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

We analyse data from the dynamic light scattering of poly(N-isopropyla crilamide) in water solution as we cross the collapse transition. Expe rimental data are interpreted by the Gaussian self-consistent Zimm mod el that takes into account two- and three-body excluded-volume effects , and Oseen hydrodynamic interactions, as well as by the standard cumu lant and Contin analyses. By fitting the dynamic structure factor we e xtract the temperature dependence of the diffusion coefficient D and t he first relaxation time tau(1) across the collapse transition for a r ange of scattering angles. The relaxation time tau(1) possesses a char acteristic 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 degr ees 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 vani shes at the onset of collapse transition.