Dynamic wetting model for the isotropic-to-nematic transition over a flat substrate

Area of Science:

• Soft matter physics
• Materials science
• Chemical engineering

Background:

• Phase ordering on substrates is crucial for soft material transformations, involving wetting, anchoring, and phase transition kinetics.
• Understanding the isotropic-to-nematic phase transition in liquid crystals (LCs) on solid surfaces is essential for material applications.

Purpose of the Study:

• To analyze the kinetics of the isotropic-to-nematic isothermal phase transition in a growing spherical LC drop on a flat solid surface.
• To develop a tractable surface phase transition kinetic model and extract the advancing dynamic contact angle and contact line speed.
• To identify elastic and wetting parameters governing the phase transformation process.

Main Methods:

• Utilized the Landau-de Gennes Q-tensor order parameter equations to model the phase transition kinetics.
• Derived interface and contact line force balances, ensuring consistency with generic models of conservative interface and contact line motions.
• Extracted the advancing dynamic contact angle equation from kinematic compatibility between the moving interface and contact line.

Main Results:

• Developed a tractable surface phase transition kinetic model yielding a constant advancing dynamic contact angle (θ) and contact line speed as a function of undercooling (ΔT).
• Demonstrated that increasing undercooling causes the surface phase transition to approach the bulk phase transition, with θ approaching π.
• Identified key elastic and wetting parameters controlling the phase transformation and proposed experiments for their determination.

Conclusions:

• The dynamic wetting and surface phase transition model expands characterization methods for LC-substrate interfaces beyond static droplet methods.
• The findings provide insights into the fundamental physics of phase transitions in confined geometries.
• The identified parameters and experimental definitions facilitate precise control and understanding of LC-substrate interactions.