Pitch-Temperature Relationship in Poly (γ-benzyl L-glutamate) Liquid Crystals -Liquid Crystalline Structures of Poly-α-amino Acids. IV.-

Abstract

The functional form for the temperature(T) dependence of the cholesteric pitch(P) of poly (γ-benzyl L-glutamate) (PBLG) was experimentally investigated, being compared with the results which have previously been reported in some literatures. The solvents used in this study were benzyl alcohol, N, N-dimethylformamide, m-cresol and 1, 4-dioxane. Concentration of PBLG was determined to 16.5 volume percent. A particular causion was paid for obtaining the value of time-independent pitch. Three functional forms were assumed for the analysis of the experimental data obtained.
We found it difficult to determine the P-T relationship over the entire range measured (Figs.4 and 5). At the temperatures above B-point where biphasic region is found at first and below C-point where gel phase disappeares, we assumed that the P-T relationship was distinct from that in anisotropic single phase (liquid crystal one in Fig.6). Therefore our discussion in this paper was limited only to the anisotropic single phase. In the four kinds of solutions studied here, a linear increase was not observed in the pitch P with increasing temperature (Fig.3), while both plots of 1/P vs. T(Fig.4) and 1/P vs.1/T(Fig.5) seem linear at first sight in the range mentioned above. We calculate the standard deviation from the straight line obtained by the least-squares method.
From the result, it was concluded that t he reciprocal pitch 1/P corresponding to the cholesteric twist angle was linear against 1/T rather than T in the variety of solvents. The result agreeds exactly with the temperature-dependent term of 1/P in the Kimura's theory on the cholesteric liquid crystals of polypeptide taking into account the effects of molecular exclusion and of attractive intermolecular force.