The influence of flexible segments on liquid crystalline properties in terms of solubility parameters. An attempt at quantitative interpretation

The phase behavior of some rodlike block molecules has been reviewed with reference to the polarity of constituent segments. It was found that the ability of the mesophase formation is connected with differences in polar character between the flexible chains and rigid cores. Thus the polar poly(oxyethylene) group connected with the polar rigid core reduces mesophase stability but is advantageous when put together with some apolar building blocks. An attempt at quantitative estimation of the incompatibilities of different parts of molecules by means of Hansen solubility parameters delta and Flory interaction parameters chi has also been made. On the basis of chi parameters the Gibbs free energies of mixing of these segments were calculated. The changes of Gibbs free energy reflecting the compatibility of segments and their tendency to the phase separation and the volume fraction of mesogenic rigid core reflecting their ability to arrangement in one direction appear to be crucial in terms of type of the mesophase formation.