Self-diffusion of rod-like viruses in the nematic phase

TL;DR

This study investigates the self-diffusion behavior of rod-like viruses in isotropic and nematic phases, revealing how diffusion constants vary with phase and concentration using fluorescence microscopy.

Contribution

It provides the first detailed measurements of anisotropic self-diffusion of rod-like viruses across phase transitions, highlighting the effects of nematic ordering.

Findings

Diffusion parallel to the nematic director increases with virus concentration.

Diffusion perpendicular to the director decreases in the nematic phase.

The ratio of parallel to perpendicular diffusion increases monotonically with concentration.

Abstract

We measure the self-diffusion of colloidal rod-like virus {\it fd} in an isotropic and nematic phase. A low volume fraction of viruses are labelled with a fluorescent dye and dissolved in a background of unlabelled rods. The trajectories of individual rods are visualized using fluorescence microscopy from which the diffusion constant is extracted. The diffusion parallel ($D_{\parallel}$) and perpendicular ($D_{\perp}$) to the nematic director is measured. The ratio ($D_{\parallel}/D_{\perp}$) increases monotonically with increasing virus concentration. Crossing the isotropic-nematic phase boundary results in increase of $D_{\parallel}$ and decrease of $D_{\perp}$ when compared to the diffusion in the isotropic phase ($D_{iso}$).