The Experts below are selected from a list of 315 Experts worldwide ranked by ideXlab platform
Howard A. Stone - One of the best experts on this subject based on the ideXlab platform.
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drag and diffusion coefficients of a spherical particle attached to a fluid fluid Interface
Journal of Fluid Mechanics, 2016Co-Authors: Aaron Dorr, Steffen Hardt, Hassan Masoud, Howard A. StoneAbstract:Explicit analytical expressions for the drag and diffusion coefficients of a spherical particle attached to the flat Interface between two immiscible fluids are constructed for the case of a vanishing viscosity ratio between the fluid phases. The model is designed to account explicitly for the dependence on the contact angle between the two fluids and the solid surface. The Lorentz reciprocal theorem is applied in the context of geometric perturbations from the limiting cases of $90^{\circ }$ and $180^{\circ }$ contact angles. The model agrees well with the experimental and numerical data from the literature. Also, an advantage of the method utilized is that the drag and diffusion coefficients can be calculated up to one order higher in the perturbation parameter than the known velocity and pressure fields. Extensions to other particle shapes with known velocity and pressure fields are straightforward.
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Viscous fluid injection into a confined channel
Physics of Fluids, 2015Co-Authors: Zhong Zheng, Laurence Rongy, Howard A. StoneAbstract:We analyze the injection of a viscous fluid into a two-dimensional horizontal confined channel initially filled with another viscous fluid of different density and viscosity. We study the flow using the lubrication approximation and assume that the mixing between the fluids and their interfacial tension are negligible. When the injection rate is maintained constant, the evolution of the Fluid-Fluid Interface can be described by a nonlinear advection-diffusion equation dependent only on the viscosity ratio between the two fluids. In the early time period, the advection-diffusion equation reduces to a well-known nonlinear diffusion equation, and a self-similar solution is obtained. In the late time period, the advection-diffusion equation is approximated by a nonlinear hyperbolic equation, and a compound wave solution is constructed to describe the time evolution of the Fluid-Fluid Interface. Numerical solutions of the full equation show good agreement with the analytical solutions in both the early and late time periods. Finally, a regime diagram is obtained to summarize the flow behaviours with regard to two dimensionless groups: the viscosity ratio of the two fluids and the dimensionless time; three different dynamical behaviours are identified in the regime diagram: a nonlinear diffusion regime, a hyperbolic regime, and a transition regime. This problem is analogous to the corresponding injection flow problem into a confined porous medium.
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marangoni flow of soluble amphiphiles
Physical Review Letters, 2014Co-Authors: Matthieu Roche, Ian M Griffiths, Sebastien Le Roux, Isabelle Cantat, Arnaud Saintjalmes, Howard A. StoneAbstract:Surfactant distribution heterogeneities at a Fluid-Fluid Interface trigger the Marangoni effect, i.e., a bulk flow due to a surface tension gradient. The influence of surfactant solubility in the bulk on these flows remains incompletely characterized. Here we study Marangoni flows sustained by injection of hydrosoluble surfactants at the air-water Interface. We show that these flows have a finite size that increases with a decrease of the critical micelle concentration of the surfactants. We document the universality of the surface velocity field of these finite flows and predict scaling laws based on hydrodynamics and surfactant physical chemistry that capture the flow features.
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Analytical Model for the Deformation of a Fluid–Fluid Interface Beneath an AFM Probe
Langmuir : the ACS journal of surfaces and colloids, 2013Co-Authors: Daniel Quinn, Jie Feng, Howard A. StoneAbstract:We present an analytical solution for the shape of a fluid–fluid Interface near a nanoscale solid sphere, which is a configuration motivated by common measurements with an atomic force microscope. The forces considered are surface tension, gravity, and the van der Waals attraction. The nonlinear governing equation has been solved previously using the method of matched asymptotic expansions, and this requires that the surface tension forces far exceed those of gravity, i.e., the Bond number is much less than one. We first present this method using a physically relevant scaling of the equations, then offer a new analytical solution valid for all Bond numbers. We show that one configuration with a large effective Bond number, and thus one requiring our new solution, is a nanothick liquid film spread over a solid substrate. The scaling implications of both analytical methods are considered, and both are compared with numerical solutions of the full equation.
