Surface and Bulk Collapse Transitions of Thermoresponsive Polymer Brushes.
(2010) Langmuir : the A C S journal of surfaces and colloids — Vol. 26, n° 2, p. 838-847 (2010)
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- Abstract
- We elucidate the sequence of events occurring during the collapse transition of thermoresponsive copolymer brushes based on poly(di(ethyleneglycol) methyl ether methacrylate) chains (PMEO2MA) 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 of 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 (approximately 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 a bulk transition T(br)(bulk) occurring on average approximately 8 degrees C below T(br)(surf) and approximately 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.
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Laloyaux, X., Mathy, B., Nysten, B., & Jonas, A. (2010). Surface and Bulk Collapse Transitions of Thermoresponsive Polymer Brushes. Langmuir : the A C S journal of surfaces and colloids, 26(2), 838-847. https://doi.org/10.1021/la902285t (Original work published 2010)