Dynamic light scattering study on sol-gel transition of poly(γ-benzyl L-glutamate)-toluene solutions

The autocorrelation function (ACF) was measured at various temperatures using the dynamic light scattering (DLS) technique for two kinds of toluene solutions of poly(γ-benzyl L-glutamate) (PBLG): one was a semidilute PBLG (M_w = 2.3 × 10⁵) solution far above the critical crossover concentration φ₂^* (PBLG-23), and the other was also a semidilute PBLG (M_w = 1.0×10⁵) solution near φ₂^* (PBLG-10). Both of the PBLG solutions were sol at elevated temperatures and gelled with decreasing temperature. For PBLG-23, the ACF obtained in the sol phase could be fit well by a double-exponential function: the fast mode was due to a cooperative diffusive motion in a transient entangled PBLG-23 network; the slow mode was considered to be diffusive motion of aggregated PBLG-23 chains. On the other hand, the ACF of PBLG-10 was characteristic and was modulated vibrationally near the gelation threshold. This fact suggested strongly underdamped coupling between aggregated domains of PBLG-10 chains.