arXiv subjects

Marco De Corato

Publications and source records attributed to Marco De Corato.

13 recordsLinked to original sources

arXiv2025

The impact of pressure oscillations on bubble rising in shear-thinning fluids

We study the rising dynamics of a bubble driven into periodic volumetric oscillations by an external pressure driving within a highly viscous shear-thinning fluid. We perform axisymmetric direct numerical simulations employing the Carreau-Yasuda model to describe the rheological behavior of the fluid and the finite element method to discretize the equations. We carry out a parametric study of the bubble rising dynamics, changing the amplitude and the frequency of the external pressure driving, and the bubble radius. Due to the external pressure oscillations, the bubble undergoes volume changes that strain the liquid at much larger rates than those due to natural rising, causing the surrounding fluid viscosity to thin. The numerical results show that the rising dynamics become highly nonlinear and unsteady due to the interplay of the shear-thinning rheology and the external driving. As a result, the period-averaged rising velocity of the bubble can increase by orders of magnitude compared to its natural rising velocity. These nonlinear effects become progressively more important as the amplitude and the frequency of the pressure driving or the bubble radius are increased. Qualitatively, the simulation model agrees with previous experimental findings in terms of average rising velocity. However, the experiments exhibit terminal velocities that are smaller than those predicted numerically, along with differences in bubble shape during the ascent. These discrepancies may be attributed to modeling the fluid rheology as a generalized Newtonian fluid rather than as a viscoelastic one.

physics.flu-dyn↗

arXiv2025

Theory of active self-organization of dense nematic structures in the actin cytoskeleton

The actin cytoskeleton is remarkably adaptable and multifunctional. It often organizes into nematic bundles such as contractile rings or stress fibers. However, how a uniform and isotropic actin gel self-organizes into dense nematic bundles is not fully understood. Here, using an active gel model accounting for nematic order and density variations, we identify an active patterning mechanism leading to localized dense nematic structures. Linear stability analysis and nonlinear finite element simulations establish the conditions for nematic bundle self-assembly and how active gel parameters control the architecture, orientation, connectivity and dynamics of self-organized patterns. Finally, we substantiate with discrete network simulations the main requirements for nematic bundle formation according to our theory, namely increased active tension perpendicular to the nematic direction and generalized active forces conjugate to nematic order. Our work portrays actin gels a reconfigurable active materials with a spontaneous tendency to develop patterns of dense nematic bundles.

physics.bio-ph↗

arXiv2025

Unravel the rotational and translational behavior of a single squirmer in flexible polymer solutions at different Reynolds numbers

Microorganisms thrive in complex environments and their behavior in fluids holds significant importance for various medical and industrial applications. By conducting Lattice Boltzmann simulations, the transport and rotational properties of a generic squirmer are investigated in solutions embedded with flexible polymers at different Reynolds numbers. The interplay of activity and heterogeneously distributed polymers have profound influences on these properties. Remarkable enhancements of up to three orders of magnitude in the rotational motion, along with apparent decays in self-propelling velocities, are observed for squirmers with non-zero active stresses. These extraordinary phenomena stem from the squirmer-polymer mechanical and hydrodynamic interactions. Specifically, polymer wrapping occurs in front of a pusher, while numerous polymers are absorbed in the rear of a puller. Both mechanisms enhance the rotational motion and simultaneously impede translations through forces and torques arising from direct contacts or asymmetric local flows induced by polymers. The source dipole flow fields generated by a neutral swimmer rapidly advect polymers to the rear, leaving no apparent impacts on its rotational and transport properties. The influences of Reynolds number Re and squirmer-polymer boundary conditions (no-slip and repulsive) on the dynamics are addressed. In short, the no-slip boundary condition results in more profound effects on both rotational and translational properties at Re = 0.8. However, at Re = 0.04, the disparity between the two boundary conditions diminishes due to the heightened fluid viscous drag, which impedes direct contacts between squirmers and polymers. Our results reveal the relevance of system heterogeneity and highlight the essential role of squirmer-polymer mechanical and hydrodynamic interactions in shaping the behavior of swimmers in viscoelastic fluids.

cond-mat.soft↗

arXiv2025

Colloidal Magnus effect in polymer solutions

Rotating particles moving in fluids undergo a transverse migration via the inertia-induced Magnus effect. This phenomenon vanishes at colloidal scales because inertia is negligible and the fluid flow is time reversible. Yet, recent experiments discovered an inverse Magnus effect of colloids in polymeric and micellar solutions supposedly because their viscoelasticity breaks the time reversibility. Our study shows that classical viscoelastic features -- normal-stress differences and/or shear-thinning cannot explain this phenomenon. Instead, it originates from local polymer density inhomogeneities due to their stress-gradient-induced transport, a mechanism increasingly important at smaller scales -- indeed relevant to colloidal experiments. Incorporating this mechanism into our model leads to quantitative agreement with the experiments without fitting parameters. Our work provides new insights into colloidal motion in complex fluids with microstructural inhomogeneities, offers a simple mechanistic theory for predicting the resulting migration, and underscores the necessity of assimilating these findings in future designs of micro-machinery including swimmers, actuators, rheometers, and so on.

