PNIPAM chain collapse depends on the molecular weight and grafting density

被引:355
作者
Plunkett, KN
Zhu, X
Moore, JS
Leckband, DE
机构
[1] Univ Illinois, Dept Chem, Urbana, IL 61801 USA
[2] Univ Illinois, Dept Chem & Biomol Engn, Urbana, IL 61801 USA
关键词
D O I
10.1021/la0531502
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
This study demonstrates that the thermally induced collapse of end-grafted poly(N-isopropylacrylamide) (PNIPAM) above the lower critical solution temperature (LCST) of 32 degrees C depends on the chain grafting density and molecular weight. The polymer was grafted from the surface of a self-assembled monolayer containing the initiator (BrC(CH3)(2)COO(CH2)(11)S)(2), using surface-initiated atom transfer radical polymerization. Varying the reaction time and monomer concentration controlled the molecular weight, and diluting the initiator in the monolayer altered the grafting density. Surface force measurements of the polymer films showed that the chain collapse above the LCST decreases with decreasing grafting density and molecular weight. At T > LCST, the advancing water contact angle increases sharply on PNIPAM films of high molecular weight and grafting density, but the change is less pronounced with films of low-molecular-weight chains at lower densities. Below the LCST, the force-distance profiles exhibit nonideal polymer behavior and suggest that the brush architecture comprises dilute outer chains and much denser chains adjacent to the surface.
引用
收藏
页码:4259 / 4266
页数:8
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