Electrostatically controlled diffusion of carboxylic acid derivatized silver 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 process is controlled through electrostatic interactions [Sastry, M.; Patil, V.; Mayya, K. S. Langmuir 1997, 13, 4490]. In this paper, we analyze the influence of colloidal particle concentration, solution pH, and film thickness on the kinetics of cluster incorporation in thermally evaporated fatty amine films obtained from quartz-crystal microgravimetry (QCM) measurements in terms of a one-dimensional (1-D) Fickian-type diffusion model. Although it is found that 1-D diffusion adequately represents the cluster mass uptake kinetics observed using QCM, an interesting film-thickness dependence on the diffusivity was observed. The nature of the cluster-diffusion curves were quite different for amine films annealed prior to immersion in the colloidal solution. In these cases, the 1-D-diffusion model with a single diffusivity fails, indicating 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 diffusion in the thermally evaporated films.