For many problems, new smart or responsive surfaces which change their properties as a response to external stimuli give new perspectives. One example are polyelectrolyte brushes which change their thickness and charge if the pH, the salt concentration or the temperature of a surrounding aqueous solution is varied. This effect is used to control e.g. the adsorption of proteins or cells on biomimetic surfaces [1]. To investigate the interaction between a weak polyelectrolyte brush (annealed brush) and colloidal particles with different surface charges in more detail, the interaction between a poly(acrylic acid) brush and model particles with different isoelectric points (silica, polystyrene) have been measured using the AFM colloidal probe technique. It allows to measure directly the force between a colloidal particle glued to an AFM cantilever and a flat surface and to calculate the geometry-independent interaction energy [2, 3]. The results of the force measurements are discussed basing on ellipsometric measurements of the brush thickness and the isoelectric point of the poly(acrylic acid) brush and the colloidal spheres obtained by zeta potential measurements.
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