Position-Dependent Three-Dimensional Diffusion in Nematic Liquid Crystal Monitored by Single-Particle Fluorescence Localization and Tracking

Abstract

Anisotropic mass diffusion in liquid crystals (LCs) is important from the point of both basic LC physics and their applications in optoelectronic devices. We use super-resolution fluorescence microscopy with astigmatic imaging to track 3D diffusion of quantum dots (QDs) in an ordered nematic LC. The method allowed us to evaluate the diffusion coefficients independently along the three spatial axes as well as to determine the absolute position of the QD with respect to the cell wall. We found variations of the diffusion coefficient along the different directions across the cell thickness and explained these as being due to changes of a tilt angle of the LC director. Close to the surface, the diffusion is slowed down due to the confinement effect of the cell wall. Overall, the QD diffusion is much slower than expected for a corresponding particle size. This phenomenon is suggested to originate from reorientation of the LC director in the vicinity of the particle.

Characterization of Porous Materials by Fluorescence Correlation Spectroscopy Super-resolution Optical Fluctuation Imaging

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Anomalous Nanoscale Optoacoustic Phonon Mixing in Nematic Mesogens

“…A landmark in the history of electro-optical displays marked in 1973 with the discovery of 4-cyano-4′-pentylbiphenyl (5CB), a nematic liquid crystal (LC) and the first of the cyanobiphenyls. Since then, these systems have been extensively studied mainly as they pertain to display-related technologies. − In doing so, however, other fascinating phenomena involving quasiparticles as phonons have barely been explored in these materials. Phonons are mechanical vibrations that exist in the form of sound and heat occurring at different frequency and length scales. − The first operates at relatively low and intermediate frequencies, and is able to travel over long distances, while the latter appears at elevated frequencies propagating at the meso- and nanoscale.…”

Fluorescence correlation spectroscopy in thin films at reflecting substrates as a means to study nanoscale structure and dynamics at soft-matter interfaces

“…Due to the diffusion anisotropy parallel and perpendicular to the LC director in 8CB, the local diffusion coefficient depends on the particular orientation of the 8CB in the different regions of the film, as was found for diffusion of CdSe quantum dots in a nematic LC cell [74]. FIG.…”