Bulk phase behavior of binary hard platelet mixtures from density functional theory.

Area of Science:

• Physical Chemistry
• Materials Science
• Statistical Mechanics

Background:

• Understanding phase behavior in anisotropic particle systems is crucial for designing advanced materials.
• Binary mixtures offer complex phase diagrams compared to single-component systems.
• Previous studies focused on limited size ratios or simpler theoretical models.

Purpose of the Study:

• To investigate phase coexistence in binary mixtures of circular platelets with varying size ratios.
• To compare predictions from Fundamental Measure Theory (FMT) with Onsager theory.
• To analyze the impact of size ratio on isotropic-nematic and nematic-nematic phase transitions.

Main Methods:

• Utilizing a Fundamental Measure Density Functional Theory (FMT) for binary mixtures of circular platelets.
• Comparing FMT results with Onsager theory, a well-established theoretical benchmark.
• Systematically varying the radial size ratio (lambda) from 1 to 5.

Main Results:

• Isotropic-nematic phase coexistence observed for lambda <= 1.7, with the biphasic region widening as lambda increases.
• For lambda >= 2, stable demixing into two nematic states occurs, potentially leading to an isotropic-nematic-nematic triple point.
• FMT predicts a smaller isotropic-nematic biphasic region and earlier transitions than Onsager theory.
• Nematic-nematic demixing is more extensive in FMT than in Onsager theory.
• Both theories show similar phase diagram topologies, with larger particles exhibiting stronger nematic order.

Conclusions:

• The size ratio significantly influences phase behavior in binary platelet mixtures, enabling nematic-nematic demixing at larger ratios.
• FMT provides a more detailed and potentially more accurate description of phase transitions compared to Onsager theory for these systems.
• The findings are relevant for the predictive design of liquid crystal phases and self-assembling materials.