MICROSTRUCTURE AND MECHANICAL PROPERTIES OF ORMOSIL THROUGH VARIATION IN SOL-GEL PROCESSING

초록

Inorganic-organic hybrids with tailorableproperties through control of sol-gel process offer many exciting properties due to combination of inorganic and organic functionalities at the molecular level. In this study, tetraethoxysilane(TEOS) and polydimethylsiloxane(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, isopropylalcohol(IPA), tetrahydrofuran(THF), H2O and PDMS were refluxed together in a flask, while in the second route PDMS was introduceddafter the solution was refluxed for 30 minutes. The porosity, surface area, density and mechnical properties of the ORMOSIL were related to the experimental variables and the microstructure of the sample was examined by scanning electron micoscopy(SEM). It was found that the average pore size of the ORMOSIL increased from 16Åto 22Åas the H20/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 1.43g/cm3. The use of lower molecular weight of PDMS (400-700) resulted in more compact ORMOSILS due to the shorter chain length in the polymer compared to large molrcular weight(1700), and this, in turn, produced ORMOSIL with larger density and smaller pore size. These results argee with the SEM observation. When PDMS was added after TEOS had been hydrolyzed completely, the resulting ORMOSIL had a lower density and hardeness compared to the ORMOSIL produced when the PDMS were mixed with other reagents from the beginning. These facts were a