cond-mat.soft↗

arXiv2024

Enhanced rotational diffusion and spontaneous rotation of an active Janus disk in a complex fluid

Active colloids and self-propelled particles moving through microstructured fluids can display different behavior compared to what is observed in simple fluids. As they are driven out of equilibrium in complex fluids they can experience enhanced translational and rotational diffusion as well as instabilities. In this work, we study the deterministic and the Brownian rotational dynamics of an active Janus disk propelling at a constant speed through a complex fluid. The interactions between the Janus disk and the complex fluid are modeled using a fluctuating advection-diffusion equation, which we solve using the finite element method. Motivated by experiments, we focus on the case of a complex fluid comprising molecules that are much smaller than the size of the active disk but much bigger than the solvent. Using numerical simulations, we elucidate the interplay between active motion and fluid microstructure that leads to enhanced rotational diffusion and spontaneous rotation observed in experiments employing Janus colloids in polymer solutions. By increasing the propulsion speed of the Janus disk, the simulations predict the onset of a spontaneous rotation and an increase of the rotational diffusion coefficient by orders of magnitude compared to its equilibrium value. These phenomena depend strongly on the number density of the constituents of the complex fluid and their interactions with the two sides of the Janus disk. Given the simplicity of our model, we expect that our findings will apply to a wide range of active systems propelling through complex media.

cond-mat.soft↗

arXiv2024

Curvature induces and enhances transport of spinning colloids through narrow channels

The effect of curvature and how it induces and enhances the transport of colloidal particles driven through narrow channels represent an unexplored research avenue. Here we combine experiments and simulations to investigate the dynamics of magnetically driven colloidal particles confined through a narrow, circular channel. We use an external precessing magnetic field to induce a net torque and spin the particles at a defined angular velocity. Due to the spinning, the particle propulsion emerges from the different hydrodynamic coupling with the inner and outer walls and strongly depends on the curvature. The experimental findings are combined with finite element numerical simulations that predict a positive rotation translation coupling in the mobility matrix. Further, we explore the collective transport of many particles across the curved geometry, making an experimental realization of a driven single file system. With our finding, we elucidate the effect of curvature on the transport of microscopic particles which could be important to understand the complex, yet rich, dynamics of particle systems driven through curved microfluidic channels.

cond-mat.soft↗

arXiv2024

Large scale zigzag pattern emerging from circulating active shakers

We report the emergence of large zigzag bands in a population of reversibly actuated magnetic rotors that behave as active shakers, namely squirmers that shake the fluid around them without moving. The shakers collectively organize into dynamic structures displaying self-similar growth, and generate topological defects in form of cusps that connect vortices of rolling particles with alternating chirality. By combining experimental analysis with particle-based simulation, we show that the special flow field created by the shakers is the only ingredient needed to reproduce the observed spatiotemporal pattern. We unveil a self-organization scenario in a collection of driven particles in an viscoelastic medium emerging from the reduced particle degrees of freedom, as here the frozen orientational motion of the shakers.

cond-mat.soft↗

arXiv2022

A theory for the flow of chemically-responsive polymer solutions: equilibrium and shear-induced phase separation

Chemically-responsive polymers are macromolecules that respond to local variations of the chemical composition of the solution by changing their conformation, with notable examples including polyelectrolytes, proteins and DNA. The polymer conformation changes can occur in response to changes to the pH, the ionic strength or to the concentration of a generic solute that interacts with the polymer. These chemical stimuli can lead to drastic variations of the polymer flexibility and even trigger a transition from a coil to a globule polymer conformation. In many situations the spatial distribution of the chemical stimuli can be highly inhomogeneous, which can lead to large spatial variations of polymer conformation and of the rheological properties of the mixture. In this paper, we develop a theory for the flow of a mixture of a solute and chemically-responsive polymers. The approach is valid for generic flows and inhomogeneous distributions of polymers and solutes. To model the polymer conformation changes introduced by the interactions with the solute, we consider the polymers as linear elastic dumbbells whose spring stiffness depends on the solute concentration. We use the Onsager's variational formalism to derive the equations governing the evolution of the variables, which unveils novel couplings between the distribution of dumbbells and that of the solute. Finally, we use a linear stability analysis to show that the governing equations predict an equilibrium phase separation and a distinct shear-induced phase separation whereby a homogeneous distribution of solute and dumbbells spontaneously demix. Similar phase transitions have been observed in previous experiments using stimuli-responsive polymers and may play an important role in living systems.

cond-mat.soft↗

arXiv2022

Onsager reciprocal relations and chemo-mechanical coupling for chemically-active colloids

