The Influence of Disorder on Thermotropic Nematic Liquid Crystals Phase Behavior
Abstract
:1. Introduction
2. Liquid Crystals: A Brief Overview
2.1. Nematic, Cholesteric and Smectic Liquid Crystals
2.2. Order Parameters
Nematic order parameter
3. Nematic-Isotropic Phase Transition: Theoretical Models
3.1. Microscopic Models
The Onsager Theory
The Maier–Saupe Model
The van der Waals (vdW) and density functional theories(DFT)
3.2. The Phenomenological Landau–de Gennes Theory
- There is no term linear in Q. This allows for the possibility of an isotropic phase (Q = 0). In the case of external fields, a linear term has to be included and the isotropic phase transforms into a paranematic phase (a phase with a very low degree of orientational order).
- If B > 0, the transition is first order (the order parameter changes discontinuous at the transition), while if B = 0 the transition is second order (the order parameter is continuous at the transition, but its first derivative with respect to temperature is discontinuous). The other possible mechanism to mimic the first order phase transition is to consider B = 0 and C < 0. In this case a stabilizing six order term with E > 0 is required.
- To ensure stability of the nematic phase, C must be positive.
3.3. Relation between Landau–de Gennes and Maier–Saupe Free Energies for Uniaxial Nematics
4. Influence of Random Field on Structural and Phase Transition Properties: A Mesoscopic Phenomenological Model
4.1. Structural Behavior : Domain-Type Patterns
Domain Coarsening Following a Fast Enough Phase Transition
Imry-Ma Domain Pattern
Simulation Results
4.2. Phase Behavior
Phase behavior of RAN
Nematic-non-Nematic Mixture
4.3. Experimental Observations
5. Concluding Remarks
Acknowledgments
References and Notes
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Popa-Nita, V.; Gerlič, I.; Kralj, S. The Influence of Disorder on Thermotropic Nematic Liquid Crystals Phase Behavior. Int. J. Mol. Sci. 2009, 10, 3971-4008. https://doi.org/10.3390/ijms10093971
Popa-Nita V, Gerlič I, Kralj S. The Influence of Disorder on Thermotropic Nematic Liquid Crystals Phase Behavior. International Journal of Molecular Sciences. 2009; 10(9):3971-4008. https://doi.org/10.3390/ijms10093971
Chicago/Turabian StylePopa-Nita, Vlad, Ivan Gerlič, and Samo Kralj. 2009. "The Influence of Disorder on Thermotropic Nematic Liquid Crystals Phase Behavior" International Journal of Molecular Sciences 10, no. 9: 3971-4008. https://doi.org/10.3390/ijms10093971