Results for "Hartmut Löwen"

total 794took 0.11s
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
Inertial delay of self-propelled particlesJul 11 2018The motion of self-propelled massive particles through a gaseous medium is dominated by inertial effects. Examples include vibrated granulates, activated complex plasmas and flying insects. However, inertia is usually neglected in standard models. Here, ... More
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
Active particles in non-inertial frames: how to self-propel on a carouselApr 29 2019Typically the motion of self-propelled active particles is described in a quiescent environment establishing an inertial frame of reference. Here we assume that friction, self-propulsion and uctuations occur relative to a non-inertial frame and thereby ... 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
Helical paths, gravitaxis, and separation phenomena for mass-anisotropic self-propelling colloids: experiment versus theoryJan 24 2017Sep 09 2017The self-propulsion mechanism of active colloidal particles often generates not only translational but also rotational motion. For particles with an anisotropic mass density under gravity, the motion is usually influenced by a downwards oriented force ... More
Hydrodynamic coupling and rotational mobilities near planar elastic membranesJun 01 2018We study theoretically and numerically the coupling and rotational hydrodynamic interactions between spherical particles near a planar elastic membrane that exhibits resistance towards shear and bending. Using a combination of the multipole expansion ... 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
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
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
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
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
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
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
Partial Clustering in Binary Two-Dimensional Colloidal SuspensionsApr 13 2006Strongly interacting binary mixtures of superparamagnetic colloidal particles confined to a two-dimensional water-air interface are examined by theory, computer simulation and experiment. The mixture exhibits a partial clustering in equilibrium: in the ... 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
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
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
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
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
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
Dynamical density functional theory for circle swimmersJul 17 2018The majority of studies on self-propelled particles and microswimmers concentrates on objects that do not feature a deterministic bending of their trajectory. However, perfect axial symmetry is hardly found in reality, and shape-asymmetric active microswimmers ... 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
Traveling band formation in feedback-driven colloidsApr 17 2019Using simulation and theory we study the dynamics of a colloidal suspension in two dimensions subject to a time-delayed repulsive feedback that depends on the positions of the colloidal particles. The colloidal particles experience an additional potential ... More
Multi-species dynamical density functional theory for microswimmers: derivation, orientational ordering, trapping potentials, and shear cellsApr 15 2019Microswimmers typically operate in complex environments. In biological systems, often diverse species are simultaneously present and interact with each other. Here, we derive a (time-dependent) particle-scale statistical description, namely a dynamical ... 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
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
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
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
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
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
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
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
Motility-induced temperature difference in coexisting phasesFeb 16 2019In nature, objects which are in thermal contact with each other, usually approach the same temperature, unless a heat source (or sink) cherishes a persistent flow of heat. Accordingly, in a well-isolated apartment flat, most items are at a similar temperature. ... 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
Dynamics in a one-dimensional ferrogel model: relaxation, pairing, shock-wave propagationMar 03 2018Ferrogels are smart soft materials, consisting of a polymeric network and embedded magnetic particles. Novel phenomena, such as the variation of the overall mechanical properties by external magnetic fields, emerge consequently. However, the dynamic behavior ... 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
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
Impedance resonance in narrow confinementOct 02 2018The article explores the ion flux response of a capacitor configuration to an alternating voltage. The model system comprises a symmetric binary electrolyte confined between plan-parallel capacitor plates. The AC response is investigated for the sparsely ... More
Simulation Study of Ion Diffusion in Charged Nanopores with Anchored Terminal GroupsApr 29 2017We present coarse-grained simulation results for enhanced ion diffusion in a charged nanopore grafted with ionomer sidechains. The pore surface is hydrophobic and its diameter is varied from 2.0 nm to 3.7 nm. The sidechains have from 2 to 16 monomers ... 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
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
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
Particle-scale statistical theory for hydrodynamically induced polar ordering in microswimmer suspensionsJul 23 2018Oct 22 2018Previous particle-based computer simulations have revealed a significantly more pronounced tendency of spontaneous global polar ordering in puller (contractile) microswimmer suspensions than in pusher (extensile) suspensions. We here evaluate a microscopic ... 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
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
Ground state of dipolar hard spheres confined in channelsMar 27 2018We investigate the ground state of a classical two-dimensional system of hard-sphere dipoles confined between two hard walls. Using lattice sum minimization techniques we reveal that at fixed wall separations, a first-order transition from a vacuum to ... 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
Compactness of the automorphism group of a topological parallelism on real projective 3-space: The disconnected caseOct 16 2017We prove that the automorphism group of a topological parallelism on real projective 3-space is compact. In a preceding article it was proved that at least the connected component of the identity is compact. The present proof does not depend on that earlier ... More
Rotational spreads and rotational parallelisms and oriented parallelisms of PG(3,R)Apr 20 2018Jun 01 2018We introduce topological parallelisms of oriented lines (briefly called oriented parallelisms). Every topological parallelism (of lines) on PG(3,R) gives rise to a parallelism of oriented lines, but we show that even the most homogeneous parallelisms ... More
A characterization of Clifford parallelism by automorphismsFeb 10 2017Betten and Riesinger have shown that Clifford parallelism on real projective space is the only topological parallelism that is left invariant by a group of dimension at least 5. We improve the bound to 4. Examples of different parallelisms admitting a ... More
Parallelisms of $\mathop{\rm PG}(3,\mathbb R)$ admitting a 3-dimensional groupJun 11 2018Jun 28 2018Betten and Riesinger constructed Parallelisms of $\mathop{\rm PG}(3,\mathbb R)$ with automorphism group $\mathop{\rm SO}(3,\mathbb R)$ by applying the reducible $\mathop{\rm SO}(3,\mathbb R)$-action to a rotational Betten spread. This was generalized ... 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
Taming Polar Active Matter with Moving Substrates: Directed Transport and Counterpropagating MacrobandsOct 12 2018Following the goal of using active particles as targeted cargo carriers aimed, for example, to deliver drugs towards cancer cells, the quest for the control of individual active particles with external fields is among the most explored topics in active ... More
Aging and rejuvenation of active matter under topological constraintsNov 10 2016Aug 20 2018The 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
Liquid crystals of hard rectangles on flat and cylindrical manifoldsOct 13 2017Using the classical density functional theory of freezing and Monte Carlo computer simulations, we explore the liquid-crystalline phase behavior of hard rectangles on flat and cylindrical manifolds. Moreover, we study the effect of a static external field ... 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
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
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
Unraveling Modular Microswimmers: From Self-Assembly to Ion-Exchange Driven MotorsJul 26 2018Dec 03 2018Active systems contain self-propelled particles and can spontaneously self-organize into patterns making them attractive candidates for the self-assembly of smart soft materials. One key limitation of our present understanding of these materials hinges ... More
Creeping motion of a solid particle inside a spherical elastic cavityJan 25 2018Aug 14 2018On the basis of the linear hydrodynamic equations, we present an analytical theory for the low-Reynolds-number motion of a solid particle moving inside a larger spherical elastic cavity which can be seen as a model system for a fluid vesicle. In the particular ... 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
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
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
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
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
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
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