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Low Reynolds number motion of bubbles, drops and rigid spheres through fluid–fluid Interfaces
Journal of Fluid Mechanics, 1995Co-Authors: Michael Manga, Howard A. StoneAbstract:The low Reynolds number buoyancy-driven translation of a deformable drop towards and through a Fluid-Fluid Interface is studied using boundary integral calculations and laboratory experiments. The Bond numbers characteristic of both the drop and the initially flat Fluid-Fluid Interface are sufficiently large that the drop and Interface become highly deformed, substantial volumes of fluid may be entrained across the Interface, and breakup of both Interfaces may occur. Specifically, drops passing from a higher- to lower-viscosity fluid are extended vertically as they pass through the Interface. For sufficiently large drop Bond numbers, the drop may deform continuously, developing either an elongating tail or enlarging cavity at the back of the drop, analogous to the deformation characteristic of a single deformable drop in an unbounded fluid. The film of fluid between the drop and Interface thins most rapidly for those cases that the drop enters a more viscous fluid or has a viscosity lower than the surrounding fluids. In the laboratory experiments, bubbles entering a less viscous fluid are extended vertically and may break into smaller bubbles. The column of fluid entrained by particles passing through the Interface may also break into drops. Further experiments with many rigid particles indicate that the spatial distribution of particles may change as the particles pass through Interfaces : particles tend to form clusters.
Anton P. J. Middelberg - One of the best experts on this subject based on the ideXlab platform.
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Stimuli-responsive peptide nanostructures at the Fluid-Fluid Interface.
Methods in molecular biology (Clifton N.J.), 2013Co-Authors: Chun-xia Zhao, Anton P. J. MiddelbergAbstract:The self-organization of peptide-based nanostructures at a confined Fluid-Fluid Interface, for example, the air-water or oil-water Interface, is important in the context of stabilizing macroscopic soft-matter foams and emulsions. The unique ability to design interfacial nanostructures by controlling the subtle cooperativity that drives peptide self-assembly, and the ability to switch molecular cooperativity by facile triggers such as pH, opens new vistas for controlling macroscopic soft matter in industries as diverse as healthcare and industrial processing. Here we describe research aimed at developing new understanding into soft-matter formation and control, through variation of peptide sequence and bulk conditions. Macroscopic foaming and microfluidic emulsification studies prove particularly useful in visualizing and hence understanding the synergistic link between molecular design, mesoscopic interfacial properties, and bulk soft-matter stability.
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reversible active switching of the mechanical properties of a peptide film at a fluid fluid Interface
Nature Materials, 2006Co-Authors: Annette F. Dexter, Andrew S. Malcolm, Anton P. J. MiddelbergAbstract:Designer peptides have recently been developed as building blocks for novel self-assembled materials with stimuli-responsive properties. To date, such materials have been based on self-assembly in bulk aqueous solution or at solid-fluid Interfaces. We have designed a 21-residue peptide, AM1, as a stimuli-responsive surfactant that switches molecular architectures at a Fluid-Fluid Interface in response to changes in bulk aqueous solution composition. In the presence of divalent zinc at neutral pH, the peptide forms a mechanically strong 'film state'. In the absence of metal ions or at acid pH, the peptide adsorbs to form a mobile 'detergent state'. The two interfacial states can be actively and reversibly switched. Switching between the two states by a change in pH or the addition of a chelating agent leads to rapid emulsion coalescence or foam collapse. This work introduces a new class of surfactants that offer an environmentally friendly approach to control the stability of Interfaces in foams, emulsions and Fluid-Fluid Interfaces more generally.
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Reversible active switching of the mechanical properties of a peptide film at a fluid–fluid Interface
Nature Materials, 2006Co-Authors: Annette F. Dexter, Andrew S. Malcolm, Anton P. J. MiddelbergAbstract:Designer peptides have recently been developed as building blocks for novel self-assembled materials with stimuli-responsive properties. To date, such materials have been based on self-assembly in bulk aqueous solution or at solid-fluid Interfaces. We have designed a 21-residue peptide, AM1, as a stimuli-responsive surfactant that switches molecular architectures at a Fluid-Fluid Interface in response to changes in bulk aqueous solution composition. In the presence of divalent zinc at neutral pH, the peptide forms a mechanically strong 'film state'. In the absence of metal ions or at acid pH, the peptide adsorbs to form a mobile 'detergent state'. The two interfacial states can be actively and reversibly switched. Switching between the two states by a change in pH or the addition of a chelating agent leads to rapid emulsion coalescence or foam collapse. This work introduces a new class of surfactants that offer an environmentally friendly approach to control the stability of Interfaces in foams, emulsions and Fluid-Fluid Interfaces more generally.
