polybithiophene, electrochemical polymerization, in-situ electrochemical conductance

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

Introduction

Polybithiophene (PBTh) is one of the most interesting conducting polymers in the past years due to its easy chemical and electrochemical synthesis and a good chemical and electrochemical stability [START_REF] Mccullough | The chemistry of conducting polythiophenes[END_REF]. In order to improve the mechanical, physical and electrical properties of conducting polymers, different types of composites have been synthesized by incorporation of carbon nanotubes (CNT's) [START_REF] Zanardi | Polythiophenes and polythiophene-based composites in amperometric sensing[END_REF][START_REF] Keru | A review on carbon nanotube/polymer composites for organic solar cells[END_REF] Several examples of these type of composites formed by the mixture of single walled carbon nanotubes (SWCNT's) [START_REF] Terasawa | High-performance PEDOT:PSS/Single-walled carbon nanotube/ionic liquid actuators combining electrostatic double-layer and faradaic capacitors[END_REF] and multiwalled carbon nanotubes (MWCNT's) [START_REF] Wang | High energy conversion efficiency conducting polymer actuators based on PEDOT:PSS/MWCNTs composite electrode[END_REF][START_REF] Swathy | AOT assisted preparation of ordered, conducting and dispersible core-shell nanostructured polythiophene-MWCNT nanocomposites[END_REF] with different polythiophenes have been studied in the last years. These materials present a considerable increase on the electroactive area and conductivity [START_REF] Wang | In-situ fabrication and enhanced thermoelectric properties of carbon nanotubes filled poly(3,4-ethylenedioxythiophene) composites[END_REF][START_REF] Wang | Thermoelectric properties of the PEDOT/SWCNT composite films prepared by a vapor phase polymerization[END_REF], allowing their use for electrochemical sensing [START_REF] Braik | Highly sensitive amperometric enzyme biosensor for detection of superoxide based on conducting polymer/CNT modified electrodes and superoxide dismutase[END_REF][START_REF] Amirzadeh | Non-enzymatic glucose sensor based on copper oxide and multi-wall carbon nanotubes using PEDOT:PSS matrix[END_REF], as supercapacitors [START_REF] Wang | High-performance stretchable supercapacitors based on intrinsically stretchable acrylate rubber/MWCNTs@conductive polymer composite electrodes[END_REF][START_REF] Zhao | Highly flexible and conductive cellulose-mediated PEDOT:PSS/MWCNT composite films for supercapacitor electrodes[END_REF] and in organic solar cells [START_REF] Keru | A review on carbon nanotube/polymer composites for organic solar cells[END_REF] Incorporation of CNT's commonly occurs during the chemical [START_REF] Dettlaff | Electrode materials for electrochemical capacitors based on poly(3,4 ethylenedioxythiophene) and functionalized multi-walled carbon nanotubes characterized in aqueous and aprotic electrolytes[END_REF] or electrochemical polymerization in a suspension mixture formed by the monomer of interest, electrolyte (electrochemical oxidation), oxidative agent (chemical oxidation) and different percentages in weight of CNT's. Since the mechanical, physical and electric properties of these materials are strongly linked to the amount of CNT's present inside the polymer matrix their efficient quantification is needed. Most of the reports that involve conducting polymer (CP) composites which incorporate CNT's (CP/CNTs) does not quantify the amount of this carbon species that have been incorporated into the polymeric matrix, and limit the composition description to the percentages in weight used of CP and CNT's in the polymerization suspension [START_REF] Braik | Highly sensitive amperometric enzyme biosensor for detection of superoxide based on conducting polymer/CNT modified electrodes and superoxide dismutase[END_REF][START_REF] Wang | High-performance stretchable supercapacitors based on intrinsically stretchable acrylate rubber/MWCNTs@conductive polymer composite electrodes[END_REF] Commonly these works assume that the incorporation of the carbon species is proportional to the quantity present during the polymerization. Other studies present the mass percent of MWCNT's in a composite by dividing the total mass of the composite by the mass of the MWCNT's used [START_REF] Song | Influence of polymerization method on the thermoelectric properties of multi-walled carbon nanotubes/polypyrrole composites[END_REF], or simply polymerizing in the same conditions with and without CNT's and weighting the obtained samples [START_REF] Bai | In situ polymerization and characterization of grafted poly (3,4-ethylenedioxythiophene)/multiwalled carbon nanotubes composite with high electrochemical performances[END_REF]. Since elemental combustion analysis is a simple and accurate method to verify the percentage of elements present in an organic sample, some recent and scarce investigations describe it use to follow the MWCNT's incorporation into the CP obtained by chemical oxidation with FeCl3 (PTh [START_REF] Swathy | AOT assisted preparation of ordered, conducting and dispersible core-shell nanostructured polythiophene-MWCNT nanocomposites[END_REF] and PEDOT [START_REF] Dettlaff | Electrode materials for electrochemical capacitors based on poly(3,4 ethylenedioxythiophene) and functionalized multi-walled carbon nanotubes characterized in aqueous and aprotic electrolytes[END_REF]) composite matrix. As far as we know, this method has not been applied to composites obtained by electrochemical polymerization, therefore, in this work we present the use of elemental combustion analysis for the simple quantification of MWCNT's inside PBTh matrix composites prepared at different scan rate and concentration of MWCNT present in the polymerization solution. Finally, in order to evaluate the properties of the PBTh/MWCNT composite obtained, in-situ electrochemical conductance analysis and atomic force microscopy (AFM) scanning electronic microscopy (SEM) and X-ray diffraction (XRD) studies were carried out. These studies demonstrate an improved electrochemical response and an interesting change in the morphology of the composite.

