Suppression of spatially periodic patterns by dc voltage

Area of Science:

• Nanoscience and Nanotechnology
• Materials Science
• Soft Matter Physics

Background:

• Nematic liquid crystals (NLCs) exhibit complex behaviors under applied electric fields.
• Spatially periodic instabilities like flexoelectric domains (FD) and electroconvection (EC) are crucial phenomena in NLCs.
• Understanding the influence of combined dc and ac electric fields is essential for controlling NLC behavior.

Purpose of the Study:

• To investigate the impact of superposed dc and ac voltages on FD and EC instabilities in NLCs.
• To determine the onset characteristics, threshold voltages, and critical wave vectors under combined field conditions.
• To analyze the influence of dc bias on electrical conductivity and its anisotropy in NLCs.

Main Methods:

• Experimental study of spatially periodic instabilities in NLCs under superposed dc and ac voltages.
• Determination of onset voltages, threshold voltages, and critical wave vectors.
• Direct measurement of electrical conductivity and its anisotropy changes induced by dc bias.

Main Results:

• Superposing dc and ac voltages generally inhibits pattern formation for both FD and EC.
• Onset voltages for instabilities are significantly higher under combined fields compared to individual dc or ac fields.
• A dc bias reduces the crossover frequency in EC regimes and induces a transition between FD types.
• Measured changes in electrical conductivity and anisotropy due to dc bias correlate with observed instability behaviors.

Conclusions:

• Combined dc and ac electric fields act antagonistically on pattern-forming mechanisms in NLCs.
• The observed inhibition and altered instability characteristics are partly explained by dc-induced changes in electrical conductivity.
• The findings provide insights into controlling NLC instabilities through tailored voltage waveforms.