Microstructure and Mechanical Properties of Ormosil Through Variation in Sol-Gel Processing

초록

Inorganic-organic hybrids with tailorable properties through control of sol-gel process offer many new exciting properties due to the combination of inorganic and organic functionalities at the molecular level. In this study, tetraethoxysilane(TEOS) and polymethylsiloxane(PDMS) were chosen as the inorganic and organic component, respectively. Silanol-terminated PDMS can condense with oxide precursors to produce metal-O-Si bond and is known for its superior relaxation. The microstructures and the mechanical properties of the SiO₂- PDMS ORMOSILS were studied by changing the experimental variables such as water content, molecular weight of PDMS and the mixing order in which the incorporation of polymers was carried out by two different routes. In the first route, TEOS, HCl, isopropyl alcohol(IPA), tetrahydrofuran(THF), H2O and PDMS were refluxed together in a flask, while in the second route PDMS was introduced after the solution was refluxed for 30 minutes. The porosity, surface area, density and mechanical properties of the ORMOSIL were related to the experimental variables and the microstructure of the samples was examined by scanning electron microscopy(SEM). It was found that the average pore size of the ORMOSIL increased from 16A to 22A as the H2O/TEOS molar ratio increased from 4 to 16 with fixed HCl concentration. At the same time, Vickers hardness values decreased from 70Hv to 40Hv, and the density also decreased from 1.59 g/cm³ to 1.43 g/cm³. The use of lower molecular weight of PDMS (400-700) resulted in more compact ORMOSIL due to the shorter chain length in the polymer compared to large molecular weight PDMS(1700), and this, in turn, produced ORMOSIL with larger density and smaller pore size. These results agree with the SEM observation. When PDMS was added after TEOS had been hydrolyzed completely, the resulting ORMOSIL had a lower density and hardness compared to the ORMOSIL produced when the PDMS were mixed with other reagents from the beginning.