Slow mode of the smectic-A-smectic-C(*)(alpha) phase transition

Area of Science:

• Condensed matter physics
• Materials science
• Physical chemistry

Background:

• Antiferroelectric liquid crystals exhibit complex phase transitions.
• Dynamic light scattering (DLS) is a key technique for studying fluctuations in materials.
• The Sm-A-Sm-C(alpha)(*) transition is of particular interest due to its unique properties.

Purpose of the Study:

• To investigate the origin of unusual slow fluctuations near the Sm-A-Sm-C(alpha)(*) phase transition.
• To elucidate the role of electrostatic coupling in these fluctuations.
• To analyze the temperature dependence of relaxation rate and intensity of the slow mode.

Main Methods:

• Dynamic light scattering (DLS) was employed to observe slow fluctuations.
• Measurements were conducted on the liquid crystal 4-(1-methylheptyloxy-carbonyl)phenyl 4(')-octyloxy biphenyl-4-carboxylate.
• Analysis focused on the relaxation rate and intensity of the observed slow mode.

Main Results:

• Unusual slow fluctuations near the Sm-A-Sm-C(alpha)(*) transition were identified.
• These fluctuations were attributed to electrostatic coupling between impurity ions and director fluctuations.
• The relaxation rate showed a linear dependence on temperature with distinct slopes in each phase.
• The intensity exhibited a Curie-Weiss divergence at the phase transition.

Conclusions:

• Electrostatic coupling is the primary mechanism driving the observed slow fluctuations.
• The findings provide direct confirmation of the electrostatic coupling model near the Sm-A-Sm-C(alpha)(*) transition.
• This study enhances the understanding of phase transition dynamics in antiferroelectric liquid crystals.