ANALYSIS OF DYNAMIC LIGHT-SCATTERING OF POLY(N-ISOPROPYLACRYLAMIDE) ACROSS THE COLLAPSE TRANSITION

We analyse data from the dynamic light scattering of poly(N-isopropylacrilamide) in water solution as we cross the collapse transition. Experimental data are interpreted by the Gaussian self-consistent Zimm model that takes into account two- and three-body excluded-volume effects, and Oseen hydrodynamic interactions, as well as by the standard cumulant and Contin analyses. By fitting the dynamic structure factor we extract the temperature dependence of the diffusion coefficient D and the first relaxation time tau(1) across the collapse transition for a range of scattering angles. The relaxation time tau(1) possesses a characteristic peak at about 32.4 degrees C due to slowing of the internal motions of the polymer at the theta-point, and a minimum at 33.4 degrees C. We interpret this as a combination of collapse closely followed by the growth of critical correlations. At large scattering angles we reach the universal k(3) regime, and observe that this behaviour vanishes at the onset of collapse transition.