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Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets
Published on: May 15, 2017
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Non-equilibrium phase transitions in a liquid crystal.
1Surface Physics and Material Science Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064, West Bengal, India.
The Journal of Chemical Physics
|September 7, 2015
Summary
This study investigates the glass transition and Nematic-Isotropic phase transition in liquid crystals using various spectroscopy methods. Findings reveal non-equilibrium behavior influenced by heating rate and initial temperature, impacting molecular ordering.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Physical Chemistry
Background:
- Liquid crystals exhibit complex phase transitions, including glass transitions and Nematic-Isotropic (N-I) transitions.
- Understanding the kinetic behavior and non-equilibrium features of these transitions is crucial for materials science applications.
- Previous studies have explored these transitions, but a comprehensive kinetic analysis considering heating rate and initial temperature effects is needed.
Purpose of the Study:
- To elucidate the kinetic behavior of the glass transition and the non-equilibrium aspects of the Nematic-Isotropic phase transition in N-(4-methoxybenzylidene)-4-butylaniline.
- To investigate the influence of heating rate and initial temperature on these transitions using multiple spectroscopic techniques.
- To provide experimental evidence for the non-equilibrium nature of the N-I transition and its underlying mechanisms.
Main Methods:
- Differential Scanning Calorimetry (DSC) to analyze heat flow and transition enthalpies.
- Fourier Transform Infrared (FTIR) spectroscopy to probe molecular vibrations and structural changes.
- Fluorescence anisotropy measurements to quantify molecular ordering and the order parameter.
Main Results:
- Glass transition exhibits a baseline shift at higher heating rates (> 5 K min⁻¹) and a distinct peak at lower rates (≤ 5 K min⁻¹), indicating a transition from ergodic to non-ergodic behavior.
- FTIR spectroscopy reveals freezing of out-of-plane vibrations and enhanced coplanarity of benzene rings near the glass transition, signifying increased molecular ordering.
- The Nematic-Isotropic transition temperature (TNI) and enthalpy change (ΔH) are dependent on the initial temperature, providing direct evidence of non-equilibrium behavior, consistent with Mesquita's extension of Landau-deGennes theory.
Conclusions:
- The study confirms the non-equilibrium nature of both the glass transition and the Nematic-Isotropic phase transition in the studied liquid crystal.
- Heating rate and initial temperature significantly influence the observed transition behaviors and molecular ordering.
- The findings contribute to a deeper understanding of liquid crystal phase transitions and their kinetic dependencies.
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