arXiv subjects

Aritra Santra

Publications and source records attributed to Aritra Santra.

7 recordsLinked to original sources

arXiv2026

Universality of the deswelling of tangentially active polymer chains in dilute solutions

Dilute solutions of linear polymer chains with tangentially active monomeric beads are simulated using a Brownian dynamics (BD) algorithm over a range of solvent quality in the thermal crossover regime between $θ$ and athermal solvents. The conformational changes with increasing P{é}clet number ($Pe$) (which is proportional to the strength of activity) suggest deswelling of the chains resulting in a collapse of the radius of gyration data to a random walk (RW) statistics at a unique value of $Pe$, independent of the solvent quality. The swelling behaviour of active polymers in the crossover regime relative to their size at the $θ$ state is found to follow the same universal characteristics as that of passive polymer chains. Furthermore, based on polymer blob theory we present a novel scaling of the thermal blob size with tangential activity of the monomeric beads which leads to the definition of a renormalized solvent quality parameter for active polymers. Altogether, this work establishes a connection between the configurational properties of active polymers and scaling laws in polymer physics, which provides a useful framework to study the dynamics of activity induced motion of polymeric molecules for various applications in biophysics and other related areas.

cond-mat.soft↗

arXiv2026

Rigidity transition in polydisperse shear-thickening suspensions

Shear thickening suspensions of non-Brownian polydisperse particles are simulated in 2D using a discrete element method based algorithm (LF-DEM) at high packing fractions ($ϕ$) and large non-dimensional stresses ($σ$). Rigidity analysis of the stress induced particle clusters is carried out using \textit{pebble game} algorithm for polydisperse suspensions and compared with the statistically equivalent bidisperse systems. A critical value of the packing fraction, $ϕ_c$, close to the shear jamming transition, $ϕ_J^μ$, ($ϕ_c<ϕ_J^μ$) is obtained where rigid particle clusters begin to grow sharply. The growth is found to be characterized by a critical transition of an order parameter ($f_\text{rig}$), defined by the fraction of particles in rigid clusters which scales as, $f_\text{rig}\sim (ϕ-ϕ_c)^β$ for $ϕ>ϕ_c$, and by the susceptibility scaling, $χ_\text{rig}\sim|ϕ-ϕ_c |^{-γ}$, with exponents having values consistent with the critical exponents in 2D percolation transition. The variations of $f_\text{rig}$ and $χ_\text{rig}$ in polydisperse suspensions are found to be identical to that of the statistically equivalent bidisperse suspensions. Finite size scaling analysis shows a divergence of correlation length near $ϕ_{c_\infty}$ following critical exponent $ν\approx 1.33$, in agreement with the 2D percolation theory. Furthermore, $ϕ_c$ and $ϕ_J^μ$ are found to vary non-monotonically with polydispersity index and depend on the particle stiffness.

cond-mat.soft↗

arXiv2025

Rigid clusters in shear-thickening suspensions: a nonequilibrium critical transition

The onset and growth of rigid clusters in a two-dimensional (2D) suspension in shear flow are studied by numerical simulations. The suspension exhibits the lubricated-to-frictional rheology transition, but the key results here are for stresses above the levels that cause extreme shear-thickening. At large solid fraction, $ϕ$, but below the stress-dependent jamming fraction, we find a critical $ϕ_{c}(σ,μ)$ where $σ$ is a dimensionless shear stress and $μ$ is the interparticle friction coefficient. For $ϕ>ϕ_c$, the proportion of particles in rigid clusters grows sharply, as $f_{\rm rig} \sim |ϕ-ϕ_{c}|^β$ with $β=1/8$. The fluctuations in the fraction of particles in rigid clusters yield a susceptibility measure $χ_{\rm rig} \sim |ϕ-ϕ_{c}|^{-γ}$ with $γ= 7/4$. The system is thus found to exhibit criticality. The results are shown to depend on an effective field $h(μ)$, which provides data collapse near $ϕ_c$ for both $f_{\rm rig}$ and $χ_{\rm rig}$. This behavior occurs over a range of stresses, with $ϕ_c(σ,μ)$ increasing as the stress decreases.

cond-mat.soft↗

arXiv2024

Evanescent Gels: Competition Between Sticker Dynamics and Single Chain Relaxation

