The isotropic-cholesteric phase transition of filamentous virus suspensions as a function of rod length and charge

TL;DR

This study investigates how the phase transition from isotropic to cholesteric in filamentous virus suspensions depends on rod length and charge, combining experiments with theoretical predictions.

Contribution

It provides experimental data on phase transitions of charged, semiflexible rods and compares results with existing theoretical models.

Findings

Transition concentrations align semi-quantitatively with theory.

Surface charge and rod length significantly influence phase behavior.

Order parameters vary with phase and experimental conditions.

Abstract

The viruses studied are genetically engineered, charged, semiflexible filamentous bacteriophages that are structurally identical to M13 virus, but differ either in contour length or surface charge. While varying contour length (L) we assume the persistence length (P) remains constant, and thus we alter the rod flexibility (L/P). Surface charge is altered both by changing solution pH and by comparing two viruses, fd and M13, which differ only by the substitution of one charged for one neutral amino acid per virus coat protein. We measure both the isotropic and cholesteric coexistence concentrations as well as the nematic order parameter after unwinding the cholesteric phase in a magnetic field. The isotropic-cholesteric transition experimental results agree semi-quantitatively with theoretical predictions for semiflexible, charged rods.