Dynamic Light Scattering Studies on Strong Interaction between Polymer Liquid Crystals and the Gelation Process.

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Static and dynamic light scattering measurements have been performed on the association and gelation processes for poly (gamma-benzyl-alpha, L-glutamate) (PBLG) -toluene systems. In the quasi-equilibrium state of gelation (I), the slow mode has been observed in the obtained autocorrelation function (ACF), which was assigned to be a cooperative self-diffusion mode for aggregated PBLG chains in an isotropic phase. In addition, the ACF measured was modulated vibrationally near the gelation threshold. The apparent frequency of this modulation was influenced by thermal hysteresis and the time of elapse. In fact, the modulation was diminished after about one day. This phenomenon could be explained by the superposition of the fluctuation of concentration and the viscoelastic interaction between pre-gel domains. Thus, these facts seem that the gelation may occur by the nucleation and growth process in this case (I). On the other hand, it has become apparent experimentally that the gelation in the quenched non-equilibrium of gelation (II) has proceeded by the spinodal decomposition process, according to the Cahn's theory. As a result, the spinodal temperature could be first determined experimentally in the PBLG-toluene phase diagram. The fractal dimension increased and the correlation length decreased with increasing concentration of toluene solution, and, especially, the correlation length in PBLG gel was shorter than the characteristic maximum wavelength for concentration fluctuation occurred just after quenching, which describes that gel formed by the quenching made a more dense structure.