Force-driven micro-rheology

Voigtmann, Thomas; Fuchs, Matthias

doi:10.1140/epjst/e2013-02060-5

Cited by 17 publications

(15 citation statements)

References 54 publications

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“…For these systems, several remarkable effects have been observed like a nonlinear thinning of supercooled liquids 7,8,10,11,13 , local melting of glassy samples 6,16 and intermittent superdiffusivity in the supercooled regime 11,14 . Because of this, there is recently a field of vivid research to provide a theoretical description of the out-of-equilibrium properties 4 , mostly in the framework of mode-coupling theory 10,16,17 . For diluted colloidal solutions, a theoretical description in terms of the two-particle correlations between the probe and the host liquid has been developed by Brady et al [18][19][20][21] .…”

Section: Introductionmentioning

confidence: 99%

Understanding the nonlinear dynamics of driven particles in supercooled liquids in terms of an effective temperature

Schroer

Heuer

2015

The Journal of Chemical Physics

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In active microrheology the mechanical properties of a material are tested by adding probe particles which are pulled by an external force. In case of supercooled liquids, strong forcing leads to a thinning of the host material which becomes more pronounced as the system approaches the glass transition. In this work we provide a quantitative theoretical description of this thinning behavior based on the properties of the Potential Energy Landscape (PEL) of a model glass-former. A key role plays the trap-like nature of the PEL. We find that the mechanical properties in the strongly driven system behave the same as in a quiescent system at an enhanced temperature, giving rise to a well-characterized effective temperature. Furthermore, this effective temperature turns out to be independent of the chosen observable and individually shows up in the thermodynamic and dynamic properties of the system. Based on this underlying theoretical understanding, we can estimate its dependence on temperature and force by the PEL-properties of the quiescent system. We furthermore critically discuss the relevance of effective temperatures obtained by scaling relations for the description of out-of-equilibrium situations.

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Section: Introductionmentioning

confidence: 99%

Understanding the nonlinear dynamics of driven particles in supercooled liquids in terms of an effective temperature

Schroer

Heuer

2015

The Journal of Chemical Physics

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“…We note that the force-induced dispersion has not been included in previous theories for active microrheology of colloidal dispersions. The previous theories have either neglected many-body interactions by assuming the suspension is dilute [Squires & Brady, 2005;Khair & Brady, 2006;Swan & Zia, 2013], or only consider steric interactions and simply discard hydrodynamic interactions [Gazuz et al, 2009;Gnann et al, 2011;Voigtmann & Fuchs, 2013].…”

Section: Simulated Microstructure and Trajectoriesmentioning

confidence: 99%

“…We show that the source of the dispersion in CF is the hydrodynamic interactions of the probe with its neighboring bath particles. This is the first study that takes into account the effect of hydrodynamic dispersion on the structure and viscosity of colloidal suspensions in active microrheology; the previous theories ignore this effect by either assuming the suspension is dilute and the interactions are limited to pair particles [Squires & Brady, 2005;Khair & Brady, 2006;Swan & Zia, 2013;Swan et al, 2014], or the HI is entirely ignored [Gazuz et al, 2009;Voigtmann & Fuchs, 2013].…”

Section: Introductionmentioning

confidence: 99%

Active microrheology of colloidal suspensions: Simulation and microstructural theory

Nazockdast

Morris

2016

Journal of Rheology

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SynopsisDiscrete particle simulations by Accelerated Stokesian Dynamics (ASD) and a microstructural theory are applied to study structure and the viscosity of hard-sphere Brownian suspensions in active microrheology (MR). The work considers moderate to dense suspensions, from near to far from equilibrium conditions. The microscopic theory explicitly considers many-body hydrodynamic interactions in active MR, and is compared with the results of the ASD simulations, which include detailed near and far field hydrodynamic interactions. We consider probe and bath particles which are spherical and of the same radius a. Two conditions of moving the probe sphere are considered: these apply constant force (CF) and constant velocity (CV), which approximately model magnetic bead and optical tweezer experiments, respectively. The structure is quantified using the probability distribution of colloidal particles around the probe, P b|p (r) = ng(r), giving the probability of finding a bath particle centered at a vector position r relative to a moving probe particle instantaneously centered at the origin; n is the bath particle number density, and is related to the suspension solid volume fraction, φ, by n = 3φ/4πa3 . The pair distribution function for the bath particles relative to the probe, g(r), is computed as a solution to the pair Smoluchowski equation (SE) for 0.2 ≤ φ ≤ 0.50, and a range of Péclet numbers, describing the ratio of external force on the probe to thermal forces and defined P e f = F ext a/(k b T ) and P e U = 6πηU ext a 2 /(k b T ) for CF and CV conditions, respectively. Results of simulation and theory demonstrate that a wake zone depleted of bath particles behind the moving probe forms at large Péclet numbers, while a boundary-layer accumulation develops upstream. The wake length saturates 1 arXiv:1509.07082v1 [cond-mat.soft] 23 Sep 2015at P e f ≫ 1 for CF while it continuously grows in CV. This contrast in behavior is related to the dispersion in the motion of the probe under CF conditions, while CV motion has no dispersion; the dispersion is a direct result of many-body hydrodynamic interactions. This effect is incorporated in the theory as a force-induced hydrodynamic diffusion flux in the pair SE. We also demonstrate that, despite this difference of structure in the two methods of moving the probe, the probability distribution of particles near the probe is primarily set by the Péclet number, for both CF and CV conditions, in agreement with dilute theories; as a consequence, similar values for apparent viscosity are found for the CF and CV conditions. Using the microscopic theory, the structural anisotropy and Brownian viscosity near equilibrium are shown to be quantitatively similar in both CF and CV motions, which is in contrast with the dilute theory which predict larger distortions and Brownian viscosities in CV, by a factor of two relative to CF microrheology. This difference relative to dilute theory arises due to the determining role of many-body interactions associated with the underlying equi...

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“…The aforementioned studies have focused on the microstructure between the probe and a bath particle; Squires (2008) and DePuit et al (2011) suggest that it is the (unsteady) nonequilibrium microstructure between pairs of bath particles advected past a moving probe that could be more indicative of the macrorheology of the dispersion, particularly when the probe is much larger than the bath particles. It should also be mentioned that the active microrheology of concentrated dispersions has been addressed via dynamic simulations [Carpen and Brady (2005); Winter et al (2012)] and mode-coupling theories [Gazuz and Fuchs (2013); Voigtmann and Fuchs (2013)]. In the context of active microrheology, the current article considers a mixture of micro-and macrorheological forcing; the probe-bath microstructure is distorted by the forced probe (micro) and ambient shear (macro).…”

Section: Introductionmentioning

confidence: 99%