Titre de la dissertation: « Design of dynamic hydrogel-based materials for near-IR thermal management fabrics »

Promoteurs de thèse: Monsieur Jean-Marie RAQUEZ  et Monsieur Eric DEVAUX

Résumé de la dissertation: This thesis is dedicated to the design of intelligent textiles capable of reflecting the infrared radiation emitted by the human body to ensure thermal comfort. Currently, the strategies used to manage thermal comfort are heating, ventilation and air conditioning (HVAC), but these systems involve considerable energy expenditure. Controlling what happens in the microclimate created between the skin and the textile could mitigate the energy demand of HVAC systems. One of the strategies to achieve this is inspired by photonic structures with multi-response to external stimuli that modulate the reflection of infrared radiation. The first stage of the research proposes the design of a dynamic system based on poly(N-isopropylacrylamide) (PNIPAM) as thermosensitive matrix and SiO2 particles as filler with favorable photonic properties are proposed. A hydrogel composite capable of reflecting infrared radiation as a function of an external stimulus is developed. The analysis of the particles distribution in the polymeric matrix and the analysis of the surface roughness allowed to define two levels of interaction with the infrared radiation, bulk level and surface level whose contribution depends on the humidity and temperature conditions. Likewise, the low emission of the hydrogels composites observed in the thermal analysis confirmed the reflection of the infrared radiation. The behavior of the hydrogels is supported by the design of thermal simulations that allow to verify the ability of the material to achieve thermal comfort. Due to the successful results obtained, the second step was the application of this dynamic system as a coating of textiles by different coating techniques and using different types of fabrics. The coating of knit fabrics by padding process increased the percentage of infrared radiation reflected by the uncoated fabric. The characterization of the coated fabrics at different humidities showed the dynamic role of the coating since variation of the reflected infrared radiation was observed as a function of the percentage of relative humidity. Using the same type of fabrics, a dip coating process is used. In this case, the results obtained do not meet expectations in particular the fabrics lost flexibility. Therefore, a new strategy is proposed and a different type of fabric is used. The coating of woven fabrics by dip-coating process almost tripled the percentage of refracted infrared radiation. Analysis of the coated fabrics shows that the reflection of infrared radiation depends on the amount and size of SiO₂ particles, and the thickness of the coating layer. In addition, thermal analysis shows that fabrics are able to increase the temperature of the microclimate created between the skin and the textile, and this behavior is confirmed by thermal imaging results showing a decrease in the emissivity of the coated fabric. The results, both in the design of the hydrogel composites and in the textile coating, are due to the thermosensitive properties of the polymeric matrix and to the distribution and size of the SiO₂ particles, achieving the development of a material capable of managing infrared radiation as a function of changes in humidity or temperature. Finally, the idea of designing a multi-responsive material that can interact with radiation as a function of temperature, humidity and strain is proposed. For this purpose, the properties of PNIPAM were exploited but this time using it as microgel particles and distributed in a new type of matrix whose main property is its elasticity. Preliminary results showed successfully synthesized microgels in terms of size and thermal properties, as well as that the dispersion of the microgels in the matrix causes changes in radiation reflection. There is still a long way to go in this proposed strategy, but the first results are promising and open the opportunity to develop a new topic of study that can also reach its application in textiles for thermoregulation.