Surfactants and Their Applications in Electroplating

Surfactants are one of the important raw materials in the field of metal surface treatment and also an indispensable component of most electroplating additives. Throughout the whole electroplating process, surfactants are used in almost every step, including chemical degreasing, pickling and rust removal, electrolytic degreasing and substrate activation in pre‑plating treatment, additives for single‑metal and alloy electroplating during electroplating, anti‑tarnishing agents and protective films for coatings in post‑plating treatment, as well as electroplating wastewater treatment. Their wide‑ranging applications benefit from the special chemical structure of surfactants and the unique properties derived therefrom.

① The addition of surfactants reduces the surface tension of electroplating solutions and promotes hydrogen evolution during cathodic electrodeposition. It prevents pits, blemishes and pinholes on coatings and improves the bonding force between coatings and substrates.

② Aqueous surfactant solutions adsorb on oil‑stained solid surfaces, wetting, penetrating, emulsifying and dispersing oil stains on solid surfaces so as to remove grease.

③ Surfactants contain hydrophilic groups and hydrophobic groups. Directional adsorption of hydrophobic groups at the electrode interface forms an electric double layer, which usually increases the overpotential of electrode reactions and enhances polarization during electrodeposition. This refines coating crystals and may change mechanical and physical properties of coatings such as internal stress, hardness and ductility.

④ Directional adsorption of surfactants at the gas‑liquid interface forms a dense surface liquid film. Combined with the foam layer produced by the foaming effect of certain surfactants, it prevents acid mist from escaping.

The solubilizing and dispersing properties of surfactants help disperse certain water‑insoluble primary brightener molecules in solutions. Their synergistic effect can produce bright coatings with good leveling performance.

Certain cationic surfactants make solid particles in plating solutions positively charged and form a protective film on particle surfaces. They reduce the surface tension of solid particles, effectively preventing solid particles from agglomerating in solutions, enabling uniform dispersion of solid particles, and allowing particles to be evenly embedded into coatings along with metal electrodeposition, thus realizing composite electroplating and endowing coatings with special functional applications.