Results for "Hartmut Löwen"

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Phase-field-crystal model for liquid crystalsJun 28 2010Based on static and dynamical density functional theory, a phase-field-crystal model is derived which involves both the translational density and the orientational degree of ordering as well as a local director field. The model exhibits stable isotropic, ... More
Introduction to colloidal dispersions in external fieldsOct 30 2013Progress in the research area of colloidal dispersions in external fields within the last years is reviewed. Colloidal dispersions play a pivotal role as model systems for phase transitions in classical statistical mechanics. In recent years the leading ... More
Effect of self-propulsion on equilibrium clusteringAug 10 2015Aug 14 2015In equilibrium, colloidal suspensions governed by short-range attractive and long-range repulsive interactions form thermodynamically stable clusters. Using Brownian dynamics computer simulations, we investigate how this equilibrium clustering is affected ... More
Dynamical density functional theory for colloidal particles with arbitrary shapeJun 12 2011Starting from the many-particle Smoluchowski equation, we derive dynamical density functional theory for Brownian particles with an arbitrary shape. Both passive and active (self-propelled) particles are considered. The resulting theory constitutes a ... More
Oscillatory driven colloidal binary mixtures: axial segregation versus laningDec 23 2008Using Brownian dynamics computer simulations we show that binary mixtures of colloids driven in opposite directions by an oscillating external field exhibit axial segregation in sheets perpendicular to the drive direction. The segregation effect is stable ... More
Influence of hydrodynamic interactions on lane formation in oppositely charged driven colloidsOct 17 2007The influence of hydrodynamic interactions on lane formation of oppositely charged driven colloidal suspensions is investigated using Brownian dynamics computer simulations performed on the Rotne-Prager level of the mobility tensor. Two cases are considered, ... More
The self-propelled Brownian spinning top: dynamics of a biaxial swimmer at low Reynolds numbersOct 10 2011Recently, the Brownian dynamics of self-propelled (active) rod-like particles was explored to model the motion of colloidal microswimmers, catalytically-driven nanorods, and bacteria. Here, we generalize this description to biaxial particles with arbitrary ... More
Dynamics of a Brownian circle swimmerMar 13 2008Aug 16 2008Self-propelled particles move along circles rather than along a straight line when their driving force does not coincide with their propagation direction. Examples include confined bacteria and spermatozoa, catalytically driven nanorods, active, anisotropic ... More
Analysis of a Living Fluid Continuum ModelApr 07 2016Generalized Navier-Stokes equations which were proposed recently to describe active turbulence in living fluids are analyzed rigorously. Results on wellposedness and stability in the $L^2(\mathbb{R}^n)$-setting are derived. Due to the presence of a Swift-Hohenberg ... More
Tailoring superelasticity of soft magnetic materialsAug 04 2015Oct 14 2015Embedding magnetic colloidal particles in an elastic polymer matrix leads to smart soft materials that can reversibly be addressed from outside by external magnetic fields. We discover a pronounced nonlinear superelastic stress-strain behavior of such ... More
Active colloidal suspensions: Clustering and phase behaviorJul 25 2014We review recent experimental, numerical, and analytical results on active suspensions of self-propelled colloidal beads moving in (quasi) two dimensions. Active colloids form part of the larger theme of active matter, which is noted for the emergence ... More
Coupling between bulk- and surface chemistry in suspensions of charged colloidsOct 28 2013Mar 12 2014The ionic composition and pair correlations in fluid phases of realistically salt-free charged colloidal sphere suspensions are calculated in the primitive model. We obtain the number densities of all ionic species in suspension, including low-molecular ... More
Stability of liquid crystalline phases in the phase-field-crystal modelMar 01 2011The phase-field-crystal model for liquid crystals is solved numerically in two spatial dimensions. This model is formulated with three position-dependent order parameters, namely the reduced translational density, the local nematic order parameter, and ... More
Negative interfacial tension in phase-separated active suspensionsDec 15 2014We study numerically a model for active suspensions of self-propelled repulsive particles, for which a stable phase separation into a dilute and a dense phase is observed. We exploit that for non-square boxes a stable "slab" configuration is reached, ... More
