Dynamics of Fractal Cluster Gels with Embedded Active Colloids

Szakasits, Megan; Zhang, Wenxuan; Solomon, Michael J.

doi:10.1103/physrevlett.119.058001

Cited by 17 publications

(24 citation statements)

References 35 publications

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“…Work, pressure and tension are well-defined mechanical concepts and can thus be computed for materials arbitrarily far from equilibrium. In recent years, the pressure of active matter [10][11][12][13][14][15] has aided in the description of many phenomena including instabilities exhibited by expanding bacterial droplets [16], the dynamics of gels [17,18] and membranes [19] embedded with active particles, and even the phase behavior of living systems [20]. Among the phenomena that active pressure has successfully described is the stability limit [21][22][23] (the spinodal) of purely repulsive active particles which are observed to separate into "liquid-" and "gas-like" regions, commonly referred to as motility-induced phase separation [24,25].…”

Section: Introductionmentioning

confidence: 99%

Microscopic origins of the swim pressure and the anomalous surface tension of active matter

2020

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The unique pressure exerted by active particles -the "swim" pressure -has proven to be a useful quantity in explaining many of the seemingly confounding behaviors of active particles. However, its use has also resulted in some puzzling findings including an extremely negative surface tension between phase separated active particles. Here, we demonstrate that this contradiction stems from the fact that the swim pressure is not a true pressure. At a boundary or interface, the reduction in particle swimming generates a net active force density -an entirely self-generated body force. The pressure at the boundary, which was previously identified as the swim pressure, is in fact an elevated (relative to the bulk) value of the traditional particle pressure that is generated by this interfacial force density. Recognizing this unique mechanism for stress generation allows us to define a much more physically plausible surface tension. We clarify the utility of the swim pressure as an "equivalent pressure" (analogous to those defined from electrostatic and gravitational body forces) and the conditions in which this concept can be appropriately applied. arXiv:1912.11727v1 [cond-mat.soft]

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Section: Introductionmentioning

confidence: 99%

Microscopic origins of the swim pressure and the anomalous surface tension of active matter

2020

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“…Furthermore, microrheology studies were made on networks where macroscopic contraction was prevented by choosing appropriate biochemical conditions or by pinning to the boundaries. The microscopic dynamics of synthetic active gels obtained by incorporating self-propelled colloidal particles in a passive network was studied by optical microscopy [46]. However, this study was restricted to systems with relatively weak activity, such that no insight could be gained on the mechanisms leading to the mesoscopic or macroscopic rupture that occurs in highly contractile networks [47,48].…”

Section: Introductionmentioning

confidence: 99%

Uncovering the dynamic precursors to motor-driven contraction of active gels

2019

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Cells and tissues have the remarkable ability to actively generate the forces required to change their shape. This active mechanical behavior is largely mediated by the actin cytoskeleton, a crosslinked network of actin filaments that is contracted by myosin motors. Experiments and active gel theories have established that the length scale over which gel contraction occurs is governed by a balance between molecular motor activity and crosslink density. By contrast, the dynamics that govern the contractile activity of the cytoskeleton remain poorly understood. Here we investigate the microscopic dynamics of reconstituted actin-myosin networks using simultaneous real-space video microscopy and Fourier-space dynamic light scattering. Light scattering reveals rich and unanticipated microscopic dynamics that evolve with sample age. We uncover two dynamical precursors that precede macroscopic gel contraction. One is characterized by a progressive acceleration of stressinduced rearrangements, while the other consists of sudden rearrangements that depend on network adhesion to the boundaries and are highly heterogeneous. Our findings reveal an intriguing analogy between self-driven rupture and collapse of active gels to the delayed rupture of passive gels under external loads.

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“…In this work, we leverage an alternative technique which circumvents this issue, and demonstrates that excellent self-assembly can be achieved by simply adding a relatively small number of purely-repulsive active particles to a solution of complex colloidal building blocks. This strategy of active doping has been explored both experimentally and theoretically by several research groups [66][67][68][69][70][71][72][73][74][75][76]. It has been shown to be an effective strategy for a range of microscopic task ranging from healing defects in colloidal crystals to modulating the structure of isotropic colloidal gels and glasses.…”

Section: Introductionmentioning

confidence: 99%

Universal reshaping of arrested colloidal gels via active doping

Mallory

Bowers

Cacciuto

2020

The Journal of Chemical Physics

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Colloids that interact via a short-range attraction serve as the primary building blocks for a broad range of self-assembled materials. However, one of the well-known drawbacks to this strategy is that these building blocks rapidly and readily condense into a metastable colloidal gel. Using computer simulations, we illustrate how the addition of a small fraction of purely repulsive self-propelled colloids, a technique referred to as active doping, can prevent the formation of this metastable gel state and drive the system toward its thermodynamically favored crystalline target structure. The simplicity and robust nature of this strategy offers a systematic and generic pathway to improving the self-assembly of a large number of complex colloidal structures. We discuss in detail the process by which this feat is accomplished and provide quantitative metrics for exploiting it to modulate self-assembly. We provide evidence for the generic nature of this approach by demonstrating that it remains robust under a number of different anisotropic short-ranged pair interactions in both two and three dimensions. In addition, we report on a novel microphase in mixtures of passive and active colloids. For a broad range of self-propelling velocities, it is possible to stabilize a suspension of fairly monodisperse finite-size crystallites. Surprisingly, this microphase is also insensitive to the underlying pair interaction between building blocks. The active stabilization of these moderatelysized monodisperse clusters is quite remarkable and should be of great utility in the design of hierarchical self-assembly strategies. This work further bolsters the notion that active forces can play a pivotal role in directing colloidal self-assembly.

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Dynamics of Fractal Cluster Gels with Embedded Active Colloids

Cited by 17 publications

References 35 publications

Microscopic origins of the swim pressure and the anomalous surface tension of active matter

Microscopic origins of the swim pressure and the anomalous surface tension of active matter

Uncovering the dynamic precursors to motor-driven contraction of active gels

Universal reshaping of arrested colloidal gels via active doping

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