Electrical Double Layer:

A double layer (double layer, also called an electrical double layer, Edouble layer) is a structure that appears on the surface of a charged object when it is placed into a liquid. This object might be a solid particle, a gas bubble, a liquid droplet, or a porous body. It consists of two parallel layers of charge. The first layer is the surface charge (either positive or negative) and coincides with the surface of the object. The other layer is in the fluid, and electrically screens the first layer.

This second layer is diffuse, because it forms from free ions in the fluid under the influence of electric attraction and thermal motion, and is thus called the diffuse layer.

Interfacial double layer is usually most apparent in systems with a large ratio of surface area to volume, such as colloid or porous bodies with particles or pores (respectively) on the scale of microns or even nanometers. However, the importance of double layers extends to other systems, e.g., double layer is fundamental to the electrochemical behavior of electrodes.

The double layer plays a fundamental role in many real-world systems. For instance, milk exists only because fat droplets are covered with a double layer that prevent their coagulation into butter. double layers exist in practically all heterogeneous fluid-based systems, such as blood, paints, inks, ceramic slurries and cement slurries.

The double layer is closely related to electrokinetic phenomena and electroacoustic phenomena.

The electrical double layer (EDL) is a structure which describes the variation of electric potential near a surface, and has a significant influence on the behaviour of colloids and other surfaces in contact with solutions or solid-state fast ion conductors.

The primary difference between a DL on an electrode and one on an interface is the mechanisms of surface charge formation. With an electrode, it is possible to regulate the surface charge by applying an external electric potential. This application, however, is impossible in colloidal and porous DLs.

EDLs are analogous to the double layer in plasma.