Reverse Marangoni surfing

2016 ◽  
Vol 811 ◽  
pp. 612-621 ◽  
Author(s):  
Vahid Vandadi ◽  
Saeed Jafari Kang ◽  
Hassan Masoud
Keyword(s):  
Surface Tension ◽  
Liquid Layer ◽  
Scalar Fields ◽  
Finite Depth ◽  
Lower Surface ◽  
Temperature Fields ◽  
Spherical Particles ◽  
Surface Tension Gradient ◽  
Oblate Spheroidal ◽  
Active Particles

We theoretically study the surfing motion of chemically and thermally active particles located at a flat liquid–gas interface that sits above a liquid layer of finite depth. The particles’ activity creates and maintains a surface tension gradient resulting in the auto-surfing. It is intuitively perceived that Marangoni surfers propel towards the direction with a higher surface tension. Remarkably, we find that the surfers may propel in the lower surface tension direction depending on their geometry and proximity to the bottom of the liquid layer. In particular, our analytical calculations for Stokes flow and diffusion-dominated scalar fields (i.e. chemical concentration and temperature fields) indicate that spherical particles undergo reverse Marangoni propulsion under confinement whereas disk-shaped surfers always move in the expected direction. We extend our results by proposing an approximate formula for the propulsion speed of oblate spheroidal particles based on the speeds of spheres and disks.

Finite amplitude cellular convection induced by surface tension

1967 ◽  
Vol 30 (1) ◽  
pp. 149-162 ◽  
Author(s):  
J. W. Scanlon ◽  
L. A. Segel
Keyword(s):  
Surface Tension ◽  
Flow Pattern ◽  
Large Class ◽  
Liquid Layer ◽  
Temperature Difference ◽  
Finite Depth ◽  
Linear Analysis ◽  
Finite Amplitude ◽  
Realistic Assumption ◽  
Gravity Driven

A non-linear analysis of cellular convection driven by surface tension in a semi-infinite liquid layer heated from below has been made. The purpose is to determine whether or not one can predict the emergence of the hexagonal flow pattern from the interaction of a certain large class of important disturbances. The principal conclusion is that, compared with gravity driven convection, there is generally a much greater band of imposed temperature difference associated with hexagonal convective patterns. Partial results for the more realistic assumption of finite depth support this conclusion.

Some Experiments on Packed-Bed Drying

1973 ◽  
Vol 187 (1) ◽  
pp. 515-521 ◽  
Author(s):  
D. R. Oliver ◽  
D. L. Clarke
Keyword(s):  
Surface Tension ◽  
Packed Bed ◽  
Lower Surface ◽  
Major Effect ◽  
Spherical Particles ◽  
Drying Rate ◽  
Experimental Conditions ◽  
Wide Range ◽  
Drying Rates ◽  
Thermal Conductivities

Drying equipment is described in which streams of air of accurately-controlled temperature and humidity may be passed over the surface of a packed bed. The materials used in the beds are sieved spherical particles of copper, glass and polystyrene whilst the liquids are water, methanol and a series of organic solvents. Experiments are described in which the effect of physical variables on drying rate is measured. Surface tension is shown to have a major effect on the shape of drying rate curves; under the experimental conditions water is the only liquid for which the rate of drying during the constant-rate period is equal to that from a free liquid surface. The equivalent period for liquids of lower surface tension corresponds to a distinctly lower drying rate. Possible reasons for this behaviour are discussed. An increase in liquid viscosity causes reduction in drying rate, but only when the rate of drying is itself high. The effect of using solids of differing thermal conductivities is investigated. At high drying rates, increasing thermal conductivity produces increasing drying rate. Surprisingly a mixed bed (e.g. of copper and glass) often dries faster than beds of the constituent materials alone. Split beds are also used (beds of which the halves are of different materials). For these beds it is possible to observe the growth of dry patches on the surface of the beds and the manner in which liquid appears to migrate across the interface between the particles of the two halves. The temperature distribution across the interface is shown to be abnormal in part of the drying cycle. A conclusion which may be drawn from the work is that it is often an advantage, from the drying standpoint, to have particles that have either a wide range of thermal conductivities or a wide range of particle sizes.

A two-dimensional model for slow convection at infinite Marangoni number

1997 ◽  
Vol 331 ◽  
pp. 283-312 ◽  
Author(s):  
A. THESS ◽  
D. SPIRN ◽  
B. JÜTTNER
Keyword(s):  
Surface Tension ◽  
Free Surface ◽  
Marangoni Convection ◽  
Point Vortex ◽  
Dynamical Evolution ◽  
Scalar Fields ◽  
Finite Depth ◽  
Present Theory ◽  
Surface Velocity ◽  
Two Dimensional

The free surface of a viscous fluid is a source of convective flow (Marangoni convection) if its surface tension is distributed non-uniformly. Such non-uniformity arises from the dependence of the surface tension on a scalar quantity, either surfactant concentration or temperature. The surface-tension-induced velocity redistributes the scalar forming a closed-loop interaction. It is shown that under the assumptions of (i) small Reynolds number and (ii) vanishing diffusivity this nonlinear process is described by a single self-consistent two-dimensional evolution equation for the scalar field at the free surface that can be derived from the three-dimensional basic equations without approximation. The formulation of this equation for a particular system requires only the knowledge of the closure law, which expresses the surface velocity as a linear functional of the active scalar at the free surface. We explicitly derive these closure laws for various systems with a planar non-deflecting surface and infinite horizontal extent, including an infinitely deep fluid, a fluid with finite depth, a rotating fluid, and an electrically conducting fluid under the influence of a magnetic field. For the canonical problem of an infinitely deep layer we demonstrate that the dynamics of singular (point-like) surfactant or temperature distributions can be further reduced to a system of ordinary differential equations, equivalent to point-vortex dynamics in two-dimensional perfect fluids. We further show, using numerical simulations, that the dynamical evolution of initially smooth scalar fields leads in general to a finite-time singularity. The present theory provides a rational framework for a simplified modelling of strongly nonlinear Marangoni convection in high-Prandtl-number fluids or systems with high Schmidt number.