Chemotactic predator-prey dynamicsSep 28 2010A discrete chemotactic predator-prey model is proposed in which the prey secrets a diffusing chemical which is sensed by the predator and vice versa. Two dynamical states corresponding to catching and escaping are identified and it is shown that steady ... More
Ionic mixtures in two dimensions: from crystals to chain and dipole gasesOct 12 2009The ground state of a two-dimensional ionic mixture composed of oppositely charged spheres is determined as a function of the size asymmetry by using a penalty method. The cascade of stable structures includes square, triangular and rhombic crystals as ... More
Stable crystalline lattices in two-dimensional binary mixtures of dipolar particlesJun 15 2007Sep 05 2007The phase diagram of binary mixtures of particles interacting via a pair potential of parallel dipoles is computed at zero temperature as a function of composition and the ratio of their magnetic susceptibilities. Using lattice sums, a rich variety of ... More
Microscopic and macroscopic theories for the dynamics of polar liquid crystalsJul 17 2011We derive and analyze the dynamic equations for polar liquid crystals in two spatial dimensions in the framework of classical dynamical density functional theory (DDFT). Translational density variations, polarization, and quadrupolar order are used as ... More
Polar liquid crystals in two spatial dimensions: the bridge from microscopic to macroscopic modelingMar 10 2011Two-dimensional polar liquid crystals have been discovered recently in monolayers of anisotropic molecules. Here, we provide a systematic theoretical description of liquid-crystalline phases for polar particles in two spatial dimensions. Starting from ... More
Magnetomechanical response of bilayered magnetic elastomersJun 24 2014Magnetic elastomers are appealing materials from an application point of view: they combine the mechanical softness and deformability of polymeric substances with the addressability by external magnetic fields. In this way, mechanical deformations can ... More
Glass transition of charged particles in two-dimensional confinementFeb 23 2015The glass transition of mesoscopic charged particles in two-dimensional confinement is studied by mode-coupling theory. We consider two types of effective interactions between the particles, corresponding to two different models for the distribution of ... More
Hard rectangles near curved hard walls: tuning the sign of the Tolman lengthSep 07 2016Combining analytic calculations, computer simulations, and classical density functional theory we determine the interfacial tension of orientable two-dimensional hard rectangles near a curved hard wall. Both a circular cavity holding the particles and ... More
Aging and rejuvenation of active matter under topological constraintsNov 10 2016The coupling of active, self-motile particles to topological constraints can give rise to novel non-equilibrium dynamical patterns that lack any passive counterpart. Here we study the behavior of self-propelled rods confined to a compact spherical manifold ... More
Structural correlations in diffusiophoretic colloidal mixtures with nonreciprocal interactionsOct 07 2015Nov 17 2015Nonreciprocal effective interaction forces can occur between mesoscopic particles in colloidal suspensions that are driven out of equilibrium. These forces violate Newton's third law actio=reactio on coarse-grained length and time scales. Here we explore ... More
Dynamical mean-field theory and weakly non-linear analysis for the phase separation of active Brownian particlesMar 29 2015Recently, we have derived an effective Cahn-Hilliard equation for the phase separation dynamics of active Brownian particles by performing a weakly non-linear analysis of the effective hydrodynamic equations for density and polarization [Phys. Rev. Lett. ... More
Brownian motion of a self-propelled particleMay 08 2010Overdamped Brownian motion of a self-propelled particle is studied by solving the Langevin equation analytically. On top of translational and rotational diffusion, in the context of the presented model, the "active" particle is driven along its internal ... More
Classical Liquids in Fractal DimensionMay 05 2015Aug 28 2015We introduce fractal liquids by generalizing classical liquids of integer dimensions $d = 1, 2, 3$ to a fractal dimension $d_f$. The particles composing the liquid are fractal objects and their configuration space is also fractal, with the same non-integer ... More
Lane formation in driven colloidal mixtures: is it continuous or discontinuous?Dec 04 2008Binary mixtures of oppositely charged colloids driven by an electric field are shown to exhibit a nonequilibrium transition towards lane formation if the driving force is increased. Brownian dynamics computer simulations and real-space experiments are ... More
Active crystals on a sphereFeb 14 2018Two-dimensional crystals on curved manifolds exhibit nontrivial defect structures. Here, we consider "active crystals" on a sphere, which are composed of self-propelled colloidal particles. Our work is based on a new phase-field-crystal-type model that ... More
