Role of particle size in individual and competitive diffusion of carboxylic acid derivatized colloidal gold particles in thermally evaporated fatty amine films

We have recently shown that nanocomposites of colloidal particles in a fatt y lipid matrix can be grown via a diffusion process controlled by selective electrostatic interactions. In this paper, a detailed investigation of the diffusion of carboxylic acid derivatized gold colloidal particles of diffe rent sizes into thermally evaporated octadecylamine films using quartz crys tal microgravimetry (QCM), transmission electron microscopy, and W-vis abso rption and Fourier transform infrared (FTIR) spectroscopies is described. T he QCM kinetics of gold cluster incorporation has been analyzed in terms of a one-dimensional Fickian-type diffusion model, and it is found that the c luster diffusivity increases with decreasing cluster size. The pH at which maximum cluster incorporation in the amine occurs was found to be dependent on the cluster size as well. FTIR spectroscopy of the fatty amine-gold par ticle composites indicated weak coupling of the clusters to the protonated amine groups as well as interesting cluster size dependent changes in the a mine and methylene antisymmetric deformations as well as the methylene scis soring bands. In a competitive diffusion process of large and small gold pa rticles, it was observed that bigger gold particles were preferentially inc orporated into the amine matrix even though the cluster diffusivity is high er for the smaller gold particles.