Ferroelectric nematic droplets in their isotropic melt

• Published in: Soft matter Vol. 19; no. 3; pp. 347 - 354
• Main Authors: Perera, Kelum, Saha, Rony, Nepal, Pawan, Dharmarathna, Rohan, Hossain, Md Sakhawat, Mostafa, Md, Adaka, Alex, Waroquet, Ronan, Twieg, Robert J, Jákli, Antal
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 18.01.2023
• Subjects: Birefringence; Crystal defects; Droplets; Electric fields; Ferroelectric materials; Ferroelectricity; Liquid crystals; Nematic crystals; Polarization
• ISSN: 1744-683X; 1744-6848
• DOI: 10.1039/d2sm01395a

The isotropic to ferroelectric nematic liquid transition was theoretically studied over one hundred years ago, but its experimental studies are rare. Here we present experimental results and theoretical considerations of novel electromechanical effects of ferroelectric nematic liquid crystal droplets coexisting with the isotropic melt. We find that the droplets have flat pancake-like shapes that are thinner than the sample thickness as long as there is room to increase the lateral droplet size. In the center of the droplets a wing-shaped defect with low birefringence is present that moves perpendicular to a weak in-plane electric field, and then extends and splits in two at higher fields. Parallel to the defect motion and extension, the entire droplet drifts along the electric field with a speed that is independent of the size of the droplet and is proportional to the amplitude of the electric field. After the field is increased above 1 mV μm −1 the entire droplet gets deformed and oscillates with the field. These observations led us to determine the polarization field and revealed the presence of a pair of positive and negative bound electric charges due to divergences of polarization around the defect volume. Pancake-like ferroelectric nematic droplets in their isotropic melt in horizontal electric fields showing defect motion and shape deformation of the droplets. White arrows show the polarization field.