Energetics of topographically designed Smectic-A oily streaks.

Missaoui, Amine; Susser, Adam L; Aharoni, Hillel; Rosenblatt, Charles · Soft Matter · 2023

basic_science · Level V

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Abstract

A thin Smectic-A liquid crystal (LC) film is deposited on a polymer vinyl alcohol-coated substrate that had been scribed with a uniform easy axis pattern over a square of side length <i>L</i> ≤ 85 μm. The small size of the patterned region facilitates material distribution to form either a hill (for a thin film) or divot (for a thick film) above the scribed square and having an oily streak (OS) texture. Optical profilometry measurements <i>vs.</i> film thickness suggest that the OS structure aims to adopt a preferred thickness <i>z</i><sub>0</sub> that depends on the nature of the molecule, the temperature, and the surface tension at the air interface. We present a phenomenological model that estimates the energy cost of the OS layer as its thickness deviates from <i>z</i><sub>0</sub>.