scholarly journals Surface viscosity and Marangoni stresses at surfactant laden interfaces

2016 ◽  
Vol 792 ◽  
pp. 712-739 ◽  
Author(s):  
Gwynn J. Elfring ◽  
L. Gary Leal ◽  
Todd M. Squires
Keyword(s):  
Material Properties ◽  
Finite Time ◽  
Time Scale ◽  
Surfactant Concentration ◽  
Marangoni Flow ◽  
Force Measurements ◽  
Surface Viscosity ◽  
Surface Shear ◽  
Marangoni Force ◽  
Soluble Surfactant

We calculate here the force on a probe at a viscous, compressible interface, laden with soluble surfactant that equilibrates on a finite time scale. The motion of the probe through the interface drives variations in the surfactant concentration at the interface that in turn leads to a Marangoni flow that contributes to the force on the probe. We demonstrate that the Marangoni force on the probe depends non-trivially on the surface shear and dilatational viscosities of the interface indicating the difficulty in extracting these material properties from force measurements at compressible interfaces.

Influence of pressure-dependent surface viscosity on dynamics of surfactant-laden drops in shear flow

2018 ◽  
Vol 858 ◽  
pp. 91-121 ◽  
Author(s):  
Zheng Yuan Luo ◽  
Xing Long Shang ◽  
Bo Feng Bai
Keyword(s):  
Shear Flow ◽  
Simple Shear ◽  
Surfactant Concentration ◽  
Constitutive Law ◽  
Simple Shear Flow ◽  
Drop Surface ◽  
Shear Surface ◽  
Surface Viscosity ◽  
Principal Axes ◽  
Surfactant Transport

We study numerically the dynamics of an insoluble surfactant-laden droplet in a simple shear flow taking surface viscosity into account. The rheology of drop surface is modelled via a Boussinesq–Scriven constitutive law with both surface tension and surface viscosity depending strongly on the surface concentration of the surfactant. Our results show that the surface viscosity exhibits non-trivial effects on the surfactant transport on the deforming drop surface. Specifically, both dilatational and shear surface viscosity tend to eliminate the non-uniformity of surfactant concentration over the drop surface. However, their underlying mechanisms are entirely different; that is, the shear surface viscosity inhibits local convection due to its suppression on drop surface motion, while the dilatational surface viscosity inhibits local dilution due to its suppression on local surface dilatation. By comparing with previous studies of droplets with surface viscosity but with no surfactant transport, we find that the coupling between surface viscosity and surfactant transport induces non-negligible deviations in the dynamics of the whole droplet. More particularly, we demonstrate that the dependence of surface viscosity on local surfactant concentration has remarkable influences on the drop deformation. Besides, we analyse the full three-dimensional shape of surfactant-laden droplets in simple shear flow and observe that the drop shape can be approximated as an ellipsoid. More importantly, this ellipsoidal shape can be described by a standard ellipsoidal equation with only one unknown owing to the finding of an unexpected relationship among the drop’s three principal axes. Moreover, this relationship remains the same for both clean and surfactant-laden droplets with or without surface viscosity.

scholarly journals Feeling the Force: Measurements of Platelet Contraction and Their Diagnostic Implications

2018 ◽  
Vol 45 (03) ◽  
pp. 285-296 ◽  
Author(s):  
Evelyn Williams ◽  
Oluwamayokun Oshinowo ◽  
Abhijit Ravindran ◽  
Wilbur Lam ◽  
David Myers
Keyword(s):  
Mechanical Properties ◽  
Heart Disease ◽  
Ischemic Heart Disease ◽  
Material Properties ◽  
Blood Cells ◽  
Ischemic Heart ◽  
Force Measurements ◽  
Blood Clots ◽  
Order Of Magnitude

AbstractIn addition to the classical biological and biochemical framework, blood clots can also be considered as active biomaterials composed of dynamically contracting platelets, nascent polymeric fibrin that functions as a matrix scaffold, and entrapped blood cells. As platelets sense, rearrange, and apply forces to the surrounding microenvironment, they dramatically change the material properties of the nascent clot, increasing its stiffness by an order of magnitude. Hence, the mechanical properties of blood clots are intricately tied to the forces applied by individual platelets. Research has also shown that the pathophysiological changes in clot mechanical properties are associated with bleeding and clotting disorders, cancer, stroke, ischemic heart disease, and more. By approaching the study of hemostasis and thrombosis from a biophysical and mechanical perspective, important insights have been made into how the mechanics of clotting and the forces applied by platelets are linked to various diseases. This review will familiarize the reader with a mechanics framework that is contextualized with relevant biology. The review also includes a discussion of relevant tools used to study platelet forces either directly or indirectly, and finally, concludes with a summary of potential links between clotting forces and disease.

