Evolution of the viscosity of mixed organically modified silane sols for the preparation of organic-inorganic monolithic glass

Abstract

Organically modified silanes (OMSs) are widely used as starting compounds for the synthesis of organic-inorganic hybrid materials in different shapes by sol-gel processing. The viscosity behaviour of the sols plays an important role in the structures and properties of the final products. In the present work, we report on the effect of composition, starting compounds and additives on the viscosity evolution of mixed organically modified silane sols and thereby on the feasability of formation of organic-inorganic glass monoliths from these sols. The experimental results demonstrate that the viscosity increase of the CH3-Si(OCH3)3-CH2(O)CHO(CH2)3Si(OCH3)3 (MG) sols is much faster than the C3H3-Si(OCH3)3-CH2(O)CHO(CH2)3Si(OCH3)3 (PG) sols and the base additives are far more effective th the MG sols than to the PG sols. The viscosity-determining silane is CH3-Si(OCH3)3 (MTMS) in the MG system whereas it is CH2(O)CH=(CH2)3Si(OCH3)3 (GPTMS) in the PG system. The possibility of forming monolithic gels by a perforation method is closely related to the viscosity behaviour of the sols. Utilization of C2H5-Si(OCH3)3 (ETMS) in replacement of M or P leads to a moderate gelling time and better capability of foring glass monoliths.