Phase behaviour of hard board-like particles.

Area of Science:

• Colloid science
• Materials science
• Condensed matter physics

Background:

• Hard board-like particles (HBPs) are model systems for studying liquid crystal phases.
• Excluded volume effects are primary drivers of phase formation in anisotropic particle suspensions.
• The formation and stability of biaxial liquid crystal phases remain areas of active research.

Purpose of the Study:

• To investigate the phase behavior of colloidal suspensions of hard board-like particles (HBPs).
• To map the phase diagram as a function of particle shape anisotropy (prolate to oblate).
• To elucidate the conditions favoring the formation of biaxial nematic and smectic phases.

Main Methods:

• Molecular dynamics simulations of HBPs with varying shape anisotropy.
• Analysis of long-range order along and perpendicular to phase directors.
• Modification and application of Onsager theory for biaxial particles.

Main Results:

• Observed nematic, smectic, and columnar liquid-crystalline phases driven by excluded volume.
• Identified stable discotic smectic phases with layer thickness matching particle minor dimension.
• Simulations and modified Onsager theory indicate smectic phases are more stable than biaxial nematic phases.

Conclusions:

• The intrinsic biaxiality of HBPs promotes translationally ordered biaxial phases but not necessarily the biaxial nematic phase.
• Discotic smectic phases are stable over significant portions of the phase diagram.
• Theoretical predictions align with simulation results, highlighting the prevalence of smectic over biaxial nematic order.