Thomas Marc, Gajda Martyna, Amiri Naini Crispin, Franzka Steffen, Ulbricht Mathias, Hartmann Nils
Physical Chemistry, Department of Chemistry, and ‡Technical Chemistry II, Department of Chemistry, University of Duisburg-Essen , 45117, Essen, Germany.
Center for Nanointegration Duisburg-Essen (CENIDE) and ∥Interdisciplinary Center for Analytics on the Nanoscale (ICAN), University of Duisburg-Essen , 47057 Duisburg, Germany.
Langmuir. 2015 Dec 15;31(49):13426-32. doi: 10.1021/acs.langmuir.5b03448. Epub 2015 Nov 30.
The temperature-dependent switching behavior of poly(N,N-dimethylaminoethyl methacrylate) brushes in alkaline, neutral, and acidic solutions is examined. A novel microscopic laser temperature-jump technique is employed in order to study characteristic thermodynamic and kinetic parameters. Static laser micromanipulation experiments allow one to determine the temperature-dependent variation of the swelling ratio. The data reveal a strong shift of the volume phase transition of the polymer brushes to higher temperatures when going from pH = 10 to pH = 4. Dynamic laser micromanipulation experiments offer a temporal resolution on a submillisecond time scale and provide a means to determine the intrinsic rate constants. Both the swelling and the deswelling rates strongly decrease in acidic solutions. Complementary experiments using in situ atomic force microscopy show an increased polymer layer thickness at these conditions. The data are discussed on the basis of pH-dependent structural changes of the polymer brushes including protonation of the amine groups and conformational rearrangements. Generally, repulsive electrostatic interactions and steric effects are assumed to hamper and slow down temperature-induced switching in acidic solutions. This imposes significant restrictions for smart polymer surfaces, sensors, and devices requiring fast response times.
研究了聚（N，N-二甲基氨基乙基甲基丙烯酸酯）刷在碱性、中性和酸性溶液中的温度依赖性开关行为。采用了一种新颖的微观激光温度跳跃技术来研究特征热力学和动力学参数。静态激光微操纵实验使人们能够确定溶胀率随温度的变化。数据显示，当从pH = 10变为pH = 4时，聚合物刷的体积相变向更高温度强烈移动。动态激光微操纵实验提供了亚毫秒时间尺度上的时间分辨率，并提供了一种确定本征速率常数的方法。在酸性溶液中，溶胀和解溶胀速率均大幅降低。使用原位原子力显微镜的补充实验表明，在这些条件下聚合物层厚度增加。基于聚合物刷的pH依赖性结构变化，包括胺基的质子化和构象重排，对数据进行了讨论。一般来说，排斥性静电相互作用和空间效应被认为会阻碍和减缓酸性溶液中温度诱导的开关过程。这对需要快速响应时间的智能聚合物表面、传感器和器件施加了重大限制。
