Description du sujet de thèse

The objective of the thesis is to study a structured membrane based on a thermosensitive polymer modifying its geometry and its optical properties to obtain a coupling between thermal properties and visual aspect. The consequences of these modifications in the visible (colour change) and mid-infrared - MIR (temperature related) domains will be studied. The ultimate goal will be to combine these dual properties for applications linking colour change and temperature. The visible properties will be linked to the use of (micro)silica particles scattering optical radiation. The MIR properties will be obtained by creating photonic gratings and by modulating the effective optical index of the material containing the particles. Finally, the dynamic aspect will be obtained via a stimulable polymer matrix that will allow the dimensions of the photonic structure to be modulated as a function of at least one external stimulus (T°, humidity, pH, etc.). This thesis is based on the complementary expertise of two partners: the University of Lille for the modelling, fabrication and photonic characterisation part and the University of Mons for the macromolecular chemistry and development of colloidal particle solutions. The technologies used will be 3D printing for silica-filled polymer multilayers, and a combination of photolithography, screen printing and hot-embossing for surface structuring.
The proposed research topic is based on two distinct points that we wish to combine in an original way in order to obtain new functionalities. The first concerns the development of photonic membranes whose properties in the mid-infrared (MIR) are modulated by an external stimulus, and the second is related to a modification of the visual aspect (colour) of these membranes. These two optical properties, MIR and visible, can be modulated simultaneously.

1.a. Properties in the mid-infrared
The human body at normal temperature (34°C) emits infrared radiation with a maximum at a wavelength near 9.5 µm. The associated heat transfer mechanism is responsible for over 50% of the total heat loss from the human body [1]. The remaining 50% is lost through thermal conduction, convection and evaporation. Much research and development in the industry has been, and still is, related to the design of textiles capable of modulating infrared radiation to provide personal thermal comfort while reducing the energy consumed for temperature control in residential buildings.
The textile industry proposes numerous technological developments to improve this thermal comfort (cooling, heating, passive or active intelligent textiles). Concerning passive heating, recently studied solutions consist in using synthetic or natural insulating layers containing particles, metallized patches to reflect thermal radiation back to the body. For outdoor use, different technologies and products have been developed, based on synthetic, natural (ThermoPlume® Insulation by PrimaLoft® or HD® Wool Insulation) or even technological materials (Skyscape inc. or Inflate Jacket by Nike). In the latter case, the textile modifies its conformation according to environmental conditions by thickening the fibres or by opening up an air-filled layer when the temperature drops. For indoor use, we can mention the Omni-Heat Dot technology used by Columbia, described as a "thermal shield" composed of metallic aluminium patches, or the use of graphene monolayers proposed by Tough Knitting Inc. We can also mention the company DAMART, which develops technological components as its historical label THERMOLACTYL (warmth benefit) but more recently through its CLYMATYL label (coolness benefit). All these technologies are based on the principles of thermal body management with conduction, evaporation, convection and contact radiation.
From an academic point of view, textile technologies for thermal management have recently attracted the interest of renowned Universities (Stanford being one of the precursor contributors [2, 3, 4]) which have published articles in high impact journals: Science, Nature Comm., Nature Sustainability, Nano Letters... . Although many efforts have been made by the scientific community, the development of textiles for personal thermoregulation remains a major scientific and technological challenge to outperform commercial products. Two paths are currently being followed, either for cooling or for heating. For passive radiative cooling, Hsu et al. have shown that a membrane [2] or nanoporous polyethylene fibres [5] provide radiative cooling, visible opacity and cotton-like softness. Indeed, nanopores ranging in size from 50 nm to 1000 nm provide mid-infrared transparency without compromising visible opacity. Doped polymers such as nanoporous PE with ZnO [6,7] or polyamide (PA) with SiO2 nanoparticles [8] have also been proposed, mainly for external cooling. Some authors deal with permeability properties such as Li et al. who demonstrated evaporative cooling using a three-layer laminated fabric (TLF) [9]. Indeed, the high water absorption of the TLF increases the cooling performance.
For passive radiative heating, the integration of silver nanowires connected in polymeric textiles has been one of the main solutions proposed in the literature [3]. In these cases, heating is generated passively by the reflection of infrared radiation from the metallic component. Compared to conventional textiles, the reflection of the doped membrane can be increased by 40%, resulting in an increase in human body temperature of up to 0.9°C. Cai et al. proposed a polyethylene membrane containing nanoparticles whose inner side is metallised to strongly reflect radiation from the human body, while the uncoated outer side minimises radiative heat emissivity [3]. This design lowers the set point by more than 7.1°C, compared to an ordinary textile (whether it is a simple cotton textile or one combining the commercial Omni-Heat technology mentioned above). This shows that the performance of commercial products is still far from optimal. For extremely cold environments, thanks to the conductive metal layer, passive heating can be supplemented by active heating generated by the Joule effect, although energy input is required. Furthermore, textiles made with connected metal nanowires are not common in the textile industry. Furthermore, to control thermal comfort in temperate environments, textiles that allow both cooling and heating have also been studied. Hsu et al. proposed an asymmetric carbon/copper bilayer embedded in a nano-PE structure, each layer providing selective infrared emissivity [4]. To control the infrared emissivity, Zhang et al. proposed a dynamic polymer whose size changes with humidity and temperature [10]. A bio-inspired structure based on squid skin has been proposed as a dynamic thermoregulator [11], using tensile forces to open/close the metallic structure deposited on the surface of a polymer membrane. Another way to control IR emissivity is to use polyaniline (PANI) [12] whose electrochromic properties have been transferred from the visible to the IR. More recently, Abebe et al. proposed a theoretical approach for a dynamic textile made of monofilaments of a stimulable polymer covered with a metallic layer [13].
1.b. Properties in the visible range
If the particles, metallic or silica, introduced into a composite can form an ordered structure of micrometer size, then the resulting composite may, under certain physical and geometrical conditions, exhibit an interference colour (so-called structural colour) due to the ordered structure [14-16]. In other words, depending on the type of filler and its dispersion in the polymer matrix, it becomes possible to give it optically interesting properties in addition to improving the mechanical performance. For example, it has been reported that a composite with a bright structural colour can be obtained by placing monodisperse spherical fillers in an ordered state in a metallic polymer matrix [17]. When incident radiation impinges on the resulting ordered structure, it interacts with the different layers of particles and results in an optical path difference between the rays reflected from successive layers. This optical path difference is characterised by a phase shift of the electromagnetic wave leading to constructive interference if the waves are in phase or destructive interference if the waves are in phase opposition. This phenomenon is described by Bragg's law, which imposes diffraction conditions depending on the wavelength of the incident radiation, the spacing between the crystal planes and the angle of incidence. As an example, Wang et al. developed a composite with an inverse opal structure by adding silica particles to a polymer matrix and then dissolving them to replace them with air to form an inverse opal structure [18]. It is then possible to modify the colour of the resulting material by varying the size of the silica particles and thus the size of the pores formed within the polymer matrix.

