Plunkett Kyle N, Zhu Xi, Moore Jeffrey S, Leckband Deborah E
Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, USA.
Langmuir. 2006 Apr 25;22(9):4259-66. doi: 10.1021/la0531502.
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)2COO(CH2)11S)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.
本研究表明，在32℃的下临界溶液温度（LCST）以上，热诱导的末端接枝聚（N-异丙基丙烯酰胺）（PNIPAM）塌陷取决于链接枝密度和分子量。使用表面引发的原子转移自由基聚合，将该聚合物从含有引发剂（BrC(CH3)2COO(CH2)11S）2的自组装单分子层表面接枝。改变反应时间和单体浓度可控制分子量，在单分子层中稀释引发剂可改变接枝密度。聚合物薄膜的表面力测量表明，在LCST以上的链塌陷随着接枝密度和分子量的降低而减小。在T>LCST时，高分子量和高接枝密度的PNIPAM薄膜上的前进水接触角急剧增加，但对于低密度的低分子量链薄膜，这种变化不太明显。在LCST以下，力-距离曲线表现出非理想的聚合物行为，并表明刷状结构由稀的外层链和与表面相邻的密度大得多的链组成。
