arXiv subjects

Mohammad Fazelzadeh

Publications and source records attributed to Mohammad Fazelzadeh.

6 recordsLinked to original sources

arXiv2026

Flexibility Controls Active-Filament Transport in Crowded Landscapes

Active filaments, ranging from motor-driven biopolymers to elongated bacteria and worms, are paradigmatic examples of deformable active matter. How filament flexibility interacts with environmental heterogeneity to control their transport in crowded environments, however, remains poorly understood. Here, we perform large-scale Brownian dynamics simulations of tangentially driven active polymers moving through ordered and disordered obstacle arrays to map the long-time diffusion as a function of obstacle density and filament flexibility. We find that flexibility can either enhance or hinder transport depending on the structure of the medium. In disordered environments, transport is optimized at intermediate filament flexibility, whereas both highly flexible and semiflexible filaments diffuse more slowly. In contrast, dense ordered arrays enhance the mobility of semiflexible filaments by promoting directed motion along periodic channels. We identify three distinct transport regimes: (i) tortuosity-controlled diffusion of highly flexible filaments, characterized by trapping-and-hopping dynamics; (ii) confinement-assisted transport of moderately flexible filaments, which enhances diffusion in dense media; and (iii) persistence-controlled transport of semiflexible filaments, which facilitates diffusion in dense ordered media, but suppresses it in disordered media. Combining theory and simulations, we show that long-time diffusion is governed by confinement-induced changes in filament conformation and reorientation dynamics. Our work uncovers general transport principles for deformable active agents in heterogeneous environments and provides a predictive framework for active-filament navigation in complex porous landscapes.

cond-mat.soft↗

arXiv2024

Locomotion of Active Polymerlike Worms in Porous Media

We investigate the locomotion of thin, living T. tubifex worms, which display active polymerlike behavior, within quasi-2D arrays of cylindrical pillars, examining varying spatial arrangements and densities. These active worms spread in crowded environments, with a dynamics dependent on both the concentration and arrangement of obstacles. In contrast to passive polymers, our results reveal that in disordered configurations, increasing the pillar density enhances the long-time diffusion of our active polymer-like worms, while we observe the opposite trend in ordered pillar arrays. We found that in disordered media, living worms reptate through available curvilinear tubes, whereas they become trapped within pores of ordered media. Intriguingly, we show that reducing the worm's activity significantly boosts its spread, enabling passive sorting of worms by activity level. Our experimental observations are corroborated through simulations of the tangentially driven polymer model with matched persistence length predicting the same trends.

cond-mat.soft↗

arXiv2024

Conformation and dynamics of wet tangentially-driven active filaments

We explore the impact of hydrodynamic interactions on the conformational and dynamical properties of wet tangentially-driven active polymers using multiparticle collision dynamics simulations. By analyzing active filaments with varying degrees of flexibility, we find that fluid-mediated interactions significantly influence both their conformation and dynamics. These interactions cause polymer conformations to shrink relative to their dry counterparts, especially for semiflexible polymers at high activity levels, where the average size of wet chains becomes nearly three times smaller, due to local buckling of wet polymers. This hydrodynamic-induced shrinkage is a hallmark of active polymers, as fluid-mediated interactions do not affect conformational properties of passive polymers. Furthermore, for tangentially-driven polymers where activity and conformation are coupled, hydrodynamic interactions significantly enhance the orientational and translational dynamics compared to their dry counterparts.

cond-mat.soft↗

arXiv2024

Active string fluids and gels formed by dipolar active Brownian particles in 3D

Self-propelled particles possessing permanent magnetic dipole moments occur naturally in magnetotactic bacteria and in man-made systems like active colloids or micro-robots. Yet, the interplay between self-propulsion and anisotropic dipole-dipole interactions on dynamic self-assembly in three dimensions (3D) remains poorly understood. We conduct Brownian dynamics simulations of active dipolar particles in 3D, focusing on the low-density regime, where dipolar hard spheres tend to form chain-like aggregates and percolated networks with increasing dipolar coupling strength. We find that strong active forces override dipolar attractions, effectively inhibiting chain-like aggregation and network formation. Conversely, activating particles with low to moderate forces results in a fluid composed of active chains and rings. At strong dipolar coupling strengths, this active fluid transitions into an active gel, consisting of a percolated network of active chains. Although the overall structure of the active gel remains interconnected, the network experiences more frequent configurational rearrangements due to the reduced bond lifetime of active dipolar particles. Consequently, particles exhibit enhanced translational and rotational diffusion within the active fluid of strings and active gels compared to their passive counterparts. We quantify the influence of activity on aggregates topology, as they transition from branched structures to unconnected chains and rings. Our findings are summarized in a state diagram, delineating the impact of dipolar coupling strength and active force magnitude on the system.

cond-mat.soft↗

arXiv2023

Active motion of tangentially-driven polymers in periodic array of obstacles

We computationally investigate the active transport of tangentially-driven polymers with varying degrees of flexibility and activity in two-dimensional square lattices of obstacles. Tight periodic confinement induces notable conformational changes and distinct modes of transport for flexible and stiff active filaments. It leads to localization and caging of flexible polymers inside the inter-obstacle pores, while promoting more elongated conformations and enhanced diffusion for stiff polymers at low to moderate activity levels. The migration of flexible active polymers occurs via hopping events, where they unfold to move from one cage to another. In contrast, stiff chains travel mainly in straight paths within inter-obstacle channels, while occasionally changing their direction of motion. Both the duration of caging and persistent directed migration within the channels decrease with increasing the activity level. As a consequence, at high active forces polymers overcome confinement effects and transport within inter-obstacle pores as swiftly as those in free space. We explain the center of mass dynamics of semiflexible polymers in terms of active force and obstacle packing fraction by developing an approximate analytical theory.

cond-mat.soft↗

arXiv2023

Effects of inertia on conformation and dynamics of tangentially-driven active filaments

Active filament-like systems propelling along their backbone exist across the scales ranging from motor-driven bio-filaments to worms and robotic chains. In macroscopic active filaments such as chain of robots, in contrast to their microscopic counterparts, inertial effects on their motion cannot be ignored. Nonetheless, consequences of interplay between inertia and flexibility on shape and dynamics of active filaments remain unexplored. Here, we examine inertial effects on flexible tangentially-driven active polymer model pertinent to above examples and we determine the conditions under which inertia becomes important. Performing Langevin dynamics simulations of active polymers with underdamped and overdamped dynamics for a wide range of contour lengths and activities, we uncover striking inertial effects on conformation and dynamics at high activities. Inertial collisions increase the persistence length of active polymers and remarkably alter their scaling behavior. In stark contrast to passive polymers, inertia leaves its fingerprint at long times by an enhanced diffusion of the center of mass. We rationalize inertia-induced enhanced dynamics by analytical calculations of center of mass velocity correlations, applicable to any active polymer model, which reveal significant contributions from active force fluctuations convoluted by inertial relaxation.

cond-mat.soft↗