Probing the Intrinsic Switching Kinetics of Ultrathin Thermoresponsive Polymer Brushes

摘要

Stimuli-responsive polymers have become versatile materials for the design and fabrication of smart functional devices, such as adaptive microoptics, microfluidic chips, membranes, and sensors. Controlled reaction schemes allow the build-up of surface-grafted polymer brush films with thicknesses down to the sub-100 nm range. This approach opens up an avenue towards miniaturized device structures with unprecedented functionalities. To establish design rules and estimate device performance, a detailed fundamental knowledge of the switching kinetics of such ultrathin polymer films is of utmost importance. It is worth noting that despite the ultrathin nature of these films, most previous studies revealed fairly long response times of several seconds or more. Highspeed measurements, though, are challenging in many respects and hence data on the intrinsic switching kinetics still are largely missing. Herein we show a novel strobo-scopic photothermal laser manipulation technique that allows for real-time measurements of the intrinsic temperature-dependent switching kinetics of poly(N-isopropylacrylamide) (PNiPAAm) brushes at the water/substrate interface.