arXiv subjects

Awaneesh Singh

Publications and source records attributed to Awaneesh Singh.

14 recordsLinked to original sources

arXiv2024

Segregation Kinetics of Miktoarm Star Polymers: A Dissipative Particle Dynamics Study

We study the phase separation kinetics of miktoarm star polymer (MSP) melts and blends with diverse architectures using dissipative particle dynamics simulations. Our study focuses on symmetric and asymmetric miktoarm star polymer (SMSP/AMSP) mixtures based on arm composition and number. For a fixed MSP chain size, the characteristic microphase-separated domains initially show diffusive growth with a growth exponent $\phi \sim 1/3$ for both melts that gradually crossover to saturation at late times. The simulation results demonstrate that the evolution morphology of SMSP melts exhibits perfect dynamic scaling with varying arm numbers; the time scale follows a power-law decay with an exponent $\theta \simeq 1$ as the number of arms increases. The structural constraints on AMSP melts cause the domain growth rate to decrease as the number of one type of arms increases while their length remains fixed. This increase in the number of arms for AMSP corresponds to increased off-criticality. The saturation length in AMSP follows a power law increase with an exponent $\lambda \simeq 2/3$ as off-criticality decreases. Additionally, macrophase separation kinetics in SMSP/AMSP blends show a transition from viscous ($\phi \sim 1$) to inertial ($\phi \sim 2/3$) hydrodynamic growth regimes at late times; this exhibits the same dynamical universality class as linear polymer blends, with slight deviations at early stages.

cond-mat.soft↗

arXiv2022

Phase separation kinetics of block copolymer melts confined under moving parallel walls: a DPD study

We use dissipative particle dynamics (DPD) simulations to study the effect of shear on domain morphology and kinetics of microphase separating critical diblock copolymer (BCP) bulk melts. The melt is confined within two parallel solid walls at the top and bottom of the simulation box. The shear is induced by allowing the walls to move in a direction with a specific velocity. We explore the following cases: (i) walls are fixed, (ii) only the top wall moves, (iii) both walls move in the same direction, and (iv) both walls move in opposite directions. After the temperature quench, we monitor the effect of shear on evolution morphology, the scaling behavior of the system, and the characteristic length scale and growth. The characteristic length scale follows typical power-law behavior at early times and saturates at late times when both walls are fixed. The length scale changes significantly with shear caused by wall velocities. The usual lamellar morphology, which is not achieved for case 1 within the considered simulation time steps, is noticed much earlier for the nonzero wall velocity cases. Specifically, it is seen much before in case 4 than in the other cases. We find that the shear viscosity decreases (shear-thinning) with wall velocity (shear rate) for all the cases at a given coarsening time. Overall, we report the influence rule of shear rates on microphase separation kinetics of BCP melts. This study can provide a scheme to anticipate and design anisotropic microstructures under the application of externally controlled wall shear that may further guide in producing the various composite materials with superior mechanical and physical properties.

cond-mat.soft↗

arXiv2022

Dissipative particle dynamics simulation study on ATRP-brush modification of variably shaped surfaces and biopolymer adsorption

We present a dissipative particle dynamics (DPD) simulation study on the surface modification of initiator embedded microparticles (MPs) of different shapes via atom transfer radical polymerization (ATRP) brush growth. The surface-initiated ATRP-brush growth leads to the formation of a more globular MP shape. We perform the comparative analysis of ATRP-brush growth on three different forms of particle surfaces: cup surface, spherical surface, and flat surface (rectangular/disk-shaped). First, we establish the chemical kinetics of the brush growth: the monomer conversion and the reaction rates. We next argue the structure changes (shape-modification) of brush-modified surfaces by computing the radial distribution function, spatial density distribution, radius of gyration, hydrodynamic radius, and shape factor. The polymer brush-modified particles are well known as the carrier materials for enzyme immobilization. Finally, we study the biopolymer adsorption on ATRP-brush modified particles in a compatible solution. In particular, we explore the effect of ATRP-brush length, biopolymer chain length, and concentration on the adsorption process. Our results illustrate the enhanced biopolymer adsorption with increased brush length, initiator concentration, and biopolymer concentration. Most importantly, the flat surface loads more biopolymers than the other two surfaces when adsorption reaches saturation. The experimental results verified the same, considering the disk-shaped flat surface particle, cup, and spherical particles.

cond-mat.soft↗

arXiv2021

Phase separation kinetics of binary mixture in the influence of bond disorder: Sensitivity to quench temperature

