@article {115050, title = {Unjamming and emergent nonreciprocity in active ploughing through a compressible viscoelastic fluid.}, journal = {Nat Commun}, volume = {13}, year = {2022}, month = {2022 Aug 04}, pages = {4533}, abstract = {

A dilute suspension of active Brownian particles in a dense compressible viscoelastic fluid, forms a natural setting to study the emergence of nonreciprocity during a dynamical phase transition. At these densities, the transport of active particles is strongly influenced by the passive medium and shows a dynamical jamming transition as a function of activity and medium density. In the process, the compressible medium is actively churned up - for low activity, the active particle gets self-trapped in a cavity of its own making, while for large activity, the active particle ploughs through the medium, either accompanied by a moving anisotropic wake, or leaving a porous trail. A hydrodynamic approach makes it evident that the active particle generates a long-range density wake which breaks fore-aft symmetry, consistent with the simulations. Accounting for the back-reaction of the compressible medium leads to (i) dynamical jamming of the active particle, and (ii) a dynamical non-reciprocal attraction between two active particles moving along the same direction, with the trailing particle catching up with the leading one in finite time. We emphasize that these nonreciprocal effects appear only when the active particles are moving and so manifest in the vicinity of the jamming-unjamming transition.

}, issn = {2041-1723}, doi = {10.1038/s41467-022-31984-z}, author = {Banerjee, Jyoti Prasad and Mandal, Rituparno and Banerjee, Deb Sankar and Thutupalli, Shashi and Rao, Madan} } @article {77995, title = {Extreme active matter at high densities.}, journal = {Nat Commun}, volume = {11}, year = {2020}, month = {2020 May 22}, pages = {2581}, abstract = {

We study the remarkable behaviour of dense active matter comprising self-propelled particles at large P{\'e}clet numbers, over a range of persistence times, from τ\ {\textrightarrow}\ 0, when the active fluid undergoes a slowing down of density relaxations leading to a glass transition as the active propulsion force f reduces, to τ\ {\textrightarrow}\ $\infty$, when as f reduces, the fluid jams at a critical point, with stresses along force-chains. For intermediate τ, a decrease in f drives the fluid through an intermittent phase before dynamical arrest at low f. This intermittency is a consequence of periods of jamming followed by bursts of plastic yielding associated with Eshelby deformations. On the other hand, an increase in f leads to an increase in the burst frequency; the correlated plastic events result in large scale vorticity and turbulence. Dense extreme active matter brings together the physics of glass, jamming, plasticity and turbulence, in a new state of driven classical matter.

}, issn = {2041-1723}, doi = {10.1038/s41467-020-16130-x}, author = {Mandal, Rituparno and Bhuyan, Pranab Jyoti and Chaudhuri, Pinaki and Dasgupta, Chandan and Rao, Madan} } @article {39427, title = {A random first-order transition theory for an active glass.}, journal = {Proc Natl Acad Sci U S A}, volume = {115}, year = {2018}, month = {2018 Jul 24}, pages = {7688-7693}, abstract = {

How does nonequilibrium activity modify the approach to a glass? This is an important question, since many experiments reveal the near-glassy nature of the cell interior, remodeled by activity. However, different simulations of dense assemblies of active particles, parametrized by a self-propulsion force, [Formula: see text], and persistence time, [Formula: see text], appear to make contradictory predictions about the influence of activity on characteristic features of glass, such as fragility. This calls for a broad conceptual framework to understand active glasses; here, we extend the random first-order transition (RFOT) theory to a dense assembly of self-propelled particles. We compute the active contribution to the configurational entropy through an effective model of a single particle in a caging potential. This simple active extension of RFOT provides excellent quantitative fits to existing simulation results. We find that whereas [Formula: see text] always inhibits glassiness, the effect of [Formula: see text] is more subtle and depends on the microscopic details of activity. In doing so, the theory automatically resolves the apparent contradiction between the simulation models. The theory also makes several testable predictions, which we verify by both existing and new simulation data, and should be viewed as a step toward a more rigorous analytical treatment of active glass.

}, issn = {1091-6490}, doi = {10.1073/pnas.1721324115}, author = {Nandi, Saroj Kumar and Mandal, Rituparno and Bhuyan, Pranab Jyoti and Dasgupta, Chandan and Rao, Madan and Gov, Nir S} } @article {29622, title = {Glassy swirls of active dumbbells.}, journal = {Phys Rev E}, volume = {96}, year = {2017}, month = {2017 Oct}, pages = {042605}, abstract = {

Is an active glass different from a conventional passive glass? To address this, we study the dynamics of a dense binary mixture of soft dumbbells, each subject to an active propulsion force and thermal fluctuations. This dense assembly shows dynamical arrest, first to a translational and then to a rotational glass, as one reduces temperature T or the self-propulsion force f. We monitor the dynamics along an iso-relaxation-time contour in the (T-f) plane. We find dramatic differences both in the fragility and in the nature of dynamical heterogeneity, which characterize the onset of glass formation-the activity-induced glass exhibits large swirls or vortices, whose scale is set by activity, and it appears to diverge as one approaches the glass transition. This large collective swirling movement should have implications for collective cell migration in epithelial layers. We construct continuum hydrodynamic equations for the simulated system, and we show that the observed behavior of this growing dynamic length scale can be understood from these equations.

}, issn = {2470-0053}, doi = {10.1103/PhysRevE.96.042605}, author = {Mandal, Rituparno and Bhuyan, Pranab Jyoti and Chaudhuri, Pinaki and Rao, Madan and Dasgupta, Chandan} } @article {8348, title = {Active fluidization in dense glassy systems.}, journal = {Soft Matter}, volume = {12}, year = {2016}, month = {2016 Jul 20}, pages = {6268-76}, abstract = {

Dense soft glasses show strong collective caging behavior at sufficiently low temperatures. Using molecular dynamics simulations of a model glass former, we show that the incorporation of activity or self-propulsion, f0, can induce cage breaking and fluidization, resulting in the disappearance of the glassy phase beyond a critical f0. The diffusion coefficient crosses over from being strongly to weakly temperature dependent as f0 is increased. In addition, we demonstrate that activity induces a crossover from a fragile to a strong glass and a tendency of active particles to cluster. Our results are of direct relevance to the collective dynamics of dense active colloidal glasses and to recent experiments on tagged particle diffusion in living cells.

}, issn = {1744-6848}, doi = {10.1039/c5sm02950c}, author = {Mandal, Rituparno and Bhuyan, Pranab Jyoti and Rao, Madan and Dasgupta, Chandan} }