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Abstract: We probe, using the Surface Forces Apparatus, the thermal response ofpolyN-isopropylacrylamide PNIPAM brushes of various grafting densities,grown from plasma-activated mica by means of surface-initiated polymerization.We thus show that dense thermoresponsive brushes collapse gradually astemperature is increased, and that grafting density greatly affects theirability to swell: the swelling ratio of the brushes, which characterizes thethickness variation between the swollen and the collapsed state, is found todecrease from $\sim 7$ to $\sim 3$ as the number of grafted chains per unitarea increases. Such a result, obtained with an unprecedent resolution ingrafting density, provides qualitative support to calculations by Mendez {\itet al.} {\it Macromolecules} {\bf 2005} {\it 38}, 174. We further show that,in contrast to swelling, adhesion between two PNIPAM brushes appears to berather insensitive to their molecular structure.



Autor: Ibrahim Bou Malham INSP, Lionel Bureau INSP

Fuente: https://arxiv.org/







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