Surface charge is the electric charge present at an interface, for instance on the surface of a semiconductor material, or for example, on the surface of a protein in water. Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. An interface is a surface forming a common boundary among two different phases, such as an insoluble Solid and a Liquid, two immiscible liquids or a liquid In Mathematics, specifically in Topology, a surface is a Two-dimensional Manifold. A semiconductor' is a Solid material that has Electrical conductivity in between a conductor and an insulator; it can vary over that Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl
There are multiple factors generating surface charge.
First of all, surface charge appears practically always on an object surface when it is placed into a fluid. In Physics, a physical body (sometimes called simply a body or even an object) is a collection of Masses taken to be one In Mathematics, specifically in Topology, a surface is a Two-dimensional Manifold. FLUID ( F ast L ight '''U'''ser '''I'''nterface D esigner is a graphical editor that is used to produce FLTK Source code All fluids contain ions, positive (cations) and negative (anions). An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge These ions interact with the object surface. This interaction might lead to adsorption some of them on the surface. Adsorption is a process that occurs when a gas or liquid Solute accumulates on the surface of a solid or a liquid (adsorbent forming a film of molecules or atoms (the If number of adsorbed cations exceeds number of adsorbed anions, surface would gain total positive electric charge. Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. This mechanism is important for colloids and other fluid based heterogeneous systems. A colloid is a type of mechanical Mixture where one substance is dispersed evenly throughout another Heterogeneous is an adjective used to describe an object or system consisting of multiple items having a large number of structural variations
There is another possible mechanism leading to surface charging in fluids. It is dissociation or Differential Solubility of the surface chemical group. Dissociation is a state of acute mental Decompensation in which certain Thoughts Emotions Sensations and/or memories are In Organic chemistry, functional groups are specific groups of Atoms within Molecules that are responsible for the characteristic Chemical reactions The two ionic components of crystals like CaCO3, AgBr, BaSO4, and CaC2O4 always obey the bulk solubility equilibrium. E. g. for AgI Ksp = [Ag+][I-]
The thermodynamic parameter used to describe charged surfaces is the surface potential. The surface potential,y0 , of an ionic crystal is related to the bulk concentration of a potential-determining ion by
y0=(RT/zF)ln(c/cpzc)
where z is the valence (including sign) of the potential-determining ion i, whose concentration is cpzc at the point of zero charge , c is the concentration of the potential determining ion, R is the gas constant,F is the Faraday constant and T is the temperature.
This equation relates the (chemical potentials) concentrations in the bulk, electrically neutral solution to that in the crystal.
i. e. AgI(s) can be precipitated by mixing aqueous solutions of AgNO3 and KI in any ratio. The equilibrium concentrations of [Ag+] and [I-] need not be equal. For mre details of the electric surfface charge description and its relation to the surface chemistry are given by Lyklema in "Fundamentals of Interface and Colloid Science" [1],
Other important example is charging of semiconductors, which originates from a disrupted lattice structure. Surface science is the study of physical and chemical phenomena that occur at the interface of two phases, including Solid - Liquid A semiconductor' is a Solid material that has Electrical conductivity in between a conductor and an insulator; it can vary over that The presence of surface charge also alters the distribution of charge in the near-surface region of the semiconductor. Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction.
In conductors of uniform resistivity at equilibrium, there can be no free charges in the bulk, instead all the charge density is on the surface. In Science and engineering, a conductor is a material which contains movable Electric charges. The linear surface or volume charge density is the amount of Electric charge in a line, Surface, or Volume.
In the case of conducting macroscopic bodies surface charge can be measured using electrostatic fieldmeters or voltmeters can also be used. An electrostatic fieldmeter is a tool used in the static control industry A voltmeter is an instrument used for measuring the Electrical potential difference between two points in an electric circuit
In the case of colloids and similar heterogeneous fluid based systems, direct measurement of the surface charge is impossible due to small sizes of the objects. A colloid is a type of mechanical Mixture where one substance is dispersed evenly throughout another Heterogeneous is an adjective used to describe an object or system consisting of multiple items having a large number of structural variations Instead, zeta potential measurement yields information for calculation surface charge. Zeta potential is an abbreviation for Electrokinetic potential in colloidal systems. Another method is titration with appropriate surface active chemical. Titration is a common laboratory method of Quantitative chemical analysis that is used to determine the unknown Concentration of a known Reactant Some details are given in the book [2]
The average surface charge density σ is given by
,
where q is the net amount of charge and A is the surface area of the interface.
The measurement of surface charge density has applications in:
- Interface and Colloid Science as a part of Double Layer, structure that is responsible for Electrokinetic phenomena and Electroacoustic phenomena
- Electrical engineering. Interface and colloid science is a branch of Chemistry dealing with Colloids Heterogeneous systems consisting of a mechanical mixture of particles between Electrokinetic phenomena is a family of several different effects that occur in Heterogeneous Fluids or in porous bodies filled with fluid Electroacoustic phenomena arises when Ultrasound propagates through a Fluid containing Ions. Electrical engineering, sometimes referred to as electrical and electronic engineering, is a field of Engineering that deals with the study and application of Electrostatic potentials and fields for systems of conducting electrodes may be obtained from the surface charge density.
- Biology. Foundations of modern biology There are five unifying principles Surface charge of proteins and other bio-macromolecules allows their separation in gel or capillary electrophoresis
References
- ^ Lyklema, J. Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl The term macromolecule by definition implies "large Molecule " Electrophoresis is the most well-known electrokinetic phenomenon. “Fundamentals of Interface and Colloid Science”, vol. 2, page. 3. 208, 1995
- ^ Dukhin, A. S. and Goetz, P. J "Ultrasound for characterizing colloids", Elsevier, 2002
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