Liquid-crystalline ordering in the solution of partially flexible macromolecules

The liquid-crystalline ordering in the solution of persistent chains which length, L, is comparable with the length of the effective Kuhn segment, l, is considered by means of a generalization of the Onsager method. The orientational entropy for this case is calculated using the method proposed by I.M. Lifshitz (for another problem) in 1968. It is shown that a slight flexibility of the persistent chain is sufficient for the complete change in the properties of the liquid-crystalline transition: for example, at Ll∼0.1 these properties are more similar to those which are characteristic for the semi-flexible limit (Ll⪢1), than for the rigid rod limit (Ll⪡1), although at such Ll the geometric form of the macromolecule is much closer to the rodlike one.