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| - Direct Observation of the Phase Transition for aPoly(N-isopropylacryamide) Layer Grafted onto a Solid Surface byAFM and QCM-D
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| - The temperature-induced structural changes of a thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) layergrafted onto a silica substrate were investigated in aqueous solution using an atomic force microscope (AFM) anda quartz crystal microbalance with dissipation (QCM-D). A PNIPAM layer was grafted onto the silicon wafer surfaceby free radical polymerization of NIPAM to obtain a high molecular weight polymer layer with low-grafting densityoverall. By AFM imaging, the transition of the grafted PNIPAM chains from a brush-like to a mushroom-like statewas clearly visualized: The surface images of the plate were featureless at temperatures below the LCST commensuratewith a brush-like layer, whereas above the LCST, a large number of domain structures with a characteristic size of∼100 nm were seen on the surface. Both frequency and dissipation data obtained using QCM-D showed a significantchange at the LCST. Analysis of these data confirmed that the observed PNIPAM structural transition was causedby a collapse of the brush-like structure as a result of dehydration of the polymer chains.
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