A surface-active agent, or surfactant, is any compound that reduces surface tension between two liquids, or between a liquid and a solid. Two categories of surfactants are of interest to Lorama -- wetting agents & dispersants.
A wetting agent reduces surface tension of the liquid, which allows the liquid to spread over a solid and wet the surface of the solid. In red oxide primers, the wetting agent reduces the surface tension between the primer and the metal substrate.
Soya Lecithin, derived from soybean oil, is an excellent wetting agent; it is not a dispersant. Soya lecithin will assist in the wetting of pigment particles but not in keeping the pigment particles dispersed.
Most long-oil and medium-oil alkyd resins are good wetting agents. Alkyd resins spread uniformly and rapidly over the surface of pigment particles. An alkyd resin with good wetting properties assists in the dispersion of pigments. However, alkyd resin does little to keep pigment particles dispersed.
A dispersant
or dispersing agent promotes uniform and maximum separation of extremely
fine, solid particles in a liquid medium. In white enamels, the dispersant
promotes the uniform and maximum separation of TiO2 in a solvent-based alkyd
resin.
Wetting Agents vs. Dispersants
Guidelines for modifying alkyd Enamels with LPRT
Methods of Lorama Polysaccharide Resin Technology Modification
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