Similar to cells, bacteria, and other microorganisms, synthetic chemically-active colloids can harness the energy from their environment through a surface chemical reaction and use its energy to self-propel in fluidic environments. In this paper, we study the chemo-mechanical coupling that leads to the self-propulsion of chemically active colloids. The coupling between chemical reactions and momentum transport is a consequence of the Onsager reciprocal relations. They state that the velocity and the surface reaction rate are related to the mechanical and chemical affinities through a symmetric matrix. A consequence of the Onsager reciprocal relations is that, if a chemical reaction drives the motion of the colloid, then an external force generates a reaction rate. Here, we investigate the Onsager reciprocal relations for a spherical active colloid that catalyzes a reversible surface chemical reaction between two species. We solve the relevant transport equations using a perturbation expansion and numerical simulations to demonstrate the validity of the reciprocal relations around the equilibrium. Our results are consistent with previous studies and highlight the key role of solute advection in preserving the symmetry of the Onsager matrix. Finally, we show that the Onsager reciprocal relations break down around a nonequilibrium steady state, which has implications for the thermal fluctuations of the active colloids used in experiments.

cond-mat.soft↗

arXiv2021

Spontaneous chiralization of polar active colloids

Polar active particles constitute a wide class of synthetic colloids that are able to propel along a preferential direction, given by their polar axis. Here, we demonstrate a generic self-phoretic mechanism that leads to their spontaneous chiralization through a symmetry breaking instability. We find that the transition of an active particle from a polar to a chiral symmetry is characterized by the emergence of active rotation and of circular trajectories. We show that the instability is driven by the advection of a solute that interacts differently with the two portions of the particle surface and it occurs through a supercritical pitchfork bifurcation.

cond-mat.soft↗

arXiv2020

Spontaneous polarization and locomotion of an active particle with surface-mobile enzymes

We examine a mechanism of locomotion of active particles whose surface is uniformly coated with mobile enzymes. The enzymes catalyze a reaction that drives phoretic flows but their homogeneous distribution forbids locomotion by symmetry. We find that the ability of the enzymes to migrate over the surface combined with self-phoresis can lead to a spontaneous symmetry breaking instability whereby the homogeneous distribution of enzymes polarizes and the particle propels. The instability is driven by the advection of enzymes by the phoretic flows and occurs above a critical Péclet number. The transition to polarized motile states occurs via a supercritical or subcritical pitchfork bifurcations, the latter of which enables hysteresis and coexistence of uniform and polarized states.

cond-mat.soft↗

arXiv2019

Oscillations of small bubbles and medium yielding in elastoviscoplastic fluids

We investigate the radial oscillations of small gas bubbles trapped in yield-stress fluid and driven by an acoustic pressure field. We model the rheological behavior of the yield-stress fluid using the recently developed elasto-visco-plastic (EVP) constitutive equation that takes into account the elastic and visco-plastic deformations of the material [P. Saramito, J. NonNewton. Fluid Mech. 158 (1-3) (2009) pp.154-161]. Assuming that the bubble remains spherical during the pressure driving, we reduce the problem to a set of ODEs and an integrodifferential equation, which we solve numerically for the case of two yield-stress fluids, a sot Carbopol gel and a stiffer Kaolin suspension. We find that, depending on the amplitude and frequency of the pressure field, the radial oscillations of the bubble produce elastic stresses that may or may not suffice to yield the surrounding material. We evaluate the critical amplitude of the acoustic pressure required to achieve yielding and we find a good agreement between numerical simulations and an analytical formula derived under the assumption of linear deformations. Finally, we examine the bubble oscillation amplitude for a very wide range of applied pressures both below and above the critical value to assess the impact of yielding on the bubble dynamics. This analysis could be used to identify a signature of yielding in experiments where the radial dynamics of a bubble is measured. More generally, these results can be used to rationalize the optimal conditions for pressure-induced bubble release from yield-stress fluids, which is relevant to various biomedical and industrial applications, including oil industry and food processing.

cond-mat.soft↗

arXiv2018

Dynamic capillary assembly of colloids at interfaces with 10,000g accelerations

Extreme deformation of soft matter is central to our understanding of the effects of shock, fracture, and phase change in a variety of systems. Yet, despite, the increasing interest in this area, far-from-equilibrium behaviours of soft matter remain challenging to probe. Colloidal suspensions are often used to visualise emergent behaviours in soft matter, as they offer precise control of interparticle interactions, and ease of visualisation by optical microscopy. However, previous studies have been limited to deformations that are orders of magnitude too slow to be representative of extreme deformation. Here we use a two-dimensional model system, a monolayer of colloids confined at a fluid interface, to probe and visualise the evolution of the microstructure during high-rate deformation driven by ultrasound. We observe the emergence of a transient network of strings, and use discrete particle simulations to show that it is caused by a delicate interplay of dynamic capillarity and hydrodynamic interactions between particles oscillating at high-frequency. Remarkably, we find evidence of inertial effects in a colloidal system, caused by accelerations approaching 10,000g. These results also suggest that extreme deformation of soft matter offers new opportunities for pattern formation and dynamic self-assembly.

cond-mat.soft↗