Investigation of Ultrafast Charge Carrier and Lattice Dynamics

2020 ◽  
Vol 29 (9) ◽  
pp. 7-10
Author(s):  
Kyungwan KIM
Keyword(s):  
Charge Carrier ◽  
Equilibrium State ◽  
Time Resolution ◽  
Material Properties ◽  
Time Scale ◽  
Lattice Dynamics ◽  
Detection Methods ◽  
Ultrafast Dynamics ◽  
Pulsed Lasers ◽  
Fundamental Interactions

When a material is driven out of an equilibrium state, fundamental interactions governing the material properties play roles in returning to the equilibrium state. The microscopic process of this recovery takes place on an ultrafast time scale far beyond the usual time resolution of usual detection methods. Thanks to the recent development of the ultrashort pulsed lasers, various ultrafast techniques are now available to investigate the ultrafast dynamics of materials. In this article, I briefly review the experiment techniques used to investigate ultrafast electronic and lattice dynamics.

Impact of surface viscosity on the stability of a droplet translating through a stagnant fluid

2021 ◽  
Vol 927 ◽  
Author(s):  
Natasha Singh ◽  
Vivek Narsimhan
Keyword(s):  
Shear Viscosity ◽  
Capillary Number ◽  
Cavity Growth ◽  
Boundary Integral ◽  
Constitutive Relationship ◽  
Surface Viscosity ◽  
Surface Shear ◽  
The Stability ◽  
The Impact ◽  
Surface Shear Viscosity

This study examines the impact of interfacial viscosity on the stability of an initially deformed droplet translating through an unbounded quiescent fluid. The boundary-integral formulation is employed to investigate the time evolution of a droplet in the Stokes flow limit. The droplet interface is modelled using the Boussinesq–Scriven constitutive relationship having surface shear viscosity $\eta _\mu$ and surface dilatational viscosity $\eta _\kappa$ . We observe that, below a critical value of the capillary number, $Ca_C$ , the initially perturbed droplet reverts to its spherical shape. Above $Ca_C$ , the translating droplet deforms continuously, growing a tail at the rear end for initial prolate perturbations and a cavity for initial oblate perturbations. We find that surface shear viscosity inhibits the tail/cavity growth at the droplet's rear end and increases the $Ca_C$ compared with a clean droplet. In contrast, surface dilatational viscosity increases tail/cavity growth and lowers $Ca_C$ compared with a clean droplet. Surprisingly, both shear and dilatational surface viscosity appear to delay the time at which pinch off occurs, and hence satellite droplets form. Lastly, we explore the combined influence of surface viscosity and surfactant transport on droplet stability by assuming a linear dependence of surface tension on surfactant concentration and exponential dependence of interfacial viscosities on the surface pressure. We find that pressure-thinning/thickening effects significantly affect the droplet dynamics for surface shear viscosity but play a small role for surface dilatational viscosity. We lastly provide phase diagrams for the critical capillary number for different values of the droplet's viscosity ratio and initial Taylor deformation parameter.

scholarly journals Irreversible particle motion in surfactant-laden interfaces due to pressure-dependent surface viscosity

2017 ◽  
Vol 473 (2205) ◽  
pp. 20170346 ◽  
Author(s):  
Harishankar Manikantan ◽  
Todd M. Squires
Keyword(s):  
Surface Pressure ◽  
Reciprocal Theorem ◽  
Coupled Modes ◽  
Surface Viscosity ◽  
Surface Shear ◽  
Perturbative Approach ◽  
Low Reynolds Number Flows ◽  
Insoluble Surfactant ◽  
Magnus Effect ◽  
Reynolds Number Flows

The surface shear viscosity of an insoluble surfactant monolayer often depends strongly on its surface pressure. Here, we show that a particle moving within a bounded monolayer breaks the kinematic reversibility of low-Reynolds-number flows. The Lorentz reciprocal theorem allows such irreversibilities to be computed without solving the full nonlinear equations, giving the leading-order contribution of surface pressure-dependent surface viscosity. In particular, we show that a disc translating or rotating near an interfacial boundary experiences a force in the direction perpendicular to that boundary. In unbounded monolayers, coupled modes of motion can also lead to non-intuitive trajectories, which we illustrate using an interfacial analogue of the Magnus effect. This perturbative approach can be extended to more complex geometries, and to two-dimensional suspensions more generally.

