Collapse kinetics for individual poly(N-isopropylmethacrylamide) chains

The kinetics for the coil-to-globule transition of linear poly(N-isopropylmethacrylamide) (PiPMA) chains has been studied by use of the fluorescence and Rayleigh scattering with a fast laser pulse infrared heating. We have observed the two-stage kinetics in the collapse transition with the characteristic relaxation times, τfast and τslow, which are attributed to the nucleation and growth of pearls on the chain and the merging and coarsening of pearls to a globule, respectively. The collapse kinetics of PiPMA is similar to that of poly(N-isopropylacrylamide) which has one less methyl in each monomeric unit, indicating that the additional methyl groups in PiPMA chains slightly influence the kinetics. In other words, the pearls are not completely coarsened to form compact globules within τslow.