Experimental

Reagents

LiClO4 (Aldrich, 99.9%), 2,2'-bithiophene (Aldrich, 97%), anhydrous ACN (Fermont HPLC grade 99.9%) and multiwall carbon nanotubes (Sunnano®, ≥ 99%, OD, 10 ~ 35 nm; L, 1~10µm) were used.

Electrochemical synthesis and characterization of PBTh/MWCNT composites

Cyclic voltammetry, for analyzing bithiophene (BTh) and the working media, was performed in a classic three-electrode cell (WE: 3 mm Pt disk) containing anhydrous acetonitrile (ACN, 5 mL) as solvent and LiClO4 as supporting electrolyte (0.1 M) by means of a BAS 100B potentiostat. The BTh concentration used for all experiments was 0.015 M.

Potentiodynamic macro-electropolymerizations were carried out using a three-electrodes cell (Figure SI-1) fitted with an alumina 0.03 µm polished Pt foil (0.48 cm 2 of electroactive area), a Pt mesh (0.6 cm 2 ) and Ag/AgNO3 used as working, counter and reference electrodes respectively. The electropolymerizations were carried out at 25 °C and at three different scan rates (v = 0.1, 0.05 and 0.02 V/s) under gentile constant stirring in order to avoid CNT's sedimentation.

After the macro-electropolymerizations, the films were wash-out with HPLC grade ACN pealed-off from the electrode and vacuum dried. The elemental combustion analysis of all the films was carried out by using an Elementar® Vario Micro cube. Since from the elemental combustion analysis the percentage of carbon (%C) and sulphur (%S) inside the sample is obtained, the total mass of carbon and sulphur (mT,Carbon and mT,sulphur respectively) can be calculated by equation 1 and 2.

% % = , (1)
% % = , (2)
Knowing that the only source of sulphur is the PBTh and per each mol of sulphur 4 mol of carbon belongs to a thiophene molecule, the amount of carbon coming from PBTh (mPBTh,carbon) may be calculated by equation [START_REF] Keru | A review on carbon nanotube/polymer composites for organic solar cells[END_REF].

