Study on the microstructural evolution of silica gel during sol-gel-gel-glass conversions using the fluorescence polarization of rhodamine B

The fluorescence polarization of rhodamine B is used as an environment prob e to study the microstructural evolution of silica gel during sol to gel to gel glass transitions. The wet gel is an amorphous porous solid of which o rganics and solvents (water and ethanol) exist in the pores. During gelatio n and heat treatment, the solvents evaporate gradually and the inorganic ne twork of the matrix forms and strengthens as a result of the collapse of po res and the structural relaxation. The rhodamine B molecules lose mobility gradually and are finally steadily isolated and adsorbed into the tiny pore s of the inorganic network, which makes the rotational diffusion of rhodami ne B molecules difficult and increases the fluorescence anisotropy and pola rization of rhodamine B.