Infrared Thermal Management with Graphene

The main purpose of textiles throughout history is to regulate heat flow and provide warmth or decrease excessive heat for the wearer. In recent times, the textile industry has developed new materials that can ensure the wearer stays dry in hot environments and that repel moisture. The main downside of these new textiles, however, is that their electromagnetic response has not been fully optimized, allowing too much radiation to be absorbed and radiated back to the skin, causing the wearer to overheat. Our work is composed of two parts: simulation and experimentation. Simulations will first be conducted to better understand graphene chemistry, as graphene will be screen printed onto textiles for testing.<br/> <br/>In this work, heterostructures made of NPG-FeCl₃-Ag mirror are considered, where NPG is nanopatterned graphene. This system is a representative of a Fabry-Perot type of cavity, where incident infrared light interacts strongly with NPG. The thickness of FeCl₃ will be chosen to be a quarter of the infrared wavelength in order for the amplitude of the infrared light to be maximal at the position of the NPG sheet.<br/> Finite-difference time domain (FDTD) simulations show narrow resonance peaks in the absorbance (=emittance) due to localized surface plasmons (LSPs) in NPG. FeCl₃ is intercalated in NPG in order to shift the Fermi energy of graphene to E_F=-0.6 eV.<br/>The positions of the resonance peaks can be tuned in the range between 3 mm and 12 mm by means of the number of graphene layers.<br/>When the number of graphene layers is increased, the conductivity is multiplied by the number of layers, which results in a blueshift of the LSP peaks. By increasing the radius of the holes and the period of the hexagonal lattice of holes, the LSP peaks are redshifted.<br/>For highly doped graphene layers with a small layer of FeCl₃ of around 50 nm between graphene and the Ag mirror, the absorbance (emittance) between 3 mm and 12 mm is around 2%, independent of the number of graphene layers. Such heterostructures could be useful for thermal management systems.<br/>Based on the simulation results, we will be fine tuning the graphene chemistry. Resultant graphene paste will be screen printed onto textiles in the form of different geometries. Graphene printed textiles will be characterized using in-house developed Delta T measurement system. In this system, anodized Aluminum with an emissivity of 0.77 is used, which is smaller than the emissivity of human skin (95% to 98%). The anodized aluminum is placed on a hot plate and a thermocouple. The hot plate is heated up to 38 C to simulate the body temperature and standoff is created between textile and hot plate. Thermocouples will be used to measure the temperature difference between the printed and plain textiles to see if the printing has a significant effect on the thermal management property of textiles.