The influence of charge and flexibility on smectic phase formation in filamentous virus suspensions

TL;DR

This study investigates how charge and flexibility affect smectic phase formation in filamentous virus suspensions, revealing complex behaviors that challenge existing theories and depend on particle properties and ionic conditions.

Contribution

It provides new experimental data on phase transitions of charged semiflexible rods, highlighting discrepancies with theoretical predictions and exploring effects of surface charge and flexibility.

Findings

Smectic phase formation depends on charge and flexibility.

Nematic-smectic transition shows unexpected ionic strength dependence.

Experimental results differ from existing theoretical models.

Abstract

We present experimental measurements of the cholesteric-smectic phase transition of suspensions of charged semiflexible rods as a function of rod flexibility and surface charge. The rod particles consist of the bacteriophage M13 and closely related mutants, which are structurally identical to this virus, but vary either in contour length and therefore ratio of persistence length to contour length, or vary in surface charge. Surface charge is altered in two ways; by changing solution pH and by comparing M13 with {\it fd} virus, a mutant which differs from M13 only by the substitution of a single charged amino acid for a neutral one per viral coat protein. Phase diagrams are measured as a function of particle length, particle charge and ionic strength. The experimental results are compared with existing theoretical predictions for the phase behavior of flexible rods and charged rods. In contrast to the isotropic-cholesteric transition, where theory and experiment agree at high ionic strength, the nematic-smectic transition exhibits complex charge and ionic strength dependence significantly different from predicted phase behavior. Possible explanations for these unexpected results are discussed.