Wringing Non-Shrink Gels

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Science  15 Feb 2002:
Vol. 295, Issue 5558, pp. 1195-1197
DOI: 10.1126/science.295.5558.1195e

Silica gels are of technical interest because they are highly porous structures with large internal surface area and because they can be readily prepared as monoliths. The gels typically are made from a precursor material that hydrolyzes in aqueous solution to form silica particles. As the gels age, they tend to shrink because the silica particles are strongly attracted to each other and move closer together. Meyer et al. show that if they incorporate a small amount (0.1 to 1.0 weight %) of cationic precursor, the resulting gel does not shrink, probably because the residual ionic charge of the silica particles keeps them apart. When the gels are struck, a ringing sound is heard; the storage modulus is high enough to produce vibrations in the audible range (200 to 1100 hertz), and the loss modulus is low enough that the vibrational energy takes a long time to be converted to heat. Varying the fraction of cationic precursor alters the ratio of the storage to loss moduli and changes the pitch. — MSL

J. Phys. Chem. B, 10.1021/jp013371q.

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