Sedimentation profiles and phase stacking diagrams in polydisperse hard rounded rectangle fluids.

Area of Science:

• Soft Matter Physics
• Colloidal Science
• Liquid Crystal Theory

Background:

• Understanding the behavior of polydisperse fluids is crucial for materials science.
• Liquid crystals exhibit diverse phases (isotropic, nematic, tetratic) influenced by particle shape and interactions.
• Sedimentation dynamics in confined or interacting systems are complex and not fully understood.

Purpose of the Study:

• To investigate the sedimentation behavior of a two-dimensional polydisperse liquid-crystal fluid.
• To explore the phase stacking phenomena arising from particle polydispersity and gravity.
• To model the interplay between excluded volume effects and gravitational forces in liquid crystals.

Main Methods:

• Utilizing a local density-functional theory (DFT) approach.
• Employing scaled particle theory (SPT) to model hard rectangular particles.
• Incorporating polydispersity through variations in particle roundness.

Main Results:

• The model predicts isotropic, nematic, and tetratic bulk phases.
• Complex phase stacking diagrams were observed during sedimentation.
• Phenomena include multiphasic stacking, inverted sequences (e.g., isotropic over nematic), and reentrant stacks (e.g., tetratic between isotropic).

Conclusions:

• Particle polydispersity and gravity intricately couple to produce rich sedimentation phenomenology.
• The developed DFT-SPT model effectively captures complex phase behaviors in polydisperse systems.
• The approach is adaptable for studying sedimentation in other polydisperse colloidal systems.