Control of morphology inside the mesoporous gelstructure in silica-gels

Abstract

The preparation and the properties of silica gels with a bimodal pore size distribution is reported. The small pores of the novel gels are in the range of 10–20 nm and are responsible for the large surface area of the gels. The large pores are in the range of 1–2 μm. The gels, both in the wet and dried state, can be prepared as large monoliths with dimension in the cm-range. The materials are prepared from the water-soluble precursor tetraglycolsilane. When mixed with water, the compound forms single-phase transparent gels which can be super-critically dried with CO 2 to large monoliths of Aerogels. When Triton X-100 is added to the aqueous precursor solutions, at first, transparent phases become turbid during the gelification process but remain in a homogeneous state. Similar gels are obtained when dimethyldimethoxysilane (DiMe) or similar compounds with hydrophobic groups are added to the precursor solutions. STEM-measurements show that the dried gels have a bi-continuous pore structure with dimension in the nm and the μm range. It is concluded that the bi-continuous pore structure is produced by a microscopic phase separation process of the Triton X-100 in the samples before they gellify. The phase separation is initiated by glycol that is produced by the hydrolysis of the silica precursor. The microscopic phase separation is arrested by the gelification process.