Nematic liquid crystals on curved surfaces - a thin film limitSep 27 2017We consider a thin film limit of a Landau-de Gennes Q-tensor model. In the limiting process we observe a continuous transition where the normal and tangential parts of the Q-tensor decouple and various intrinsic and extrinsic contributions emerge. Main ... More
Ultra-fast quenching of binary colloidal suspensions in an external magnetic fieldNov 10 2008Mar 17 2009An ultra-fast quench is applied to binary mixtures of superparamagnetic colloidal particles confined at a two-dimensional water-air interface by a sudden increase of an external magnetic field. This quench realizes a virtually instantaneous cooling which ... More
Close packing of rods on spherical surfacesFeb 24 2016Mar 07 2016We study the optimal packing of short, hard spherocylinders confined to lie tangential to a spherical surface, using simulated annealing and molecular dynamics simulations. For clusters of up to twelve particles, we map out the changes in the geometry ... More
Swim pressure on walls with curves and cornersApr 20 2015Oct 01 2015The concept of swim pressure quantifies the average force exerted by microswimmers on confining walls in non-equilibrium. Here we explore how the swim pressure depends on the wall curvature and on the presence of sharp corners in the wall. For active ... More
Relaxation back to equilibrium after cessation of shear for confined colloidal bilayersJun 24 2005Crystalline bilayers of charged colloidal suspensions which are confined between two parallel plates and sheared via a relative motion of the two plates are studied by extensive Brownian dynamics computer simulations. The charge-stabilized suspension ... More
Dynamical clustering and phase separation in suspensions of self-propelled colloidal particlesMay 17 2013We study experimentally and numerically a (quasi) two dimensional colloidal suspension of self-propelled spherical particles. The particles are carbon-coated Janus particles, which are propelled due to diffusiophoresis in a near-critical water-lutidine ... More
Unwrapping of DNA-protein complexes under external stretchingMar 15 2004A DNA-protein complex modelled by a semiflexible chain and an attractive spherical core is studied in the situation when an external stretching force is acting on one end monomer of the chain while the other end monomer is kept fixed in space. Without ... More
Unusual swelling of a polymer in a bacterial bathJun 11 2014The equilibrium structure and dynamics of a single polymer chain in a thermal solvent is by now well-understood in terms of scaling laws. Here we consider a polymer in a bacterial bath, i.e. in a solvent consisting of active particles which bring in nonequilibrium ... More
Colloidal brazil nut effect in sediments of binary charged suspensionsJan 02 2004Equilibrium sedimentation density profiles of charged binary colloidal suspensions are calculated by computer simulations and density functional theory. For deionized samples, we predict a colloidal ``brazil nut'' effect: heavy colloidal particles sediment ... More
Huge broadening of the crystal-fluid interface for sedimenting colloidsJul 14 2011For sedimenting colloidal hard spheres, the propagation and broadening of the crystal-fluid interface is studied by Brownian dynamics computer simulations of an initially homogeneous sample. Two different types of interface broadenings are observed: the ... More
Colloidal suspensions of C-particles: Entanglement, percolation and microrheologyFeb 17 2016We explore structural and dynamical behavior of concentrated colloidal suspensions made up by C-shape particles using Brownian dynamics computer simulations and theory. In particular, we focus on the entanglement process between nearby particles for almost ... More
Structural control of elastic moduli in ferrogels and the importance of non-affine deformationsJul 01 2014Oct 21 2014One of the central appealing properties of magnetic gels and elastomers is that their elastic moduli can reversibly be adjusted from outside by applying magnetic fields. The impact of the internal magnetic particle distribution on this effect has been ... More
Dynamics of a deformable active particle under shear flowJul 08 2013Aug 21 2013The motion of a deformable active particle in linear shear flow is explored theoretically. Based on symmetry considerations, in two spatial dimensions, we propose coupled nonlinear dynamical equations for the particle position, velocity, deformation, ... More
How does a thermal binary crystal break under shear?Nov 21 2014When exposed to strong shearing, the particles in a crystal will rearrange and ultimately, the crystal will break by forming large nonaffine defects. Even for the initial stage of this process, only little effort has been devoted to the understanding ... More
