Effect of shape biaxiality on the phase behavior of colloidal liquid-crystal monolayers

Abstract

We extend our previous work on monolayers of uniaxial particles [J. Chem. Phys. 140, 204906 (2014)] to study the effect of particle biaxiality on the phase behavior of liquid-crystal monolayers. Particles are modelled as board-like hard bodies with three different edge lengths ${\sigma }_1\ge {\sigma }_2\ge {\sigma }_3$, and use is made of the restricted-orientation approximation (Zwanzig model). A density-functional formalism based on the fundamental-measure theory is used to calculate phase diagrams for a wide range of values of the largest aspect ratio (${\kappa }_1={\sigma }_1/{\sigma }_3\in [1,100]$). We find that particle biaxiality in general destabilizes the biaxial nematic phase already present in monolayers of uniaxial particles. While plate-like particles exhibit strong biaxial ordering, rod-like ones with ${\kappa }_1>21.34$ exhibit reentrant uniaxial and biaxial phases. As particle geometry is changed from uniaxial- to increasingly biaxial-rod-like, the region of biaxiality is reduced, eventually ending in a critical-end point. For ${\kappa }_1>60$, a density gap opens up in which the biaxial nematic phase is stable for any particle biaxiality. Regions of the phase diagram where packing-fraction inversion occurs (i.e. packing fraction is a decreasing function of density) are found. Our results are compared with the recent experimental studies on nematic phases of magnetic nanorods.

arXiv comment24 pages, 6 figures

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Cited by in corpus (5)

• Monolayers of hard rods on planar substrates: I. Equilibrium
• Monte Carlo simulation of binary mixtures of hard colloidal cuboids
• Monolayers of hard rods on planar substrates: II. Growth
• Effect of orientational restriction on monolayers of hard ellipsoids
• Biaxial nematic phase stability and demixing behaviour in monolayers of rod-plate mixtures