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Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets
Published on: May 15, 2017
Subdiffusive dynamics of a liquid crystal in the isotropic phase
Luca De Gaetani1, Giacomo Prampolini, Alessandro Tani
1Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Risorgimento 35, I-56126 Pisa, Italy. degaetani@dcci.unipi.it
The Journal of Chemical Physics
|May 27, 2008
Summary
Molecular dynamics simulations reveal subdiffusive dynamics in supercooled 4-n-hexyl-4'-cyano-biphenyl (6CB) liquid crystals. Both translational and orientational dynamics exhibit a beta-relaxation regime, with orientational dynamics freezing earlier than translational dynamics.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Computational Chemistry
Background:
- Understanding the dynamics of liquid crystals is crucial for their technological applications.
- The isotropic phase, even when supercooled, exhibits complex dynamics influenced by molecular interactions.
Purpose of the Study:
- To investigate the isotropic phase dynamics of 4-n-hexyl-4 omino-biphenyl (6CB) using molecular dynamics simulations.
- To explore the interplay between translational and orientational degrees of freedom (TDOF and ODOF) in supercooled 6CB.
- To compare simulation results with Mode Coupling Theory (MCT) predictions.
Main Methods:
- Molecular dynamics (MD) simulations of 6CB molecules.
- Analysis of translational (TDOF) and orientational (ODOF) dynamics.
- Calculation of mean square displacement, scattering functions, and correlation functions.
- Application of Mode Coupling Theory (MCT) framework.
Main Results:
- Evidence of subdiffusive dynamics in both TDOF and ODOF, more pronounced at lower temperatures.
- Observation of a plateau in various dynamic functions, characteristic of the MCT beta-relaxation regime.
- Time-temperature superposition and factorization properties consistent with idealized MCT.
- Calculated critical temperatures (Tc) for TDOF and ODOF freezing, indicating ODOF freezes earlier.
- Anisotropic molecular environment in the isotropic phase influences dynamics and cage lifetimes.
Conclusions:
- The isotropic phase of 6CB exhibits complex dynamics, including subdiffusion and beta-relaxation, as predicted by MCT.
- The anisotropic nature of the molecular environment significantly impacts ODOF, leading to earlier freezing compared to TDOF.
- Simulation results provide valuable insights into the fundamental dynamics of liquid crystals and validate theoretical models like MCT.
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