Can the self-propulsion of anisotropic microswimmers be described by using forces and torques?Oct 24 2014The self-propulsion of artificial and biological microswimmers (i.e., active colloidal particles) has often been modelled by using a force and a torque entering into the overdamped equations for the Brownian motion of passive particles. This seemingly ... More
Traveling and resting crystals in active systemsSep 17 2012A microscopic field theory for crystallization in active systems is proposed which unifies the phase-field-crystal model of freezing with the Toner-Tu theory for self-propelled particles. A wealth of different active crystalline states are predicted and ... More
Direct observation of hydrodynamic instabilities in driven non-uniform colloidal dispersionsOct 07 2008A Rayleigh-Taylor-like instability of a dense colloidal layer under gravity in a capillary of microfluidic dimensions is considered. We access all relevant lengthscales with particle-level microscopy and computer simulations which incorporate long-range ... More
Reply to Comment on "Circular Motion of Asymmetric Self-Propelling Particles"Jul 15 2014In a Comment [Phys. Rev. Lett. 113, 029801 (2014)] on our Letter on self-propelled asymmetric particles [Phys. Rev. Lett. 110, 198302 (2013); arXiv:1302.5787], Felderhof claims that our theory based on Langevin equations would be conceptually wrong. In ... More
Multilayered crystals of macroions under slit-confinementApr 21 2009Dec 23 2009The crystalline ground state of macroions confined between two neutral parallel plates in the presence of their homogeneously spread counterions is calculated by lattice-sum minimization of candidate phases involving up to six layers. For increasing macroion ... More
Nucleation pathway and kinetics of phase-separating active Brownian particlesFeb 24 2016Suspensions of purely repulsive but self-propelled Brownian particles might undergo phase separation, a phenomenon that strongly resembles the phase separation of passive particles with attractions. Here we employ computer simulations to study the nucleation ... More
Compatibility waves drive crystal growth on patterned substratesJul 08 2013We explore the crystallization in a colloidal monolayer on a structured template starting from a few-particle nucleus. The competition between the substrate structure and that of the growing crystal induces a new crystal growth scenario. Unlike with the ... More
Dynamics of a microorganism moving by chemotaxis in its own secretionMay 08 2009Sep 03 2009The Brownian dynamics of a single microorganism coupled by chemotaxis to a diffusing concentration field which is secreted by the microorganism itself is studied by computer simulations in spatial dimensions $d=1,2,3$. Both cases of a chemoattractant ... More
Soft effective interactions between weakly charged polyelectrolyte chainsMay 17 2004Jun 14 2004We apply extensive Molecular Dynamics simulations and analytical considerations in order to study the conformations and the effective interactions between weakly charged, flexible polyelectrolyte chains in salt-free conditions. We focus on charging fractions ... More
Extended dynamical density functional theory for colloidal mixtures with temperature gradientsSep 28 2012In the past decade, classical dynamical density functional theory (DDFT) has been developed and widely applied to the Brownian dynamics of interacting colloidal particles. One of the possible derivation routes of DDFT from the microscopic dynamics is ... More
Superelastic stress-strain behavior in ferrogels of different types of magneto-elastic couplingAug 31 2016Colloidal magnetic particles embedded in an elastic polymer matrix constitute a smart material called ferrogel. It responds to an applied external magnetic field by changes in elastic properties, which can be exploited for various applications like dampers, ... More
Statistics of polymer adsorption under shear flowOct 09 2009Using non-equilibrium Brownian dynamics computer simulations, we have investigated the steady state statistics of a polymer chain under three different shear environments: i) linear shear flow in the bulk (no walls), ii) shear vorticity normal to the ... More
Active dipole clusters: from helical motion to fissionMar 11 2015May 29 2015The structure of a finite particle cluster is typically determined by total energy minimization. Here we consider the case where a cluster of soft sphere dipoles becomes active, i.e. when the individual particles exhibit an additional self-propulsion ... More
A deformable microswimmer in a swirl: capturing and scattering dynamicsJan 15 2014Sep 10 2014Inspired by the classical Kepler and Rutherford problem, we investigate an analogous set-up in the context of active microswimmers: the behavior of a deformable microswimmer in a swirl flow. First we identify new steady bound states in the swirl flow ... More
Brownian motion of a circle swimmer in a harmonic trapSep 30 2016We study the dynamics of a Brownian circle swimmer with a time-dependent self-propulsion velocity in an external temporally varying harmonic potential. For several situations, the noise-free swimming paths, the noise-averaged mean trajectories, and the ... More