, ! "#!$ %&. ( ! "#!$ ) * + $, - ! "#!$ ) &. + $, - + $, - = ./0 , (3)
If the total amount of carbon (mTcarbon) is equal to the sum of carbon present in PBTh and MWCNT, the difference between the carbon of the PBTh and the total amount of carbon is equal to the amount of carbon coming from the MWCNT (mMWCNT,carbon) (equation 4).

1 23456,789:;< = , -./ , (4)
With this value the percentage in weight of MWCNT (%MWCNTT) inside the composite can be calculated (equation 5).

1 23456,789:;< ,+ $, - ) >100 = %23456 6 (5)
In-situ electrochemical-conductance measurements were carried out using a HEKA CIP 2 bipotentiostat system specially built for this application. As working electrodes were used interdigital microarrange electrodes (IDMAE) of 1 cm x 0. Conductance was calculated according to Ohm law, which is directly related with specific conductivity. Even though without an exact thickness value it is not possible to determine the polymer conductivity, conductance behavior is generally accepted to get a first indirect insight of the conductivity changes with the redox change (see supporting information for details) [START_REF] Salinas | Electrochemical polymerization, characterization and in-situ conductivity studies of poly-3,4-ortho-xylendioxythiophene (PXDOT)[END_REF]. More details about this technique and examples of the use of conductance measurements in conducting polymers can be found elsewhere in the literature [START_REF] Salinas | Analysis of conjugated polymers conductivity by in situ electrochemical-conductance method[END_REF].

For the morphology, surface and structure characterization, atomic force microscopy Diffractometer Bruker D8 Advance using CuKα radiation and equipped with a Linxeye detector was used.

Results and discussion

The cyclic voltammetry of BTh ( Ag/AgNO3 respectively at different scan rates (Figure 1). No change on the oxidation onset potential of the charge/discharge process in the presence of the MWCNT at different scan rates was observed.

Figure 1 here

The weight percentage of MWCNT's inside the different PBTh composites was obtained from the macro-electropolymerizations films using equations 1-5 at different concentrations of MWCNT's and scan rates (Table I). As it can be seen from these results the highest weight percentage of MWCNT's was obtained at low scan rates values. Since, during the macro-electropolymerization, MWCNT's are attracted to the charged oligomers of bithiophene, low scan rates values allow a longer residence time in potentials where these oligomers are in an oxidized state, therefore, the amount of MWCNT's inside the PBTh matrix increase. The amount of MWCNT's in suspension does not influence in an important way in the weight percentage of MWCNT inside the PBTh matrix. This observation is important because reports sometimes assume that the quantity of carbon species inside of the matrix, could be related with the material added to the polymerization solution and this is not the reality as shows the present study. Since the amount of MWCNT's that PBTh can insert in the matrix strongly depends on the polymerization kinetics and this depends on the scan rate and temperature, thus at constant scan rate and temperature the incorporated material is almost the same. However higher concentration of MWCNT's in suspension, improves the reproducibility of the experiment. This probably indicates that the interface concentration tends to be constant all along the experiment because polymerization is carried out under gentile stirring. By this method a real evaluation of the quantity of MWCNT's inside of the PBTh matrix was obtained, in comparison with other studies where only the amount of NT's in suspension is indicated [START_REF] Swathy | AOT assisted preparation of ordered, conducting and dispersible core-shell nanostructured polythiophene-MWCNT nanocomposites[END_REF][START_REF] Braik | Highly sensitive amperometric enzyme biosensor for detection of superoxide based on conducting polymer/CNT modified electrodes and superoxide dismutase[END_REF][START_REF] Wang | High-performance stretchable supercapacitors based on intrinsically stretchable acrylate rubber/MWCNTs@conductive polymer composite electrodes[END_REF]. The amount found to be incorporated agrees with the weight percentage found in other CP/CNTs (PEDOT) composites, value that oscillates between 19-43% depending on the experimental conditions used, determined by a similar method [START_REF] Dettlaff | Electrode materials for electrochemical capacitors based on poly(3,4 ethylenedioxythiophene) and functionalized multi-walled carbon nanotubes characterized in aqueous and aprotic electrolytes[END_REF]. From this literature antecedent where PEDOT was used, seems that CNTs incorporation might be controlled by the polymer backbone structure (thiophenes in both cases). In this moment of our study the real answer is not clear. Properties of the composite materials, CP/carbon species, strongly depend on the quantity of carbon species incorporated into the polymeric matrix. Therefore, this method could help to determine precisely the quantity of material that modulates the desired properties for example electrochemical conductivities.

