On the stability and finite-size effects of a columnar phase in single-component systems of hard-rod-like particles

Abstract

Colloidal rod-like particles self-assemble into a variety of liquid crystal phases. In contrast to the formation of the nematic and smectic phases for which it is well understood that it can be driven by entropy, the stabilisation mechanism of a prolate columnar phase (Col + ), observed for example in fd-virus suspensions, is still unclear. Here, we investigate whether or not a Col + phase can exist in a purely entropy-driven single-component system. We perform computer simulations of hard particles with different shapes: spherocylinders, top-shaped rods, cuboidal particles, and crooked rods. We show that the Col + phases observed in previous simulation studies are mere artefacts due to either finite-size effects or simulation boxes that are incommensurate with the stable thermodynamic phase. In particular, we observe that the characteristic layering of the stable smectic or crystal phase disappears when the dimension of the simulation box along the direction of the layers is too small. Such a system-size effect depends both on particle shape and the competing phases, and appears to be more pronounced for less anisotropic particles. ARTICLE HISTORY

Observation of liquid glass in suspensions of ellipsoidal colloids

“…By contrast, the formation of a liquid glass above and below requires long-range correlations, which cannot be captured in the simulation box sizes currently accessible. This is especially true for shape anisotropic particles, for which it has been shown that simulations are susceptible to finite size effects ( 47 ). Solvent-mediated interactions, which were neglected in the simulations, could also play a role, but have been shown to be of minor importance in the structural dynamics of spherical colloids ( 48 ).…”

Biaxial, Twist-bend, and Splay-bend Nematic Phases of Banana-shaped Particles Revealed by Lifting the “Smectic Blanket”

“…[69]-where the regime Ψ > π=2 was investigated-except for the stable columnar phase reported in Ref. [69], which turned out to be an artifact of finite-size effects [73]. However, these findings differ from the work by Teixeira et al [32], who presented a phase diagram based on Onsager theory featuring N þ , N − , and N b phases for L=D → ∞ and Ψ ∈ ½π=2; π.…”

Phase behaviour of hard cylinders

“…For instance, the phase diagram of hard ellipsoids 16 is different from the phase diagram of hard spherocylinders, in spite of the significant similarities in their shapes. This issue goes far beyond a simple academic problem in view of the strong propensity of nucleosomes 14,15 and filamentous viruses 17,18 to form a columnar phase, whose existence in the phase diagram of spherocylinders has been ruled out by recent detailed numerical simulations 19 for prolate particles even if it were predicted theoretically 20 for oblate ones.…”

“…By monitoring the appropriate order parameters and correlation functions, we provide the corresponding phase diagram in the L/D volume fraction plane and compare it with the corresponding phase diagram of the hard spherocylinders 8 . Particular care has been devoted in avoiding possible finite size effects along the lines of a recent similar analysis for spherocylinders 19 .…”