Flow of colloidal solids and fluids through constrictions: dynamical density functional theory versus simulationDec 02 2015Using both dynamical density functional theory and particle-resolved Brownian dynamics simulations, we explore the flow of two-dimensional colloidal solids and fluids driven through a linear channel with a geometric constriction. The flow is generated ... More
Swimming path statistics of an active Brownian particle with time-dependent self-propulsionDec 05 2013Feb 14 2014Typically, in the description of active Brownian particles, a constant effective propulsion force is assumed, which is then subjected to fluctuations in orientation and translation leading to a persistent random walk with an enlarged long-time diffusion ... More
Microscopic theory for the phase separation of self-propelled repulsive disksJul 18 2013Motivated by recent experiments on colloidal suspensions, we study analytically and numerically a microscopic model for self-propelled particles lacking alignment interactions. In this model, even for purely repulsive interactions, a dynamical instability ... More
Simulation Study of Sulfonate Cluster Swelling in IonomersSep 03 2009We have performed simulations to study how increasing humidity affects the structure of Nafion-like ionomers under conditions of low sulfonate concentration and low humidity. At the onset of membrane hydration, the clusters split into smaller parts. These ... More
Dynamic Elastic Moduli in Magnetic Gels: Normal Modes and Linear ResponseJun 29 2016Aug 25 2016In the perspective of developing smart hybrid materials with customized features, ferrogels and magnetorheological elastomers allow a synergy of elasticity and magnetism. The interplay between elastic and magnetic properties gives rise to a unique reversible ... More
Following fluctuating signs: anomalous active superdiffusion of swimmers in anisotropic mediaMar 02 2016Active (i.e., self-propelled or swimming) particles moving through an isotropic fluid exhibit conventional diffusive behavior. We report anomalous diffusion of an active particle moving in an anisotropic, nematic background. Whilst the translational motion ... More
Active crystals and their stabilityJan 21 2014A recently introduced active phase field crystal model describes the formation of ordered resting and traveling crystals in systems of self-propelled particles. Increasing the active drive, a resting crystal can be forced to perform collectively ordered ... More
Crystallization in a dense suspension of self-propelled particlesDec 22 2011Using Brownian dynamics computer simulations we show that a two-dimensional suspension of self-propelled ("active") colloidal particles crystallizes at sufficiently high densities. Compared to the equilibrium freezing of passive particles the freezing ... More
Brownian dynamics of a self-propelled particle in shear flowJun 02 2011Brownian dynamics of a self-propelled particle in linear shear flow is studied analytically by solving the Langevin equation and in simulation. The particle has a constant propagation speed along a fluctuating orientation and is additionally subjected ... More
Symmetry-breaking in clogging for oppositely driven particlesNov 10 2015The clogging behavior of a symmetric binary mixture of particles that are driven in opposite directions through constrictions is explored by Brownian dynamics simulations and theory. A dynamical state with a spontaneously broken symmetry occurs where ... More
Dynamics of a linear magnetic "microswimmer molecule"Nov 12 2015In analogy to nanoscopic molecules that are composed of individual atoms, we consider an active "microswimmer molecule". It is built up from three individual magnetic colloidal microswimmers that are connected by harmonic springs and hydrodynamically ... More
Microscopic approach to entropy productionDec 08 2012It is a great challenge of nonequilibrium statistical mechanics to calculate entropy production within a microscopic theory. In the framework of linear irreversible thermodynamics, we combine the Mori-Zwanzig-Forster projection operator technique with ... More
Derivation of a three-dimensional phase-field-crystal model for liquid crystals from density functional theoryJul 09 2010Using a generalized order parameter gradient expansion within density functional theory, we derive a phase-field-crystal model for liquid crystals composed by apolar particles in three spatial dimensions. Both the translational density and the orientational ... More
Crystalline multilayers of the confined Yukawa systemNov 28 2008Mar 18 2009The phase diagram of Yukawa particles confined between two parallel hard walls is calculated at zero-temperature beyond the bilayer regime by lattice-sum-minimization. Tuning the screening, a rich phase behavior is found in the regime bounded by stable ... More
