Laser induced phase transition in aqueous solutions of hydrophobically modified poly(N-isopropylacrylamide).

Phase transitions of amphiphilic copolymer solutions can be achieved by irradiating aqueous solutions of this polymer with an IR-laser beam. As a result, a single microparticle up to 15 mu m is formed, whereas thermal heating of the solution results in submicrometer particles. Both the photo-thermal effect (due to absorption of 1064 nm by the H2O overtone) and the radiation force cause the unusual large particle formation (up to 15 Gem). Furthermore, the present study shows that the conformational distribution and associations of polymers in solution can be controlled with the radiation force of a focused laser beam.