Electrically induced transformations of defects in cholesteric layer with tangential-conical boundary conditions

Area of Science:

• Materials Science
• Condensed Matter Physics
• Soft Matter Physics

Background:

• Cholesteric liquid crystals exhibit complex orientational structures.
• Surface anchoring conditions significantly influence liquid crystal behavior.
• Electric fields are commonly used to manipulate liquid crystal phases.

Purpose of the Study:

• Investigate electric-field-induced changes in cholesteric liquid crystal orientational structures.
• Analyze the formation and behavior of defect structures under applied electric fields.
• Determine the influence of electric fields on defect line characteristics.

Main Methods:

• Experimental investigation of cholesteric liquid crystal layers with specific thickness-to-pitch ratios (d/p = 0.57).
• Application of perpendicularly oriented electric fields.
• Observation and analysis of director field distribution using polarizing microscopy.

Main Results:

• Applied electric fields decrease the azimuthal director angle at conical surface anchoring.
• Defect loops with under-twisted and over-twisted regions form in thicker cells (22 μm) and shrink/disappear under electric fields.
• In thinner cells (13 μm), over-twisted and under-twisted defect lines form, shortening or transforming into third-type defects with applied voltage.
• The length ratio of over-twisted to third-type defect lines is controllable via electric field.

Conclusions:

• Electric fields induce significant structural changes in cholesteric liquid crystals, including defect loop annihilation and defect line transformation.
• The study demonstrates electric field controllability over the morphology and dynamics of topological defects in liquid crystals.
• Findings offer insights into the electro-optic response of cholesteric liquid crystals with specific boundary conditions.