Structure and properties of polymethylsilsesquioxane aerogels synthesized with surfactant n-hexadecyltrimethylammonium chloride

Structure and physical properties of monolithic polymethylsilsesquioxane (PMSQ, CH3SiO1.5) aerogels have been systematically examined with varied starting compositions using a sol–gel system containing surfactant n-hexadecyltrimethylammonium chloride (CTAC). The precursor methyltrimethoxysilane (MTMS) undergoes hydrolysis and polycondensation under an acid–base two-step reaction to obtain uniform gels as a one-pot reaction. To compare the samples, each factor of starting composition, such as amount of CTAC, concentration of aqueous acetic acid solution, volume of solvent and amount of urea, is independently varied. With appropriate concentrations of surfactant CTAC, the aerogels with high light transmittance (at 550 nm) are obtained, owing to the effective suppression of macroscopic phase separation. Acid–base catalysts, acetic acid and urea also impose significant effects on the properties of obtained aerogels including their molecular-level structures. The aerogel with 91% of light transmittance was obtained under an optimized condition. The lowest density of the PMSQ aerogel in this system reaches 0.045 g cm−3.

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► One-pot sol–gel synthesis of transparent polymethylsilsesquioxane aerogels is studied.
► Effects of starting compositions on the properties of aerogels are investigated.
► Surfactant suppresses phase separation of hydrophobic networks.
► Rapid pH increase during polycondensation increases the homogeneity of networks.
► The lowest density reaches 0.045 g cm−3 (97% porosity).