Developing a novel thermal management fabric for solar heat shielding through a bionic method

Abstract

A great many of insects have demonstrated amazing capability in surviving extremely high temperatures and keeping cool. A vivid instance could be seen in silver ants (SSAnt) in Saharan Desert. The creature leverages its dense arrays of bar shaped micro hairs to enhance strong Mie scattering and total internal reflection, thus effectively minimizing heat gain in the visible and near-infrared (NIR) from the sun, and maximizing heat emission in the mid-infrared (MIR) radiated by its body. In contrast, the intensive solar heat stress could harm humans' health and reduce their productivity, which further impacts economic development. As global warming continues to worsen and extreme climates occur more often, world's sustainability faces graver challenges. Therefore, it is of great urgency to develop efficient materials and reliable technologies for outdoor thermal management. Thermoregulation by using advanced functional textile is one such promising technology, given the fact that fabric itself is a mass production material and usually wearable. Yet conventional fabrics demonstrated limited performance in thermal management as they are not capable of blocking intensive solar radiation and achieve efficient cooling in burning summers. In this thesis, inspired by the microstructure and thermal shielding capability of the Saharan silver ant hair, some novel strategies based on the advancements in photonic engineering and microfabrication technologies were developed to fabricate thermal management fabric (TMF), including the synthesis of artificial scattering particle, the fabrication of several scattering particles embedded coating agent and the assembly method, the particle shape and loading effect of the TMF performance, and the development of the dual-mode TMF. The unique design of self-adaptive coating on the substrate fabric not only improves the user's comfort but also enables new functions to be added to the fabric. In this thesis, the fabrication methods and mechanisms of TMF are introduced and reviewed to understand the current techniques and cooling mechanisms, including FDTD simulation and Mie scattering, for further research. Under the guidance of literature review, the study demonstrates a new wet chemical synthesis method for zinc oxide micro (ZnO) crystal bar production (MCB) under atmospheric pressure. Subsequently, the ZnO MCB is selected to work as artificial SSAnt micro hair, and then coated onto polyester fabric with polydimethylsiloxane (PDMS) via Meyer rod method to achieve high reflectance of solar heat. The shape and loading of ZnO MCB on the bionic fabrication of the solar heat shielding fabric are discussed afterwards. The result reveals that, compared to commercial ZnO micro particle (irregular shape), the ZnO MCB coated fabric exhibits a remarkable solar heat shielding performance as expected, and the Vis-NIR reflectance improves as the amount of ZnO MCB increases. As for large scale production, commercial scattering particle materials, including potassium titanate whisker (PTW) and T-shaped ZnO (TZ) whisker, are introduced in the bionic fabrication of TMF. These artificial SSAnt micro hairs work to enhance strong Mie scattering, and thus significantly driving up the reflectance of the solar irradiation together with the polymer matrices. In summary, the proposed bionic fabrication strategies possess thermal shielding capability similar to SSAnt's micro hairs, and promising application potential in the textile industry for both personal thermal management and energy-saving conservation of buildings.