Biaxial nematics and nematic-nematic demixing in polydisperse mixtures of hard board-like particle fluids
Y. Martínez-Ratón, D. de las Heras, and E. Velasco
ArXiv, -, 2609.13410, (2026) DOI: 10.48550/arXiv.2609.13410
Full text: journal, pdf
Abstract:
We study the bulk phase behavior of a polydisperse liquid crystal fluid made of biaxial boards
with restricted orientations using both fundamental measure theory and Monte Carlo computer
simulations. The continuous polydispersity is included in the intermediate particle length of the
boards via a truncated Schulz distribution. By calculating several phase diagrams across a range of
polydispersity coefficients, we find that polydispersity (i) enhances demixing between two uniaxial
nematic phases and (ii) expands the stability region of the biaxial phase. Although metastable
with respect to non-uniform phases, we identify certain mixtures exhibiting two-phase coexistence
paths involving uniaxial-uniaxial and uniaxial-biaxial phase separations. Whether these paths can be
completed depends on the precise shape of the parent distribution function. Monte Carlo simulations
performed for a representative case exhibit the same phase diagram topology predicted by theory,
thereby validating the theoretical approach. The main difference between both approaches lies in
quantitative agreement, with simulated phase transitions systematically occurring at higher packing
fractions than those predicted theoretically. Our combined theoretical and simulation results may
prove relevant to the design and interpretation of sedimentation experiments on colloidal suspensions of polydisperse anisotropic particles.
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