Viscosity peaks at the cholesteric-isotropic phase transitions.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Physical Chemistry

Background:

• Cholesteryl liquid crystals exhibit complex phase transitions, including the formation of blue phases.
• Understanding the effective viscosity during these transitions is crucial for characterizing material behavior.

Purpose of the Study:

• To investigate the effective viscosity of cholesteryl myristate and cholesteryl nonanoate liquid crystals.
• To analyze the viscosity behavior as a function of temperature around the cholesteric-to-isotropic phase transition.
• To determine the contribution of large-scale fluctuations to viscosity and calculate critical exponents.

Main Methods:

• Experimental study of effective viscosity in liquid crystals.
• Temperature-dependent measurements around phase transitions.
• Application of scale change analysis to viscosity data.
• Calculation of critical exponents from experimental data.

Main Results:

• Viscosity peaks characterizing the phase transitions were found to be shape invariant.
• Large-scale fluctuations in the two-point correlation function were identified as a significant contributor to observed viscosity.
• Critical exponents were calculated for both cholesteryl myristate and cholesteryl nonanoate.
• Results showed good agreement with critical exponents of the nematic-isotropic phase transition.

Conclusions:

• The shape invariance of viscosity peaks suggests a universal mechanism driven by large-scale fluctuations.
• The study provides insights into the critical phenomena occurring during liquid crystal phase transitions.
• Calculated critical exponents are consistent with established theories for similar phase transitions.