24 research outputs found
Microphase separation in oil-water mixtures containing hydrophilic and hydrophobic ions
We develop a lattice-based Monte Carlo simulation method for charged mixtures
capable of treating dielectric heterogeneities. Using this method, we study
oil-water mixtures containing an antagonistic salt, with hydrophilic cations
and hydrophobic anions. Our simulations reveal several phases with a spatially
modulated solvent composition, in which the ions partition between water-rich
and water-poor regions according to their affinity. In addition to the recently
observed lamellar phase, we find tubular, droplet, and even gyroid phases
reminiscent of those found in block copolymers and surfactant systems.
Interestingly, these structures stem from ion-mediated interactions, which
allows for tuning of the phase behavior via the concentrations, the ionic
properties, and the temperature.Comment: 5 pages, 4 figure
Hard competition: stabilizing the elusive biaxial nematic phase in suspensions of colloidal particles with extreme lengths
We use computer simulations to study the existence and stability of a biaxial
nematic phase in systems of hard polyhedral cuboids, triangular prisms,
and rhombic platelets, characterized by a long (), medium (), and short
() particle axis. For all three shape families, we find stable states
provided the shape is not only close to the so-called dual shape with but also sufficiently anisotropic with for rhombi,
prisms, and cuboids, respectively, corresponding to anisotropies not considered
before. Surprisingly, a direct isotropic- transition does not occur in
these systems due to a destabilization of by a smectic (for cuboids and
prisms) or a columnar (for platelets) phase at small , or by an
intervening uniaxial nematic phase at large . Our results are confirmed by
a density functional theory provided the third virial coefficient is included
and a continuous rather than a discrete (Zwanzig) set of particle orientations
is taken into account.Comment: minor changes to the introduction, numbering of bibliography
correcte
Critical Casimir Forces and Colloidal Phase Transitions in a Near-Critical Solvent : A Simple Model Reveals a Rich Phase Diagram
From experimental studies it is well-known that colloidal particles suspended
in a near-critical binary solvent exhibit interesting aggregation phenomena,
often associated with colloidal phase transitions, and assumed to be driven by
long-ranged solvent mediated (SM) interactions (critical Casimir forces), set
by the (diverging) correlation length of the solvent. We present the first
simulation and theoretical study of an explicit model of a ternary mixture that
mimics this situation. Both the effective SM pair interactions and the full
ternary phase diagram are determined for Brownian discs suspended in an
explicit two-dimensional supercritical binary liquid mixture. Gas-liquid and
fluid-solid transitions are observed in a region that extends well-away from
criticality of the solvent reservoir. We discuss to what extent an effective
pair-potential description can account for the phase behavior we observe. Our
study provides a fresh perspective on how critical fluctuations of the solvent
might influence colloidal self-assembly.Comment: 4 pages, 4 figure
Structural diversity in three-dimensional self-assembly of nanoplatelets by spherical confinement
Nanoplatelets offer many possibilities to construct advanced materials due to new properties associated with their (semi)two-dimensional shapes. However, precise control of both positional and orientational order of the nanoplatelets in three dimensions, which is required to achieve emerging and collective properties, is challenging to realize. Here, we combine experiments, advanced electron tomography and computer simulations to explore the structure of supraparticles self-assembled from nanoplatelets in slowly drying emulsion droplets. We demonstrate that the rich phase behaviour of nanoplatelets, and its sensitivity to subtle changes in shape and interaction potential can be used to guide the self-assembly into a wide range of different structures, offering precise control over both orientation and position order of the nanoplatelets. Our research is expected to shed light on the design of hierarchically structured metamaterials with distinct shape- and orientation- dependent properties
Interplay between spherical confinement and particle shape on the self-assembly of rounded cubes.
Self-assembly of nanoparticles (NPs) inside drying emulsion droplets provides a general strategy for hierarchical structuring of matter at different length scales. The local orientation of neighboring crystalline NPs can be crucial to optimize for instance the optical and electronic properties of the self-assembled superstructures. By integrating experiments and computer simulations, we demonstrate that the orientational correlations of cubic NPs inside drying emulsion droplets are significantly determined by their flat faces. We analyze the rich interplay of positional and orientational order as the particle shape changes from a sharp cube to a rounded cube. Sharp cubes strongly align to form simple-cubic superstructures whereas rounded cubes assemble into icosahedral clusters with additionally strong local orientational correlations. This demonstrates that the interplay between packing, confinement and shape can be utilized to develop new materials with novel properties
Glassy dynamics of convex polyhedra
Self-assembly of polyhedral-shaped particles has attracted huge interest with the advent of new synthesis methods that realize these faceted particles in the lab. Recent studies have shown that polyhedral-shaped particles exhibit a rich phase behavior by excluded volume interactions alone; some of these particles are even alleged to show a transition to a glass phase by quenching the liquid sufficiently fast beyond the glass transition (supercooling), such that the formation of structures with long-range order is suppressed. Despite the recent progress, no study has been made on the glass formation of polyhedral-shaped particles. Here, we study the glass behavior of polyhedral particles using advanced Monte Carlo methods. We investigate the formation of a glass of monodisperse hard polyhedral-shaped particles, namely, octahedra, tetrahedra, and triangular cupola, using simulations. Finally, the fragility of these particles is determined and compared to that of a polydisperse hard-sphere system. (C) 2014 AIP Publishing LLC
Hard Competition : Stabilizing the Elusive Biaxial Nematic Phase in Suspensions of Colloidal Particles with Extreme Lengths
We use computer simulations to study the existence and stability of a biaxial nematic Nb phase in systems of hard polyhedral cuboids, triangular prisms, and rhombic platelets, characterized by a long (L), medium (M), and short (S) particle axis. For all three shape families, we find stable Nb states provided the shape is not only close to the so-called dual shape with M=LS but also sufficiently anisotropic with L/S>9,11,14,23 for rhombi, (two types of) triangular prisms, and cuboids, respectively, corresponding to anisotropies not considered before. Surprisingly, a direct isotropic-Nb transition does not occur in these systems due to a destabilization of Nb by a smectic (for cuboids and prisms) or a columnar (for platelets) phase at small L/S or by an intervening uniaxial nematic phase at large L/S. Our results are confirmed by a density functional theory provided the third virial coefficient is included and a continuous rather than a discrete (Zwanzig) set of particle orientations is taken into account.</p
Hard Competition : Stabilizing the Elusive Biaxial Nematic Phase in Suspensions of Colloidal Particles with Extreme Lengths
We use computer simulations to study the existence and stability of a biaxial nematic Nb phase in systems of hard polyhedral cuboids, triangular prisms, and rhombic platelets, characterized by a long (L), medium (M), and short (S) particle axis. For all three shape families, we find stable Nb states provided the shape is not only close to the so-called dual shape with M=LS but also sufficiently anisotropic with L/S>9,11,14,23 for rhombi, (two types of) triangular prisms, and cuboids, respectively, corresponding to anisotropies not considered before. Surprisingly, a direct isotropic-Nb transition does not occur in these systems due to a destabilization of Nb by a smectic (for cuboids and prisms) or a columnar (for platelets) phase at small L/S or by an intervening uniaxial nematic phase at large L/S. Our results are confirmed by a density functional theory provided the third virial coefficient is included and a continuous rather than a discrete (Zwanzig) set of particle orientations is taken into account