Some Experiments on Packed-Bed Drying

1973 ◽  
Vol 187 (1) ◽  
pp. 515-521
Author(s):  
D. R. Oliver ◽  
D. L. Clarke
Keyword(s):  
Surface Tension ◽  
Packed Bed ◽  
Lower Surface ◽  
Major Effect ◽  
Spherical Particles ◽  
Drying Rate ◽  
Experimental Conditions ◽  
Wide Range ◽  
Drying Rates ◽  
Thermal Conductivities

Drying equipment is described in which streams of air of accurately-controlled temperature and humidity may be passed over the surface of a packed bed. The materials used in the beds are sieved spherical particles of copper, glass and polystyrene whilst the liquids are water, methanol and a series of organic solvents. Experiments are described in which the effect of physical variables on drying rate is measured. Surface tension is shown to have a major effect on the shape of drying rate curves; under the experimental conditions water is the only liquid for which the rate of drying during the constant-rate period is equal to that from a free liquid surface. The equivalent period for liquids of lower surface tension corresponds to a distinctly lower drying rate. Possible reasons for this behaviour are discussed. An increase in liquid viscosity causes reduction in drying rate, but only when the rate of drying is itself high. The effect of using solids of differing thermal conductivities is investigated. At high drying rates, increasing thermal conductivity produces increasing drying rate. Surprisingly a mixed bed (e.g. of copper and glass) often dries faster than beds of the constituent materials alone. Split beds are also used (beds of which the halves are of different materials). For these beds it is possible to observe the growth of dry patches on the surface of the beds and the manner in which liquid appears to migrate across the interface between the particles of the two halves. The temperature distribution across the interface is shown to be abnormal in part of the drying cycle. A conclusion which may be drawn from the work is that it is often an advantage, from the drying standpoint, to have particles that have either a wide range of thermal conductivities or a wide range of particle sizes.

Breakdown of Evaporating Falling Films as a Function of Surface Tension Gradient

1996 ◽  
Vol 17 (4) ◽  
pp. 72-81 ◽  
Author(s):  
ALI G. BUDIMAN ◽  
C. FLORIJANTO ◽  
J. W. PALEN
Keyword(s):  
Surface Tension ◽  
Surface Tension Gradient ◽  
Falling Films

scholarly journals Effect of a surface tension gradient on the slip flow along a superhydrophobic air-water interface

2018 ◽  
Vol 3 (3) ◽  
Author(s):  
Dong Song ◽  
Baowei Song ◽  
Haibao Hu ◽  
Xiaosong Du ◽  
Peng Du ◽  
...  
Keyword(s):  
Surface Tension ◽  
Slip Flow ◽  
Surface Tension Gradient ◽  
Water Interface ◽  
Air Water Interface

Numerical Simulation of Oil-Droplet Cleavage by Surfactant

1996 ◽  
Vol 118 (2) ◽  
pp. 201-209 ◽  
Author(s):  
Xiaoyi He ◽  
Micah Dembo
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Surface Tension ◽  
Large Deformation ◽  
Concentration Gradient ◽  
Surface Tension Gradient ◽  
Oil Droplets ◽  
Numerical Computations ◽  
Oil Droplet ◽  
Pure Surface

We present numerical computations of the deformation of an oil-droplet under the influence of a surface tension gradient generated by the surfactant released at the poles (the Greenspan experiment). We find this deformation to be very small under the pure surface tension gradient. To explain the large deformation of oil droplets observed in Greenspan’s experiments, we propose the existence of a phoretic force generated by the concentration gradient of the surfactant. We show that this hypothesis successfully explains the available experimental data and we propose some further tests.

scholarly journals Tackling the Short-Lived Marangoni Motion Using a Supramolecular Strategy

CCS Chemistry ◽  
2019 ◽  
Vol 1 (2) ◽  
pp. 148-155 ◽  
Author(s):  
Mengjiao Cheng ◽  
Dequn Zhang ◽  
Shu Zhang ◽  
Zuankai Wang ◽  
Feng Shi
Keyword(s):  
Surface Tension ◽  
Electricity Generation ◽  
Adsorption Equilibrium ◽  
Molecular Level ◽  
Surface Tension Gradient ◽  
Aggregation State ◽  
Physical Limit ◽  
Competitive Kinetics ◽  
Air Liquid Interface ◽  
Spontaneous Motion

Inspired by the intriguing capability of beetles to quickly slide on water, scientists have long translated this surface-tension-gradient–dominated Marangoni motion into various applications, for example, self-propulsion. However, this classical spontaneous motion is limited by a short lifetime due to the loss of the surface tension gradient. Indeed, the propellant of amphiphilic surfactants can rapidly reach an adsorption equilibrium and an excessive aggregation state at the air/liquid interface. Here, we demonstrate a supramolecular host–guest chemistry strategy that allows the breaking of the physical limit of the adsorption equilibrium and the simultaneous removal of surfactant molecules from the interface. By balancing the competitive kinetics between the two processes, we have prolonged the lifetime of the motion 40-fold. Our work presents an important advance in the query of long-lived self-propulsion transport through flexible interference at the molecular level and holds promise in electricity generation applications .

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