Effect of the addition of hydroxyl-terminated polydimethylsiloxane to TEOS-based stone protective materials

Abstract

Inorganic–organic hybrid crack-free xerogels were obtained by using a surfactant n-octylamine as a catalyst containing tetraethoxyorthosilicate (TEOS) and hydroxyl-terminated polydimethylsiloxane as an additive. We studied the effect of gelling time and viscosity on PDMS–OH concentration. We have demonstrated that the addition of poly(dimethylsiloxane) (PDMS) to a silica oligomer associated with a neutral catalyst, in the presence of a surfactant, accelerated the gelling process; this reduction of the time needed for the product to gel in carbonate stones helped to achieve effective stone protection. It was found that PDMS–OH was chemically incorporated into the gel matrix via Si–O–Si bonds by FTIR analysis and an appreciable reduction of gel fracture for hybrids prepared from 3 % w/w of PDMS. Nitrogen adsorption–desorption isotherms of xerogels were measured, it showed the pore size of xerogels decrease with the addition of PDMS when concentration of PDMS was below 6 %, while xerogels showed pores in the macroporous range when adding 12 % w/w of PDMS. The protective performance evaluated by its ability to resist acid rain reveals that the protective effects were satisfying.