Solutions of polymer chains are modelled using non-equilibrium Brownian dynamics simulations, with physically associative beads which form reversible crosslinks to establish a system-spanning physical gel network. Rheological properties such as the zero-shear-rate viscosity and relaxation modulus are investigated systematically as functions of polymer concentration and the binding energy between associative sites. It is shown that a system-spanning network can form regardless of binding energy at sufficiently high concentration. However, the contribution to the stress sustained by this physical network can decay faster than other relaxation processes, even single chain relaxations. If the polymer relaxation time scales overlap with short-lived associations, the mechanical response of a gel becomes ``evanescent'', decaying before it can be rheologically observed, even though the network is instantaneously mechanically rigid. In our simulations, the concentration of elastically active chains and the dynamic modulii are computed independently. This makes it possible to combine structural and rheological information to identify the concentration at which the sol-gel transition occurs as a function of binding energy. Further, it is shown that the competition of scales between the sticker dissociation time and the single-polymer relaxation time determines if the gel is in the evanescent regime.

cond-mat.soft↗

arXiv2022

Universality of dilute solutions of ring polymers in the thermal crossover region between $θ$ and athermal solvents

Due to their unique topology of having no chain ends, dilute solutions of ring polymers exhibit behaviour distinct from their linear chain counterparts. The universality of their static and dynamic properties, as a function of solvent quality $z$ in the thermal crossover regime between $θ$ and athermal solvents, is studied here using Brownian dynamics simulations. The universal ratio $U_{\text{RD}}$ of the radius of gyration $R_g$ to the hydrodynamic radius $R_H$ is determined, and a comparative study of the swelling ratio $α_g$ of the radius of gyration, the swelling ratio $α_H$ of the hydrodynamic radius, and the swelling ratio $α_X$ of the mean polymer stretch $X$ along the $x$-axis, for linear and ring polymers, is carried out. The ratio $U_{\text{RD}}$ for dilute ring polymer solutions is found to converge asymptotically to a constant value as $z \to \infty$, which is a major difference from the behaviour of solutions of linear chains, where no such asymptotic limit exists. Additionally, the ratio of the mean stretch along the $x$-axis to the hydrodynamic radius, $(X/R_H)$, is found to be independent of $z$ for polymeric rings, unlike in the case for linear polymers. These results indicate a fundamental difference in the scaling of static and dynamic properties of rings and linear chains in the thermal crossover regime.

cond-mat.soft↗

arXiv2021

Universal scaling and characterisation of gelation in associative polymer solutions

A Brownian dynamics algorithm is used to describe the static behaviour of associative polymer solutions. Predictions for the fractions of stickers bound by intra-chain and inter-chain association, as a function of system parameters, such as the number of stickers, the number of monomers between stickers, the solvent quality, and concentration are obtained. A systematic comparison with the scaling relations predicted by the mean-field theory of Dobrynin (Macromolecules, 37, 3881, 2004) is carried out. Different regimes of scaling behaviour are identified depending on the monomer concentration, the density of stickers on a chain, and the solvent quality for backbone monomers. Simulation results validate the predictions of the mean-field theory across a wide range of parameter values in all the scaling regimes. The value of the des Cloizeaux exponent proposed by Dobrynin for sticky polymer solutions, is shown to lead to a collapse of simulation data for all the scaling relations considered here. Three different signatures for the characterisation of gelation are identified, with each leading to a different value of the concentration at the sol-gel transition. The modified Flory-Stockmayer expression is found to be validated by simulations for all three gelation signatures. Simulation results confirm the prediction of scaling theory for the gelation line that separates sol and gel phases, when the modified Flory-Stockmayer expression is used. Phase separation is found to occur with increasing concentration for systems in which the backbone monomers are under theta-solvent conditions, and is shown to coincide with a breakdown in the predictions of scaling theory.

cond-mat.soft↗

arXiv2019

Universality of the collapse transition of sticky polymers

The universality of the swelling of the radius of gyration of a homopolymer relative to its value in the $θ$ state, independent of polymer-solvent chemistry, in the crossover regime between $θ$ and athermal solvent conditions, is well known. Here we study, by Brownian dynamics, a polymer model where a subset of monomers is labelled as "stickers". The mutual interaction of the stickers is more attractive than those of the other ("backbone") monomers, and has the additional important characteristic of "functionality" $φ$, i.e., the maximum number of stickers that can locally bind to a given sticker. A saturated bond formed in this manner remains bound until it breaks due to thermal fluctuations, a requirement which can be viewed as an additional Boolean degree of freedom that describes the bonding. This, in turn, makes the question of the order of the collapse transition a non-trivial one. Nevertheless, for the parameters that we have studied (in particular, $φ=1$), we find a standard second-order $θ$ collapse, using a renormalised solvent quality parameter that takes into account the increased average attraction due to the presence of stickers. We examine the swelling of the radius of gyration of such a sticky polymer relative to its value in the altered $θ$ state, using a novel potential to model the various excluded volume interactions that occur between the monomers on the chain. We find that the swelling of such sticky polymers is identical to the universal swelling of homopolymers in the thermal crossover regime. Additionally, for our model, the Kuhn segment length under $θ$ conditions is found to be the same for chains with and without stickers.

cond-mat.soft↗