arXiv subjects

Antina Ghosh

Publications and source records attributed to Antina Ghosh.

8 recordsLinked to original sources

arXiv2024

Onset of slow dynamics in dense suspensions of active colloids

Slow relaxation and heterogeneous dynamics are characteristic features of glasses. The presence of glassy dynamics in nonequilibrium systems, such as active matter, is of significant interest due to its implications for living systems and material science. In this study, we use dense suspensions of self-propelled Janus particles moving on a substrate to investigate the onset of slow dynamics. Our findings show that dense active suspensions exhibit several hallmark features of slow dynamics similar to systems approaching equilibrium. The relaxation time fits well with the Vogel-Fulcher-Tamman (VFT) equation, and the system displays heterogeneous dynamics. Furthermore, increasing the activity leads to faster relaxation of the system, and the glass transition density predicted by the VFT equation shifts to higher densities. The measurement of the cage length and persistence length reveal they are of the same order over the range of activities explored in our study. These results are in agreement with recent particle simulations.

cond-mat.soft↗

arXiv2023

Microscopic strain correlations in sheared amorphous solids

We investigate spatial correlations of strain fluctuations in sheared colloidal glasses and simulations of sheared amorphous solids. The correlations reveal a quadrupolar symmetry reminiscent of the strain field due to an Eshelby's inclusion. However, they display an algebraic decay $1/r^α$, where the exponent $α$ is close to $1$ in the steady state, unlike the Eshelby field, for which $α=3$ . The exponent takes values between $3$ to $1$ in the transient stages of deformation. We explain these observations using a simple model based on interacting Eshelby inclusions. As the system is sheared beyond the linear response to plastic flow, the density correlations of inclusions are enhanced and it emerges as key to understanding the elastoplastic response of the system to applied shear.

physics.app-ph↗

arXiv2019

Modelling of strain fields in sheared colloidal glasses using Eshelby inclusions

When amorphous solids are strained they display elastic deformation at small strain, however, beyond a critical strain they yield and begin to flow plastically. The origin of this plasticity lies in the irreversible rearrangement of particles. Such rearrangements have been shown to give rise to a long-ranged quadrupolar strain field, similar to Eshebly's spherical inclusions. However, their spatio-temporal organisation at finite temperatures and finite shear rate remains unclear. Here, we have investigated the strain field in sheared colloidal glasses. We show that the strain field in homogeneous flows can be modelled using a distribution of Eshelby inclusions. In particular, we show that the non-trivial decay of spatial strain correlations in sheared colloidal glasses is a result of elastic interactions between plastic rearrangements that form at spatially correlated locations.

cond-mat.soft↗

arXiv2017

Direct observation of percolation in the yielding transition of colloidal glasses

When strained beyond the linear regime, soft colloidal glasses yield to steady-state plastic flow in a way that is similar to the deformation of conventional amorphous solids. Due to the much larger size of the colloidal particles with respect to the atoms comprising an amorphous solid, colloidal glasses allow to obtain microscopic insight into the nature of the yielding transition, as we illustrate here combining experiments, atomistic simulations, and mesoscopic modeling. Our results unanimously show growing clusters of non-affine deformation percolating at yielding. In agreement with percolation theory, the spanning cluster is fractal with a fractal dimension d_f~2, and the correlation length diverges upon approaching the critical yield strain. These results indicate that percolation of highly non-affine particles is the hallmark of the yielding transition in disordered glassy systems.

cond-mat.soft↗

arXiv2014

Jamming Percolation in Three Dimensions

We introduce a three-dimensional model for jamming and glasses, and prove that the fraction of frozen particles is discontinuous at the directed-percolation critical density. In agreement with the accepted scenario for jamming- and glass-transitions, this is a mixed-order transition; the discontinuity is accompanied by diverging length- and time-scales. Because one-dimensional directed-percolation paths comprise the backbone of frozen particles, the unfrozen rattlers may use the third dimension to travel between their cages. Thus the dynamics are diffusive on long-times even above the critical density for jamming.

cond-mat.stat-mech↗

arXiv2011

Connecting Structural Relaxation with the Low Frequency Modes in a Hard-Sphere Colloidal Glass

Structural relaxation in hard-sphere colloidal glasses has been studied using confocal microscopy. The motion of individual particles is followed over long time scales to detect the rearranging regions in the system. We have used normal mode analysis to understand the origin of the rearranging regions. The low frequency modes, obtained over short time scales, show strong spatial correlation with the rearrangements that happen on long time scales.

cond-mat.soft↗

arXiv2011

Low energy modes and Debye behaviour in a colloidal crystal

We study the vibrational spectrum and the low energy modes of a three dimensional colloidal crystal using confocal microscopy. This is done in a two-dimensional cut through a three-dimensional crystal. We find that the observed density of states is incompatible with the standard Debye form in either two or three dimensions. These results are confirmed by numerical simulations. We show that an effective theory for the projections of the modes onto the two-dimensional cut describes the experimental and simulation data in a satisfactory way.

cond-mat.soft↗

arXiv2009

Density of states of colloidal glasses

Glasses are structurally liquid-like, but mechanically solid-like. Most attempts to understand glasses start from liquid state theory. Here we take the opposite point of view, and use concepts from solid state physics. We determine the vibrational modes of a colloidal glass experimentally, and find soft low-frequency modes that are very different in nature from the usual acoustic vibrations of ordinary solids. These modes extend over surprisingly large length scales.

cond-mat.soft↗