Combined experimental and simulation study of self-assembly of colloidal gold nanoparticles on silanized glass

Understanding the kinetics of metal nanoparticle self-assembly on functionalized surfaces is key for a variety of applications. In this work, we present a combined experimental and Monte Carlo simulation analysis of the monolayer formation of Au nanoparticles (Au NPs) on a glass surface functionalized with 3-aminopropyltrimethoxysilane (APTMS). The effect of particle size on the deposition process is analyzed by a wet chemical synthesis of Au NPs with sizes ranging from 14.65 +/- 1.85 to 101.81 +/- 10.3 nm. The adsorption kinetics is studied by measuring the peak optical absorbance, which increases with the surface concentration of Au NPs on the glass. Also, with the increase in nanoparticle size the surface concentration is found to decrease. To understand the adsorption process, the Frumkin isotherm is used to analyse the adsorption isotherms by choosing Au NPs of three different sizes, 38.31 +/- 3.55, 77.32 +/- 7.14, and 101.81 +/- 10.3 nm. The fitted parameters of this isotherm indicate that as the size increases the decrease in the affinity between the particles and the modified surface leads to reduced surface saturation. Correspondingly, the increased attractive interaction between the Au NPs causes agglomeration. To further interpret the experimental results, a Monte Carlo simulation was carried out to relate the adsorption kinetics with the surface coverage of the substrate. The simulations confirmed the linear relationship between the probability of NPs being adsorbed on the substrate and solution bulk concentration of the NPs. The immobilization of nanoparticles is governed by both the electrostatic interaction between the substrate and the nanoparticles and the bulk diffusion of the particles. As the diffusivity of the nanoparticles is inversely proportional to the size, the deposition decreases with particle size. The overall insight of this study helps to develop a systematic framework for the fabrication of a monolayer of Au NPs with different particle sizes for various applications.