Isotropic-nematic phase transition in suspensions of filamentous virus and the neutral polymer Dextran

TL;DR

This study investigates how adding neutral polymer Dextran affects the isotropic-nematic phase transition in charged semi-flexible rods (fd virus), revealing dependence on ionic strength and polymer molecular weight with experimental validation against theoretical models.

Contribution

It provides the first comprehensive experimental phase diagram of fd virus and Dextran mixtures, highlighting the influence of ionic strength and polymer properties on phase behavior.

Findings

Polymer widens the coexistence region at high ionic strength.

Polymer has no effect at low ionic strength.

Nematic order parameter remains unaffected by polymer concentration.

Abstract

We present an experimental study of the isotropic-nematic phase transition in an aqueous mixture of charged semi-flexible rods (fd virus) and neutral polymer (Dextran). A complete phase diagram is measured as a function of ionic strength and polymer molecular weight. At high ionic strength we find that adding polymer widens the isotropic-nematic coexistence region with polymers preferentially partitioning into the isotropic phase, while at low ionic strength the added polymer has no effect on the phase transition. The nematic order parameter is determined from birefringence measurements and is found to be independent of polymer concentration (or equivalently the strength of attraction). The experimental results are compared with the existing theoretical predictions for the isotropic-nematic transition in rods with attractive interactions.