Late stages of phase separation/gelation of isotropic solutions of rod-like polymers by video microscopy

Abstract

The late stages of phase separation/gelation in concentrated solutions of poly(γ-benzyl-α, L-glutamate) in N,N-dimethylformamide containing 2% added water have been observed by video optical microscopy. Microscopic phase separation is directly evident on cooling homogeneous, isotropic solutions. Within the phase separating mixture, diffuse structural features are separated from one another by a characteristic distance. Fourier transforms of the real space images, equivalent to scattering patterns, show a radially symmetric ring, which collapses to lower wave number as gelation proceeds. The wave number associated with the maximum intensity, qm, obeys a scaling relationship consistent with the Lifshitz–Slyozov evaporation/condensation model, also consistent with the Binder–Stauffer cluster dynamics model: qm=t−1/3, where t is time. A more general scaling relationship proposed by Furukawa is obeyed very well if the dimensionality of the growth of the new phases is 3. The advantages of video microscopy for such studies and possible implications for the role of spinodal decomposition in rod-like polymer solutions are discussed.