Multiscale aggregation of PMMA stereocomplexes at a surface: An atomic force microscopy investigation

After briefly discussing the particularity of the adsorption process of PMM A aggregates in terms of aggregative adsorption, the patterns formed by pol y(methyl methacrylate) (PMMA) stereocomplexes at the surface of silicon waf ers, glass, and mica were investigated by tapping mode atomic force microsc opy. The effects of the solvent nature, PMMA concentration, ils-ratio, and surface nature on the morphology of the stereocomplex layer at a surface we re addressed. The aggregation phenomena are well described by the diffusion -Limited cluster-cluster aggregation model (DLA) and the fractal exponent D calculated. Solvent was shown to play a major role on the structure of the polymer assembly observed on silicon. The i/s-ratio strongly influences th e fractal exponent D, since slow or fast aggregation can be involved. Dilut e polymer solutions were used and the concentrations were varied from 0.1 t o 1 g/L in acetone to reach a 2D network of connecting aggregates. The size of the aggregates increases with the PMMA concentration and is always high er than the size of the aggregates in solution measured by light scattering . This is the result of an enhanced surface aggregation of the polymer asse mbly indicated by the difference in size of the aggregates observed on diff erent substrates of varying surface energy.