Analysis of the pitch in binary cholesteric liquid crystal mixtures

The pitch p in the cholesteric liquid crystal phase of mixtures of cholesteryl chloride and p−azoxyanisole has been measured as a function of the composition c. The function p−1 (c) deviates considerably from linearity and shows an inversion of the helical twist sense. The results, as well as those of five other binary cholesteric systems published in the literature, have been analyzed in terms of the molecular theory of Goossens. In the discussion of the results of the analysis, the requirements for a consistent physical interpretation of the interaction parameters that appear in the theory have been emphasized. The results indicate that these requirements are satisfied only in simple systems that do not deviate strongly from linear behavior of p−1 (c). In more complicated systems the specific properties of the individual molecules probably play an important role in determining the cholesteric helix.