Janus helices: From fully attractive to hard helices

TL;DR

This study explores how adding short-range attractions to hard helices influences their phase behavior, revealing stable screw phases and marginal effects on liquid crystal phases across different temperature regimes.

Contribution

It introduces a systematic analysis of attractive interactions in hard helices and their impact on phase diagrams using Monte Carlo and Molecular Dynamics simulations.

Findings

Screw phases remain stable across temperature ranges.

Increasing attraction lowers pressure and stabilizes smectic phases.

Phase transition lines are not simply dependent on attraction fraction.

Abstract

The phase diagram of hard helices differs from its hard rods counterpart by the presence of chiral "screw" phases stemming from the characteristic helical shape, in addition to the conventional liquid crystal phases also found for rod-like particles. Using extensive Monte Carlo and Molecular Dynamics simulations, we study the effect of the addition of a short-range attractive tail representing solvent-induced interactions to a fraction of the sites forming the hard helices, ranging from a single-site attraction to fully attractive helices for a specific helical shape. Different temperature regimes exist for different fractions of the attractive sites, as assessed in terms of the relative Boyle temperatures, that are found to be rather insensitive to the specific shape of the helical particle. The temperature range probed by the present study is well above the corresponding Boyle temperatures, with the phase behaviour still mainly entropically dominated and with the existence and location of the various liquid crystal phases only marginally affected. The pressure in the equation of state is found to decrease upon increasing the fraction of attractive beads and/or on lowering the temperature at fixed volume fraction, as expected on physical grounds. All screw phases are found to be stable within the considered range of temperatures with the smectic phase becoming more stable on lowering the temperature. By contrast, the location of the transition lines do not display a simple dependence on the fraction of attractive beads in the considered range of temperatures.