Search results for "Condensed Matter - Soft Condensed Matter"
showing 10 items of 364 documents
COOLING RATE DEPENDENCE AND DYNAMIC HETEROGENEITY BELOW THE GLASS TRANSITION IN A LENNARD–JONES GLASS
1999
We investigate a binary Lennard-Jones mixture with molecular dynamics simulations. We consider first a system cooled linearly in time with the cooling rate gamma. By varying gamma over almost four decades we study the influence of the cooling rate on the glass transition and on the resulting glass. We find for all investigated quantities a cooling rate dependence; with decreasing cooling rate the system falls out of equilibrium at decreasing temperatures, reaches lower enthalpies and obtains increasing local order. Next we study the dynamics of the melting process by investigating the most immobile and most mobile particles in the glass. We find that their spatial distribution is heterogene…
Dense ionic fluids confined in planar capacitors: in- and out-of-plane structure from classical density functional theory
2016
The ongoing scientific interest in the properties and structure of electric double layers (EDLs) stems from their pivotal role in (super)capacitive energy storage, energy harvesting, and water treatment technologies. Classical density functional theory (DFT) is a promising framework for the study of the in- and out-of-plane structural properties of double layers. Supported by molecular dynamics simulations, we demonstrate the adequate performance of DFT for analyzing charge layering in the EDL perpendicular to the electrodes. We discuss charge storage and capacitance of the EDL and the impact of screening due to dielectric solvents. We further calculate, for the first time, the in-plane str…
Polymer-enforced crystallization of a eutectic binary hard sphere mixture
2010
We prepared a buoyancy matched binary mixture of polydisperse polystyrene microgel spheres of size ratio 0.785 and at a volume fraction of 0.567 just below the kinetic glass transition. In line with theoretical expectations, a eutectic phase behavior was observed, but only a minor fraction of the samples crystallized at all. By adding a short non-adsorbing polymer we enforce inter-species fractionation into coexisting pure component crystals, which in turn also shows signs of intra-species fractionation. We show that in formerly inaccessible regions of the phase diagram binary hard sphere physics is made observable using attractive hard spheres. Ancillary files: Correction to Soft Matter 20…
Curvature as a Guiding Field for Patterns in Thin Block Copolymer Films
2018
Experimental data on thin films of cylinder-forming block copolymers (BC)—free-standing BCmembranes as well as supported BC films—strongly suggest that the local orientation of the BC patternsis coupled to the geometry in which the patterns are embedded. We analyze this phenomenon using generalsymmetry considerations and numerical self-consistent field studies of curved BC films in cylindricalgeometry. The stability of the films against curvature-induced dewetting is also analyzed. In goodagreement with experiments, we find that the BC cylinders tend to align along the direction of curvature athigh curvatures. At low curvatures, we identify a transition from perpendicular to parallel alignm…
Orientational dynamics of colloidal ribbons self-assembled from microscopic magnetic ellipsoids
2016
We combine experiments and theory to investigate the orientational dynamics of dipolar ellipsoids, which self-assemble into elongated ribbon-like structures due to the presence of a permanent magnetic moment, perpendicular to the long axis in each particle. Monodisperse hematite ellipsoids are synthesized via the sol-gel technique and arrange into ribbons in the presence of static or time-dependent magnetic fields. We find that under an oscillating field, the ribbons reorient perpendicular to the field direction, in contrast with the behaviour observed under a static field. This observation is explained theoretically by treating a chain of interacting ellipsoids as a single particle with or…
Mode expansion for the density profiles of crystal–fluid interfaces: hard spheres as a test case
2012
We present a technique for analyzing the full three-dimensional density profiles of a planar crystal-fluid interface in terms of density modes. These density modes can also be related to crystallinity order parameter profiles which are used in coarse-grained, phase field type models of the statics and dynamics of crystal-fluid interfaces and are an alternative to crystallinity order parameters extracted from simulations using local crystallinity criteria. We illustrate our results for the hard sphere system using finely-resolved, three-dimensional density profiles from density functional theory of fundamental measure type.
Deformation of flexible ferromagnetic filaments under a rotating magnetic field
2019
Research on magnetic particles dispersed in a fluid medium, actuated by a rotating magnetic field, is becoming increasingly active for both lab-on-chip and bio-sensing applications. In this study, we experimentally investigate the behaviour of ferromagnetic filaments in a rotating field. Filaments are synthesized by linking micron-sized ferromagnetic particles with DNA strands. The experiments were conducted under different magnetic field strengths, frequencies and filament sizes, and deformation of the filaments was registered via microscope and camera. The results obtained showed that the body deformation is larger for longer filaments and higher frequencies and lower for larger magnetic …
Osmotic compression of droplets of hard rods: a computer simulation study
2009
By means of computer simulations, we study how droplets of hard, rodlike particles optimize their shape and internal structure under the influence of the osmotic compression caused by the presence of spherical particles that act as depletion agents. At sufficiently high osmotic pressures, the rods that make up the drops spontaneously align to turn them into uniaxial nematic liquid-crystalline droplets. The nematic droplets or "tactoids" that are formed this way are not spherical but elongated, resulting from the competition between the anisotropic surface tension and the elastic deformation of the director field. In agreement with recent theoretical predictions, we find that sufficiently sm…
From equilibrium to steady state: The transient dynamics of colloidal liquids under shear
2008
We investigate stresses and particle motion during the start up of flow in a colloidal dispersion close to arrest into a glassy state. A combination of molecular dynamics simulation, mode coupling theory and confocal microscopy experiment is used to investigate the origins of the widely observed stress overshoot and (previously not reported) super-diffusive motion in the transient dynamics. A link between the macro-rheological stress versus strain curves and the microscopic particle motion is established. Negative correlations in the transient auto-correlation function of the potential stresses are found responsible for both phenomena, and arise even for homogeneous flows and almost Gaussia…
Wave-Vector Dependence of the Dynamics in Supercooled Metallic Liquids
2020
Physical review letters 125(5), 055701 (2020). doi:10.1103/PhysRevLett.125.055701