Morphologies in phase separating systems can significantly influence the final properties of materials. We present extensive Monte Carlo (MC) simulation results on the segregation kinetics of the critical binary (AB) mixture with a fraction of bond disorder (BD) introduced in a regular manner. We focus on studying the effect of various quench temperatures on the growth kinetics and scaling properties of evolving morphologies. The two-dimensional (2d) kinetic Ising system with conserved spin exchange kinetics is used to model the system. We observe that domain morphologies change from their usual interconnected bicontinuous isotropic patterns at zero BD to short strips and lamellar patterns (anisotropy) with increasing BD at shallow quench. The domain evolution remains extremely slow at deep quench and for lower fractions of BD, and thus, morphologies appear very similar; however, we observed lamellar patterns at high BD. The scaling behavior represented by the correlation function and the structure factor changes significantly with quench depths for a higher fraction of BD. In contrast, a tiny deviation from the scaling is observed at a lower fraction of disorder for shallow quenches. The growth law is consistent with the Lifshitz-Slyozov (LS) growth law (\phi->1/3) for shallow quench and at low fractions of BD studied here. At a high fraction of BD, the length scale crossovers gradually from an early time LS growth to the diffusion dynamics (\phi->1/2) during intermediate times for both deep and shallow quenches. The domain growth freezes (\phi->0) to a finite size when the system evolves to an equilibrium (stable) lamellar morphology in the asymptotic time limit on the time scale of our simulation. However, no significant changes are observed in the scaling behavior at lower fractions of BD for the deep quench.

cond-mat.soft↗

arXiv2020

Photo-induced bond breaking during phase separation kinetics of block copolymer melts: A dissipative particle dynamics study

Using dissipative particle dynamics (DPD) simulation method, we study the phase separation dynamics in block copolymer (BCP) melt in $d=3$, subjected to external stimuli such as light. An initial homogeneous BCP melt is rapidly quenched to a temperature $T < T_c$, where $T_c$ is the critical temperature. We then let the system go through alternate light "on" and "off" cycles. An on-cycle breaks the stimuli-sensitive bonds connecting both the blocks A and B in BCP melt, and during the off-cycle, broken bonds reconnect. By simulating the effect of light, we isolate scenarios where phase separation begins with the light off (set 1); the cooperative interactions within the system allow it to undergo microphase separation. When the phase separation starts with the light on (set 2), the system undergoes macrophase separation due to the bond breaking. Here, we report the role of alternate cycles on domain morphology by varying bond-breaking probability for both the sets 1 and 2, respectively. We observe that the scaling functions depend upon the conditions mentioned above that change the time scale of the evolving morphologies in various cycles. However, in all the cases, the average domain size respects the power-law growth: $R(t)\sim t^{\phi}$ at late times, here $\phi$ is the dynamic growth exponent. After a short-lived diffusive growth ($\phi \sim 1/3$) at early times, $\phi$ illustrates a crossover from the viscous hydrodynamic ($\phi \sim 1$) to the inertial hydrodynamic ($\phi \sim 2/3$) regimes at late times.

cond-mat.soft↗

arXiv2018

Role of a polymeric component in the phase separation of ternary fluid mixtures: A dissipative particle dynamics study

We present the results from dissipative particle dynamics (DPD) simulations of phase separation dynamics in ternary (ABC) fluids mixture in $d=3$ where components A and B represent the simple fluids and component C represents a polymeric fluid. Here, we study the role of polymeric fluid (C) on domain morphology by varying composition ratio, polymer chain length, and polymer stiffness. We observe that the system under consideration lies in the same dynamical universality class as a simple ternary fluids mixture. However, the scaling functions depend upon the parameters mentioned above as they change the time scale of the evolution morphologies. In all cases, the characteristic domain size follows: $l(t) \sim t^{\phi} $ with dynamic growth exponent $\phi$, showing a crossover from the viscous hydrodynamic regime $(\phi=1)$ to the inertial hydrodynamic regime $(\phi=2/3)$ in the system at late times.

cond-mat.soft↗

arXiv2017

Effect of bond-disorder on the phase-separation kinetics of binary mixtures: a Monte Carlo simulation study

We present Monte Carlo (MC) simulation studies of phase separation in binary (AB) mixtures with bond-disorder that is introduced in two different ways: (i) at randomly selected lattice sites and (ii) at regularly selected sites. The Ising model with spin exchange (Kawasaki) dynamics represents the segregation kinetics in conserved binary mixtures. We find that the dynamical scaling changes significantly by varying the number of disordered sites in the case where bond-disorder is introduced at the randomly selected sites. On the other hand, when we introduce the bond-disorder in a regular fashion, the system follows the dynamical scaling for the modest number of disordered sites. For higher number of disordered sites, the evolution morphology illustrates a lamellar pattern formation. Our MC results are consistent with the Lifshitz-Slyozov (LS) power-law growth in all the cases.

