Competition between Anisometric and Aliphatic Entities: An Unusual Phase Sequence with the Induction of a Phase in an n-Alkane–Liquid Crystal Binary System

Abstract

In this work, we demonstrate two important features that arise out of introducing a liquid-crystalline (LC) compound into the rotator phase matrix and the consequent competition between the anisometric segments of the LC moieties and the aliphatic units. First, we show that the change in the structural character of the mixed medium depends on which of the entities forms the minority concentration: in the case of this being the alkane, the two components of the binary system are nanophase segregated, whereas if the LC molecules are present in a small concentration, then the layered structure merely gets roughened without any segregation. The second and more significant result of the calorimetric and X-ray experiments, at low LC concentrations, is the induction of a rotator phase that leads to unusual phase sequence not reported hitherto. Possible scenarios for the molecular arrangement are discussed. A Landau model is also presented that explains some of the observed features.

Effect of the liquid crystal solute on the rotator phase transitions of n-alkanes

“…(iv) R V -X, in addition to the IL-R II transition. Experimental results 29 show that the above transitions are possible.…”

“…Thus, the addition of the liquid crystal component BBOA to the pure n-alkane C 24 H 50 forms a two phase region. Experimental results 29 show the possibility of the formation of the R V + X and R II + R I two phase regions. The above analysis agrees well with experimental phase diagrams (Fig.…”

“…and 29 have shown that the R V -X transition temperature decreases with the addition of the liquid crystal component BBOA to the pure alkane. The decrease in the R V -X transition temperature is connected with the width of the two phase region and the entropy of the transition.…”

“…[25][26][27][28] Experimental results [25][26][27][28] show that these substances can greatly enhance the physical properties of n-alkanes and rotator phases. [25][26][27][28] Very recently, Kumar et al 29 carried out calorimetric and X-ray investigations on a binary system of n-tetracosane (C 24 H 50 ) and the liquid crystalline compound butyloxybenzilideneoctylaniine (BBOA). According to the literature, 8,11,15 pure C 24 H 50 exhibits the following four phases: an orthorhombic crystalline phase (X), a R V phase, a R I phase and a R II phase.…”

“…Owing to the chemical dissimilarity between the alkane and the liquid crystal molecule, the latter could act like an impurity and therefore try to destabilize the system. Kumar et al 29 observed that if the alkane (C 24 H 50 ) is present in a small concentration, the binary system (C 24 H 50 -BBOA) is nanophase segregated, whereas if the liquid crystal molecules are present in a small concentration, the layered structure merely gets roughened without any segregation. The more signicant result of their experiments, at low liquid crystal concentration, is the induction of the R III phase between the R I and R V phases.…”