Dynamics Of Suspensions Research Articles

Correction: Non-linear alignment dynamics in suspensions of platelets under rotating magnetic fields

Correction for ‘Non-linear alignment dynamics in suspensions of platelets under rotating magnetic fields’ by Randall M. Erb et al., Soft Matter, 2012, 8, 7604–7609.

Concentration dependence of the dynamics of microgel suspensions investigated by dynamic light scattering.

The dynamics of colloidal gel particle suspensions, i.e., microgel suspensions, has been investigated by dynamic light scattering (DLS) over a wide concentration range from the (I) dilute (φ < φcp) to the (II) intermediate (φ ≈ φcp) and (III) high concentration regions (φ ≫ φcp), where φ and φcp are the volume fraction of the gel particles in the suspension and the random close packing fraction, φcp ≈ 0.64, respectively. The time-intensity correlation function exhibited a distinct change with increasing φ, i.e., from ergodic behaviour (region I and II) to nonergodic behaviour (region III). A mode transition from translational (region I) to cooperative diffusion (the so-called gel mode) (region II) was also observed due to the soft and deformable nature of the microgels. Different from the dynamics of hard colloidal glass suspensions, the gel mode remained even at φ ≫ φcp. By using the ensemble-averaged time-correlation function, IE, we quantify the relationship between φ and their dynamics, and show that the soft microgels are deswollen in the densely packed state.

Long-wavelength fluctuations and static correlations in quasi-2D colloidal suspensions.

Dimensionality strongly affects thermal fluctuations and critical dynamics of equilibrium systems. These influences persist in amorphous systems going through the nonequilibrium glass transition. Here, we experimentally study the glass transition of quasi-2D suspensions of spherical and ellipsoidal particles under different degrees of circular confinement. We show that the strength of the long-wavelength fluctuations increases logarithmically with system sizes and displays the signature of the Mermin-Wagner fluctuations. Moreover, using confinement as a tool, we also measure static structural correlations and extract a growing static correlation length in 2D supercooled liquids. Finally, we explore the influence of the Mermin-Wagner fluctuations on the translational and orientational relaxations of 2D ellipsoidal suspensions, which leads to a new interpretation of the two-step glass transition and the orientational glass phase of anisotropic particles. Our study reveals the importance of long-wavelength fluctuations in 2D supercooled liquids and provides new insights into the role of dimensionality in the glass transition.

Using FM Dyes to Study Endomembranes and Their Dynamics in Plants and Cell Suspensions.

FM (Fei-Mao) styryl dyes are commonly used for the fluorescence imaging of plasma membrane (PM) and endocytosis in vivo. Thanks to their amphiphilic character, these dyes are incorporated in the outer leaflet of the PM lipid bilayer and emit fluorescence in its hydrophobic environment. The endocytic pathway of FM dye uptake starts with rapid PM staining and continues in PM invaginations and membrane vesicles during endocytosis, followed by staining of trans-Golgi network (TGN) and ending in tonoplast (vacuolar membrane). FM dyes do not stain endoplasmic reticulum and nuclear membrane. The time-lapse fluorescence microscopy could track endocytic vesicles and characterize the rate of endocytosis in vivo. On the other hand, fixable FM dyes (FX) can be used for the visualization of particular steps in the FM dye uptake in situ. Staining with FM dyes and subsequent microscopic observations could be performed on both tissue and cellular level. Here, we describe simple procedures for the effective FM dye staining and destaining in root tip of Arabidopsis thaliana seedlings and suspension-cultured tobacco cells.

Soil granular dynamics on-a-chip: fluidization inception under scrutiny.

