ELECTROSTATICALLY CONTROLLED DIFFUSION OF CARBOXYLIC-ACID DERIVATIZEDSILVER COLLOIDAL PARTICLES IN THERMALLY EVAPORATED FATTY AMINE FILMS

We have recently demonstrated that carboxylic acid derivatized silver colloidal particles can be incorporated in thermally evaporated fatty amine films by immersion of the films in the silver sol and that the p rocess is controlled through electrostatic interactions [Sastry, M.; P atil, V.; Mayya, K. S. Langmuir 1997, 13, 4490]. In this paper, we ana lyze the influence of colloidal particle concentration, solution pH, a nd film thickness on the kinetics of cluster incorporation in thermall y evaporated fatty amine films obtained from quartz-crystal microgravi metry (QCM) measurements in terms of a one-dimensional (1-D) Fickian-t ype diffusion model. Although it is found that 1-D diffusion adequatel y represents the cluster mass uptake kinetics observed using QCM, an i nteresting film-thickness dependence on the diffusivity was observed. The nature of the cluster-diffusion curves were quite different for am ine films annealed prior to immersion in the colloidal solution. In th ese cases, the 1-D-diffusion model with a single diffusivity fails, in dicating the possible occurrence of additional diffusion channels for cluster incorporation. In situ QCM and optical absorption spectroscopy measurements have been made to elucidate the mechanism for cluster di ffusion in the thermally evaporated films.