SPINODAL DECOMPOSITION AND GEL STRUCTURE OF QUENCHED POLY(GAMMA-BENZYL L-GLUTAMATE)-TOLUENE SOLUTIONS

Poly(gamma-benzyl L-glutamate) (PBLG)-toluene solutions were quenched rapidly from an isotropic phase at elevated temperatures to the coexis tence region of the isotropic and liquid crystal (I + LC) phases. The intensity of scattered light, I-s, was measured with time after quench ing at various scattering angles and quenching temperatures. The avera ge molecular weights, M-w, of PBLG used were 1.0 x 10(5) (PBLG-10), an d 2.3 x 10(5) (PBLG-23), and the ratios of the actual concentrations t o the corresponding crossover concentration phi(2)/phi(2) were equal to 1, 5, and 10 in the semidilute regime (hereinafter, PBLG-X-Y: X = 1 0 or 23; Y corresponds to phi 2/phi(2)). 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 fra ctal dimension D and the correlation length xi at the later stage were determined according to a generalized Zimm relation containing the fr actal dimension. For PBLG-10-1, D and xi were 2.6 and 610 nm, respecti vely, whereas the same physical quantities for PBLG-10-5 were respecti vely 2.7 and 250 nm. The former case indicates that the initial (modul ated) phase-separation structure induced by the SD-like mechanism was frozen (or pinned), as it is at the later stage, and the latter indica tes 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.