Nonliquid Crystals Research Articles

Dependence of Molecular Structure on Mesomorphic Behavior with Special Reference to Central Bridge

A novel homologous series of liquid crystalline 4-(4′-n-alkoxy cinnamoyloxy)-4″-methoxy benzyl cinnamates was synthesized and studied with a view to understand and establish the effects of molecular structure on liquid crystal behavior. The series consists of eleven members of the series. None of the homologue derivatives are either nonliquid crystal or smectogenic, i.e. all the eleven members of the novel homologous series are enantiotropcially nematogenic only. Transition and melting temperatures as well as textures of the nematic mesophase were determined on an optical polarizing microscope equipped with a heating stage. The transition curves of the phase diagram show phase behavior in a normal expected manner. An odd-even effect is observed for the nematic-isotropic transition curve. The textures of the nematic mesophase are threaded or Schlieren as determined a by miscibility method. Analytical and spectral data confirm the molecular structures of the homologues. The average thermal stability for nematic is 213.8°C. The isotropic temperatures vary between 190°C and 240°C. The nematogenic mesophase length varies from 17°C to 102°C. Thus, the novel homologous series is entirely nematogenic without the exhibition of smectogenic character. The liquid crystal (LC) properties of the present novel series are compared with structurally similar other known homologous series.

Synthesis, Characterization, and Dilatometric Studies on N-(p-n-Alkoxybenzylidene)-p-n-pentyloxyanilines Compounds

Synthesis, textural characterization, differential scanning calorimetry, and dilatometry studies are carried out on a new homologous series of N-(p-n-alkoxy benzylidene)-p-n-pentyloxy anilines (nO.O5) where n = 1–18. The lower homologues of this series (n = 1–5) and a higher homologue (n = 16) exhibit monotropic Liquid Crystal (LC) phase. The other members of the series show enantiotropic LC phases, while 18O.O5 is a nonliquid crystal. The dilatometric studies on 7O.O5, 10O.O5, 13O.O5 and 16O.O5 reveal the first-order nature of Isotropic to Nematic Phase (IN), Isotropic to Smectic A Phase (IA), Nematic to Smectic C Phase (NC), Smectic A to Smectic B Phase (AB), Smectic C to Smectic B Phase (CB), and Smectic A to Krystal Phase (AK) transitions. The pretransition effects are estimated from dilatometry results. The results are compared with the available data on nO.m compounds.

Charge transfer interaction between the nematogen 5CB and non-liquid crystal

In general, when a non-nematic solute is added to a nematic, the nematic-isotropic phase transition temperature (T NI) decreases with increase in non-nematic concentration. But when there are hydrogen bonded complexes or π-complexes of suitable strength formed between the nematic and the solute molecules, the T NI can rise. Mixing of p-terphenyl or anthracene with 5CB (4-cyano-4'-pentylbiphenyl) results in a T NI rise. On the other hand, in a binary system consisting of a substance with strong acceptor properties (e.g. tetracyanoethylene; TCNE) and nematic 5CB, T NI fell remarkably. We have now studied the effect of intermolecular interactions on the T NI of 5CB by using various acceptor molecules and donor molecules as solutes. We have found that for binary systems in which 5CB and a solute molecule form distinct one-to-one complexes, T NI falls rather rapidly. When the solute molecules have a strong acceptor power, the rate of T NI fall with solute concentration is found to be correlated well with the electonegativity of the solute molecules.