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    Adsorption Isotherms and Dissipation of Adsorbed Poly(N-isopropylacrylamide) in Its Swelling and Collapsed States

    Year: 2007

    Journal: J. Phys. Chem. B 2007, 111, 8723-8727, 20100827

    Authors: Wu K †, Wu B †, Wang P †, Hou Y †, Zhang G †, Zhu D-M * † ‡

    Last authors: Da-Ming Zhu

    Organizations: Department of Modern Physics and Department of Chemical Physics, UniVersity of Science and Technology of China, Hefei 230027 China, and UniVersity of Missouri-Kansas City, Kansas City, Missouri 64110

    Country: USA, US, United States of America

    Poly(N-isopropylacrylamide) (PNIPAM) physisorbed on gold surfaces in aqueous solutions has been studied using a quartz crystal microbalance with dissipation monitoring (QCM-D). The adsorption isotherms of the polymer, that is, the adsorbed mass versus the concentration of PNIPAM in solution, show distinctly different behaviors at temperatures below and above a lower critical solution temperature (LCST). Below the LCST, PNIPAM forms a single compact layer in solutions with concentrations up to 100 ppm in weight; above the LCST, much thicker films of PNIPAM form in the same concentration range. Changes in the dissipation factor versus solvent concentration show a behavior similar to those in the isotherms. The difference in the adsorption behavior below and above the LCST can be qualitatively explained in terms of the conformation difference of the polymer in its swelling and collapsed states.