cond-mat.stat-mech↗

arXiv2015

Ordering Dynamics in Neuron Activity Pattern Model: An insight to Brain Functionality

We study the ordering kinetics in $d=2$ ferromagnets which corresponds to populated neuron activities with long-ranged interactions, $V(r)\sim r^{-n}$ associated with short-ranged interaction. We present the results from comprehensive Monte Carlo (MC) simulations for the nonconserved Ising model with $n\ge 2$. Our results of long-ranged neuron kinetics are consistent with the same dynamical behavior of short-ranged case ($n > 4$). The calculated characteristic length scale in long-ranged interaction is found to be $n$ dependent ($L(t)\sim t^{1/(n-2)}$), whereas short-ranged interaction follows $L(t)\sim t^{1/2}$ law and approximately preserve universality in domain kinetics. Further, we did the comparative study of phase ordering near the critical temperature which follows different behaviours of domain ordering near and far critical temperature but follows universal scaling law.

q-bio.NC↗

arXiv2013

Kinetics of Phase Transitions in Quark Matter

We study the kinetics of chiral transitions in quark matter using a phenomenological framework (Ginzburg-Landau model). We focus on the effect of inertial terms on the coarsening dynamics subsequent to a quench from the massless quark phase to the massive quark phase. The domain growth process shows a crossover from a fast inertial regime [with $L(t) \sim t (\ln t)^{1/2}$] to a diffusive Cahn-Allen regime [with $L(t)\sim t^{1/2}$].

hep-ph↗

arXiv2012

Domain Growth in Chiral Phase Transitions: Inertial Dynamics

We investigate the kinetics of phase transitions for chiral symmetry breaking in heavy-ion collisions. We use a Langevin description for order-parameter kinetics in the chiral transition. The Langevin equation of motion includes {\it dissipation} and an {\it inertial term}. We study the ordering dynamics subsequent to a quench from the massless quark phase to the massive quark phase, and discuss the effect of inertia on the growth kinetics.

hep-ph↗

arXiv2011

Kinetics of Chiral Phase Transitions in Quark Matter

We study the kinetics of chiral transitions in quark matter using a microscopic framework (Nambu-Jona-Lasinio model) and a phenomenological model (Ginzburg-Landau free energy). We focus on the coarsening dynamics subsequent to a quench from the massless quark phase to the massive quark phase. The morphology of the ordering system is characterized by the scaling of the order-parameter correlation function. The domain growth process obeys the Allen-Cahn growth law, $L(t)\sim t^{1/2}$. We also study the growth of bubbles of the stable massive phase from the metastable massless phase.

hep-ph↗

arXiv2011

Domain Growth and Ordering Kinetics in Dense Quark Matter

The kinetics of chiral transitions in quark matter is studied in a two flavor Nambu-Jona-Lasinio model. We focus on the phase ordering dynamics subsequent to a temperature quench from the massless quark phase to the massive quark phase. We study the dynamics by considering a phenomenological model (Ginzburg-Landau free-energy functional). The morphology of the ordering system is characterized by the scaling of the order-parameter correlation function.

hep-ph↗

arXiv2011

Domain Growth in Chiral Phase Transitions

We investigate the kinetics of chiral phase transitions in quark matter. We discuss the phase diagram of this system in both a microscopic framework (using the Nambu-Jona-Lasinio model) and a phenomenological framework (using a Landau free energy). Then, we study the far-from-equilibrium coarsening dynamics subsequent to a quench from the chirally-symmetric phase to the massive quark phase. Depending on the nature of the quench, the system evolves via either {\it spinodal decomposition} or {\it nucleation and growth}. The morphology of the ordering system is characterized using the order-parameter correlation function, structure factor, domain growth laws, etc.

hep-ph↗

arXiv2010

Kinetics of chiral phase transition in hot and dense quark matter

The kinetics of chiral transitions in hot and dense quark matter is studied via a microscopic framework (Nambu-Jona-Lasinio model) and a phenomenological model (Ginzburg-Landau free energy). We focus on the far-from-equilibrium ordering dynamics subsequent to a quench from the massless quark phase to the massive quark phase. The morphology of the ordering system is characterized by the scaling of the order-parameter correlation function. The domain growth process obeys the Allen-Cahn growth law, $L(t)\sim t^{1/2}$. We also study the growth of bubble of the stable massive phase in a background of the metastable massive phase.

hep-ph↗