Predicting soil evolution remains a scientific challenge. This process involves poorly understood aspects of disordered granular matter and dense suspension dynamics. This study presents a novel two-dimensional experiment on a small-scale chip structure; this allows the observation of the deformation at the particle scale of a large-grained sediment bed, under conditions where friction dominates over cohesive and thermal forces, and with an imposed fluid flow. Experiments are performed under conditions which span the particle resuspension criterion, and particle motion is detected and analyzed. The void size population and statistics of particle trajectories bring insight into the sediment dynamics near fluidization conditions. Specifically, particle rearrangement and net bed compaction are observed at flow rates significantly below the criterion for instability growth. Above a threshold flowrate, a channel forms and grows in the vertical direction; and eventually it crosses the entire bed. In the range of flow rates where channelization can occur, the coexistence of compacting and dilating bed scenarios is observed. The results of the study enhance our capacity for modeling of both slow dynamics and eventual rapid destabilization of sediment beds. Microfluidic channel soil-on-a-chip studies open avenues to new investigations including dissolution-precipitation, fine particle transport, or micro-organism swimming and population growth, which may depend on the mechanics of the porous medium itself.

Particle dynamics in sheared particulate suspensions

Measurements of particle dynamics of neutrally buoyant suspensions of non‐Brownian glass beads in a Couette cell using dynamic sound scattering are reported. The dynamics were studied under steady shear flow across the entire gap between the stator and rotor for shear rates from 0.26 to 6.59 s −1 and particle concentrations from 20% to 50%, thereby enabling a comprehensive investigation of the dynamics to be carried out. The average particle velocity profile varies linearly with depth inside the cell for all shear rates and concentrations. The fluctuations in the particle velocities are large, indicating that the particles are not confined to streamlines but continue to fluctuate substantially during steady flow. Our data indicate that the fluctuations are anisotropic. The components of the velocity fluctuations (granular temperature) parallel to the flow and in the vertical direction are much larger than in the radial direction. The fluctuation anisotropy decreases as the concentration increases. © 2018 American Institute of Chemical Engineers AIChE J, 65: 840–849, 2019

Estimation of road frictional force and wheel slip for effective antilock braking system (ABS) control

SummaryThe introduction of electric braking via brake‐by‐wire systems in electric vehicles) has reduced the high transportation delays usually involved in conventional friction braking systems. This has facilitated the design of more efficient and advanced control schemes for antilock braking systems (ABSs). However, accurate estimation of the tire‐road friction coefficient, which cannot be measured directly, is required. This paper presents a review of existing estimation methods, focusing on sliding‐mode techniques, followed by the development of a novel friction estimation technique, which is used to design an efficient ABS control system. This is a novel slip‐based estimation method, which accommodates the coupling between the vehicle dynamics, wheel dynamics, and suspension dynamics in a cascaded structure. A higher‐order sliding‐mode observer–based scheme is designed, considering the nonlinear relationship between friction and slip. A first‐order sliding‐mode observer is also designed based on a purely linear relationship. A key feature of the proposed estimation schemes is the inclusion of road slope and the effective radius of the tire as an estimated state. These parameters impact significantly on the accuracy of slip and friction estimation. The performance of the proposed estimation schemes are validated and benchmarked against a Kalman filter (KF) by a series of simulation tests. It is demonstrated that the sliding‐mode observer paradigm is an important tool in developing the next generation ABS systems for electric vehicles.

Dynamics of soft nanoparticle suspensions at hard X-ray FEL sources below the radiation-damage threshold.

The application of X-ray photon correlation spectroscopy (XPCS) at free-electron laser (FEL) facilities enables, for the first time, the study of dynamics on a (sub-)nanometre scale in an unreached time range between femtoseconds and seconds. For soft-matter materials, radiation damage is a major limitation when going beyond single-shot applications. Here, an XPCS study is presented at a hard X-ray FEL on radiation-sensitive polymeric poly(N-isopropylacrylamide) (PNIPAM) nanoparticles. The dynamics of aqueous suspensions of densely packed silica-PNIPAM core-shell particles and a PNIPAM nanogel below the radiation-damage threshold are determined. The XPCS data indicate non-diffusive behaviour, suggesting ballistic and stress-dominated heterogeneous particle motions. These results demonstrate the feasibility of XPCS experiments on radiation-sensitive soft-matter materials at FEL sources and pave the way for future applications at MHz repetition rates as well as ultrafast modes using split-pulse devices.

Rod Construction of an Isotropic Elastic Suspension of Inertial Mass

In this article, the dynamics of a mechanical isotropic elastic rod suspension of inertial mass in the linear formulation is examined as one of the possible options for implementing an inertial information sensor.

