Wu Yaodong, Wiese Susanne, Balaceanu Andreea, Richtering Walter, Pich Andrij
Functional and Interactive Polymers, Institute of Technical and Macromolecular Chemistry, and DWI Leibniz Institute for Interactive Materials, Rheinisch-Westfaelische Technische Hochschule (RWTH) Aachen University , Forckenbeckstraße 50, 52056 Aachen, Germany.
Langmuir. 2014 Jul 8;30(26):7660-9. doi: 10.1021/la501181k. Epub 2014 Jun 25.
Herein, we investigate the interfacial behavior of temperature-sensitive aqueous microgels on the toluene/water interface. Copolymer microgels based on N-vinylcaprolactam (VCL) and two acrylamides, N-isopropylacrylamide (NIPAm) and N-isopropylmethacrylamide (NIPMAm), with various copolymer compositions were used in this study. It is revealed that these copolymer microgels have the similar internal structure, regardless of the chemical composition. A classic kinetics of interfacial tension with three distinct regimes is found in the dynamic interfacial tension plots of copolymer microgels, which is similar to inorganic nanoparticles and proteins. The influences of the copolymer composition and the temperature on the interfacial behavior of microgels are investigated. The results show that the interfacial behavior of copolymer microgels at the toluene/water interface follows exactly the trend of the volume phase behavior of microgels but, on the other hand, strongly depends upon the chemical compositions of copolymer microgels. In contrast, with respect to the size range of microgels studied here (50-500 nm), the size of the microgel has no influence on the interfacial tension. Below the volume phase transition temperature (VPTT), the equilibrium interfacial tensions of all microgel systems decrease as the temperature increases. Above VPTT, the equilibrium interfacial tension remains at a certain level for poly(N-vinylcaprolactam) (PVCL)- and poly(N-isopropylmethacrylamide) (PNIPMAm)-rich microgel systems and increases slightly for poly(N-isopropylacrylamide) (PNIPAm)-rich microgel systems. The evolution of dynamic interfacial tension for microgel solutions against toluene at T < VPTT is faster than that at T > VPTT, because of the reduced deformability of the microgel with the increase of the temperature. The softer microgels with lower cross-linking degrees exhibit faster kinetics of reduction of interfacial tension compared to those with more cross-linked degrees, which strongly supports the deformation-controlled interfacial behavior of microgels.
在此，我们研究了温度敏感型水性微凝胶在甲苯/水界面的界面行为。本研究使用了基于N-乙烯基己内酰胺（VCL）以及两种丙烯酰胺（N-异丙基丙烯酰胺（NIPAm）和N-异丙基甲基丙烯酰胺（NIPMAm））且具有不同共聚物组成的共聚物微凝胶。结果表明，无论化学组成如何，这些共聚物微凝胶都具有相似的内部结构。在共聚物微凝胶的动态界面张力图中发现了具有三个不同阶段的经典界面张力动力学，这与无机纳米颗粒和蛋白质相似。研究了共聚物组成和温度对微凝胶界面行为的影响。结果表明，共聚物微凝胶在甲苯/水界面的界面行为与微凝胶的体积相行为趋势完全一致，但另一方面，又强烈依赖于共聚物微凝胶的化学组成。相比之下，对于此处研究的微凝胶尺寸范围（50 - 500 nm），微凝胶的尺寸对界面张力没有影响。在体积相转变温度（VPTT）以下，所有微凝胶体系的平衡界面张力随温度升高而降低。在VPTT以上，富含聚（N-乙烯基己内酰胺）（PVCL）和聚（N-异丙基甲基丙烯酰胺）（PNIPMAm）的微凝胶体系的平衡界面张力保持在一定水平，而富含聚（N-异丙基丙烯酰胺）（PNIPAm）的微凝胶体系的平衡界面张力略有增加。由于微凝胶随温度升高而变形性降低，在T < VPTT时微凝胶溶液与甲苯的动态界面张力的变化比T > VPTT时更快。与交联度更高的微凝胶相比，交联度较低的较软微凝胶表现出更快的界面张力降低动力学，这有力地支持了微凝胶的变形控制界面行为。
