Energetics of topographically designed Smectic-A oily streaks

Area of Science:

• Materials Science
• Soft Matter Physics
• Surface Science

Background:

• Thin films of Smectic-A liquid crystals (LCs) exhibit complex behaviors when deposited on patterned surfaces.
• Surface topography, such as scribed patterns, can significantly influence LC film morphology and stability.
• Understanding these interactions is crucial for developing advanced LC-based devices.

Purpose of the Study:

• To investigate the formation and characteristics of oily streak (OS) textures in thin LC films on patterned polymer substrates.
• To determine the factors influencing the preferred thickness of OS structures.
• To develop a phenomenological model for the energy cost associated with deviations from this preferred thickness.

Main Methods:

• Deposition of thin Smectic-A liquid crystal films onto vinyl alcohol-coated substrates with pre-scribed easy axis patterns (L ≤ 85 μm).
• Utilizing optical profilometry to measure film thickness and analyze surface morphology.
• Developing a phenomenological model to quantify the energy landscape of the OS layer.

Main Results:

• The patterned region induced either a hill (thin film) or divot (thick film) morphology with an OS texture.
• The OS structure self-organizes to a preferred thickness (z₀) dependent on molecular nature, temperature, and surface tension.
• The model successfully estimated the energy cost related to the OS layer's thickness variations.

Conclusions:

• The interplay between substrate topography and LC properties dictates the formation of stable, preferred-thickness OS structures.
• The identified preferred thickness is a critical parameter for controlling LC film morphology.
• The developed model provides a framework for understanding the energetic stability of these complex liquid crystal thin films.