The synthesis procedures and physical properties of the ambient dried hydrophobic silica aerogels by using different contents of ethanol (EtOH)/trimethylchlorosilane (TMCS)/n-Hexane as surface modification agent were investigated. One-step solvent exchange and surface modification were simultaneously progressed by immersing silica hydrogels in EtOH/TMCS/n-Hexane solution. It is found that microstructures as well as properties of silica aerogels like porosity, specific density and specific surface area are affected by the contents of surface modification agent in the sol from the results of SEM, TEM morphology, FT-IR chemical structure, BET surface area and BJH pore size analyses. The volume of TMCS is of 10% and 20% of hydrogels, and the final product is hydrophilic xerogels. When TMCS’s percent (v/v) is elevated to 75%–100%, hydrophobic silica aerogels with good performance are synthesized, the porosities of aerogels are in the range of 93.5%–95.8% and the average pore size diameter is less than 20 nm.
