Direct measurement of the viscoelectric effect in water

The viscoelectric effect concerns the increase in viscosity of a polar liquid in an electric field due to its interaction with the dipolar molecules and was first determined for polar organic liquids more than 80 y ago. For the case of water, however, the most common polar liquid, direct measurement of the viscoelectric effect is challenging and has not to date been carried out, despite its importance in a wide range of electrokinetic and flow effects. In consequence, estimates of its magnitude for water vary by more than three orders of magnitude. Here, we measure the viscoelectric effect in water directly using a surface force balance by measuring the dynamic approach of two molecularly smooth surfaces with a controlled, uniform electric field between them across highly purified water. As the water is squeezed out of the gap between the approaching surfaces, viscous damping dominates the approach dynamics; this is modulated by the viscoelectric effect under the uniform transverse electric field across the water, enabling its magnitude to be directly determined as a function of the field. We measured a value for this magnitude, which differs by one and by two orders of magnitude, respectively, from its highest and lowest previously estimated values.

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The vibration of electrified water drops

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1971.0082 ◽

1971 ◽

Vol 322 (1551) ◽

pp. 523-534 ◽

Cited By ~ 20

Keyword(s):

Electric Field ◽

Electric Fields ◽

Axial Ratio ◽

Uniform Electric Field ◽

Interferometric Technique ◽

Photographic Analysis ◽

Wide Range ◽

Water Drops ◽

Strength And Deformation ◽

A Charge

Pressure has been used as the principal parameter in calculations of the fundamental vibrational frequencies of spherical drops of radius R , density ρ, and surface tension T carrying a charge Q or uncharged spheroidal drops of axial ratio a / b situated in a uniform electric field of strength E . Freely vibrating charged drops have a frequency f = f 0 ( 1 - Q 2 /16π R 3 T ) ½ , as shown previously by Rayleigh (1882) using energy considerations; f 0 is the vibrational frequency of non-electrified drops (Rayleigh 1879). The fundamental frequency of an uncharged drop in an electric field will decrease with increasing field strength and deformation a / b and will equal zero when E ( R )/ T ) ½ = 1.625 and a / b = 1.86; these critical values correspond to the disintegration conditions derived by Taylor (1964). An interferometric technique involving a laser confirmed the accuracy of the calculations concerned with charged drops. The vibration of water drops of radius around 2 mm was studied over a wide range of temperatures as they fell through electric fields either by suspending them in a vertical wind tunnel or allowing them to fall between a pair of vertical electrodes. Photographic analysis of the vibrations revealed good agreement between theory and experiment over the entire range of conditions studied even though the larger drops were not accurately spheroidal and the amplitude of the vibrations was large.

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Electroconvective instability in a fluid layer

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1970.0007 ◽

1970 ◽

Vol 314 (1517) ◽

pp. 269-283 ◽

Cited By ~ 10

Keyword(s):

Electrical Conductivity ◽

Electric Field ◽

Field Intensity ◽

Electric Field Intensity ◽

Hartmann Number ◽

Fluid Layer ◽

Uniform Electric Field ◽

Steady Flows ◽

Wide Range ◽

Unstable Configuration

Steady flows of a fluid of slight electrical conductivity under the influence of an applied electric field intensity are often unstable. A study is described to illustrate with experiments and an analytical model the fundamental aspects of a wide range of instabilities that are characterized by the incipience of steady cellular convection as the electric Hartmann number H a e = ∈ E /√(μσ) is of the order of unity (∈ is the permittivity, E the imposed electric field intensity, μ the viscosity, and σ the electrical conductivity). A non-uniform electric field is used to induce an unstable configuration of surface charge and electric field intensity at a planar interface. The resulting instability leads to cellular convection in the plane of the interface. Predictions of the electric Hartmann number and wavelength for incipience of instability compare favourably to measurements. The dependence of the measured cellular convection velocity, resulting from the instability, on electric Hartmann number and electric Reynolds number are also in satisfactory agreement with the predictions from the simple model.

