Infrared Laser-Induced Photo-Thermal Phase Transition of an Aqueous Poly(N-isopropylacrylamide) Solution in the Micrometer Dimension

The phase transition of an aqueous poly(N-isopropylacrylamide) solution (PNIPAM, wt% = 1.8—3.6%) was induced by the irradiation of a focused (ca. 1 μm) 1064-nm laser beam; this brought about the formation of a single PNIPAM microparticle. The diameter of the particle was controlled to 2—9 μm through the laser power, polymer concentration, and solution temperature. The primary origin of particle formation was the photo-thermal phase transition of the polymer solution through the local heating of water (H2O) by the laser beam. The characteristic features of the phenomena, including manipulation of the PNIPAM particle by the incident laser beam and the role of radiation force for the particle formation, are discussed.