Equilibrium properties of highly asymmetric star-polymer mixturesMay 17 2004Jul 14 2004We employ effective interaction potentials to study the equilibrium structure and phase behavior of highly asymmetric mixtures of star polymers. We consider in particular the influence of the addition of a component with a small number of arms and a small ... More
Getting drowned in a swirl: deformable bead-spring model microswimmers in external flow fieldsOct 08 2015Dec 27 2015Deformability is a central feature of many types of microswimmers, e.g. for artificially generated self-propelled droplets. Here, we analyze deformable bead-spring microswimmers in an externally imposed solvent flow field as simple theoretical model systems. ... More
Freezing of parallel hard cubes with rounded edgesFeb 09 2012The freezing transition in a classical three-dimensional system of parallel hard cubes with rounded edges is studied by computer simulation and fundamental-measure density functional theory. By switching the rounding parameter s from zero to one, one ... More
Highly asymmetric electrolytes in the primitive model: Hypernetted chain solution in arbitrary spatial dimensionsJul 16 2013The pair-correlation functions for fluid ionic mixtures in arbitrary spatial dimensions are computed in hypernetted chain (HNC) approximation. In the primitive model, all ions are approximated as non-overlapping hyperspheres with Coulomb interactions. ... More
Fission and fusion scenarios for magnetic microswimmer clustersNov 22 2016Fission and fusion processes of particles clusters occur in many areas of physics and chemistry from subnuclear to astronomic length scales. Here we study fission and fusion of magnetic microswimmer clusters as governed by their hydrodynamic and dipolar ... More
Effective Cahn-Hilliard equation for the phase separation of active Brownian particlesDec 27 2013The kinetic separation of repulsive active Brownian particles into a dense and a dilute phase is analyzed using a systematic coarse-graining strategy. We derive an effective Cahn-Hilliard equation on large length and time scales, which implies that the ... More
Two-dimensional colloidal mixtures in magnetic and gravitational fieldsOct 30 2013This mini-review is concerned with two-dimensional colloidal mixtures exposed to various kinds of external fields. By a magnetic field perpendicular to the plane, dipole moments are induced in paramagnetic particles which give rise to repulsive interactions ... More
Soft repulsive mixtures under gravity: brazil-nut effect, depletion bubbles, boundary layering, nonequilibrium shakingDec 28 2011A binary mixture of particles interacting via long-ranged repulsive forces is studied in gravity by computer simulation and theory. The more repulsive A-particles create a depletion zone of less repulsive B-particles around them reminiscent to a bubble. ... More
Crystallization of magnetic dipolar monolayers: a density functional approachApr 21 2008We employ density functional theory to study in detail the crystallization of super-paramagnetic particles in two dimensions under the influence of an external magnetic field that lies perpendicular to the confining plane. The field induces non-fluctuating ... More
Structure and dynamics of interfaces between two coexisting liquid crystalline phasesFeb 01 2013The phase-field-crystal model is used to access the structure and thermodynamics of interfaces between two coexisting liquid crystalline phases in two spatial dimensions. Depending on the model parameters there is a variety of possible coexistences between ... More
Motion of two micro-wedges in a turbulent bacterial bathNov 04 2014Mar 12 2015The motion of a pair of micro-wedges ("carriers") in a turbulent bacterial bath is explored using computer simulations with explicit modeling of the bacteria and experiments. The orientation of the two micro-wedges is parallel and fixed by an applied ... More
Vacancy diffusion in colloidal crystals as determined by dynamical density-functional theory and the phase-field-crystal modelFeb 05 2013A two-dimensional crystal of repulsive dipolar particles is studied in the vicinity of its melting transition by using Brownian dynamics computer simulation, dynamical density functional theory and phase-field crystal modelling. A vacancy is created by ... More
Two-dimensional melting under quenched disorderMay 16 2013We study the influence of quenched disorder on the two-dimensional melting behavior by using both video-microscopy of superparamagnetic colloidal particles and computer simulations of repulsive parallel dipoles. Quenched disorder is provided by pinning ... More
Emerging activity in bilayered dispersions with wake-mediated interactionsJul 31 2015Apr 05 2016In a bilayered system of particles with wake-mediated interactions, the action-reaction symmetry for the effective forces between particles of different layers is broken. Under quite general conditions we show that, if the interaction nonreciprocity exceeds ... More
