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 fatty 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 different sizes into thermally evaporated octadecylamine films using quartz crystal microgravimetry (QCM), transmission electron microscopy, and W-vis absorption and Fourier transform infrared (FTIR) spectroscopies is described. The 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 cluster 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 particle composites indicated weak coupling of the clusters to the protonated amine groups as well as interesting cluster size dependent changes in the amine and methylene antisymmetric deformations as well as the methylene scissoring bands. In a competitive diffusion process of large and small gold particles, it was observed that bigger gold particles were preferentially incorporated into the amine matrix even though the cluster diffusivity is higher for the smaller gold particles.