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| - Collapse and Swelling of Thermally Sensitive Poly(N-isopropylacrylamide) BrushesMonitored with a Quartz Crystal Microbalance
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| - Thermally sensitive poly(N-isopropylacrylamide) (PNIPAM) brushes grafted on SiO2-coated quartz crystalsurface were prepared with a surface-immobilized initiator. Using quartz crystal microbalance (QCM), weinvestigated the collapse and swelling of the brushes in water in real time. Both frequency and dissipation ofPNIPAM brushes were found to gradually change throughout a temperature range 20−38 °C, indicating thatPNIPAM brushes undergo a continuous collapse transition in contrast with PNIPAM chains free in dilutesolution exhibiting a sharp coil-to-globule transition. This result is in accordance with the previous theoreticalprediction. The nonuniformity and stretching of PNIPAM brushes as well as the cooperativity between collapseand dehydration transitions are thought to be responsible for the continuity. On the other hand, a hysteresiswas also observed in the cooling process. This is not only due to the intrachain and interchain interactionsformed in the collapsed state but also to the nonuniform structure and stretching of the high-density brushes.
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