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Improper orientational ordering regime and tricritical behavior in a lyotropic liquid crystal
1Departamento de Física, Universidade Federal de Santa Catarina, 88040-900, Florianópolis, SC, Brazil. dmitriev@fsc.ufsc.br
Summary
Researchers mapped the phase diagram of ternary mixtures using multiple techniques. They found a linear dependence of the nematic order parameter on temperature and identified a tricritical point in the nematic-to-lamellar phase transition.
Area of Science:
- Physical Chemistry
- Materials Science
- Liquid Crystals
Background:
- Ternary mixtures containing surfactants, salts, and solvents exhibit complex phase behaviors.
- Understanding the phase transitions and order parameters is crucial for materials science applications.
Purpose of the Study:
- To map the phase diagram of pentadecafluorooctanoate acid ammonium salt (APFO), heavy water (D2O), and ammonium chloride (NH4Cl) mixtures.
- To investigate the nematic order parameter variation (S) as a function of temperature (T).
- To develop a phenomenological model describing the observed phase behavior and identify critical points.
Main Methods:
- Optical microscopy
- Deuteron quadrupolar Nuclear Magnetic Resonance (NMR)
- X-ray diffraction
- Electrical conductivity measurements
Main Results:
- The phase diagram of the ternary mixture was successfully mapped.
- A linear dependence of the nematic order parameter (S) on temperature (T) was observed across the nematic stability region.
- A tricritical point was identified at the transition line between the nematic and lamellar phases.
Conclusions:
- The study provides a consistent description of the nematic phase behavior in the ternary mixture.
- The developed phenomenological model accurately captures the linear S(T) dependence and the tricritical point.
- The findings contribute to the understanding of phase transitions in complex fluid systems.