Dynamic surface coatings through the hierarchical self-assembly of responsive colloidal building blocks

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The project aims at exploring a novel strategy for the assembly of polymeric coatings which show pronounced responsiveness towards changes in pH or irradiation with light while simultaneously providing a compartmentalized structure with nm feature sizes and full reversibility of structural changes. The assembly strategy uses different colloidal building blocks: either pH-responsive micelles formed from ampholytic triblock terpolymers are used or, as an alternative, spherical polyelectrolyte brushes with an ampholytic diblock copolymer corona are prepared. These building blocks allow multilayer formation via layer-by-layer electrostatic self-assembly. In both cases, the interactions between adjacent colloidal building blocks as well as with potential adsorbents on the surface can be controlled via external stimuli, i.e. switching from attractive to repulsive interactions can be realized. In that way, we aim at light- and pH-responsive materials which are capable of interacting with different systems upon adhesion or film formation. Whereas the incorporation of pH-sensitive segments in block copolymer-based multi-compartment micelles (MCMs) leads to charge-invertible nanostructures, light as external trigger is implemented by exploiting the photo-acidity of TiO2 upon irradiation. TiO2 can act as a light sensitizer, as illumination of TiO2 with light of suitable wavelength results in local pH changes, triggering changes in the charge and conformation of attached polyelectrolytes. The immobilization of colloidal building blocks on surfaces can be directly achieved from aqueous solutions using non-covalent interactions. Thus, coatings can be formed under environmentally friendly conditions on a large variety of surfaces including metals, metal-oxides or polymeric materials and with varying thickness. While our study is of fundamental nature, we envision potential applications of these coatings as switchable cell culture surfaces or switchable elements in 3D cell cultures in the future.