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Hydration Structure and Shear Viscosity of Water Nanoconfined Between Mica Surfaces

Volume 2: Fora ◽

10.1115/fedsm2006-98468 ◽

2006 ◽

Cited By ~ 1

Author(s):

Yongsheng Leng ◽

Peter T. Cummings

Keyword(s):

Molecular Dynamics ◽

Liquid Phase ◽

Shear Rate ◽

Shear Viscosity ◽

Surface Force ◽

Md Simulations ◽

Force Balance ◽

Density Distributions ◽

Wide Range ◽

Hydration Layers

Molecular dynamics (MD) simulations have been performed to investigate the structure, shear viscosity and dynamics of hydration layers of the thickness of D = 0.61 ∼ 2.44 nm confined between two mica surfaces. For D = 0.92 ∼ 2.44 nm films, water O density distributions indicate that the hydration layers are in liquid phase. The corresponding shear responses are fluidic and similar to those observed in surface force balance (SFB) experiment. However, further increase in confinement leads to the formation of a bilayer ice (D = 0.61 nm) which shows significant shear enhancement and shear thinning over a wide range of shear rate in MD regime, consistent with recent experimental results by shear resonant apparatus for the two mica surfaces in registry.

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Electrohydrodynamic settling of drop in uniform electric field: beyond Stokes flow regime

Journal of Fluid Mechanics ◽

10.1017/jfm.2019.744 ◽

2019 ◽

Vol 881 ◽

pp. 498-523 ◽

Cited By ~ 3

Author(s):

Nalinikanta Behera ◽

Shubhadeep Mandal ◽

Suman Chakraborty

Keyword(s):

Electric Field ◽

Flow Regime ◽

Stokes Flow ◽

Capillary Number ◽

Uniform Electric Field ◽

Fluid Inertia ◽

Drop Shape ◽

Wide Range ◽

Settling Speed ◽

Leaky Dielectric

The electrohydrodynamics of a weakly conducting buoyant drop under the combined influence of gravity and a uniform electric field is studied computationally, focusing on the inertia-dominated regime. Numerical simulations are performed for both perfectly dielectric and leaky dielectric drops over a wide range of dimensionless parameters to explore the interplay of fluid inertia and electrical stress to govern the drop shape and charge convection. For perfectly dielectric drops, the fluid inertia alters the drop shape and the deformation behaviour of the drop follows a non-monotonic path. The drop shape at steady state exhibits the transition from oblate to prolate shape on increasing the electric field strength, in sharp contrast to the cases concerning the Stokes flow regime. Similar behaviour is also obtained for leaky dielectric drops for certain fluid properties. For leaky dielectric drops, the fluid inertia also affects the convective transport of charges at the drop surface and thereby alters the drop dynamics. Unlike the Stokes flow regime, where surface charge convection has little effect on the settling speed, the same modifies the drop settling speed quite significantly in the finite inertial regime depending on the combination of electrical conductivity ratio and permittivity ratio. For oblate drops at low capillary number, charge convection alters drop shape, while keeping the nature of deformation unaltered. However, for relatively large capillary number, the oblate drop transforms into a dimpled shape due to charge convection. For all cases, an interesting fact is noticed that under the combined action of electric and inertial forces, the resultant deformation is less than the summation of the deformations caused by individual effects, when inertial effects are strong. These results are likely to provide deep insights into the interplay of various nonlinearities towards altering electrohydrodynamic settling of drops and bubbles.

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Axisymmetric deformation and stability of a viscous drop in a steady electric field

Journal of Fluid Mechanics ◽

10.1017/s0022112007007999 ◽

2007 ◽

Vol 590 ◽

pp. 239-264 ◽

Cited By ~ 124

Author(s):

ETIENNE LAC ◽

G. M. HOMSY

Keyword(s):

