Entropic Interactions in Suspensions of Semi-Flexible Rods: Short-Range Effects of Flexibility

TL;DR

This paper models the entropic interactions between colloidal spheres in a suspension of semi-flexible rods, revealing how flexibility influences short-range forces and providing insights into the rods' persistence length.

Contribution

The study introduces a model treating semi-flexible rods as bent at fixed angles, capturing rotational degrees of freedom and explaining experimental observations.

Findings

Entropic forces are quantitatively captured by the model.

Persistence length of fd-virus is estimated to be 2-3 times smaller than previous values.

Model explains short-range interaction observations in experiments.

Abstract

We compute the entropic interactions between two colloidal spheres immersed in a dilute suspension of semi-flexible rods. Our model treats the semi-flexible rod as a bent rod at fixed angle, set by the rod contour and persistence lengths. The entropic forces arising from this additional rotational degree of freedom are captured quantitatively by the model, and account for observations at short range in a recent experiment. Global fits to the interaction potential data suggest the persistence length of fd-virus is about two to three times smaller than the commonly used value of $2.2 \mu {m}$.