Chemical and optical mechanism of microparticle formation of poly(N-vinylcarbazole) in N,N-dimethylformamide by photon pressure of a focused near-infrared laser beam

We focus our attention to the laser-controlled association process of poly(N-vinylcarbazole) by "pure" photon pressure effect. A few wt % N,N-dimethylformamide solution of the polymer was irradiated with a focused 1064 nm laser beam of sub wattage power, and a resultant condensation (microparticle formation) at a focal point of the microscope was initially probed by backscattering of He-Ne laser and later observed by transmission image of the microscope. To understand in detail the behavior of the polymer induced by the photon force, the relation between laser power and particle diameter, as well as repeated irradiation effect, were investigated The laser-controlled association was successfully demonstrated even for short polymer chains of about 20 mean degrees of polymerization. Fluorescence spectra and their rise and decay curves were measured microspectroscopically for a formed microparticle. The results are different from those of the polymer in solution, suggesting the association structure is characteristic of photon pressure effect.