We demonstrate liquid–liquid phase separation involving both coacervation and coil-to-globule phase transition of a thermoresponsive polymer. By focusing a near-infrared laser beam into an aqueous solution of poly(N-isopropylacrylamide) (PNIPAM), a single phase-separated polymer microdroplet can be formed and stably trapped at the focal point. Such droplet formation is induced by a local elevation in temperature (induced by a photothermal effect) and an optical force. The technique allows us to selectively analyze a single polymer droplet trapped at the focal point. In this study, we applied this technique to poly(N,N-diethylacrylamide) (PDEA) in water and generated a double-layered PDEA droplet. Such an inhomogeneous and complex microstructure has not been previously observed both in steady-state heating of a PDEA solution and in the PNIPAM system. Moreover, we used micro-Raman spectroscopy to clarify that PDEA underwent dehydration due to a coil-to-globule phase transition. Despite this, the polymer concentration (C_poly) of the trapped PDEA droplet was very low and was around 30 wt %. C_poly depended on the molecular weight of PDEA and the laser power that regulates the temperature elevation. These results strongly indicate that PDEA undergoes coacervation in addition to a coil-to-globule phase transition. This study will help provide us with a fundamental understanding of the phase separation mechanisms of thermoresponsive polymers.

中文翻译：

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激光镊子在水中形成聚（N，N-二乙基丙烯酰胺）单层凝聚层

我们证明了液相-液相分离涉及热响应性聚合物的凝聚和盘绕-球状相变。通过将近红外激光束聚焦到聚（N-异丙基丙烯酰胺）（PNIPAM）的水溶液中，可以形成单相分离的聚合物微滴并将其稳定地捕获在焦点处。这种液滴的形成是由温度的局部升高（由光热效应引起）和光学力引起的。该技术使我们能够选择性地分析捕获在焦点处的单个聚合物液滴。在这项研究中，我们将此技术应用于poly（N，N-二乙基丙烯酰胺）（PDEA）在水中并生成双层PDEA液滴。先前在PDEA溶液的稳态加热和PNIPAM系统中均未观察到这种不均匀和复杂的微观结构。此外，我们使用显微拉曼光谱法来阐明PDEA由于线圈到球的相变而经历了脱水。尽管如此，捕获的PDEA液滴的聚合物浓度（C _poly）非常低，约为30重量％。C_聚取决于PDEA的分子量和调节温度升高的激光功率。这些结果强烈表明，PDEA除了线圈到球的相变外还发生凝聚。这项研究将帮助我们对热敏性聚合物的相分离机理有一个基本的了解。