Table I here

In order to verify this proposal, in-situ electrochemical-conductance measurements were performed (Figure 2) during the potentiodynamic electropolymerization of both, BTh and BTh/MWCNT's. From the current values obtained in all our samples we can propose that the thickness of the polymerizations of BTh without and with MWCNT are in the same order of magnitude. If this characteristic is fulfilled, then makes sense to propose that conductance value gives information of the specific conductivity behavior of the composite films. These studies showed the classical current increase of the anodic and cathodic signals and interestingly almost no difference was observed in the presence of the carbon species in the cyclic voltammetry behavior. On the other hand, conductance response showed fast electropolymerization kinetics for both experiments where the maximal conductance value is higher in the presence of the CNT's (47 mS for PBTh and ca. 63 mS for the PBTh/MWCNT's composite). The maximal value showed that the incorporation of the CNT's into the PBTh matrix increases the electrical performance; therefore, electrical transport in the composite is facilitated with the presence of the MWCNT's as has been previously reported [START_REF] Swathy | AOT assisted preparation of ordered, conducting and dispersible core-shell nanostructured polythiophene-MWCNT nanocomposites[END_REF][START_REF] Wang | In-situ fabrication and enhanced thermoelectric properties of carbon nanotubes filled poly(3,4-ethylenedioxythiophene) composites[END_REF][START_REF] Wang | Thermoelectric properties of the PEDOT/SWCNT composite films prepared by a vapor phase polymerization[END_REF]. The conductance curve tailing observed at the end of the conducting to isolating state transition, can be related to the kinetics evolution between both states. In the case of PBTh, tailing is long and ends at -0.70 V vs Ag/AgNO3, whereas the PBTh/MWCNT's composite shows a shorter tailing that ends at -0.25 V vs Ag/AgNO3.

