Selected Topics:

Thermoelectric heat engine

Thermodynamics and Information

Self-propelled particle

Vesicles in flow

Membrane Adhesion

Hidden degree of freedom


 

Soft Matter in Flow

Crystallization in a sheared colloidal suspension

Soft matter

By increasing the density, the equilibrium configuration of a charge-stabilized colloidal suspension turns from liquid to crystalline at some point. The corresponding freezing process is typically a first-order phase transition proceeding via a nucleation and growth scenario. Avoiding nucleation, e. g., by increasing the density very quickly, the suspension can be prepared in a metastable liquid state with a density beyond the thermodynamic freezing density. In this project, we study the subsequent crystallization process under the influence of simple shear flow. We find that the effect of the shearing on crystallization is two-fold: while it suppresses the initial nucleation, once a large enough critical nucleus has formed its growth is enhanced by the shear flow. Combining both effects implies an optimal strain rate at which the overall crystallization rate has a maximum. This maximum results from two shear-dependent effects affecting the crystallization at different stages. At the nucleation stage, shear flow inhibits the formation of crystalline nuclei by disrupting prestructuring in the liquid. At the growth stage the shearing strongly facilitates the crystallization growth. Tentatively, this acceleration can be related to convection.

Related publications

Crystallization in a sheared colloidal suspension
B. Lander, U. Seifert, and T. Speck
J. Chem. Phys. 138, 224907, 2013
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Tagged particle in a sheared colloidal suspension

The mobility of a colloidal particle immersed in a solvent determines the velocity of the particle in response to an applied external force. In thermal equilibrium, the Einstein relation expresses the deep connection between this linear response coefficient and the diffusivity of this particle. However, driving the system beyond the linear response regime around equilibrium this relation does not apply. By means of extensive Langevin dynamics simulations, we aim to understand the nonequilibrium behaviour of colloidal suspensions by analyzing characteristic quantities such as mobility and diffusion constants. Furthermore, we investigate under which circumstances and to what extent the definition of an effective nonequilibrium temperature as a fluctuation-dissipation ratio is a good approximation.

Related publications

Effective confinement as origin of the equivalence of kinetic temperature and fluctuation-dissipation ratio in dense shear driven suspension
B. Lander, U. Seifert and T. Speck
Phys. Rev. E 85, 021103, 2012
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Mobility and diffusion of a tagged particle in a driven colloidal suspension
B. Lander, U. Seifert and T. Speck
EPL 92, 58001, 2010
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Fluctuation-dissipation theorem in nonequilibrium steady states
U. Seifert and T. Speck
EPL 89, 10007, 2010
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Extended fluctuation-dissipation theorem for soft matter in stationary flow
T. Speck and U. Seifert
Phys. Rev. E 79 , 040102 (R), 2009
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Dynamics of fluid vesicles and micro-capsules in linear flow

Bild

Fluid vesicles such as liposomes and micro-capsules like red blood cells are ubiquitous in the human body. Their response to an applied external flow determines for example the rheology of the cardiovascular circulation and is thus of great physical and biological relevance. We investigate theoretically the dynamics of single vesicles and capsules in linear flow by using analytical models with a restricted number of degrees of freedom. In particular, we focus on the effect of thermal  fluctuations on the different dynamical regimes and the transitions between these. Our aim is to construct then corresponding phase diagrams that include thermal noise.

 

Related publications

Wrinkling instability of vesicles in steady linear flow
M. Levant, D. Abreu, U. Seifert, and V. Steinberg
EPL 107, 28001, 2014
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Fluid vesicles in flow
D. Abreu, M. Levant, V. Steinberg, and U. Seifert
Adv. Colloid Interface Sci. 208, 129-141, 2014
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Noisy nonlinear dynamics of vesicles in flow
D. Abreu and U. Seifert
Phys. Rev. Lett. 110, 238103, 2013
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Effect of thermal noise on vesicles and capsules in shear flow
D. Abreu and U. Seifert
Phys. Rev. E 86, 010902, 2012 
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Micro-capsules in shear flow
R. Finken, S. Kessler, and U. Seifert
J. Phys. Cond. Mat. 23, 184113, 2011 
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Elastic capsules in shear flow: Analytical solutions for constant and time-dependent shear rates
S. Kessler, R. Finken, and U. Seifert
Eur. Phys. J. E 29, 399-413, 2009 
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Swinging and tumbling of elastic capsules in shear flow
S. Kessler, R. Finken, and U. Seifert
J. Fluid Mech. 605, 207-226, 2008 
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Efficiency of self-propelled particlesSelf-propelled particle

We study the dynamics and thermodynamics of one of the very few artificially realizable models for micro- and nano-machines. Chemical reactions on the surface of a microscopic particle can produce a gradient of reactant concentration, which pushes the particle forward. We investigate this mechanism through detailed analytical modeling in order to find generic factors determining the efficiency of microscopic machines and to optimize their performance.

 

Related publications

Nonlinear, electrocatalytic swimming in the presence of salt
B. Sabass and U. Seifert
J. Chem. Phys. 136, 214507, 2012 
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Dynamics and efficiency of a self-propelled, diffusiophoretic swimmer
B. Sabass and U. Seifert
J. Chem. Phys. 136, 064508, 2012 
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Efficiency of surface-driven motion: nano-swimmers beat micro-swimmers
B. Sabass and U. Seifert
Phys. Rev. Lett. 105, 218103, 2010 
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