What Does Helmholtz Double Layer (HDL) Mean?
Helmholtz double layer (HDL) refers to the structural representation of the accumulation of electrical charges present at the boundary of an electrode and electrolyte when they are in contact with each other. HDL is most readily identifiable in fluid-based mixture systems, such as paints used for corrosion prevention.
Corrosionpedia Explains Helmholtz Double Layer (HDL)
In 1853, Hermann von Helmholtz first identified that two layers of opposite polarity exist at the junction interface between an electrode and electrolyte. An electrical double layer is a molecular dielectric stored charge. HDLs are made up of two layers of opposite charges. When an electrical conductor is in contact with an electrolyte, a common boundary between the two phases is created.
HDL is in general composed of adsorbed water molecules at the surface of the electrode, followed by a layer of electrolytic ions. Such a dynamic exists when coatings are applied to a metal substrate to be protected against corrosion.