Phase Behavior of Colloidal Superballs: Shape Interpolation from Spheres to Cubes

Abstract

The phase behavior of hard superballs is examined using molecular dynamics within a deformable periodic simulation box. A superball's interior is defined by the inequality $|x{|}^{2q}+|y{|}^{2q}+|z{|}^{2q}\le 1$, which provides a versatile family of convex particles ($q\ge 0.5$) with cube-like and octahedron-like shapes as well as concave particles ($q<0.5$) with octahedron-like shapes. Here, we consider the convex case with a deformation parameter q between the sphere point (q = 1) and the cube (q = 1). We find that the asphericity plays a significant role in the extent of cubatic ordering of both the liquid and crystal phases. Calculation of the first few virial coefficients shows that superballs that are visually similar to cubes can have low-density equations of state closer to spheres than to cubes. Dense liquids of superballs display cubatic orientational order that extends over several particle lengths only for large q. Along the ordered, high-density equation of state, superballs with 1 < q < 3 exhibit clear evidence of a phase transition from a crystal state to a state with reduced long-ranged orientational order upon the reduction of density. For $q\ge 3$, long-ranged orientational order persists until the melting transition. The width of coexistence region between the liquid and ordered, high-density phase decreases with q up to q = 4.0. The structures of the high-density phases are examined using certain order parameters, distribution functions, and orientational correlation functions. We also find that a fixed simulation cell induces artificial phase transitions that are out of equilibrium. Current fabrication techniques allow for the synthesis of colloidal superballs, and thus the phase behavior of such systems can be investigated experimentally.

33 pages, 14 figures

References in corpus (7)

• Dense Packings of the Platonic and Archimedean Solids
• Packing Hyperspheres in High-Dimensional Euclidean Spaces
• Dense Packings of Polyhedra: Platonic and Archimedean Solids
• Novel Features Arising in the Maximally Random Jammed Packings of Superballs
• Dense Packings of Superdisks and the Role of Symmetry
• Exact Constructions of a Family of Dense Periodic Packings of Tetrahedra
• Non-uniform liquid--crystalline phases of parallel hard rod-shaped particles: From ellipsoids to cylinders

Cited by in corpus (26)

• Phase diagram of colloidal hard superballs: from cubes via spheres to octahedra
• Basic Understanding of Condensed Phases of Matter via Packing Models
• Scalable Metropolis Monte Carlo for simulation of hard shapes
• Densest binary sphere packings
• Effect of Shape and Friction on the Packing and Flow of Granular Materials
• Equilibrium Phase Behavior and Maximally Random Jammed State of Truncated Tetrahedra
• Organizing Principles for Dense Packings of Nonspherical Hard Particles: Not All Shapes Are Created Equal
• Athermal jamming of soft frictionless Platonic solids
• Freezing of parallel hard cubes with rounded edges
• Ordering and Dynamics of Vibrated Hard Squares
• Phase Behavior of a Family of Truncated Hard Cubes
• Magnetic coupling in colloidal clusters for hierarchical self-assembly
• Characterization of Void Space, Large-Scale Structure, and Transport Properties of Maximally Random Jammed Packings of Superballs
• Free Minimization of the Fundamental Measure Theory Functional: Freezing of Parallel Hard Squares and Cubes
• Phase diagram of a system of hard cubes on the cubic lattice
• Crystallization of the Lewis-Wahnström ortho-terphenyl model
• Thermodynamic stability of hard sphere crystals in dimensions 3 through 10
• Hard convex lens-shaped particles: Characterization of dense disordered packings
• Kinetics of isotropic to string-like phase switching in electrorheological fluids of nanocubes
• Hard core lattice gas with third next-nearest neighbor exclusion on triangular lattice: one or two phase transitions?
• Self-assembly and entropic effects in pear-shaped colloid systems: I. Shape sensitivity of bilayer phases in colloidal pear-shaped particle systems
• Controlling morphology in hybrid isotropic/patchy particle assemblies
• Hybrid models for complex fluids with multipolar interactions
• Symmetry-specific orientational order parameters for complex structures
• Understanding orientational disorder in crystalline assemblies of hard convex polyhedra
• Entropy-Driven Phase Transitions in Colloidal Systems