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The Electrical Double Layer01:30

The Electrical Double Layer

In the region where two bulk phases meet, an intricate electric charge distribution arises due to charge transfer, ion adsorption, molecular orientation, and charge distortion. This complex distribution is commonly referred to as the electrical double layer.When a solid electrode interfaces with ions in an electrolyte solution, the speed of electron transfer dictates the rates of oxidation and reduction. The electrode acquires a charge through the escape of atoms into the solution as cations or...
Electric Field of a Non Uniformly Charged Sphere01:22

Electric Field of a Non Uniformly Charged Sphere

Gauss's law states that the electric flux through any closed surface equals the net charge enclosed within the surface. This law is beneficial for determining the expressions for the electric field for a particular charge distribution if the electric flux is known.
Consider a non-uniformly charged sphere, for which the density of charge depends only on the distance from a point in space and not on the direction. Such a sphere has a spherically symmetrical charge distribution. Here, the electric...
Electric Field of a Charged Disk01:23

Electric Field of a Charged Disk

The simplest case of a surface charge distribution is the uniformly charged disk. Calculating its electric field also helps us calculate the electric field of a large plane of charge.
The system's symmetry is in the cylindrical directions across the plane of the charge. As a result, the electric fields created by various surface charge elements nullify each other in the direction parallel to the surface. Thereby, the resulting electric field is perpendicular to the plane. Since the disk is...
Gauss's Law: Spherical Symmetry01:26

Gauss's Law: Spherical Symmetry

A charge distribution has spherical symmetry if the density of charge depends only on the distance from a point in space and not on the direction. In other words, if the system is rotated, it doesn't look different. For instance, if a sphere of radius R is uniformly charged with charge density ρ0, then the distribution has spherical symmetry. On the other hand, if a sphere of radius R is charged so that the top half of the sphere has a uniform charge density ρ1 and the bottom half has a uniform...
Spherical and Cylindrical Capacitor01:26

Spherical and Cylindrical Capacitor

A spherical capacitor consists of two concentric conducting spherical shells of radii R1 (inner shell) and R2 (outer shell). The shells have equal and opposite charges of +Q and −Q, respectively. For an isolated conducting spherical capacitor, the radius of the outer shell can be considered to be infinite.
Conventionally, considering the symmetry, the electric field between the concentric shells of a spherical capacitor is directed radially outward. The magnitude of the field, calculated by...
Electrostatic Boundary Conditions in Dielectrics01:27

Electrostatic Boundary Conditions in Dielectrics

When an electric field passes from one homogeneous medium to another, crossing the boundary between the two mediums imparts a discontinuity in the electric field. This results in electrostatic boundary conditions that depend on the type of mediums the field propagates through.
Consider a case where both the mediums across a boundary are two different dielectric materials. Recall that the electric field and electric displacement are proportional and related through the material's permittivity.

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Related Experiment Video

Updated: Jul 12, 2026

Finite Element Modelling of a Cellular Electric Microenvironment
08:23

Finite Element Modelling of a Cellular Electric Microenvironment

Published on: May 18, 2021

Electrical double layer around a spherical colloid particle: the excluded volume effect.

J J López-García1, M J Aranda-Rascón, J Horno

  • 1Departamento de Física, Universidad de Jaén, Campus de Las Lagunillas, Ed. A-3, 23071, Jaén, Spain.

Journal of Colloid and Interface Science
|September 1, 2007
PubMed
Summary

The excluded volume effect significantly alters ion distribution and increases surface potential around particles. Researchers developed a new equation for surface charge density, essential for understanding colloid systems.

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Last Updated: Jul 12, 2026

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Area of Science:

  • Colloid and Interface Science
  • Physical Chemistry
  • Electrochemistry

Background:

  • The electrical double layer (EDL) around charged particles is crucial in colloid science.
  • Traditional models often assume point-like ions, neglecting finite ion size effects.
  • Excluded volume effects, due to finite ion size, can significantly impact EDL properties.

Purpose of the Study:

  • To investigate the influence of the excluded volume effect on ionic and electrostatic potential distributions near a suspended spherical particle.
  • To determine the adequacy of existing parameters (like kappa*a) for characterizing the EDL under finite ion size conditions.
  • To develop a more accurate model for surface charge density in colloidal systems.

Main Methods:

  • Modification of the Poisson-Boltzmann equation to incorporate finite ion size using a Langmuir-type correction.
  • Analysis of spatial and electrostatic potential distributions around a spherical particle.
  • Derivation of an approximate equation for surface charge density.

Main Results:

  • The parameter kappa*a is insufficient for characterizing the electrical double layer when finite ion size is considered; both kappa and particle radius 'a' are necessary.
  • The excluded volume effect substantially increases surface potential compared to ideal ion models.
  • A new approximate equation for surface charge density was derived, applicable across a broad range of parameters.

Conclusions:

  • Finite ion size is critical and cannot be ignored in EDL modeling.
  • Surface charge density is a more reliable parameter than surface potential for characterizing colloidal systems with excluded volume effects.
  • The derived equation provides a valuable tool for predicting surface charge density in diverse colloidal applications.