Equilibrium structures of anisometric, quadrupolar particles confined to a monolayer

Abstract

We investigate the structural properties of a two-dimensional system of ellipsoidal particles carrying a linear quadrupole moment in their center. These particles represent a simple model for a variety of uncharged, non-polar conjugated organic molecules. Using optimization tools based on ideas of evolutionary algorithms, we first examine the ground state structures as we vary the aspect ratio of the particles and the pressure. Interestingly, we find, besides the intuitively expected T-like configurations, a variety of complex structures, characterized with up to three different particle orientations. In an effort to explore the impact of thermal fluctuations, we perform constant-pressure molecular dynamics simulations within a range of rather low temperatures. We observe that ground state structures formed by particles with a large aspect ratio are in particular suited to withstand fluctuations up to rather high temperatures. Our comprehensive investigations allow for a deeper understanding of molecular or colloidal monolayer arrangements under the influence of a typical electrostatic interaction on a coarse-grained level.

Generalized van der Waals theory for phase behavior of two-dimensional nematic liquid crystals: Phase ordering and the equation of state

“…(1) the interaction parameters, as defined, should be inversely proportional to temperature]. As positional order is not accounted for in this theory, the purely orientationally ordered phases analyzed in this paper may be metastable with respect to crystalline or smectic order for small L/B or large interactions, where positionally ordered phases were observed in simulations [17,26,33].…”

“…Both types of interactions (repulsive and attractive) were considered by Heinemann et al [33], who performed molecular dynamics simulations for ellipses with linear quadrupolar interactions confined to a plane. They found that, for relatively small aspect ratios, a plethora of ground state crystalline structures can exist, and they persist to finite temperatures.…”

Biaxial nematic phase stability and demixing behaviour in monolayers of rod–plate mixtures

“…The ground states of monolayers of hard ellipsoids interacting through a quadrupole pair-potential were recently found. 23 Apart from the T-like configurations, three more particle orientations were predicted to be stable.…”

“…In particular, the effect of orientational restriction of ellipsoids on the orientational properties of monolayers was studied. The ground states of monolayers of hard ellipsoids interacting through a quadrupole pair-potential were recently found [23]. Apart from the T-like configurations, three more particle orientations were predicted to be stable.…”

Steady states of non-axial dipolar rods driven by rotating fields

“…Anisotropic colloids are an exciting and relevant system due to their primary role in soft matter systems. The possibility of manipulation of their shapes and interaction brings a wide range of applications in the selfassembly of colloidal matter [1][2][3], in microfluidics [4][5][6] and in the design of functional devices such as probes and sensors [7][8][9][10][11]. As a particular class of colloids with anisotropic interaction, we mention magnetic colloids, which are micro-sized building blocks with an embedded magnetic moment with dipolar interaction, i.e., particles composed of a magnetic mono-domain having a typical size ranging from 1 to 150 nm [12].…”