Dynamics of a faceted nematic-smectic-B front in thin-sample directional solidification

Area of Science:

• Materials Science
• Condensed Matter Physics
• Crystallography

Background:

• Nematic-smectic-B liquid crystals exhibit complex interface dynamics during solidification.
• Understanding these dynamics is crucial for controlling material properties and predicting phase transitions.

Purpose of the Study:

• To experimentally investigate the directional-solidification patterns of a nematic-smectic-B front in thin liquid crystal samples.
• To establish the morphology diagram and analyze phenomena above the Mullins-Sekerka instability threshold.

Main Methods:

• Utilized 12 micrometer-thick samples of C4H9-(C6H10)2CN (CCH4) in a planar configuration.
• Measured the Mullins-Sekerka instability threshold and solidification rate (V).
• Analyzed the morphology diagram as a function of V and the angle (θ(0)) between the facet and isotherms.

Main Results:

• Observed a faceted nematic-smectic-B interface, with facets parallel to smectic layers.
• Identified drifting shallow cells and solitary waves termed "facetons" above the instability threshold.
• Facetons exhibit stationary or oscillatory propagation, with low growth rates relative to the liquid.

Conclusions:

• The study elucidates the dynamics of facetons, providing insights into microscopic growth mechanisms of facets in liquid crystals.
• The findings contribute to a deeper understanding of interfacial phenomena in soft matter systems.
• The established morphology diagram aids in predicting and controlling solidification patterns.