Dielectric behavior of organically modified siloxane melting gels

Hybrid melting gels were prepared by a sol–gel process, starting with a mono-substituted alkoxysilane and a di-substituted alkoxysilane, methyltriethoxysilane (MTES) together with dimethyldiethoxysilane (DMDES). Five gel compositions were prepared with concentrations between 50% MTES–50% DMDES and 75% MTES–25% DMDES (in mol%). The index of refraction was measured using a Becke line method. The index of refraction decreased slightly as the amount of mono-substituted alkoxysilane decreased. The dielectric constant was determined from impedance spectrometry that followed dielectric constant and dielectric loss as a function of frequency. The dielectric constant was lowest in the 50% MTES–50% DMDES composition at frequencies greater than 1 kHz, around 3.3. Since direct SiC bonds are less polarizable than SiOSi, the di-substituted alkoxysilane component decreases the dielectric constant.