Analysis of the difference between coupling agents and surfactants

In the process of coating manufacturing, it is necessary to disperse hydrophilic polar substances such as pigments and fillers into hydrophobic non-polar organic binders. In order to increase the affinity between inorganic substances and organic polymers, coupling agents or other surfactants are generally used to treat the surface of inorganic substances, transforming them from hydrophilic to hydrophobic, thereby promoting interfacial bonding between inorganic and organic substances.

Coupling agents and surfactants have some similarities in molecular structure and application performance, but there are also differences. Both are composed of hydrophilic and hydrophobic functional groups.

Surfactants selectively adsorb onto the surface of inorganic pigments and fillers through hydrophilic groups in their molecules, forming a monolayer. This is a physical adsorption phenomenon that improves the dispersibility and wettability of pigments and fillers in the base material. Therefore, only physical adsorption is required, and surfactants have migration phenomena that affect gloss, appearance, and adhesion.

Coupling agents are used to couple and bind inorganic pigments and fillers on the surface through chemical reactions, and crosslink with polymer substrates to combine two substances with different properties, playing a bridging role. In terms of bonding strength, improving the dispersion program of pigments and fillers in the substrate, and reducing the amplitude of interfacial free energy, coupling agents greatly outperform surfactants.