A Multi-Time-Scale Finite Time Controller for the Quadrotor UAVs with Uncertainties

2018 ◽  
Vol 94 (2) ◽  
pp. 521-533 ◽  
Author(s):  
Zhen Zhou ◽  
Hongbin Wang ◽  
Zhongquan Hu ◽  
Yueling Wang ◽  
Hong Wang
Keyword(s):  
Finite Time ◽  
Time Scale ◽  
Quadrotor Uavs

scholarly journals Capillary waves with surface viscosity

2018 ◽  
Vol 847 ◽  
pp. 644-663 ◽  
Author(s):  
Li Shen ◽  
Fabian Denner ◽  
Neal Morgan ◽  
Berend van Wachem ◽  
Daniele Dini
Keyword(s):  
Marangoni Effect ◽  
Surfactant Solution ◽  
Surface Concentration ◽  
Capillary Waves ◽  
Initial Value ◽  
Surface Viscosity ◽  
Surface Shear ◽  
Viscosity Effects ◽  
Rate Of Increase ◽  
The Stability

Experiments over the last 50 years have suggested a tentative correlation between the surface (shear) viscosity and the stability of a foam or emulsion. We examine this link theoretically using small-amplitude capillary waves in the presence of a surfactant solution of dilute concentration, where the associated Marangoni and surface viscosity effects are modelled via the Boussinesq–Scriven formulation. The resulting integro-differential initial value problem is solved analytically, and surface viscosity is found to contribute an overall damping effect to the amplitude of the capillary wave with varying degree depending on the length scale of the system. Numerically, we find that the critical damping wavelength increases for increasing surface concentration but the rate of increase remains different for both the surface viscosity and the Marangoni effect.

The theory of absolute surface shear viscosity III. The rotating ring problem

1971 ◽  
Vol 320 (1543) ◽  
pp. 537-547 ◽  
Keyword(s):  
Laminar Flow ◽  
Shear Viscosity ◽  
Liquid Surface ◽  
Fluid Interface ◽  
Surface Viscosity ◽  
Surface Shear ◽  
Ring Problem ◽  
The Absolute ◽  
Interpolation Polynomials ◽  
Steady Laminar

The problem of steady, laminar flow in the vicinity of a rotating ring inserted into a semi-infinite fluid interface is solved when the liquid surface is covered with an insoluble film possessing an intrinsic surface viscosity. The results are presented as interpolation polynomials which permit calculation of the absolute surface viscosity of the film from measured values of the torque exerted on the ring.

scholarly journals Influence of Material Structure on Forces Measured during Abrasive Waterjet (AWJ) Machining

Materials ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 3878 ◽  
Author(s):  
Libor M. Hlaváč ◽  
Adam Štefek ◽  
Martin Tyč ◽  
Daniel Krajcarz
Keyword(s):  
Material Properties ◽  
Traverse Speed ◽  
Abrasive Waterjet ◽  
Material Structure ◽  
Machining Efficiency ◽  
Force Measurements ◽  
Material Response ◽  
Factors Influencing ◽  
Force Ratio ◽  
Deformation Force

Material structure is one of the important factors influencing abrasive waterjet (AWJ) machining efficiency and quality. The force measurements were performed on samples prepared from two very similar steels with different thicknesses and heat treatment. The samples were austenitized at 850 °C, quenched in polymer and tempered at various temperatures between 20 °C and 640 °C. The resulting states of material substantially differed in strength and hardness. Therefore, samples prepared from these material states are ideal for testing of material response to AWJ. The force measurements were chosen to test the possible influence of material structure on the material response to the AWJ impact. The results show that differences in material structure and respective material properties influence the limit traverse speed. The cutting to deformation force ratio seems to be a function of relative traverse speed independently on material structure.

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