Two-Dimensional Aggregation of Species with Weak and Strong Bonding Interactions:  Modeling the Growth of Self-Assembled Alkylsiloxane Monolayers

A simple two-dimensional model for the growth of self-assembled alkylsiloxane monolayers on hydroxylated substrates is suggested, which, for the first time, takes the principal weak and strong bonding interactions of the aggregating species into account. The model considers the adsorption, diffusion, vertical grafting, and lateral cross-linking of preordered alkylsilanol clusters. All model parameters are adjusted to experimental estimates of the respective rate constants. Despite the simplicity of the model, the simulations qualitatively reproduce many morphological aspects of the experimentally observed island growth and provide a simple explanation for the deviations from first-order Langmuir adsorption kinetics observed in various ex situ investigations.