Daeyeon Lee - One of the best experts on this subject based on the ideXlab platform.
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configuration of nonspherical amphiphilic particles at a fluid fluid Interface
Soft Matter, 2012Co-Authors: Bum Jun Park, Daeyeon LeeAbstract:We present the equilibrium configuration of amphiphilic ellipsoids and amphiphilic dumbbells with asymmetric shape (i.e., unequal surface areas for apolar and polar sides) and surface wetting properties at an oil–water Interface. The equilibrium configurations are obtained by minimizing the attachment energy of each amphiphilic particle as a function of orientation angle and vertical displacement of the particle with respect to the Interface. We find that the orientation and vertical displacement of nonspherical amphiphilic particles are significantly influenced by their shape, aspect ratio, surface properties, and the location of the wettability separation line. In particular, due to the asymmetry in the particle geometry and wettability of these amphiphilic particles, we observe unique configurations that are not expected in symmetric Janus ellipsoids and dumbbells at fluid–fluid Interfaces. In the case of amphiphilic ellipsoids, their orientation as a function of particle geometry and wettability can be divided into three regimes: upright orientation, tilted orientation, and coexistence of upright and tilted orientations due to the presence of secondary energy minima under appropriate conditions. In general, the secondary energy minimum is present when the aspect ratio of the ellipsoids becomes high. As for amphiphilic dumbbells, in addition to upright and tilted orientations, they can adopt intermediate orientations, especially when the size of the two spheres is significantly different, which leads to the detachment of one of the two spheres from the oil–water Interface. This study provides guidelines for designing nonspherical amphiphilic particles with suitable geometry and wettability to tailor their properties as solid surfactants for emulsion stabilization and fluid Interface modification.
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Configuration of nonspherical amphiphilic particles at a fluid–fluid Interface
Soft Matter, 2012Co-Authors: B. Jun Park, Daeyeon LeeAbstract:We present the equilibrium configuration of amphiphilic ellipsoids and amphiphilic dumbbells with asymmetric shape (i.e., unequal surface areas for apolar and polar sides) and surface wetting properties at an oil-water Interface. The equilibrium configurations are obtained by minimizing the attachment energy of each amphiphilic particle as a function of orientation angle and vertical displacement of the particle with respect to the Interface. We find that the orientation and vertical displacement of nonspherical amphiphilic particles are significantly influenced by their shape, aspect ratio, surface properties, and the location of the wettability separation line. In particular, due to the asymmetry in the particle geometry and wettability of these amphiphilic particles, we observe unique configurations that are not expected in symmetric Janus ellipsoids and dumbbells at Fluid-Fluid Interfaces. In the case of amphiphilic ellipsoids, their orientation as a function of particle geometry and wettability can be divided into three regimes: upright orientation, tilted orientation, and coexistence of upright and tilted orientations due to the presence of secondary energy minima under appropriate conditions. In general, the secondary energy minimum is present when the aspect ratio of the ellipsoids becomes high. As for amphiphilic dumbbells, in addition to upright and tilted orientations, they can adopt intermediate orientations, especially when the size of the two spheres is significantly different, which leads to the detachment of one of the two spheres from the oil-water Interface. This study provides guidelines for designing nonspherical amphiphilic particles with suitable geometry and wettability to tailor their properties as solid surfactants for emulsion stabilization and fluid Interface modification.
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janus particles at an oil water Interface
Soft Matter, 2011Co-Authors: Bum Jun Park, Teresa Brugarolas, Daeyeon LeeAbstract:We study the behaviour of Janus particles at an oil–water Interface. Amphiphilic Janus particles exhibit attractive interactions at the fluid–fluid Interface. The attractive interactions are likely due to the pinning of contact line around the diffuse boundary between the two hemispheres. The undulation of the three-phase contact line around Janus particles leads to quadrupolar capillary interactions, which we confirm by measuring the interparticle forces. We also show that Janus particles with two negatively charged-hydrophilic hemispheres show repulsive interactions.
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Janus particles at an oil–water Interface
Soft Matter, 2011Co-Authors: B. Jun Park, Teresa Brugarolas, Daeyeon LeeAbstract:We study the behaviour of Janus particles at an oil-water Interface. Amphiphilic Janus particles exhibit attractive interactions at the Fluid-Fluid Interface. The attractive interactions are likely due to the pinning of contact line around the diffuse boundary between the two hemispheres. The undulation of the three-phase contact line around Janus particles leads to quadrupolar capillary interactions, which we confirm by measuring the interparticle forces. We also show that Janus particles with two negatively charged-hydrophilic hemispheres show repulsive interactions.
