Co-revolving topological defects in a nematic liquid crystal

Area of Science:

• Physics
• Materials Science
• Soft Matter Physics

Background:

• Patterned surface defects with integer strength (m=+1) can decompose into pairs of half-integer strength (m=+1/2) defects.
• Liquid crystals with negative dielectric anisotropy exhibit complex behaviors under applied electric fields.

Purpose of the Study:

• To experimentally investigate the azimuthal wobbling and antipodal co-revolution of half-integer surface defects in liquid crystals.
• To elucidate the relationship between defect behavior, applied AC electric field strength (E), and frequency (ν).
• To understand the role of nematic electrohydrodynamic instabilities in driving defect dynamics.

Main Methods:

• Experimental observation of defect behavior under varying AC electric field strengths and frequencies.
• Analysis of the threshold field for defect co-revolution and its dependence on field frequency.
• Investigation of nematic electrohydrodynamic instabilities and their correlation with defect motion.

Main Results:

• Half-integer defects exhibit azimuthal wobbling above a threshold electric field.
• At higher fields, defects co-revolve antipodally around a central point.
• The threshold field for co-revolution scales with the square root of frequency (ν^1/2).
• A phase diagram reveals coupling between defect motion and hydrodynamic instabilities.

Conclusions:

• The co-revolution of liquid crystal defects is strongly coupled to and driven by nematic electrohydrodynamic instabilities.
• The observed behavior suggests a Lehmann-like mechanism is responsible for driving the defect co-revolution.
• Understanding these dynamics is crucial for controlling defect behavior in liquid crystal systems.