arXiv subjects

Gaurav P. Shrivastav

Publications and source records attributed to Gaurav P. Shrivastav.

10 recordsLinked to original sources

arXiv2025

Static and dynamic properties of a binary, symmetric mixture of ultrasoft particles in the vicinity of criticality

We investigate the static and the dynamic properties of an binary, equimolar, size-symmetric mixture of ultrasoft particles in the vicinity of the critical point of the system. Based on the generalized exponential potential (GEM) of order four for the particle interaction and using extensive molecular dynamics simulations in the canonical ensemble we investigate the above mentioned properties for various scenarios: we consider several super- and subcritical states, we expose the system to rapid quenches and to external shearing forces. Based on an accurate determination of the phase diagram and of the location of the critical point we study the static structure of the system in terms of particle-based radial distribution functions. As systems of GEM particles are prone to cluster formation we complement these investigations by a detailed analysis of the composition of the clusters and of their spatial correlations for the different scenarios introduced above. Furthermore we analyse the temperature dependence of the diffusivity of the particles and of the shear viscosity of the system. All these data provide a detailed and profound insight into the properties of the system under phase separation conditions and near criticality.

cond-mat.soft↗

arXiv2024

Phase separation dynamics in a symmetric binary mixture of ultrasoft particles

Phase separation plays an role in determining the self-assembly of biological and soft-matter systems. In biological systems, liquid-liquid phase separation inside a cell leads to the formation of various macromolecular aggregates. The interaction among these aggregates is soft, i.e., these can significantly overlap at a small energy cost. From the computer simulation point of view, these complex macromolecular aggregates are generally modeled by the so-called soft particles. The effective interaction between two particles is defined via the generalized exponential potential (GEM-n) with n = 4. Here, using molecular dynamics simulations, we study the phase separation dynamics of a size-symmetric binary mixture of ultrasoft particles. We find that when the mixture is quenched to a lower temperature below the critical temperature, the two components spontaneously start to separate. Domains of the two components form, and the equal-time order parameter reveals that the domains grow in a power-law manner with exponent 1/3, which is consistent with the Lifshitz-Slyozov law for conserved systems. Further, the static structure factor shows a power-law decay with exponent 4 consistent with the Porod law.

cond-mat.soft↗

arXiv2021

On the yielding of a defect-rich model crystal under shear: insights from molecular dynamics simulations

Point defects in real crystals at finite temperatures are inevitable. Their dynamics severely influence the mechanical properties of crystals under shear giving rise to nonlinear effects such as ductility. Therefore, it is crucial to explore the interplay of the equilibrium point-defect diffusion timescales and shear-induced timescales to understand the plastic deformation of crystals. Using extensive nonequilibrium molecular dynamics simulations, we present a study on the yielding behavior of cluster crystals (CC), an archetypal model for defect-rich crystals where the crystalline structure is characterized by multiple occupancies (cluster) of particles at a lattice site. In equilibrium, particles diffuse via site-to-site hopping keeping the crystalline structure intact. We consider the CCs at a fixed density and different temperatures where it remains in the FCC structure, and the diffusion timescales of particles vary depending on the temperature. We choose the range of shear rates, which covers timescales higher and much lower than the equilibrium diffusion timescales at high temperatures. For the considered range of shear rates and temperatures, both the macro and microscopic responses of CCs to the shear suggest that the yielding scenario remains independent of the diffusion of particles. It involves the plastic deformation of the underlying crystalline structure. The averaged local bond order parameters and local angle measurements demonstrate the structural changes and cooperative movement of the center of masses of the clusters close to the yield point. A comparison with the soft-sphere (SS) FCC crystal reveals the similarities in the yielding behavior of both systems. Nonetheless, diffusion of particles influences certain features, such as a less prominent increase in the local bond order parameters and local angles close to the yield point.

cond-mat.soft↗

arXiv2020

Flow heterogeneities in supercooled liquids and glasses under shear

Using extensive non-equilibrium molecular dynamics simulations, we investigate a glassforming binary Lennard-Jones mixture under shear. Both supercooled liquids and glasses are considered. Our focus is on the characterization of inhomogeneous flow patterns such as shear bands that appear as a transient response to the external shear. For the supercooled liquids, we analyze the crossover from Newtonian to non-Newtonian behavior with increasing shear rate $\dotγ$. Above a critical shear rate $\dotγ_c$ where a non-Newtonian response sets in, the transient dynamics are associated with the occurrence of short-lived vertical shear bands, i.e. bands of high mobility that form perpendicular to the flow direction. In the glass states, long-lived horizontal shear bands, i.e. bands of high mobility parallel to the flow direction, are observed in addition to vertical ones. The systems with shear bands are characterized in terms of mobility maps, stress-strain relations, mean-squared displacements, and (local) potential energies. The initial formation of a horizontal shear band provides an efficient stress release, corresponds to a local minimum of the potential energy, and is followed by a slow broadening of the band towards the homogeneously flowing fluid in the steady-state. Whether a horizontal or a vertical shear band forms cannot be predicted from the initial undeformed sample. Furthermore, we show that with increasing system size the probability for the occurrence of horizontal shear bands increases.

cond-mat.soft↗

arXiv2019

Steady-state rheology and structure of soft hybrid mixtures of liquid crystals and magnetic nanoparticles

