Structural characteristics and thermal conductivity of ambient pressure dried silica aerogels with one-step solvent exchange/surface modification

The paper reports the synthesis procedures as well as structural properties and thermal conductivity of the ambient dried hydrophobic silica aerogels with ethanol (EtOH)/trimethylchlorosilane (TMCS)/n-hexane as surface modification agent. One-step solvent exchange and surface modification were simultaneously progressed by immersing the hydrogels in EtOH/TMCS/n-hexane solution. When P(VTMCS/VHydrogels) ranges from 10 to 20%, the final product is hydrophilic xerogel, which is porous material with porosity of 78–89% and the specific density is over 0.24 g cm−3. When P(VTMCS/VHydrogels) is at the scope of 75–100%, the specific densities of the aerogels range from 0.10 to 0.14 g cm−3 and the porosity is in range of 93.5–95.8%. The silica aerogels modified with 75–100% TMCS (V/V) present good performance with the specific surface area in range of 745–770 m2 g−1 and the average pore sizes are about 20 nm. Furthermore, using granular silica aerogels (P(VTMCS/VHydrogels) = 100%) as the fillings, the thermal conductivities of granular aerogels are analyzed by guarded hot plate method. When temperature ranges from 30 to 60° C, thermal conductivity coefficients of the samples are lower than 0.03 W (m K)−1.