Communication: From rods to helices: Evidence of a screw-like nematic phase

Abstract

Evidence of a special chiral nematic phase is provided using numerical simulation and Onsager theory for systems of hard helical particles. This phase appears at the high density end of the nematic phase, when helices are well aligned, and is characterized by the C2 symmetry axes of the helices spiraling around the nematic director with periodicity equal to the particle pitch. This coupling between translational and rotational degrees of freedom allows a more efficient packing and hence an increase of translational entropy. Suitable order parameters and correlation functions are introduced to identify this screw-like phase, whose main features are then studied as a function of radius and pitch of the helical particles. Our study highlights the physical mechanism underlying a similar ordering observed in colloidal helical flagella [E. Barry, Z. Hensel, Z. Dogic, M. Shribak, and R. Oldenbourg, Phys. Rev. Lett. 96, 018305 (2006)] and raises the question of whether it could be observed in other helical particle systems, such as DNA, at sufficiently high densities.

Self-assembly of hard helices: a rich and unconventional polymorphism

“…[14] More importantly, we have also provided evidence for the existence of a new chiral nematic phase, named screw-nematic, the helix twofold symmetry axes spiral around the main phase director. [16] This was the phase observed in experiments on systems of colloidal helical filaments, [17] but our results on such a basic model suggest this screw-nematic phase to be a general feature of any helical particle system, including DNA suspensions at sufficiently high densities. [18] In the present work, we build upon past work by extending it in several respects.…”

“…(i) We present a complete phase diagram in the density-pressure plane, with a special emphasis on the smectic phases occurring at densities higher than those typical of the conventional and screw-nematic phases, and discuss how the screw-nematic order merges with a tendency to layering to produce new chiral, screw-like, smectic phases. (ii) We perform a detailed study of the isotropic-nematic coexistence; (iii) We extend the second-virial theory for the nematic-to-screw-nematic phase transition [16] by adding the third-virial contribution, and validate it against numerical simulations.…”

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.…”

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

“…The regime of weakly curled rods (qδ 1) is dominated by uniaxial nematic order while biaxiality enters only at very high particle concentration. The highdensity biaxial nematic phase has both chiral and polar symmetry and should be similar in nature to the screwlike nematic phase recently found in simulation [21,33] and previously observed in dense assemblies of helical…”

“…The main motivation for using a second-virial theory resides in the fact that the excluded volume of weakly deformed helices can be determined analytically thus greatly expediting the calculation of the elastic and torque-field parameters that govern the helical mesostructure. In addition, we wish to broaden the context of the theory beyond mere cholesteric order by attempting to gauge the possibility of alternative types of chiral mesophases such as the twistbend [30][31][32] and screw-like nematics reported for nonconvex elongated particle shapes [33].…”