Eligiusz Wajnryb - One of the best experts on this subject based on the ideXlab platform.
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Hydrodynamic coupling of spherical particles to a planar Fluid-Fluid Interface: theoretical analysis.
The Journal of chemical physics, 2010Co-Authors: Jerzy Blawzdziewicz, Maria L. Ekiel-jeżewska, Eligiusz WajnrybAbstract:We have developed a new technique (based on our Cartesian-representation method) to describe hydrodynamic interactions of a spherical particle with an undeformable planar Fluid-Fluid Interface under creeping-flow conditions. The Interface can be either surfactant-free or covered with an incompressible surfactant monolayer. We consider the effect of surface incompressibility and surface viscosity on particle motion. The new algorithm allows to calculate particle mobility coefficients for hydrodynamically coupled particles, moving either on the same or on the opposite sides of the Interface.
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motion of a spherical particle near a planar fluid fluid Interface the effect of surface incompressibility
Journal of Chemical Physics, 2010Co-Authors: Jerzy Blawzdziewicz, Maria L Ekieljezewska, Eligiusz WajnrybAbstract:Hydrodynamic coupling of a spherical particle to an undeformable planar Fluid-Fluid Interface under creeping-flow conditions is discussed. The Interface can be either surfactant-free or covered with an incompressible surfactant monolayer. In the incompressible surfactant limit, a uniform surfactant concentration is maintained by Marangoni stresses associated with infinitesimal surfactant redistribution. Our detailed numerical calculations show that the effect of surface incompressibility on lateral particle motion is accurately accounted for by the first reflection of the flow from the Interface. For small particle-Interface distances, the remaining contributions are significant, but they are weakly affected by the surface incompressibility. We show that for small particle-wall gaps, the transverse and lateral particle resistance coefficients can be rescaled onto corresponding universal master curves. The scaling functions depend on a scaling variable that combines the particle-wall gap with the viscosity ratio between fluids on both sides of the Interface. A logarithmic dependence of the contact value of the lateral resistance function on the viscosity ratio is derived. Accurate numerical calculations are performed using our Cartesian-representation method.
Jerzy Blawzdziewicz - One of the best experts on this subject based on the ideXlab platform.
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Hydrodynamic coupling of spherical particles to a planar Fluid-Fluid Interface: theoretical analysis.
The Journal of chemical physics, 2010Co-Authors: Jerzy Blawzdziewicz, Maria L. Ekiel-jeżewska, Eligiusz WajnrybAbstract:We have developed a new technique (based on our Cartesian-representation method) to describe hydrodynamic interactions of a spherical particle with an undeformable planar Fluid-Fluid Interface under creeping-flow conditions. The Interface can be either surfactant-free or covered with an incompressible surfactant monolayer. We consider the effect of surface incompressibility and surface viscosity on particle motion. The new algorithm allows to calculate particle mobility coefficients for hydrodynamically coupled particles, moving either on the same or on the opposite sides of the Interface.
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motion of a spherical particle near a planar fluid fluid Interface the effect of surface incompressibility
Journal of Chemical Physics, 2010Co-Authors: Jerzy Blawzdziewicz, Maria L Ekieljezewska, Eligiusz WajnrybAbstract:Hydrodynamic coupling of a spherical particle to an undeformable planar Fluid-Fluid Interface under creeping-flow conditions is discussed. The Interface can be either surfactant-free or covered with an incompressible surfactant monolayer. In the incompressible surfactant limit, a uniform surfactant concentration is maintained by Marangoni stresses associated with infinitesimal surfactant redistribution. Our detailed numerical calculations show that the effect of surface incompressibility on lateral particle motion is accurately accounted for by the first reflection of the flow from the Interface. For small particle-Interface distances, the remaining contributions are significant, but they are weakly affected by the surface incompressibility. We show that for small particle-wall gaps, the transverse and lateral particle resistance coefficients can be rescaled onto corresponding universal master curves. The scaling functions depend on a scaling variable that combines the particle-wall gap with the viscosity ratio between fluids on both sides of the Interface. A logarithmic dependence of the contact value of the lateral resistance function on the viscosity ratio is derived. Accurate numerical calculations are performed using our Cartesian-representation method.