Superior hydrophobicity of nano-SiO2 porous thermal insulating material treated by oil-in-water microemulsion

Nano-SiO2 porous thermal insulating material (TIM) has drawn tremendous research interests due to its advantages of low density, high porosity and low thermal conductivity. However, its long-term stability in humid environment can be severely deteriorated by the high hydrophilicity resulting from tetrahedral coordination of oxygen and capillary effect of porous structure. It is still a great challenge to cost-effectively fabricate bulk TIM with superior hydrophobicity and consequent remarkable self-cleaning capability. Herein, via an oil-in-water microemulsion treatment, we have proposed a new strategy to construct 3D superior hydrophobic nano-SiO2 porous TIM. The polymethylhydrosiloxane-modified TIM exhibits a large water contact angle of 166 degrees, and corresponding excellent self-cleaning characteristic while maintaining low thermal conductivity of 0.031 W/ m.K. Moreover, our high hydrophobicity of TIM exhibits excellent durability under high temperature up to 400 degrees C, high humidity of 100%, and chemical erosions. Detailed knowledge of the physical chemistry basis of the superior hydrophobic nano-SiO2 porous TIM can provide great opportunity to fabricate advanced self-cleaning and heat insulating devices especially targeted for harsh environments.