When the hydrophilic group of surfactant is in the center of two hydrophobic chains

2021-03-22 09:25:37

One of the important applications of surfactants in coating industry is as wetting agent. To improve the wettability of pigment and substrate surface. Wetting generally refers to using liquid to displace air on the surface of solid, but wetting is also related to reducing the interfacial tension between solid and liquid.

Most surface coatings contain solid particles such as pigments and fillers. The dispersion of these particles requires effective wetting first. The interfacial tension between solid and liquid can be reduced by adding surfactant to the water containing pigment, so that the water can wet the pigment particles.

When the hydrophilic group of the surfactant is in the center of the two hydrophobic chains, the surfactant has strong wettability, such as sodium Diisooctyl succinate sulfonate (aerosol OT) and alkynol surfactant (SURFYNOL 104) are very effective wetting agents.

Among the nonionic surfactants, the surfactants with hydrophobic chain of 10 ~ 11 carbon atoms and polyoxyethylene chain of 6 ~ 8 EO units seem to be the best wetting agents. In the peo-pp copolymer, the wetting force increases with the increase of the molecular weight of the PEO segment, and reaches a high wetting force when the EO content is low. However, in order to obtain soluble and surface active molecules in the aqueous phase, there must be a certain number of EO units.

The efficiency and quality of dispersion process can be improved by adding wetting agent into abrasives, and the wettability of substrate can be improved by adding wetting agent into coatings. However, the dosage of such surfactants should be as low as possible to avoid water sensitivity and foaming.

Many surfactants are detergents and have the effect of solubilizer and detergent. Such surfactants usually have a straight chain structure with a hydrophilic group at one end, such as sodium lauryl sulfate. Detergents are sometimes used in coatings, but they are usually used as the main component of the cleaning agent for the substrate to be coated. The cleaning of substrate is very important for the good performance of coatings. However, the residual detergent on the substrate will reduce the wettability and adhesion of the coating.

When detergents are included in paint formulations, they usually act as wetting agents. For example, octylphenol polyoxyethylene (9) ether (Triton X-100) is a common additive for this purpose. However, this kind of wetting agent is not as effective as other surfactants, and has no effect of reducing dynamic surface tension in waterborne coatings.