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Pressure-driven changes to spontaneous flow in active nematic liquid crystals.

Joshua Walton1, Geoffrey McKay2, Michael Grinfeld1

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A pressure gradient significantly alters spontaneous flow in active nematic liquid crystals within channels. This study reveals how pressure influences flow stability and director orientation, even creating new non-flow states.

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Area of Science:

  • Soft Matter Physics
  • Liquid Crystal Dynamics
  • Non-equilibrium Systems

Background:

  • Active nematic liquid crystals exhibit spontaneous flows due to internal stresses.
  • Channel confinement and boundary conditions (planar anchoring, no-slip) influence flow behavior.
  • Understanding active fluid dynamics is crucial for materials science and microfluidics.

Purpose of the Study:

  • To investigate the impact of pressure gradients on active nematic liquid crystal flow in channels.
  • To analyze how pressure affects spontaneous flow patterns and director orientation.
  • To explore the interplay between activity, pressure, and flow states.

Main Methods:

  • Utilizing a model based on Ericksen-Leslie theory with active stress.
  • Directly solving the flow equation and obtaining asymptotic solutions for the director angle.
  • Numerically solving full nonlinear equations to examine equilibria and stability.

Main Results:

  • Pressure gradients disrupt the inherent symmetries of flow solutions (symmetric/antisymmetric).
  • New branches of stable and unstable equilibria emerge, some disconnected from the no-flow state.
  • For sufficiently large pressure gradients, non-trivial director angle solutions exist across all activity values.

Conclusions:

  • Pressure gradients are a critical factor in controlling active nematic flows in confined geometries.
  • The study predicts the behavior of different solution types in the activity-pressure state space.
  • This work offers insights into designing and manipulating active soft matter systems.