Generation of Acoustic Disturbances by a Moving Charged Gas Suspension

Consideration is given to the dynamics of a charged gas suspension in an external electric field. The process of generation of acoustic waves in the carrier medium on instantaneous switch-on of the external electric field setting the dispersed phase in motion is described. The influence of the size of particles and of the volume content of the dispersed phase on the intensity of acoustic disturbance is considered.

Numerical modeling of the powder materials spraying

On the basis of the numerical solution of polydisperse gas suspension dynamics system of equations, the process of powder spraying on a plane surface in an electric field is described. The model includes motion equations of the carrier medium and disperse phase fractions under aerodynamic friction and Coulomb forces action taking into account interfacial exchange of pulse and energy. The system solves by an explicit predictor-corrector method with splitting on the spatial directions and the non-linear correction scheme. The numerical model is applied to gas suspension speed and density fields receiving in interelectrode space and on target electrode surface. The system of equations was written in the generalized curvilinear coordinates: the physical region of a current in variables (x, y) was written in a canonical computational region in variables (ξ,η) and was solved by an explicit second-order Mac-Cormack method. The Poisson equation for the electric field potential was written in the generalized coordinates and was solved by finite difference method with the use of the iterative Seidel scheme on a gas-dynamic computational mesh.

Spectral structure of surface waves and its influence on sediment dynamics

Summary Analysis of the influence of wave energy frequency distribution on the dynamics of suspension over the sea-bottom is the main objective of this study. We revealed the differences between the response of the eroded sea-bottom to external disturbances represented by irregular surface waves with permanent integral characteristics (significant wave height and frequency of the spectrum peak) and variable frequency of the wave energy distribution.

A fluctuating boundary integral method for Brownian suspensions

We present a fluctuating boundary integral method (FBIM) for overdamped Brownian Dynamics (BD) of two-dimensional periodic suspensions of rigid particles of complex shape immersed in a Stokes fluid. We develop a novel approach for generating Brownian displacements that arise in response to the thermal fluctuations in the fluid. Our approach relies on a first-kind boundary integral formulation of a mobility problem in which a random surface velocity is prescribed on the particle surface, with zero mean and covariance proportional to the Green's function for Stokes flow (Stokeslet). This approach yields an algorithm that scales linearly in the number of particles for both deterministic and stochastic dynamics, handles particles of complex shape, achieves high order of accuracy, and can be generalized to three dimensions and other boundary conditions. We show that Brownian displacements generated by our method obey the discrete fluctuation–dissipation balance relation (DFDB). Based on a recently-developed Positively Split Ewald method Fiore et al. (2017) [24], near-field contributions to the Brownian displacements are efficiently approximated by iterative methods in real space, while far-field contributions are rapidly generated by fast Fourier-space methods based on fluctuating hydrodynamics. FBIM provides the key ingredient for time integration of the overdamped Langevin equations for Brownian suspensions of rigid particles. We demonstrate that FBIM obeys DFDB by performing equilibrium BD simulations of suspensions of starfish-shaped bodies using a random finite difference temporal integrator.

Size-Dependent Orientational Dynamics of Brownian Nanorods.

Successful assembly of suspended nanoscale rod-like particles depends on fundamental phenomena controlling rotational and translational diffusion. Despite the significant developments in fluidic fabrication of nanostructured materials, the ability to quantify the dynamics in processing systems remains challenging. Here we demonstrate an experimental method for characterization of the orientation dynamics of nanorod suspensions in assembly flows using orientation relaxation. This relaxation, measured by birefringence and obtained after rapidly stopping the flow, is deconvoluted with an inverse Laplace transform to extract a length distribution of aligned nanorods. The methodology is illustrated using nanocelluloses as model systems, where the coupling of rotational diffusion coefficients to particle size distributions as well as flow-induced orientation mechanisms are elucidated.

Dynamic Analysis of an Optimal Active Suspension System Using Global Search Optimization

This paper addresses ride comfort for quarter car active suspension system. Suspension dynamics are modelled by using two degree of freedom vibrating system, linear with time invariant quarter car model to capture the system dynamics when it is subjected to the road disturbance with different velocities. Global search optimization method is a strategy that overcomes the defects of the suspension system performance index formula, objective function (discontinuity, non-smooth) is used to find the optimal suspension spring stiffness and damping coefficient. The optimal active suspension system design is tested when the active elements is malfunctioned. The optimal design is compared with optimal passive suspension system in terms of ride comfort. The results showed that the optimal passive elements of optimal active suspension system provided better ride comfort ( ) even at the absent of the active elements compared to optimal passive suspension system.

