Abstract
Physical properties and microstructure of new coumarin 4 doped SiO2-PDMS ORMOSILs, synthesized by one-step (OS, acid-catalysis) and two-step (TS, acid-base catalysis) routes of sol-gel method with varying pH (0.6 to 7) and dye content (5 x 10(-4) to 5 x 10(-2) mole), are reported. BET, UV-visible spectroscopy and SEM were used for characterizations. The increase in acid or base concentration increased the size of pores and aggregated silica particles. The samples with pH less than or equal to 2.5 were transparent and attributed to the small size of pores (similar to20 Angstrom) and silica particles. The samples with pH > 2.5 were translucent or opaque due to non-uniform pore system formed by voids and large aggregated silica particles. The surface area was found a key factor controlling the interactions between the gel matrix and the dye. The OS samples with the highest dye concentration exhibited the minimal values of pore size, surface area and silica particle size, resulting in the concentration-quenching phenomenon.