Formation kinetics of small gold crystallites in photoresponsive polymer gels

AuCl4- ions are transformed into Au crystallites via two consecutive photoreactions inside cross-linked polymers of diallyldimethylammonium chloride swollen with methanol. The photoreactions are markedly influenced by the gel matrix, which facilitates pathways not observed in homogeneous solutions and controls the direction of propagation. Initially, the reactions are repressed by air, but at longer times they are aided by products from the O-2-reduction. The first process is an efficient monophotonic chain reduction of AuCl4- with chain lengths in excess of 80 and an atypical pseudofirst-order termination. Kinetic data from fully swollen gels is understood in terms of a mechanism involving solution reactions of .CH2OH radical chain carriers. Light-absorbing products of the first photoreaction, believed to be gold clusters, initiate the second process that yields metal particles. Several common kinetic features are displayed by both photoreactions. However, generation of An crystallites takes place via an unusual biphotonic chain reaction, with reaction rates that are correlated to the number of particle formation and decay cycles.