Surfactants and dispersants both appear as additives, and what relationship should they have during their use? And what should be noted during the addition process? Next, the editor of Jianyi Chemical will introduce it to everyone!
The commonly used system is the water dispersion system, which can be used to analyze the relationship between the structure and dispersibility of surfactants. As hydrophobic solid particles, it can adsorb hydrophobic groups of surfactants. If it is an anionic surfactant, it will cause the hydrophilic genes facing outward to have the same charge and repel each other. Obviously, the adsorption efficiency of surfactants increases with the length of the hydrophobic group, so long carbon chains have better dispersibility than short carbon chains.
If the hydrophilicity of surfactants is increased, their solubility in water is often increased, thereby reducing the adsorption on the surface of particles. If the interaction force between the surfactant and the particles is weak, this effect is even greater. When preparing dye water dispersion systems, using highly sulfonated lignosulfonate dispersants for strongly hydrophobic dyes can form dispersion systems with good thermal stability; When using the same dispersant for hydrophilic dyes, the thermal stability is poor, but using lignosulfonate with a lower degree of sulfonation as a dispersant can obtain a dispersion system with better thermal stability. The reason is that high sulfonated dispersants have a high solubility at high temperatures, making them easy to detach from the already weak hydrophilic dye surface, thereby reducing dispersibility.
If the dispersed particles themselves carry charges and surfactants with opposite charges are used, flocculation may occur before the charges carried by the particles are neutralized. Only by adsorbing a second layer of surfactant on particles with neutralized charges can they be well dispersed. If surfactants with the same charge are used, it is difficult for particles to adsorb surfactants, and only at high concentrations can there be sufficient adsorption to stabilize the dispersion. In fact, the ionic dispersants used often contain multiple ionic groups distributed throughout the surface active agent molecule, while the hydrophobic groups contain unsaturated hydrocarbon chains with polar groups such as aromatic rings or ether bonds.
The highly hydrated polyoxyethylene chains of nonionic surfactant molecules extend into the aqueous phase in a curled shape, forming a good spatial barrier for solid particle aggregation. At the same time, the thick layers of hydrated polyoxyethylene greatly reduce the van der Waals attraction between particles, making it an excellent dispersant. Especially for block copolymers of propylene oxide and ethylene oxide, their polyoxyethylene chains are longer, increasing solubility, while the hydrophobic groups of propylene oxide grow, increasing the adsorption of solid particles. Therefore, both are longer and are very suitable as dispersants.
When combining ionic and non-ionic surfactants, on the one hand, it causes molecules to extend into the aqueous phase, forming spatial barriers that prevent particles from approaching each other; On the other hand, it enhances the strength of the solid particle interface facial mask. Therefore, after mixing, as long as the increase in their solubility in the aqueous phase does not significantly affect the adsorption on the particle surface, dispersants with longer hydrophobic groups have stronger dispersibility.
