MLZ is a cooperation between:> Technische Universität München> Helmholtz-Zentrum Geesthacht> Forschungszentrum Jülich
Stimuli-responsive surfaces are in the focus of interest for a multitude of applications such as sensors1, anti-fouling coatings  and cell culture substrates . For the latter, coatings made of thermoresponsive Poly-(N-isopropylacrylamide) pNIPAm microgels have been found to allow reversible switching of cell adhesion upon heating and cooling [3-5]. In these works the microgel layer was deposited on the substrate intended for use by printing or spin-coating. Hence, the dimensions and material properties of the substrate can strongly influence the adsorption of the microgel particles. The present talk will review our efforts in this area. The microgels itself were characterized using photon correlation spectroscopy (PCS), small angle neutron scattering (SANS), neutron spin-echo and UV/Vis-turbidity measurements. The adsorbed state of these responsive colloids is studied by GISANS.
Moreover, the preparation of free standing transferable membranes from cross-linkable microgels will be presented. Such membranes can be transferred to different surfaces and overcome problems arising from direct deposition of microgels. The approach is based on the deposition of microgels, containing aromatic moieties, by spin-coating the particles on a sacrificial-polyelectrolyte layer.
During this work the monomer N-Benzhydrylacrylamide for copolymerization with NIPAm has been synthesized. In a precipitation reaction using a solvent mixture copolymer particles from NIPAm and the aromatic comonomer are obtained, with different comonomer concentration, 2.5 mol-%, 5 mol-% and 10 mol-%. To confirm the incorporation of the aromatic component into the microgel structure the purified particles were analyzed with NMR-spectroscopy.
Monolayers of the microgels were spin-coated onto a silicon-wafer covered with a polyelectrolyte. Atomic force microscopy (AFM) was used to study the surface coverage, topography and the thickness in addition to ellipsometry measurements. Both methods for the characterization of the surface were done in dry and wet state to determine the thermoresponsive properties of the layers. The layers are subsequently cross-linked by e-beam irradiation. Such layers are transferable and can e.g. be used to modulate the ion flux in electrochemical cells.
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|Time||14.30 - 15.30 h|
|Room||HS 3, Physics Department TUM|
|Speaker||Prof. Dr. Thomas Hellweg (Bielefeld University)|