This behavior let to propose that the presence of the CNT's increases the kinetics of the charge/discharge process. A second argument that reinforces this statement is the observation that as the scans evolve, an increase of the hysteresis value (∆EG) can be observed for both films. The hysteresis value for the charge-discharge conductance curve (ΔEG) can be used to characterize the easiness of switching between the insulatingconducting states giving also indirectly information about the internal organization of the polymer matrix [START_REF] Nalin De Silva | Long-chain 3,4-ethylenedioxythiophene/thiophene oligomers and semiconducting thin films prepared by their electropolymerization[END_REF]. In the presence of the MWCNT's ΔEG decreases ca. 100 mV compared to the observed with PBTh showing that the transition between the conductive thin film region and insulating regions is faster and less energetically demanding when MWCNT's are present in the polymeric matrix. Therefore, an improvement in the transition between the insulating-conducting states is confirmed and is caused by a better internal organization of the polymer matrix and higher conductivity of the composite. These two phenomena can be attributed to the additional possibility of extracting charged species that the presence of the incorporated material causes (Figure 2) [START_REF] Porras-Gutiérrez | In situ characterization by cyclic voltammetry and conductance of composites based on polypyrrole, multi-walled carbon nanotubes and cobalt phthalocyanine[END_REF]. This is attributed to a templating growth of the polybithiophene coating the MWCNT's surface. AFM experiments show, in the case of the polymer deposit (Figure 3a) a surface with globular structures with sizes of 833.24 nm in length and a Z value of 0.8 µm is observed. These structures are superimposed and at the same time present ultra-structure, causing that their percentage of surface is higher (44.25%) than in the case of the MWCNT's coated with the polymer (10.35%, Figure 3b). The ultrastructure of PBTh has an RMS value ranging from 774.562 to 966.183 nm (average value 870.3 nm), considering an area of 1 μm 2 . In the case of the composite material, the incorporation of the NT was verified by phase analysis images ( [START_REF] Sato | Dual Photoluminescence of polythiophenes thin films[END_REF][START_REF] Wang | Preparation and thermoelectric properties of polythiophene/multiwalled carbon nanotube composites[END_REF]. In fact, it has been described [START_REF] Swathy | AOT assisted preparation of ordered, conducting and dispersible core-shell nanostructured polythiophene-MWCNT nanocomposites[END_REF] that the characteristic broad peak observed in powder XRD at 2θ values ranging between 12° and 25° with its maximum is centered at 18.23° attributed to the amorphous domains of the PBTh chains obtained by chemical oxidation, disappears when polymerization is carried out in the presence of MWCNT's and a new sharp peak observed at a 2θ value of 26.48° is observed in the composite material. We agree with the authors of this work, were their proposal for rationalize this observation is that aromatic rings of carbon nanotubes and polythiophene would have undergone good solid-state ordering via π-π packing, that would let to explain the templating growth of the polybithiophene. This nano fibrous structure also explains the better conductivity and fast transition between the isolating and conducting states previously described and also attributed to a better arrangement of the composite macrostructure. In addition, an improvement in the transition between the insulating-conducting states due to a better internal organization of the polymer matrix was observed. SEM, AFM and XRD analysis let to distinguish unambiguously the presence of CNT's in the PBTh composite. A granular growth of polybithiophene covering along the CNT's structure was observed. This nano fibrous structure allows to explain he improvement on the conductivity and the fast

  5 cm, featuring separated Pt bands (10 µm) deposited on it (Figure SI-2). A three-electrode electrochemical cell fitted with a Pt foil counter electrode separated 0.5 cm from the working electrode (parallel and of the same size of the working electrode), an Ag/AgNO3 reference electrode and the IDMAE where used for the studies. A constant potential difference of 10 mV provided by one potentiostat was applied between the IDMAE branches to generate the drain current that circulates through the polymer during conductance determinations. The electropolymerizations were carried out at the same temperature mentioned previously.

(

  AFM) scanning electronic microscopy (SEM) and X-ray diffraction (XRD) experiments were carried out. An atomic force microscope model MFP-3D Origin from the Asylum Research brand of Oxford Instrument was used. Image acquisition was in AC Air Topography mode and image processing and data acquisition was done with Igor Pro 6.34A software. The probes used for the analysis are AC 240-TS (70 kHz and 2 N/m), reporting an average drive frequency of 74.8 kHz. The images corresponding to the PBTh and MWCNT/PBTh samples were obtained directly on the Pt foil covered with the material, scanning with a drive amplitude value of 0.240, 1.03, 0.996 V, a scan rate of 0.30, 0.18 and 0.22 Hz respectively and a final image of 416 points and lines in all cases. SEM experiments were carried out using a Hitachi TM-1000 tabletop microscope. Powder

