Solvent-Free High-Temperature Capillary Stamping of Stimuli-Responsive Polymers: Wettability Management by Orthogonal Substrate Functionalization

The wettability ofsurfaces determines their antifouling,antifogging,anti-icing, and self-cleaning properties as well as their usabilityfor sensing, oil-water separation, water collection, and waterpurification. Solvent-free high-temperature capillary stamping ofstimuli-responsive polymers yielding arrays of stimuli-responsivepolymer microdots on differently modified substrates enables the flexiblegeneration of switchable surfaces with different water contact angles(WCAs). Potential problems associated with the deposition of polymersolutions, such as the handling of volatile organic solvents, phaseseparation induced by solvent evaporation, and capillarity-drivenflow processes, are circumvented. We used composite stamps with topographicallypatterned contact surfaces consisting of metallic nickel cores andporous MnO2 coatings taking up the stimuli-responsive polymers.The short transport paths from the MnO2 contact layersto the counterpart substrates enabled the stamping of polymer meltscontaining components impeding flow, such as carbon nanotubes (CNTs).Thus-obtained arrays of polymer-CNT hybrid microdots prevent problemsassociated with continuous coatings including delamination and crackpropagation. Moreover, the range within which the properties of thestamped stimuli-responsive polymer microdots are switchable can betuned by orthogonal substrate modification. As an example, we stampedhybrid microdots consisting of poly(2-(methacryloyloxy)ethyl ferrocenecarboxylate)(PFcMA) and CNTs onto indium tin oxide (ITO) substrates. Coating theITO substrates with a poly(ethylene oxide)-terminated silane shiftedthe WCAs obtained by switching the PFcMA between its oxidized andreduced states by nearly 50 & DEG;.