Using non-equilibrium molecular dynamics simulations, we study the rheology of a model hybrid mixture of liquid crystals (LCs) and dipolar soft spheres (DSS) representing magnetic nanoparticles. The bulk isotropic LC-DSS mixture is sheared with different shear rates using Lees-Edwards periodic boundary conditions. The steady-state rheological properties and the effect of the shear on the microstructure of the mixture are studied for different strengths of the dipolar coupling, $λ$, among the DSS. We find that at large shear rates, the mixture shows a shear-thinning behavior for all considered values of $λ$. At low and intermediate values of $λ$, a crossover from Newtonian to non-Newtonian behavior is observed as the rate of applied shear is increased. In contrast, for large values of $λ$, such a crossover is not observed within the range of shear rates considered. Also, the extent of the non-Newtonian regime increases as $λ$ is increased. These features can be understood via the shear-induced changes of the microstructure. In particular, the LCs display a shear-induced isotropic-to-nematic transition at large shear rates with a shear-rate dependent degree of nematic ordering. The DSS show a shear-induced nematic ordering only for large values of $λ$, where the particles self-assemble into chains. Moreover, at large $λ$ and low shear rates, our simulations indicate that the DSS form ferromagnetic domains.

cond-mat.soft↗

arXiv2019

Non-monotonic response of a sheared magnetic liquid crystal to an external field

Utilizing molecular dynamics simulations, we report a non-monotonic dependence of the shear stress on the strength of an external magnetic field ($H$) in a liquid-crystalline mixture of magnetic and non-magnetic anisotropic particles. This non-monotonic behavior is in sharp contrast with the well-studied monotonic $H$-dependency of the shear stress in conventional ferrofluids, where the shear stress increases with $H$ until it reaches a saturation value. We relate the origin of this non-monotonicity to the competing effects of particle alignment along the shear-induced direction, on the one hand, and the magnetic field direction, on the other hand. To isolate the role of these competing effects, we consider a two-component mixture composed of particles with effectively identical steric interactions, where the orientations of a small fraction, i.e.\ the magnetic ones, are coupled to the external magnetic field. By increasing $H$ from zero, the orientations of the magnetic particles show a Fréederickz-like transition and eventually start deviating from the shear-induced orientation, leading to an increase in shear stress. Upon further increase of $H$, a demixing of the magnetic particles from the non-magnetic ones occurs which leads to a drop in shear stress, hence creating a non-monotonic response to $H$. Unlike the equilibrium demixing phenomena reported in previous studies, the demixing observed here is neither due to size-polydispersity nor due to a wall-induced nematic transition. Based on a simplified Onsager analysis, we rather argue that it occurs solely due to packing entropy of particles with different shear- or magnetic-field-induced orientations.

cond-mat.soft↗

arXiv2018

Anomalous transport of magnetic colloids in a liquid crystal-magnetic colloid mixture

We report an extensive molecular dynamics study on the translational dynamics of a hybrid system composed of dipolar soft spheres (DSS), representing ferromagnetic particles, suspended in a liquid crystal (LC) matrix. We observe that the LC matrix strongly modifies the dynamics of the DSS. In the isotropic regime, the DSS show a crossover from subdiffusive to normal diffusive behavior at long times, with an increase of the subdiffusive regime as the dipolar coupling strength is increased. In the nematic regime, the LC matrix, due to collective reorientation of LC particles, imposes a cylindrical confinement on the DSS chains. This leads to a diffusive dynamics of DSS along the nematic director and a subdiffusive dynamics (with an exponent $\sim 0.5$) in the perpendicular direction. The confinement provided by the LC matrix is also reflected by oscillatory behavior of the components of the velocity autocorrelation function of the DSS in the nematic phase.

cond-mat.soft↗

arXiv2011

Scattering Properties of Paramagnetic Ground States in the Three-Dimensional Random-Field Ising Model

We study the ground-state (T = 0) morphologies in the d = 3 random-field Ising model (RFIM) using a computationally efficient graph-cut method. We focus on paramagnetic states which arise for disorder strengths Δ> Δc, where Δc is the critical disorder strength at T = 0. These paramagnetic states consist of correlated "domains" of up and down spins which are separated by rough, fractal interfaces. They show novel scattering properties with a cusp singularity in the correlation function at short distances.

cond-mat.stat-mech↗

arXiv2010

Mass-Transport Models with Fragmentation and Aggregation

We present a review of nonequilibrium phase transitions in mass-transport models with kinetic processes like fragmentation, diffusion, aggregation, etc. These models have been used extensively to study a wide range of physical problems. We provide a detailed discussion of the analytical and numerical techniques used to study mass-transport phenomena.

cond-mat.stat-mech↗

arXiv2010

Mass-Transport Models with Multiple-Chipping Processes

We study mass-transport models with multiple-chipping processes. The rates of these processes are dependent on the chip size and mass of the fragmenting site. In this context, we consider k-chip moves (where k = 1, 2, 3, ....); and combinations of 1-chip, 2-chip and 3-chip moves. The corresponding mean-field (MF) equations are solved to obtain the steady-state probability distributions, P (m) vs. m. We also undertake Monte Carlo (MC) simulations of these models. The MC results are in excellent agreement with the corresponding MF results, demonstrating that MF theory is exact for these models.

cond-mat.stat-mech↗