  Figure SI-3) and the experiments in the presence of different concentrations of MWCNT (Figure SI-4) using an inversion potential (Eλ) at the peak potential of the monomer oxidation (1.20 V vs Ag/AgNO3) present an irreversible oxidation process on the surface of the Pt electrode in the ACN/LiClO4 system, showing in the first reverse cycle of the voltammogram the typical trace-crossing effect observedduring the electrochemical polymerization of π-conjugated systems[START_REF] Heinze | On the origin of the so-called nucleation loop during electropolymerization of conducting polymers[END_REF]. This monomer oxidation process generates a PBTh/MWCNT composite[START_REF] Porras-Gutiérrez | In situ characterization by cyclic voltammetry and conductance of composites based on polypyrrole, multi-walled carbon nanotubes and cobalt phthalocyanine[END_REF]. A current increase of the anodic and cathodic signals, which is characteristic of the growth of this type of polymers, was observed (Figure1). During the potentiodynamic macro BTh polymerization in the presence of the different amount of MWCNT it was observed a higher current (ca. twothree times) in the associated voltammetric curves, which is indicative of its incorporation into the PBTh matrix (FigureSI-4). Similar changes have been reported for PPy-MWCNT composites growth electrochemically[START_REF] Hughes | Electrochemical Capacitance of a Nanoporous Composite of Carbon Nanotubes and Polypyrrole[END_REF]. The current observed in the cyclic voltammetry curves of BTh in the presence of different amounts of MWCNT, seems at first sight to show some indications of current increase with the MWCNT content, but unfortunately not logical trend of this tendency was possible to confirm. A large dispersity of current values was observed during the electrodeposition experiments carried out to construct table 1.Consequently, figureSI-4shows only examples of this curves. Macroelectropolymerization of BTh and the composites were performed by cyclic voltammetry (Qa,Total = 100 mC), sweeping between -0.40 V and 1.2 V vs Ag/AgNO3 and 1.25 V vs

Figure 2 here

 2 Figure 2 here

Figure SI- 6 )

 6 , since the NT coated with the polymer have an increase in density, this analysis let to distinguish unambiguously from the rest of the CNT's-free polymeric material. This composite material follows the longitudinal structure of the MWCNT (Figure3b), which allowed the measurement of roughness (RMS) and the generation of a topographic profile (Figure SI-6a). The amplitude and phase analysis (Figure SI-6b and c, respectively) shows the typical granular growth of polybithiophene whose width corresponds to a polymer coating of ca. 250 nm towards both sides in the thickest part. The CNT's covering is similar to a core-shell structure described previously when the chemical oxidation (FeCl3) of thiophene is carried out in the presence of sodium bis(2-ethylhexyl) sulfosuccinate[START_REF] Swathy | AOT assisted preparation of ordered, conducting and dispersible core-shell nanostructured polythiophene-MWCNT nanocomposites[END_REF]. The micrograph also shows an interesting variation of the polythiophene surface, clearly identified by the phase analysis of the deposited material. Finally, XRD analysis of the PBTh/MWCNT's composite shows two characteristic broad diffraction peaks centered at 2θ = 17.7° and 26° indicating the presence of PBTh and CNT's in the composite matrix (Figure SI-7)

Figure 3 here 4 .

 4 Figure 3 here

Figure 1 .

 1 Figure 1. Macro-electropolymerization of BTh/MWCNT mixture in a ACN/LiClO4 0.1 M,

Figure 2 .

 2 Figure 2. Electrochemical (left axis) and conductance (right axis) simultaneous study for

21 Figure 3 .

 213 Figure 3. AFM micrographs of (a) PBTh and (b) PBTh/MWCNT composite obtained in

Table 1 .

 1 Percentage weight of MWCNT's incorporated in PBTh matrix composites obtained by elemental combustion analysis, for different scan rates and mass content of MWCNT in the electropolymerization suspension. The results shown are the average of three independent experiments.

	Scan rate		MWCNT's
		10 mg	20 mg	40 mg
	0.02 V/s 27.66 % ± 5.07 28.25 %± 5.54 31.48 % ± 0.56
	0.05 V/s 19.17 % ± 4.63 21.34 % ± 0.03 21.58 % ± 1.63
	0.1 V/s	15.53 %± 1.91 15.16 % ± 3.87 16.59 % ± 1.39

transition between the isolating and conducting states observed for the PBTh/MWCNT composite.

Acknowledgements

The authors are grateful to PAPIIT DGAPA-UNAM Project IN208919. Ing. Citlalit Martinez (CCIQS UAEMéx-UNAM), Dr. Uvaldo Hernandez Balderas and Angel Ivan Torres-Pichardo are acknowledged for technical support.