Uncovering Instabilities in the Spatiotemporal Dynamics of a Shear-Thickening Cornstarch Suspension

Recent theories predict that discontinuous shear-thickening (DST) involves an instability, the nature of which remains elusive. Here, we explore unsteady dynamics in a dense cornstarch suspension by coupling long rheological measurements under constant shear stresses to ultrasound imaging. We demonstrate that unsteadiness in DST results from localized bands that travel along the vorticity direction with a specific signature on the global shear rate response. These propagating events coexist with quiescent phases for stresses slightly above DST onset, resulting in intermittent, turbulent-like dynamics. Deeper into DST, events proliferate, leading to simpler, Gaussian dynamics. We interpret our results in terms of unstable vorticity bands as inferred from recent model and numerical simulations.

Process of the Deposition of Charged Polydisperse Gas Suspension on the Plate Surface in an Electrical Field

The process of powder sputtering onto a flat surface in an electric field is described on the basis of the numerical solution of a system of equations of the dynamics of a polydisperse gas suspension. The model includes equations for the motion of the carrier and disperse phases under the action of the aerodynamic friction force and the Coulomb force, taking into account the interphase exchange of momentum and energy. The system is solved by the explicit predictor–corrector method with splitting over the spatial directions and the nonlinear correction scheme. The numerical model is used to obtain the velocity and density fields of the gas suspension in the interelectrode space and on the surface of the target electrode.

Numerical simulation of vortex structures in the spraying of electrically charged gas suspension on a plate

Based on the numerical solution of polydisperse gas suspension dynamics system of equations, the process of powder spraying on a plane surface in an electric field is described. The model includes motion equations of the carrier medium and disperse phase fractions under aerodynamic friction and Coulomb forces action taking into account interfacial exchange of pulse and energy. The system solves by an explicit predictor-corrector method with splitting on the spatial directions and the non-linear correction scheme. The numerical model is applied to gas suspension speed and density fields receiving in interelectrode space and on target electrode surface. The system of equations was written in the generalized curvilinear coordinates: the physical region of a current in variables (x, y) was written in a canonical computational region in variables (ξ,η) and was solved by an explicit second-order Mac-Cormack method. The Poisson equation for the electric field potential was written in the generalized coordinates and was solved by finite difference method with the use of the iterative Seidel scheme on a gas-dynamic computational mesh.

Symmetric shear banding and swarming vortices in bacterial superfluids

Bacterial suspensions-a premier example of active fluids-show an unusual response to shear stresses. Instead of increasing the viscosity of the suspending fluid, the emergent collective motions of swimming bacteria can turn a suspension into a superfluid with zero apparent viscosity. Although the existence of active superfluids has been demonstrated in bulk rheological measurements, the microscopic origin and dynamics of such an exotic phase have not been experimentally probed. Here, using high-speed confocal rheometry, we study the dynamics of concentrated bacterial suspensions under simple planar shear. We find that bacterial superfluids under shear exhibit unusual symmetric shear bands, defying the conventional wisdom on shear banding of complex fluids, where the formation of steady shear bands necessarily breaks the symmetry of unsheared samples. We propose a simple hydrodynamic model based on the local stress balance and the ergodic sampling of nonequilibrium shear configurations, which quantitatively describes the observed symmetric shear-banding structure. The model also successfully predicts various interesting features of swarming vortices in stationary bacterial suspensions. Our study provides insights into the physical properties of collective swarming in active fluids and illustrates their profound influences on transport processes.

Orientation dynamics of dilute functionalized graphene suspensions in oscillatory flow

Orientation dynamics of graphene suspensions is investigated in oscillatory shear flow via flow dichroism. To evaluate whether graphene sheets behave as flexible or rigid sheets during flow, the experimental data are compared with predictions from a single particle Smoluchowski equation for spheroids.