Mechanisms of carrier transport induced by a microswimmer bathAug 08 2014Recently, it was found that a wedgelike microparticle (referred to as "carrier") which is only allowed to translate but not to rotate exhibits a directed translational motion along the wedge cusp if it is exposed to a bath of microswimmers. Here we model ... More
Phototaxis of synthetic microswimmers in optical landscapesSep 30 2016Many microorganisms, with phytoplankton and zooplankton as prominent examples, display phototactic behaviour, that is, the ability to perform directed motion within a light gradient. Here we experimentally demonstrate that sensing of light gradients can ... More
Colloidal crystal growth at externally imposed nucleation clustersFeb 15 2008We study the conditions under which and how an imposed cluster of fixed colloidal particles at prescribed positions triggers crystal nucleation from a metastable colloidal fluid. Dynamical density functional theory of freezing and Brownian dynamics simulations ... More
Density functional theory of freezing for soft interactions in two dimensionsApr 18 2006A density functional theory of two-dimensional freezing is presented for a soft interaction potential that scales as inverse cube of particle distance. This repulsive potential between parallel, induced dipoles is realized for paramagnetic colloids on ... More
Derivation of the phase field crystal model for colloidal solidificationFeb 19 2009May 28 2009The phase-field crystal model is by now widely used in order to predict crystal nucleation and growth. For colloidal solidification with completely overdamped individual particle motion, we show that the phase-field crystal dynamics can be derived from ... More
DDFT calibration and investigation of an anisotropic phase-field crystal modelMar 05 2011The anisotropic phase-field crystal model recently proposed and used by Prieler et al. [J. Phys.: Condens. Matter 21, 464110 (2009)] is derived from microscopic density functional theory for anisotropic particles with fixed orientation. Further its morphology ... More
Non-Gaussian behaviour of a self-propelled particle on a substrateJun 18 2009The overdamped Brownian motion of a self-propelled particle which is driven by a projected internal force is studied by solving the Langevin equation analytically. The "active" particle under study is restricted to move along a linear channel. The direction ... More
Non-equilibrium melting of colloidal crystals in confinementNov 14 2008We report on a novel and flexible experiment to investigate the non-equilibrium melting behaviour of model crystals made from charged colloidal spheres. In a slit geometry polycrystalline material formed in a low salt region is driven by hydrostatic pressure ... More
Capillary Condensation and Interface Structure of a Model Colloid-Polymer Mixture in a Porous MediumAug 06 2003We consider the Asakura-Oosawa model of hard sphere colloids and ideal polymers in contact with a porous matrix modeled by immobilized configurations of hard spheres. For this ternary mixture a fundamental measure density functional theory is employed, ... More
Dynamical Density Functional Theory For MicroswimmersOct 26 2015Jan 07 2016Dynamical density functional theory (DDFT) has been successfully derived and applied to describe on the one hand passive colloidal suspensions, including hydrodynamic interactions between individual particles. On the other hand, active "dry" crowds of ... More
Depolarized light scattering from prolate anisotropic particles: the influence of the particle shape on the field autocorrelation functionMar 19 2015Jul 30 2015We provide a theoretical analysis for the intermediate scattering function typically measured in depolarized dynamic light scattering experiments. We calculate the field autocorrelation function $g_1^{\rm VH}(Q,t)$ in dependence on the wave vector $Q$ ... More
Molecular view of the Rayleigh-Taylor instability in compressible Brownian fluidsFeb 11 2004The onset of the Rayleigh-Taylor instability is studied a compressible Brownian Yukawa fluid mixture on the ``molecular'' length and time scales of the individual particles. As a model, a two-dimensional phase-separated symmetric binary mixture of colloidal ... More
Self-energy and vertex functions from hybridization expansion continuous-time quantum Monte Carlo for impurity models with retarded interactionNov 22 2013Jun 26 2014Optimized measurements for the susceptibility, self-energy, as well as three-leg and four-leg vertex functions are introduced for the continuous-time hybridization expansion quantum Monte Carlo solver for the impurity model in presence of a retarded interaction. ... More
On Arthur Merlin Games in Communication ComplexityJan 03 2011We show several results related to interactive proof modes of communication complexity. First we show lower bounds for the QMA-communication complexity of the functions Inner Product and Disjointness. We describe a general method to prove lower bounds ... More