PHASE-SEPARATION IN PMMA SILICA SOL-GEL SYSTEMS

The mechanism of phase separation of sol-gel alkoxy-derived silica sys tems obtained by acid catalysis in the presence of poly(methyl methacr ylate) (PMMA) and tetrahydrofuran was investigated by light scattering . Spinodal decomposition (SD) was confirmed for systems with intermedi ate PMMA/alkoxy compositions occurring with a simultaneous viscosity i ncrease. The initial stages of phase separation followed the linear th eory proposed by Cahn. For systems with low PMMA content, a behaviour typical of nucleation and growth was detected. In this case gelation t ook place after demixing. The morphology of the final PMMA/silica hybr id material was investigated by scanning and transmission electron mic roscopy with element-specific analysis. A matrix/disperse domains morp hology was also verified for systems which demixed by SD, indicating t hat phase coarsening occurs. A micellar/lamellar microstructure was ob served inside the separated phases.