Spinodal decomposition and gel structure of quenched poly(γ-benzyl L-glutamate)-toluene solutions

Poly(γ-benzyl L-glutamate) (PBLG)-toluene solutions were quenched rapidly from an isotropic phase at elevated temperatures to the coexistence region of the isotropic and liquid crystal (I + LC) phases. The intensity of scattered light, I_s, was measured with time after quenching at various scattering angles and quenching temperatures. The average molecular weights, M_w, of PBLG used were 1.0 × 10⁵ (PBLG-10), and 2.3 × 10⁵ (PBLG-23), and the ratios of the actual concentrations to the corresponding crossover concentration φ₂/φ₂* were equal to 1, 5, and 10 in the semidilute regime (hereinafter, PBLG-X-Y: X = 10 or 23; Y corresponds to φ₂/φ₂*). The spinodal decomposition (SD)-like phase separation was suggested to occur at the initial stage of gelation for quenched PBLG-10-1 and PBLG-10-5. In addition, the fractal dimension D and the correlation length ξ at the later stage were determined according to a generalized Zimm relation containing the fractal dimension. For PBLG-10-1, D and ξ were 2.6 and 610 nm, respectively, whereas the same physical quantities for PBLG-10-5 were respectively 2.7 and 250 nm. The former case indicates that the initial (modulated) phase-separation structure induced by the SD-like mechanism was frozen (or pinned), as it is at the later stage, and the latter indicates that the initial structure might grow by superposing a nucleation and growth (NG)-like phase separation on the SD-like process. There was no concrete evidence of SD in the other quenched PBLG samples.