Cholesteric order in systems of helical Yukawa rods

Abstract

We consider the interaction potential between two chiral rod-like colloids which consist of a thin cylindrical backbone decorated with a helical charge distribution on the cylinder surface. For sufficiently slender helical rods a simple scaling expression is derived which relates the chiral 'twisting' potential to the microscopic properties of the particles, such as the internal helical pitch, charge density and electrostatic screening parameter. To predict the behaviour of the macroscopic cholesteric pitch of the fluid bulk phase we invoke a simple second-virial theory generalized to treat anisotropic states with weakly twisted director fields. It is shown that, while particles with weakly coiled helices always form a cholesteric phase whose helical sense is commensurate with that of the internal helix, more strongly coiled rods lead to the formation of a cholesteric state of opposite sense. The correlation between the helical symmetry at the microscopic and macroscopic scale is found to be very sensitive to the pitch of the Yukawa helix. Mixing helical particles of sufficiently disparate length and internal pitch may give rise to a demixing of the uniform cholesteric phase into two fractions with a different macroscopic pitch. Our findings could be relevant to the interpretation of experimental observations in systems of cellulose and chitin microfibres, DNA and fd virus rods.

Equilibrium Liquid Crystal Phase Diagrams and Detection of Kinetic Arrest in Cellulose Nanocrystal Suspensions

“…In the literature, several models for chiral rods have been proposed, and their ensembles were shown to form cholesteric phases under certain conditions. These studies were either based on Onsager/Straley theory (Wensink and Jackson, 2011;Frezza et al, 2014), density functional theory (Dussi et al, 2015), or Monte Carlo simulations (Memmer, 2001;Germano et al, 2002;Varga and Jackson, 2003;Frezza et al, 2013;Kolli et al, 2014). They provide interesting information about various aspects of the phase behavior of chiral rods, yet the parameter space of the problem is vast and no study so far has focused specifically on the part that is relevant for CNC.…”

Understanding and Describing the Liquid-Crystalline States of Polypeptide Solutions: A Coarse-Grained Model of PBLG in DMF

“…A number of studies have been carried out after the early attempts by Kimura 71 to describe the properties of a system which combines Onsager's hard-rod model with anisotropic dispersion forces. [72][73][74][75][76][77][78][79][80][81][82][83] Some progress has also been made in introducing dipolar [84][85][86][87][88][89] or chiral [90][91][92][93] interactions between LC molecules. Of particular relevance to our current work is the closed-form algebraic equation of state developed within a van der Waals-Onsager treatment for systems of attractive hard-core particles, 94 in which the attractive potential is expanded in spherical harmonics 95 representing different multipolar contributions to the anisotropic attractions.…”

Chiral assembly of weakly curled hard rods: Effect of steric chirality and polarity

“…Several conclusions can be drawn from this result. As expected, the cholesteric pitch length 2π/k * decreases with concentration but the quadratic scaling differs from the linear one predicted for longranged chiral interaction based on a pseudoscalar potential [16,19,41]. This suggests that purely steric helicity leads to a much harsher microscopic twist compared to those generated by long-ranged dispersion forces.…”