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

After briefly discussing the particularity of the adsorption process of PMMA aggregates in terms of aggregative adsorption, the patterns formed by poly(methyl methacrylate) (PMMA) stereocomplexes at the surface of silicon wafers, glass, and mica were investigated by tapping mode atomic force microscopy. The effects of the solvent nature, PMMA concentration, ils-ratio, and surface nature on the morphology of the stereocomplex layer at a surface were 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 the fractal exponent D, since slow or fast aggregation can be involved. Dilute polymer solutions were used and the concentrations were varied from 0.1 to 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 higher than the size of the aggregates in solution measured by light scattering. This is the result of an enhanced surface aggregation of the polymer assembly indicated by the difference in size of the aggregates observed on different substrates of varying surface energy.