Surfactants prevent flocculation and sedimentation of coatings

2020-09-16 11:13:02

In order to prevent flocculation and sedimentation of coatings, and keep the viscosity of coatings as low as possible, so as to obtain good fluidity and coating adaptability, surfactants must be used as dispersants. In order to improve the speed of coating locomotive and save energy, it is necessary to use high solid content coatings. As a kind of surfactant with excellent performance, fluorine surfactant has little dosage and excellent effect, so it is an ideal dispersant for coatings. In order to prevent flocculation and sedimentation of coatings, and keep the viscosity of coatings as low as possible, so as to obtain good fluidity and coating adaptability, surfactants must be used as dispersants.

Because of the special structure of FS, fluorine atom is used to replace the hydrogen atom on the hydrophobic group of common surfactant, and the structure of C-H bond is changed into the form of C-F bond. Therefore, FS shows some unique excellent properties of fluorocarbons, and it has the characteristics of both hydrophobic and oleophobic. The high surface activity of FS depends on the strong hydrophobicity and low molecular cohesion of the fluorocarbon bond.

It can reduce the surface tension of water to a very low value, but the concentration used is very small. Generally, the application concentration of hydrocarbon chain surfactant should be between 0.1% - 1%, and the surface tension of aqueous solution can only be reduced to 30-35 dyne / cm, while the surface tension of aqueous solution can be reduced to less than 20 dyne / cm when the dosage of fluorocarbon surfactant is 0.005% - 0.1%. In addition, FS also shows good surface activity in organic solvents, especially the introduction of N-substituted perfluorooctamides, which can reduce the surface tension of hydrocarbon solvents by 5-15 dyne / cm. The excellent thermal stability and chemical inertia of FS are mainly due to the fact that the bond energy (116 kcal / mol) of C-F bond is greater than that of C-H after the hydrophobic group of hydrocarbon chain is replaced by hydrophobic group of fluorocarbon chain The bond energy of C-F bond is 99.5 kcal / mol, so C-F bond is more stable than C-H bond and is not easy to break.

Because the volume of fluorine atom is larger than that of hydrogen atom, the C-C bond is protected by the shielding effect of fluorine atom, so the C-C bond with low bond energy is also stable, which makes the C-C bond stable, which makes FS have the chemical stability and thermal stability that the hydrocarbon surfactant does not have. For example, the use temperature of c9f17oc6h4so3k can be about 300 ℃, and the intermediate c9f17oc6h5 will not decompose in 50% sulfuric acid or 25% sodium hydroxide solution at 80 ℃ for 48 hours.