Electrokinetic phenomena are a family of several different effects that occur in
heterogeneous
Homogeneity and heterogeneity are concepts often used in the sciences and statistics relating to the uniformity of a substance or organism. A material or image that is homogeneous is uniform in composition or character (i.e. color, shape, siz ...
fluids
In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...
, or in porous bodies filled with fluid, or in a fast flow over a flat surface. The term
heterogeneous
Homogeneity and heterogeneity are concepts often used in the sciences and statistics relating to the uniformity of a substance or organism. A material or image that is homogeneous is uniform in composition or character (i.e. color, shape, siz ...
here means a fluid containing particles. Particles can be
solid
Solid is one of the State of matter#Four fundamental states, four fundamental states of matter (the others being liquid, gas, and Plasma (physics), plasma). The molecules in a solid are closely packed together and contain the least amount o ...
, liquid or
gas
Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma).
A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...
bubbles with sizes on the scale of a
micrometer Micrometer can mean:
* Micrometer (device), used for accurate measurements by means of a calibrated screw
* American spelling of micrometre
The micrometre ( international spelling as used by the International Bureau of Weights and Measures; ...
or
nanometer
330px, Different lengths as in respect to the molecular scale.
The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm) or nanometer (American and British English spelling differences#-re ...
.
[Dukhin, A. S. and Goetz, P. J. ''Characterization of liquids, nano- and micro- particulates and porous bodies using Ultrasound'', Elsevier, 2017
] There is a common source of all these effects—the so-called
interfacial 'double layer' of charges. Influence of an external
force
In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a p ...
on the
diffuse layer
A double layer (DL, also called an electrical double layer, EDL) is a structure that appears on the surface of an object when it is exposed to a fluid. The object might be a solid particle, a gas bubble, a liquid droplet, or a porous body. The D ...
generates tangential motion of a fluid with respect to an adjacent charged surface. This force might be
electric
Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by ...
,
pressure gradient
In atmospheric science, the pressure gradient (typically of Earth's atmosphere, air but more generally of any fluid) is a physical quantity that describes in which direction and at what rate the pressure increases the most rapidly around a particu ...
,
concentration gradient
Molecular diffusion, often simply called diffusion, is the thermal motion of all (liquid or gas) particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size (mass) of ...
, or
gravity
In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
. In addition, the moving phase might be either continuous
fluid
In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...
or
dispersed phase
A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others extend ...
.
Family
Various combinations of the driving force and moving phase determine various electrokinetic effects. According to J.Lyklema, the complete family of electrokinetic phenomena includes:
*
electrophoresis
Electrophoresis, from Ancient Greek ἤλεκτρον (ḗlektron, "amber") and φόρησις (phórēsis, "the act of bearing"), is the motion of dispersed particles relative to a fluid under the influence of a spatially uniform electric fie ...
, as motion of particles under influence of electric field;
*
electro-osmosis Electroosmotic flow (or electro-osmotic flow, often abbreviated EOF; synonymous with electroosmosis or electroendosmosis) is the motion of liquid induced by an applied potential across a porous material, capillary tube, membrane, microchannel, or an ...
, as motion of liquid in porous body under influence of electric field;
*
diffusiophoresis
Diffusiophoresis is the spontaneous motion of colloidal particles or molecules in a fluid, induced by a concentration gradient of a different substance. In other words, it is motion of one species, A, in response to a concentration gradient in an ...
, as motion of particles under influence of a
chemical potential
In thermodynamics, the chemical potential of a species is the energy that can be absorbed or released due to a change of the particle number of the given species, e.g. in a chemical reaction or phase transition. The chemical potential of a species ...
gradient
In vector calculus, the gradient of a scalar-valued differentiable function of several variables is the vector field (or vector-valued function) \nabla f whose value at a point p is the "direction and rate of fastest increase". If the gradi ...
;
*
capillary osmosis, as motion of liquid in porous body under influence of the
chemical potential
In thermodynamics, the chemical potential of a species is the energy that can be absorbed or released due to a change of the particle number of the given species, e.g. in a chemical reaction or phase transition. The chemical potential of a species ...
gradient
In vector calculus, the gradient of a scalar-valued differentiable function of several variables is the vector field (or vector-valued function) \nabla f whose value at a point p is the "direction and rate of fastest increase". If the gradi ...
;
*
sedimentation potential, as electric field generated by sedimenting
colloid
A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others extend ...
particles;
*
streaming potential/current, as either electric potential or current generated by fluid moving through porous body, or relative to flat surface;
*
colloid vibration current
Colloid vibration current is an electroacoustic phenomenon that arises when ultrasound propagates through a fluid that contains ions and either solid particles or emulsion droplets. Dukhin, A.S. and Goetz, P.J"Characterization of liquids, nano- a ...
, as electric current generated by particles moving in fluid under influence of
ultrasound
Ultrasound is sound waves with frequency, frequencies higher than the upper audible limit of human hearing range, hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hea ...
;
*
electric sonic amplitude, as ultrasound generated by colloidal particles in oscillating electric field.
Further reading
There are detailed descriptions of electrokinetic phenomena in many books on
interface and colloid science
Interface and colloid science is an interdisciplinary intersection of branches of chemistry, physics, nanoscience and other fields dealing with colloids, heterogeneous systems consisting of a mechanical mixture of particles between 1 nm and ...
.
[Lyklema, J. (1995) ''Fundamentals of Interface and Colloid Science'', Vol. 2, p. 3.208.][Kruyt, H.R. (1952) ''Colloid Science'', Elsevier. Volume 1, Irreversible systems.][Anand Plappally, Alfred Soboyejo, Norman Fausey, Winston Soboyejo and Larry Brown]
Stochastic Modeling of Filtrate Alkalinity in Water Filtration Devices: Transport through Micro/Nano Porous Clay Based Ceramic Materials
" J Nat Env Sci 2010 1(2):96-105.
See also
*
Isotachophoresis
Isotachophoresis (ITP) is a technique in analytical chemistry used for selective separation and concentration of ionic analytes. It is a form of electrophoresis; charged analytes are separated based on ionic mobility, a quantity which tells ...
*
Onsager reciprocal relations
In thermodynamics, the Onsager reciprocal relations express the equality of certain ratios between flows and forces in thermodynamic systems out of equilibrium, but where a notion of local equilibrium exists.
"Reciprocal relations" occur betw ...
*
Surface charge
Surface charge is a two-dimensional surface with non-zero electric charge. These electric charges are constrained on this 2-D surface, and surface charge density, measured in coulombs per square meter (C•m−2), is used to describe the charge di ...
*
Cationization of cotton
Cationization of cotton is an electro kinetic phenomena ( zeta potential and electro kinetic) for surface charge of cotton. The cotton surface is charged with positive ions. Cationization alters the characterization of the surface of the cotton w ...
References
{{DEFAULTSORT:Electrokinetic Phenomena
Colloidal chemistry
Condensed matter physics
Soft matter
Non-equilibrium thermodynamics
Electrochemistry