Ion Specifictiy at Charged Surfaces

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The projects proposed here will focus on compound systems which consist of flexible membranes or solid substrates in contact with charged and uncharged colloids such as polymers and nanoparticles. These colloids may be dispersed in the surrounding solution, which is the situation encountered in adsorption phenomena, or they may be attached to the membrane or substrate by anchor or grafting segments. In the case of flexible membranes the interactions with colloids change the preferred curvature of the membranes and modulate their adhesive and cohesive properties. Two specific problems which we propose here are: (P1) Adhesive colloids which stick to the membranes, and (P2) Membrane/colloid interactions arising from electric charges. Experimental applications are for example proteins which are either attached to a membrane via hydrophobic anchor segments, bound indirectly to the membrane through the glycocalix, or physisorbed. Electrostatic interactions supposedly play an important role in biological and biomimetic systems, since almost all proteins are charged. In the case of solid substrates, the dependence and structure of the adsorption layer on the substrate-colloids interaction and the properties of the colloidal solution are of prime interest. The specific problems we have in mind here are (P3) The influence of additional short-ranged substrate-polymer attraction for the adsorption of charged polymers (polyelectrolytes) on charged substrates and (P4) The influence of polymer rigidity on the adsorption behaivor of polymers. The connection to the main-body of research proposed in the French-German Network for this part results from the fact that biopolymers are in general rather stiff and charged at the same time.