Phase diagram of tobacco mosaic virus solutions

Abstract

The phase behavior of an aqueous suspension of rodlike tobacco mosaic viruses is investigated theoretically as a function of the virus density and the concentration of added salt. The total free energy involves ''volume terms'' from the microscopic counter-and co-ions and an effective pair interaction between the colloidal rods described by a Yukawa-segment model according to linear screening theory. Within a thermodynamic perturbation approach, the short-range repulsion between the rods is mapped onto a reference system of effective hard spherocylinders. The free energy of the spherocylinder system is gained from combining a cell model with scaled particle theory, which yields a reasonable phase diagram. The remaining long-range interaction is treated within a mean-field approximation. As a result we find stable fluid, nematic, and smectic phases as well as AAA-and ABC-stacked crystals. For increasing salt concentration at fixed rod concentration, there is a nematic reentrant transition. We finally discuss our results in view of experimental data.

Effective shape and phase behavior of short charged rods

“…This coexistence regime is characterized by a small rod charge density, such that the effective geometry of the rod is no longer needle-like. Another limit that was studied in detail is the limit of weak electrostatic interactions, which naturally leads to a perturbative description [37,39,40]. These schemes are very successful at describing the effective (non-needle-like) geometry that shows up in the angular dependence of the second virial coefficient.…”

“…With the notable exception of Ref. [40], however, most of these works on charged rods focus on the isotropic and nematic phases and hence, implicitly, on rods which are sufficiently elongated to give liquid crystalline phases at all.…”

Do cylinders exhibit a cubatic phase?

“…Recent extensions of the Onsager theory to higher densities and smaller aspect ratios can account for these novel phases. [6][7][8][9] In order to study the behavior of disklike objects, Eppenga and Frenkel performed simulations of a system of infinitely thin disks. 10 By construction, the packing fraction of such a system is zero.…”

Steric asymmetry vs charge asymmetry in dilute solution containing large weakly charged ions

“…[10] and [11]. The majority of these works study the effect of excluded volume on phase transitions and consider the domain of relatively high concentrations; the influence of electrostatic interactions is taken into account via screened Coulomb potentials and renormalized second virial coefficients [8,11,12]. This approach is entirely appropriate at strong screening conditions.…”