Dynamical field theories for biaxial liquid crystals

Phase field crystal (PFC) models constitute central tools for a microscopic understanding of the dynamics of complex systems in soft matter physics. They have found widespread application in the modeling of the uniaxial orientational ordering of liquid crystals. However, only very limited progress has been made in applying them to the more complex cases of biaxial phases and biaxial particles. Here, we discuss the microscopic derivation of PFC models for biaxial liquid crystals. We illustrate it by presenting two models, one involving four scalar orientational order parameters relevant for the dynamics of biaxial particles, and one involving two scalar order parameters and a director field to describe biaxial phases in a three-dimensional uniaxial nematic liquid crystal. These models allow for an efficient simulation of spatially inhomogeneous biaxial orientational ordering dynamics. We also combine a microscopic and macroscopic approach to extract model coefficients for a full biaxial model from the microscopic derivation for a simple special case. This universal method also enables to perform derivations for other low-symmetry particles where, due to the complexity of the general case, this has not been previously attempted.

💡 Research Summary

The paper presents a systematic derivation of phase‑field crystal (PFC) models tailored for biaxial liquid crystals, extending the well‑established framework that has so far been limited to uniaxial particles. Starting from classical density‑functional theory (DFT), the authors introduce a six‑dimensional one‑particle density ρ(R,Ω) that depends on the particle’s centre‑of‑mass position R and its orientation Ω (three Euler angles). The grand‑canonical functional Ω