To our knowledge, the coupling of optical properties in the mid-infrared with those in the visible is quite original and would allow to obtain multifunctional surfaces linking thermal properties (thermal insulation or cooling) and visual aspect (passive colour change according to external stimuli).

Contexte de travail

This co-supervised thesis will be carried out in two different laboratories. At the IEMN (University of Lille - CNRS) and at the University of Mons (Belgium). The first 18 months will be spent in Belgium, the next 18 in France with regular exchanges between the two sites (train travel possible).

The status of the subject in the two host laboratories is as follows:

In the mid-infrared
The IEMN has been working for several years on the interactions between electromagnetic radiation in the infrared and matter for thermal comfort problems. After studying model silicon surfaces (technological realisation, optical characterisation and modelling) through the thesis of M. Viallon, defended in 2019, we have begun to study the transfer of this knowledge to polymer membranes by associating the study of thermal properties (theses of S. Assaf - 2020 and M. Boutghatin - 2022) [19]. This work was carried out through an Interreg Photonitex contract (2018-2022) and a collaboration with the industrialist Damart, which co-financed part of this work. We are currently working within an ANR PRCE project with Damart on the elaboration of photonic surfaces for thermal comfort with elaboration criteria compatible with the textile industry (choice of materials, manufacturing processes and extent of feasible surfaces). To summarise our work and its progress, we have been able to manufacture membranes, from inert polymers, which, either charged with particles or structured at the micron scale, show properties, in the infrared range, synonymous with a thermal gain of the order of 1.5°C compared to a membrane not charged with particles or not structured [20]. This work, at the state of the art, is only related to the use of non-dynamic polymers (such as PDMS or Polyimide) and has no specific properties in the visible range.
[19] Polymer photonic crystal membrane for thermo-regulating textile, ASSAF S., BOUTGHATIN M., PENNEC Y., THOMY V., KOROVIN, A., TREIZEBRE A., CARETTE M., AKJOUJ A., DJAFARI-ROUHANI B., Scientific Report (2020), 10:9855 https://doi.org/10.1038/s41598-020-66731-1
[20] Impact of SiO2 Particles in Polyethylene Textile Membrane for Indoor Personal Heating, BOUTGHATIN M., ASSAF S., PENNEC Y., CARETTE M., THOMY V., AKJOUJ A., DJAFARI-ROUHANI B. Nanomaterials (2020),10, 1968 https://doi.org/10.3390/nano10101968

In the visible range
In this context, the SMPC at UMONS has recently developed a composite with anti-adhesive properties consisting of a biocompatible elastomeric matrix additivated with silica particles [21]. Although these particles interact with light, they cannot impart colour to the synthesised materials because the size of the particles is in the order of a hundred nanometres and therefore refract in the UV wavelength range. On the other hand, it is possible to obtain coloured materials by modifying the size of the added particles. The SMPC has recently developed a composite consisting of an elastomeric matrix additivated with spherical silica particles with a size of 179 nm [22]. Depending on the amount of particles added to the matrix, we have shown that it is possible to obtain a fairly wide range of colours from red to blue and green. In addition to their colouring, the addition of SiO2 also allows us to obtain composites with high mechanical performance in terms of both stiffness and extensibility. We have also shown the possibility of using them as stress sensors, which can measure the amount of stress applied according to the position of the reflection peak produced by the composite.

[21] Asai, F.; Seki, T.; Sugawara-Narutaki, A.; Sato, K.; Odent, J.; Coulembier, O.; Raquez, J.-M.; Takeoka, Y. Tough and Three-Dimensional-Printable Poly(2-methoxyethyl acrylate)–Silica Composite Elastomer with Antiplatelet Adhesion Property, ACS Applied Materials & Interfaces 2020 12 (41), 46621-46628
[22] Miwa, E.; Watanabe, K.; Asai, F.; Seki, T.; Urayama, K.; Odent, J.; Raquez, J.-M.; Takeoka, Y. Composite Elastomer Exhibiting a Stress-Dependent Color Change and High Toughness Prepared by Self-Assembly of Silica Particles in a Polymer Network, ACS Applied Polymer Materials 2020 2 (9), 4078-4089

Contraintes et risques

Constraints specific to work in a polymer chemistry laboratory and in a micro/nanotechnology clean room.

Informations complémentaires

Application to be submitted online only