What is Helmholtz Electrical Double Layer? Explain with example.

Helmholtz electrical double layer is an double layer of positive and negative charges one molecule  which occurs at the surface where two different materials are in contact.The first layer, the surface charge (either positive or negative), comprises ions adsorbed directly onto the object due to a host of chemical interactions. The second layer is composed of ions attracted to the surface charge via the coulomb force, electrically screening the first layer. This second layer is loosely associated with the object, because it is made of free ions which move in the fluid under the influence of electric attraction and thermal motion rather than being firmly anchored. It is thus called the diffuse layer. Nature of solid predicts that which charge is in fixed state and which charge is in mobile layer.