Dr. Martin Müller, Dr. Simona Schwarz

The performance of materials with certain bulk properties can be changed or optimized by thin polymer layers adsorbed on their surfaces. The scope of that working area is to create and optimize polyelectrolyte (PEL) based surface modification concepts performing fundamental studies as well as research studies close to industrial demands. PELs are polymers containing either positively or negatively charged groups and can adopt in solution, in interpolymer complexes and at surfaces a plethora of conformations and supramolecular structures in depen-dence of their constitution and external parameters (solvent, commonly water: concentration, pH, ionic strength, T). PEL can be deposited from aqueous solutions by electrostatic attraction on a variety of materials by simple adsorption techniques. For that charged surface groups are used, which are already present on the material or are generated by various pretreatments like plasma or chemical modification techniques.

Wet chemical surface modification by PELs is applied in many industrialprocessing steps for a long time. Beside classical applications such as colloidstabilization and flocculation for water treatment and paper making, adsorbedPEL layers are under way to address novel application fields in nano andbiomaterial engineering. Especially their potential concerning charging,hydrophilizing, binding (biomolecular recognition), repelling (bioinertness)and vertical and horizontal structuring is promising for the development ofsensors, biomaterials, membranes and carrier systems.

In the working group PEL interaction studies at both complicated interfacialsystems like dispersed or suspended colloids (i), (textile) fibres (ii) orfiltration membranes (iii) and ideal and analytically well accessible planarsystems like silicon wafers and polymer layers (iv) are performed (Fig. 1). Itis the red line in our working area to interrelate phenomena found in either ofthe systems (i, ii). In general three PEL-based surface modification conceptsare used, which are shown in Fig. 2.

Fig. 1. Common substrates (S) to be modified
Fig. 2. Polyelectrolyte based surface modification concepts: (a) PEL adsorption, (b) consecutive PEL adsorption, (c) PEC adsorption

Beside the single component PEL adsorption (a), e.g. of polycations at negatively charged surfaces, mixed systems of polycations and polyanions are predominantly used in the working group. These include the deposition of polyelectrolyte multilayers initiated by Decher and the adsorption of preformed polyelectrolyte complex (PEC) nanoparticles (c), which has been initiated by Lunkwitz and Buchhammer (IPF). The PEMs are visionalized as novel biomimetic and conductive coatings. The PEC nanoparticles are visionalized as novel flocculating agents as well as colloid carrier systems, whose shape, density and sorption capacity can be induced by external parameters (pH, T, salt)