Post-Tanner spreading of nematic droplets

Area of Science:

• Physics
• Materials Science
• Physical Chemistry

Background:

• The Tanner law describes quasistationary liquid drop spreading on solid substrates, typically governed by capillary forces for small droplets.
• Nematic liquid crystals exhibit anomalous spreading behavior, deviating from the Tanner law at longer timescales.

Purpose of the Study:

• To investigate the accelerated spreading of nematic liquid crystal drops beyond the Tanner law.
• To model this phenomenon using a thin film approach, considering substrate-liquid interactions specific to nematics.

Main Methods:

• Utilizing the thin film model (lubrication approximation) to describe droplet dynamics.
• Numerically solving the thin film equation to simulate spreading behavior.
• Comparing simulation results with experimental data for nematic liquid crystals.

Main Results:

• The study identifies a transition to a faster spreading regime (R∼t(α), α > 1/10) for nematic liquid crystals.
• Numerical solutions align well with experimental observations, validating the proposed model.
• The accelerated spreading is attributed to strong substrate-liquid interactions, specifically antagonistic anchoring.

Conclusions:

• The findings introduce a 'post-Tanner' stage in liquid drop spreading theory.
• This regime is driven by nematic-specific interactions, complementing the standard capillarity-dominated model.
• The spreading process can transition from capillary control to a diffusive film regime.