Electric Field ◽

Stable Solution ◽

Physical Property ◽

Linear Instability ◽

Axisymmetric Deformation ◽

Creeping Flow ◽

Uniform Electric Field ◽

Electric Stress ◽

Wide Range ◽

Break Up

We consider a neutrally buoyant and initially uncharged drop in a second liquid subjected to a uniform electric field. Both liquids are taken to be leaky dielectrics. The jump in electrical properties creates an electric stress balanced by hydrodynamic and capillary stresses. Assuming creeping flow conditions and axisymmetry of the problem, the electric and flow fields are solved numerically withboundary integral techniques. The system is characterized by the physical property ratios R (resistivities), Q (permitivities) and λ (dynamic viscosities). Depending on these parameters, the drop deforms into a prolate or an oblate spheroid. The relative importance of the electric stress and of the drop/medium interfacial tension is measured by the dimensionless electric capillary number, Cae. For λ = 1, we present a survey of the various behaviours obtained for a wide range of R and Q. We delineate regions in the (R,Q)-plane in which the drop either attains a steady shape under any field strength or reaches a fold-point instability past a critical Cae. We identify the latter with linear instability of the steady shape to axisymmetric disturbances. Various break-up modes are identified, as well as more complex behaviours such as bifurcations and transition from unstable to stable solution branches. We also show how the viscosity contrast can stabilize the drop or advance break-up in the different situations encountered for λ = 1.

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Enhanced heat flux in non-uniform electric fields

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1973.0080 ◽

1973 ◽

Vol 334 (1596) ◽

pp. 71-82 ◽

Cited By ~ 10

Keyword(s):

Heat Flux ◽

Electric Field ◽

Electric Fields ◽

Significant Contribution ◽

Nucleate Boiling ◽

Polar Liquid ◽

Uniform Electric Field ◽

Burn Out ◽

Concentration Of Ions ◽

Polarity Effects

Heat transfer by convection from a thin wire to a liquid was very appreciably increased by the application of a non-uniform electric field of several hundred kilovolts per centimetre which was confocal with the temperature field. This enhancement of the heat flux was much larger in a polar, slightly conducting liquid than in a practically ion-free liquid; the behaviour of a non-polar liquid which contained traces of a polar impurity was intermediate between the two. The polarity of the electric field affected the magnitude of the enhancement of the heat flux in the polar liquid and to a lesser extent also in the non-polar liquid which had a slight content of a polar contamination, but the direction of the field had no influence what-soever on the enhancement of the heat flux in the ion-free liquid. With each of these three liquids the electrostatic field delayed and even suppressed the transition to nucleate boiling and therefore reduced the risk of ‘burn-out'. It appears that dielectrophoresis is primarily responsible for the increased convection, but that an ion transport phenomenon can make a further significant contribution. The observed polarity effects, in the presence of a minute concentration of ions, suggest that this could be an ion wind. For large values of the electrical number ( El ) the incremental increase of the Nusselt number ( Nu ) by dielectrophoresis can be of the order of one hundred.

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Microwaves: Application in Electron Microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100158248 ◽

1990 ◽

Vol 48 (3) ◽

pp. 140-141

Author(s):

Anthony S-Y Leong ◽

David W Gove

Keyword(s):

Electron Microscopy ◽

Light Microscopy ◽

Chemical Reactions ◽

Electromagnetic Waves ◽

Tissue Fixation ◽

Primary Method ◽

Dipolar Molecules ◽

Wide Range ◽

Time Required ◽

Cryostat Sections

Microwaves (MW) are electromagnetic waves which are commonly generated at a frequency of 2.45 GHz. When dipolar molecules such as water, the polar side chains of proteins and other molecules with an uneven distribution of electrical charge are exposed to such non-ionizing radiation, they oscillate through 180° at a rate of 2,450 million cycles/s. This rapid kinetic movement results in accelerated chemical reactions and produces instantaneous heat. MWs have recently been applied to a wide range of procedures for light microscopy. MWs generated by domestic ovens have been used as a primary method of tissue fixation, it has been applied to the various stages of tissue processing as well as to a wide variety of staining procedures. This use of MWs has not only resulted in drastic reductions in the time required for tissue fixation, processing and staining, but have also produced better cytologic images in cryostat sections, and more importantly, have resulted in better preservation of cellular antigens.

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