arXiv subjects

Giovanniantonio Natale

Publications and source records attributed to Giovanniantonio Natale.

6 recordsLinked to original sources

arXiv2025

Colloidal rod dynamics under large amplitude oscillatory extensional flow

We perform a combined experimental and theoretical investigation of the orientational dynamics of rod-like colloidal particles in dilute suspension as they are subjected to a time-dependent homogeneous planar elongational flow. Our experimental approach involves the flow of dilute suspensions of cellulose nanocrystals (CNC) within a cross-slot-type stagnation point microfluidic device through which the extension rate is modulated sinusoidally over a wide range of Péclet number amplitudes ($Pe_0$) and Deborah numbers ($De$). The time-dependent orientation of the CNC is assessed via quantitative flow-induced birefringence measurements. For small $Pe_0 \lesssim 1$ and small $De \lesssim 0.03$, the birefringence response is sinusoidal and in phase with the strain rate, i.e., the response is linear. With increasing $Pe_0$, the response becomes non-sinusoidal (i.e., nonlinear) as the birefringence saturates due to the high degree of particle alignment at higher strain rates during the cycle. With increasing $De$, the CNC rods have insufficient time to respond to the rapidly changing strain rate, leading to asymmetry in the birefringence response around the minima and a residual effect as the strain rate passes through zero. These varied dynamical responses of the rod-like CNC are captured in a detailed series of Lissajous plots of the birefringence versus the strain rate. Experimental measurements are compared with simulations performed on both monodisperse and polydisperse systems, with rotational diffusion coefficients $D_r$ matched to the CNC. A semiquantitative agreement is found for simulations of a polydisperse system with $D_r$ heavily weighted to the longest rods in the measured CNC distribution. The results will be valuable for understanding, predicting, and optimizing the orientation of rod-like colloids during transient processing flows such as fiber spinning and film casting.

cond-mat.soft↗

arXiv2024

Polymer Concentration Regimes from Fractional Microrheology

In this work, a framework for deriving theoretical equations for mean squared displacement (MSD) and fractional Fokker-Planck (FFP) is developed for any arbitrary rheological model. The obtained general results are then specified for different fractional rheological models. To test the novel equations extracted from our framework and bridge the gap between microrheology and fractional rheological models, microrheology of polystyrene (PS) in tetrahydrofuran (THF) solutions at several polymer concentrations is measured. By comparing the experimental and theoretical MSDs, we find the fractional rheological parameters and demonstrate for the first time that the polymer concentration regimes can be distinguished using the fractional exponent and relaxation time data because of the existence of a distinct behavior in each regime. We suggest simple approximations for the critical overlap concentration and the shear viscosity of viscoelastic liquid-like solutions. This work provides a more sensitive approach for distinguishing different polymer concentration regimes and measuring the critical overlap concentration and shear viscosity of polymeric solutions, which is useful when conventional rheological characterization methods are unreliable due to the volatility and low viscosity of the samples.

cond-mat.soft↗

arXiv2023

Dynamics and rheology of 2D colloidal crystals with active anisotropic impurities

Active motion at complex fluid-fluid interfaces is a ubiquitous phenomenon in nature. However, an intriguing question that is not fully addressed is how active motion affects and gets influenced by its complex environment. Here, we design a 2D colloidal crystal containing active particles as a model system to understand the mechanics of complex interfaces in the presence of activity. We characterize the dynamics, rheology and phase behavior of 2D colloidal crystals formed using spherical polystyrene (PS) particles in the presence of active PS-Platinum Janus particles. In the presence of activity, the overall crystal becomes dynamic with a heterogeneous spatial distribution of disorder. Through particle-tracking microrheology and interfacial shear rheology, we report the discovery of a phase transition from solid-like to liquid-like interface driven by the active motion of a small number of active impurities in the crystal. The local perturbations induced by the active impurities have long-range effects on the dynamics of particles in 2D colloidal crystals modifying their overall viscoelasticity. The correlations between microstructure and dynamics from our experiments can provide insights into the behavior of a broad range of complex systems such as, motion of particles at oil-water interfaces in Pickering emulsion microreactors and the motion of molecular motors on cell membranes.

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↗

arXiv2017

Autophoretic locomotion in weakly viscoelastic fluids at finite Péclet number

In this work, we numerically investigate the dynamics of a self-propelling autophoretic Janus particle in a weakly viscoelastic fluid. The self-propulsion is achieved by an asymmetry in the properties of the surface of the Janus particle that drives a surface slip velocity and bulk flow. Here we investigate the effect of viscoelasticity on this advection-diffusion problem over a range of Péclet and Damköhler numbers. Particles are found to swim faster, or slower, in viscoelastic fluids, and we show how reaction and diffusion rates affect the viscoelastic stresses that lead to changes in propulsion.

physics.flu-dyn↗

arXiv2017

An active particle in a complex fluid

In this work, we study active particles with prescribed surface velocities in non-Newtonian fluids. We employ the reciprocal theorem to obtain the velocity of an active spherical particle with an arbitrary axisymmetric slip-velocity in an otherwise quiescent second-order fluid. We then determine how the motion of a diffusiophoretic Janus particle is affected by complex fluid rheology, namely viscoelasticity and shear-thinning viscosity, compared to a Newtonian fluid, assuming a fixed slip-velocity. We find that a Janus particle may go faster or slower in a viscoelastic fluid, but is always slower in a shear-thinning fluid as compared to a Newtonian fluid.

physics.flu-dyn↗