Effects of water content and sol viscosity on morphology of porous silica thermal insulating layer

Amorphous porous silica thin films as a thermal insulating layer in pyroelectric infrared (IR) detector were prepared by a modified sol–gel method. These silica films possessed sponge-like disordered pore structure. The effects of water content and sol viscosity on morphology of the films were investigated. The results shown: with decreasing water content and increasing sol viscosity, the pore size, root-mean-square surface roughness (RMSSR), and thickness of the films increased obviously. However, the porosity did not change greatly. While the values of the water content and the sol viscosity changed from 91.69 to 79.58 wt.% and 5.59 to 59.37 cP, respectively, the thickness of single layer film increased from 0.34 to 1.50 μm, and the values of porosity just fluctuated between 45 and 50%. A crack-free, uniform porous silica films with porosity of 45% and thickness of 15 μm also could be obtained by repeating coating procedure easily.