LIQUID-CRYSTALLINE SOLVENTS AS MECHANISTIC PROBES .52. LIQUID-CRYSTALLINE BEHAVIOR FROM BINARY-MIXTURES OF NONMESOGENIC 4-ALKYL-N-(4-CYANOPHENYL) PIPERIDINES

A relatively rare phenomenon, the induction of thermotropic mesophases from combinations of homologues of non-mesogenic compounds, is examin ed in some detail. Thus, monotropic nematic phases have been obtained from binary mixtures of 4-alkyl-N-(4-cyanophenyl)piperidines (I). Exce pt for the hexyl homologue, the compounds I with butyl to nonyl as alk yl groups are non-mesomorphic as neat materials. From phase diagrams, the nematic clearing temperatures of the binary mixtures are found to vary linearly with composition and to increase as the molecular length s of the components are increased. By introducing a methyl group at th e 1-position of the alkyl chain, the melting points of the neat compon ents are depressed, and the nematic clearing temperatures of the binar y mixtures are lowered. Factors associated with the induction of this mesomorphism and with the 'kinetic' and thermodynamic stabilities of t he monotropic nematic phases are discussed. Among these is the orienta tion between the rings of the core groups in I and in the more common mesogens, the trans-4-alkyl-1-(4-cyanophenyl) cyclohexanes, II.