Active nematic liquid crystals simulated by particle-based mesoscopic methods.

Area of Science:

• Physics
• Soft Matter Physics
• Computational Physics

Background:

• Nematic liquid crystals exhibit complex behavior influenced by molecular orientation.
• Active nematics incorporate self-propulsion, leading to emergent phenomena like defect dynamics.
• Mesoscopic simulation methods are crucial for bridging scales in complex fluid dynamics.

Purpose of the Study:

• To generalize existing Multi-particle Collision Dynamics (MPCD) algorithms for simulating active nematic liquid crystals.
• To incorporate activity into MPCD models based on orientation vectors and order parameter tensors.
• To investigate the resulting topological defect dynamics and compare different MPCD approaches.

Main Methods:

• Generalization of the Shendruk-Yeomans MPCD algorithm (orientation vector) and the Mandal-Mazza MPCD algorithm (order parameter tensor).
• Introduction of activity via a force proportional to the divergence of the local average order parameter tensor.
• Analysis of disclination curves, nucleation, self-annihilation, and comparison of length-scales between methods.

Main Results:

• Both generalized MPCD algorithms successfully reproduce active nematic behavior.
• Observed nucleation and self-annihilation dynamics of disclination curves, consistent with experimental findings in 3D active nematics.
• Structure and dynamics of orientation and flow fields align with continuum 3D active nematic simulations.

Conclusions:

• Mesoscopic particle-based approaches, specifically generalized MPCD, are effective for simulating active liquid crystals.
• These methods enable the study of active nematics in nonequilibrium states, including flow-driven systems and colloidal suspensions.
• The study provides a framework for comparing different MPCD techniques for active matter simulations.