Reentrant behavior of poly(N-isopropylacrylamide) brushes in water-methanol mixtures investigated with a quartz crystal microbalance |
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Authors: | Liu Guangming Zhang Guangzhao |
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Institution: | Hefei National Laboratory for Physical Sciences at Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui, China. |
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Abstract: | The solvent composition induced reentrant behavior of poly(N-isopropylacrylamide) (PNIPAM) chains grafted on a SiO2 surface in water-methanol mixtures was investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D) at 20 degrees C. The frequency and energy dissipation responses showed that the grafted PNIPAM chains sharply collapse when the methanol content (x(m)) reaches approximately 17 mol %. In the range 17-50 mol %, the grafted chains remain in a collapsed state. Further increase of the methanol content leads to an abrupt reswelling of the collapsed chains at x(m) > approximately 50 mol %. The sharp reentrant swelling-to-collapse-to-swelling transition was attributed to the water-methanol complexation instead of the preferential adsorption effect. Our results also suggest that the water-methanol complexation is not induced by hydrophobic interaction but by hydrogen bonding. |
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