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Download fileFormation of Single Double-Layered Coacervate of Poly(N,N-diethylacrylamide) in Water by a Laser Tweezer
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posted on 2021-02-22, 16:05 authored by Mitsuhiro Matsumoto, Taka-Aki Asoh, Tatsuya Shoji, Yasuyuki TsuboiWe
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.
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double-layered PDEA dropletmicro-Raman spectroscopyphase separation mechanismstemperature elevationSingle Double-Layered Coacervatecoil-to-globule phase transitionthermoresponsive polymersPNIPAM systemnear-infrared laser beamSuch droplet formationpolymer dropletthermoresponsive polymerLaser TweezerPDEA solutionphase-separated polymer microdropletlaser powerPDEA dropletpolymer concentrationC polyphotothermal effect