Isotropic-nematic transition in hard-rod fluids: relation between continuous and restricted-orientation models

Area of Science:

• Statistical Mechanics
• Soft Matter Physics
• Thermodynamics

Background:

• Hard-rod fluids exhibit complex phase behavior, including isotropic and nematic phases.
• Onsager's second virial theory provides a theoretical framework for understanding these fluids.
• Discretization of molecular orientations is a common simplification in computational models.

Purpose of the Study:

• To investigate the impact of finite orientation discretization on the phase diagrams of hard-rod fluids.
• To analyze the emergence and characteristics of artificial phases due to orientation discretization.
• To assess the influence of these artificial phases on the accuracy of bulk phase diagrams.

Main Methods:

• Modeling hard-rod fluids with a limited set of discrete orientations.
• Constructing bulk phase diagrams using Onsager's second virial theory.
• Analyzing the coexistence of artificial and physical nematic and isotropic phases.

Main Results:

• Discretization introduces an artificial, nearly perfectly aligned nematic phase.
• This artificial phase coexists with physical nematic or isotropic phases depending on the number of orientations.
• A higher number of orientations is needed in binary mixtures to prevent interference with physical phase diagrams.

Conclusions:

• The discretization of orientations in hard-rod fluid models can lead to artificial phases.
• The accuracy of phase diagram predictions is sensitive to the number of sampled orientations.
• Careful consideration of orientation discretization is crucial for reliable modeling of fluid phase behavior.