Tailoring structure and properties of silica aerogels by varying the content of the Tetramethoxysilane added in batches

Silica aerogels with high optical transparency and ultra-low thermal conductivity are ideal candidates for energy-saving windows. Often such applications require rather exquisite control of microstructure (i.e., cluster size and cluster packing geometry). In this research, a series of silica aerogels with the same composition and density but different microstructures and properties are prepared by varying the content of the Tetramethoxysilane (TMOS) added in batches. It was found that the mean pore size and thermal conductivity of the silica aerogels initially decrease with the decrease in the content of the pre-added TMOS before bottoming out and eventually increasing again, while the specific surface area, pore volume and light transmittance show the reverse change trend. Compared with the conventionally initial addition of total TMOS, the specific surface area and transparency ratio of the silica aerogels prepared under the optimum level of the pre-added TMOS increase from 845 to 1060 m2/g and from 71% (550 nm) to 88% (550 nm), respectively. Meanwhile, the thermal conductivity of the silica aerogels decreases from 24.6 to 20.2 mW/(m∙K) with the mean pore size decreases from 20.7 to 16.6 nm. This method provides a new approach to design structure and properties of silica aerogels.