Related Experiment Video
Updated: Jun 5, 2026

High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal
Published on: October 31, 2019
Calorimetric study of the nematic to smectic-A phase transition in octylcyanobiphenyl-hexane binary mixtures
Krishna P Sigdel1, Germano S Iannacchione
1Department of Physics, Worcester Polytechnic Institute, Worcester, Massachusetts 01609, USA.
Abstract:
The continuous nematic to smectic-A (N-SmA) phase transition has been studied by high-resolution ac-calorimetry in binary mixtures of the liquid crystal octylcyanobiphenyl (8CB) and a nonmesogenic, low-molecular weight, solvent n-hexane (hex) as a function of temperature and solvent concentration. Heating and cooling scans about the N-SmA transition temperature were repeatedly performed on pure and six 8CB+hex samples having hexane molar concentration ranging from x(hex)=0.02 to 0.12. All 8CB+hex samples in this range of x(hex) remain macroscopically miscible and exhibit an N-SmA heat capacity peak that shifts nonmonotonically to lower temperature and evolves in shape, with a reproducible hysteresis, as x(hex) increases. The imaginary part of heat capacity remains zero up to x(hex)(TCP) ≃ 0.07 above which the distinct peak is observed, corresponding to a jump in both the real and imaginary enthalpy, indicating the onset of first-order behavior. A simple power-law analysis reveals an effective exponent that increases smoothly from 0.30 to 0.50 with an amplitude ratio A-/A+→1 as x(hex)→x(hex)(TCP). This observed crossover of the N-SmA toward a tricritical point driven by solvent concentration is consistent with previous results and can be understood as a solvent softening of the liquid crystal and concument promoting of nematic fluctuations.
Related Concept Videos
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR
Phase Diagrams of Ternary Systems
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
Phase Transitions: Melting and Freezing
Solid–Solid Solutions
Phase Transitions

