What is the origin of chirality in the cholesteric phase of virus suspensions ?

TL;DR

This study investigates the origin of chirality in virus suspensions by examining how the cholesteric pitch varies with ionic strength and viral length, revealing unexpected behaviors that challenge existing theories.

Contribution

It demonstrates that grafted polymers do not eliminate chiral interactions and shows the cholesteric pitch depends on ionic strength and viral length, providing new insights into the origin of chirality.

Findings

Cholesteric phase persists after polymer coating, indicating chiral interactions are not fully screened.

Cholesteric pitch varies with ionic strength, contrary to expectations.

Pitch decreases with increasing viral length, opposite to theoretical predictions.

Abstract

We report a study of the cholesteric phase in monodisperse suspensions of the rod-like virus fd sterically stabilized with the polymer polyethylene glycol (PEG). After coating the virus with neutral polymers, the phase diagram and nematic order parameter of the fd-PEG system then become independent of ionic strength. Surprisingly, the fd-PEG suspensions not only continue to exhibit a cholesteric phase, which means that the grafted polymer does not screen all chiral interactions between rods, but paradoxically the cholesteric pitch of this sterically stabilized fd-PEG system varies with ionic strength. Furthermore, we observe that the cholesteric pitch decreases with increasing viral contour length, in contrast to theories which predict the opposite trend. Different models of the origin of chirality in colloidal liquid crystals are discussed.