- Formation of Single Double-Layered Coacervate of Poly(N,N-diethylacrylamide) in Water by a Laser Tweezer
- Mitsuhiro Matsumoto, Taka-Aki Asoh, Tatsuya Shoji, Yasuyuki Tsuboi
- Langmuir, 37 (2021), 2874-2883.
- DOI: 10.1021/acs.langmuir.0c03009
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 (Cpoly) of the trapped PDEA droplet was very low and was around 30 wt %. Cpoly 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.https://pubs.acs.org/doi/abs/10.1021/acs.langmuir.0c03009