A kinetic study of drying of TEOS-derived gels under nearly isothermal conditions

Abstract

The drying of wet Tetraethoxysilane-derived gels was studied by means of thermogravimetric analysis as a function of the time, from the instant when the samples were placed into a pre-heated oven, kept at 70, 83 and 100 °C. The precursor sol of the gel was obtained by sono-hydrolysis of the Tetraethoxysilane under acid condition and the final [Water]/[Tetraethoxysilane] molar ratio was adjusted to 30. The wet gels were cylindrical (2.5 cm height and 1.2 cm diameter) after 30 days of aging at 30 °C in a hermetically sealed container. The changes in volume and weight during drying are compatible with a mechanism controlled by evaporation from a flat liquid-vapour interface at the surface of the body and contraction of the gel by capillary forces, together with structural changes induced by polycondensation, which partially account for the irreversible shrinkage of the gel. The employed thermogravimetric method does not permit to unequivocally follow the small and slow final loss of weight associated to the falling rate periods

Preparation and properties of silicone‐containing poly(methyl methacrylate) gels

“…There are many chemical and biomedical applications which require polymer gels with excellent absorption and mechanical properties 1–11. These materials are prepared mainly by free radical copolymerization of monovinyl (MVM) and divinyl monomers (DVM) in a suitable solvent 12–22.…”

Investigation of the tetraethoxysilane‐derived sol–gel process by rheological oscillation test and the effect of different synthetic parameters

“…A liquid that suspends colloidal particles with a diameter of 1-100 nm is called a sol, while a gel is an arbitrarily interconnected polymer or covalently rigid network or chain with very small void spaces or pores. 12 Hence, the sol-gel process involves the conversion of silicon alkoxides to sol through hydrolysis reactions and the formation of gel through polycondensation of growing sol. 13,14 During the condensation process, we can distinguish a critical threshold point -the gelation time, which is the time point when "macroscopic cluster starts to appear", 15 which is usually judged qualitatively by the test-tube tilt detection method (visual method).…”

“…Silica gels are usually prepared by silicon alkoxides such as tetramethoxysilane (TMOS) or tetraethoxysilane (TEOS), 9–11 and then through a sol–gel process. A liquid that suspends colloidal particles with a diameter of 1–100 nm is called a sol, while a gel is an arbitrarily interconnected polymer or covalently rigid network or chain with very small void spaces or pores 12 . Hence, the sol–gel process involves the conversion of silicon alkoxides to sol through hydrolysis reactions and the formation of gel through polycondensation of growing sol 13,14 .…”

Preventing Glass Alteration in Museum Objects using ALD Deposited Amorphous Alumina Coatings

“…For example, a change in solution chemistry may cause the formation of crystalline secondary alteration products, which may in turn change the rate of alteration [7]. Hydrolysis and ion exchange can result in the formation of a hydrated silicate gel layer on the surface of the glass, the swelling/contraction of which produce stress across the interface between the alteration layer and the glass driving crack nucleation [10,11]. Micro-crack networks in the gel layer and ultimately, the formation of salt precipitates on the surface, may result in a hazed and crusted appearance most often associated with degraded glass as shown in Figure 1 [7].…”