Surface and Bulk Collapse Transitions of Thermo responsive Polymer Brushes

被引:89
作者
Laloyaux, Xavier [1 ]
Mathy, Bertrand [1 ]
Nysten, Bernard [1 ]
Jonas, Alain M. [1 ]
机构
[1] Catholic Univ Louvain, Inst Condensed Matter & Nanosci, B-1348 Louvain, Belgium
关键词
QUARTZ-CRYSTAL MICROBALANCE; N-ISOPROPYLACRYLAMIDE BRUSHES; TEMPERATURE-DEPENDENCE; PHASE-TRANSITIONS; MOLECULAR-WEIGHT; FILMS; WATER; ACTUATION; PARAMETER; BEHAVIOR;
D O I
10.1021/la902285t
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
We elucidate the sequence of events occurring during the collapse transition of thermoresponsive copolymer brushes based on poly(di(ethyleneglycol) methyl ether methacrylate) chains (PMEO(2)MA) grown by atom-transfer radical polymerization (ATRP). The collapse of the bulk of the brush is followed by quartz crystal microbalance measurements with dissipation monitoring (QCM-D), and the collapse or its outer surface is assessed by measuring equilibrium water contact angles in the captive bubble configuration. The bulk of the brush collapses over a broad temperature interval (similar to 25 degrees C), and the end of this process is signaled by a sharp first-order transition of the surface of the brush. These observations support theoretical predictions regarding the occurrence of a vertical phase separation during collapse, with surface properties of thermoresponsive brushes exhibiting a sharp variation at a temperature of T-br(surf). in contrast, the bulk properties of the brush vary smoothly, with it bulk transition T-br(bulk) occurring oil average similar to 8 degrees C below T-br(surf) and similar to 5 degrees C below the lower critical Solution temperature (LCST) of free chains in solution. These observations should also be valid for planar brushes of other neutral, water-soluble thermoresponsive polymers such as poly(N-isopropylacrylamide) (PNIPAM). We also propose a way to analyze more quantitatively the temperature dependence of the QCM-D response of thermoresponsive brushes and deliver a simple thermodynamic interpretation of equilibrium contact angles, which can be of use for other complex temperature-responsive solvophilic systems.
引用
收藏
页码:838 / 847
页数:10
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