| Silica aerogel films, as a new kind of insulation material, have been widely used in energy-saving building, aerospace and aviation science and microelectronic technology due to their low density, high porosity, large surface area and superlow thermal conductivity, and have become one of the new research focus around the world. It is the purpose of this work that is to prepare silica aerogel hydrophobic insulation films by using sol-gel method, study the main influencing factors of preparation process, hydrophobic and insulation properties of silica aerogel films, analyze the interface thermal resistance between of the films and glass slide and provide an predicting method for thermal conductivity of silica aerogel films.Using tetraethoxysilane as silica sources, silica aerogel hydrophobic insulation films were prepared in ambient pressure drying via sol-gel technology with acid/ base two-step catalytic. The influencing factors of fabricating silica sol, preparation of silica wetgel films and post-treatment of the wet gel films have been analyzed. The result shows that the suitable silica sol could be fabricated in room temperature when the reaction ratio of sol is H2O/TEOS =3, EtOH/TEOS=6, HCl/TEOS=6.0×10-4, NH3-H2O/TEOS=0.040 with 50 min for the acid/base catalytic interval time. The silica wetgel films with excellent quality can be prepared by controlling the sol viscosity with 7-23 mPa-s and adjusting the suitable dip-coating period, times and rate. The silica aerogel hydrophobic insulation films with good properties could be obtained at 50℃as the following processes:aging of the silica wetgel films in ethanol for three times with 12h each time, solvent exchange with n-heaptane with 15h, surface modification of the films by 7 vol. % hexamethyldisilazane solution for three times with 24 h each time and washing the films by n-heaptane for three times and drying at ambient pressure successively.The hydrophobicity of silica aerogel hydrophobic insulation films have been investigated and the effects of modifying agents, volume-concentration, modification period and heat treatment on the hydrophobic property of the films have also been analyzed here by means of FT-IR, contact angle instrument and DSC-TG. The results show that the volume-concentration of hexamethyldisilazane in the range of 7～9 vol. %, the modification period for 24h and heat treatment temperature lower than 440℃are well established for obtaining the modified films with excellent hydrophobicity and high transparency.Further, the insulation property of silica aerogel hydrophobic insulation films has been studied, and the effects of types of modifying agents and its volume-concentration, density and thickness of the films and drying control chemical additive DMF on the thermal conductivity of the films are also discussed. The results show that 5 vol. % of trimethylchlorosilane is beneficial to obtain the silica aerogel hydrophobic insulation films with the lowest thermal conductivity, and the films modified with 7 vol. % of hexamethyldisilazane also has a lower thermal conductivity. Meanwhile, the thermal conductivity of the films decreased exponentially as a function of the decreases of density and thickness. Besides, drying control chemical additive DMF is help to adjust uniformity of the pores, which would lead to the thermal conductivity decreased and improve the insulation property of the films.According to the testing prinpicle of 3ωmethod for the thermal conductivity of silica aerogel hydrophobic insulation films, the interface thermal resistance between the films and glass slide has been discussed theoretically, and the formula for predicting the thermal conductivity of the film has also been obtained by analyzing the cubic unit cell structure model of the films. Comparison of the predictive value and the experimental value of the films, the percentage deviation between them within±8% has been revealed, so that refrences for thermal design of silica aerogel hydrophobic insulation films is provided.
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