Phase Diagram for Solutions of α-Helical Poly(l-glutamate)s in m-Cresol Including Isotropic, Cholesteric, and Columnar Phases

Abstract

The temperature-concentration phase diagram was constructed for lyotropic solutions of poly(γ-phenylpropyl L-glutamate) in m-cresol in the temperature range from 0 to 70 °C and in the concentration range from 0 to 100 vol %. Visual and microscopic observations and the X-ray measurement were employed to determine the phase structures and phase boundaries. The well-known transition from the isotropic phase to the cholesteric phase is observed in the low concentration range of 8 to 14 vol %, as predicted using the Flory lattice theory and reported from experiments. At higher concentrations, however, a novel phase behavior is observed. The cholesteric phase is transformed to the hexagonal columnar phase through the coexistence region. The critical concentration of the columnar phase appearing from the cholesteric one is 49 vol %. The removal of solvents from this columnar solution leads to the solid state structure with the hexagonal packing symmetry. Thus, the phase diagram was well clarified, and found to include three phases: isotropic, cholesteric, and columnar phases. According to this phase diagram, at high temperatures, the isotropic-cholesteric-columnar phase transition takes place upon increasing the concentration, whereas at low temperatures, the isotropic solution directly transforms to the columnar phase. Similar phase diagrams are presumed for other poly(γ-alky L-glutamates) and poly(γ-phenylalky L-glutamates), although the critical concentration of the columnar phase will increase with an increase in side-chain length.