The skeletal structure of aerogel is determined before, during, and after the gel is formed. Supercritical drying of aerogel largely preserves the pore structure that is determined near the time of gelation. To better understand gel-formation mechanisms, measurements of the time evolution of light scattering in a series of gels prepared without conventional acid or base catalysis were conducted. Ultraviolet light was used to catalyze the formation of silica gels made from hydrolysis of tetraethylorthosilicate and partly prehydrolyzed tetraethylorthosilicate in ethanol. Time evolution of light scattering provides information regarding the rate and geometrical nature of the assembly of the primary silica particles formed in the sol. UV-catalyzed gels show volumetric growth typical of acid-catalyzed gels, except when UV exposure is discontinued at the gel point, where gels then show linear chain formation typical of base-catalyzed gels. Long-term UV exposure leads to coarsening of the pore network, a decrease in the clarity of the aerogel, and an increase in the surface area of the aerogel. Additionally, UV exposure up to the gel point leads to increased crystallinity in the final aerogel.
BT - Journal of Non-Crystalline Solids LA - eng LB - Semi-Conduct N1 -0022-3093doi: DOI: 10.1016/S0022-3093(98)00132-X
N2 -The skeletal structure of aerogel is determined before, during, and after the gel is formed. Supercritical drying of aerogel largely preserves the pore structure that is determined near the time of gelation. To better understand gel-formation mechanisms, measurements of the time evolution of light scattering in a series of gels prepared without conventional acid or base catalysis were conducted. Ultraviolet light was used to catalyze the formation of silica gels made from hydrolysis of tetraethylorthosilicate and partly prehydrolyzed tetraethylorthosilicate in ethanol. Time evolution of light scattering provides information regarding the rate and geometrical nature of the assembly of the primary silica particles formed in the sol. UV-catalyzed gels show volumetric growth typical of acid-catalyzed gels, except when UV exposure is discontinued at the gel point, where gels then show linear chain formation typical of base-catalyzed gels. Long-term UV exposure leads to coarsening of the pore network, a decrease in the clarity of the aerogel, and an increase in the surface area of the aerogel. Additionally, UV exposure up to the gel point leads to increased crystallinity in the final aerogel.
PY - 1998 SP - 325 EP - 329 T2 - Journal of Non-Crystalline Solids TI - Light scattering studies of UV-catalyzed gel and aerogel structure VL - 225 ER -