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Silicification and biosilicification : part 2. Silicification at pH 7 in the presence of a cationically charged polymer in solution and immobilized on substrates

Patwardhan, Siddharth and Durstock, M F and Clarson, Stephen J. (2003) Silicification and biosilicification : part 2. Silicification at pH 7 in the presence of a cationically charged polymer in solution and immobilized on substrates. In: Synthesis and properties of silicones and silicone-modified materials. ACS Symposium series . American Chemical Society, Washington, pp. 366-374. ISBN 0841238049

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Abstract

Biosilicification is facilitated by proteins and occurs under modest conditions in an aqueous medium (pH 7 and ambient temperature). Silicification at neutral pH in vitro has been shown to occur in the presence of various cationically charged synthetic macromolecules in solution. Here, the synthesis of silica from an aqueous silica precursor in the presence of poly(allylamine hydrochloride) (PAH) and polyacrylic acid (PAA) both in solution and immobilized on substrates is investigated. The results show that the formation of ordered silica structures under these modest conditions was favored for the PAH and the PAH-PAA in solution but neither for PAA in solution nor when the polymers were immobilized as PAH-PAA bilayers on flat substrates. It is possible that the immobilization of the PAH by the electrostatically self-assembly (ESA) technique may allow it to retain its catalytic function, while not allowing it to fulfill its role as a template / structure directing agent. The silica structures were characterized using scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). For the PAH system in solution silica spheres were seen and for PAH-PAA in solution hexagonal silica structures were observed in co-existence with silica spheres. The results presented herein may be helpful in elucidating biosilicification mechanism(s) and should lead to a better understanding of silicification.