Aqueous dispersion system
Aqueous dispersion system, often used to analyze the relationship between surfactant structure and dispersibility. As a hydrophobic solid particle, it can adsorb the hydrophobic group of surfactant, and in the case of anionic surfactant, the hydrophilic group facing outward will be repelled by the same charge. Obviously, the adsorption efficiency of surfactants increases with the increase of the length of hydrophobic group, so the long carbon chain is better dispersed than the short carbon chain.
If the hydrophilicity of the surfactant is increased, it tends to increase its solubility in water, which reduces the adsorption on the particle surface. This effect is even greater if the force between the surfactant and the particles is weak. Such as the preparation of dyestuff water dispersion system, strong hydrophobic dyestuff with high sulfonation of lignosulfonate dispersant, can form a good thermal stability of the dispersion system; and hydrophilic dyestuff with the same dispersant, the thermal stability is poor, but with a lower degree of sulfonation of lignosulfonate as a dispersant, but can be obtained with a good thermal stability of the dispersion system. The reason is that the dispersant with high degree of sulfonation is very soluble at high temperature, and thus it is easy to detach from the hydrophilic dyestuff surface where the effect is weak, thus reducing the dispersibility.
If the dispersed particles themselves are electrically charged and surfactants with opposite charges are used, flocculation may occur before the charges of the particles are neutralized. Only after the second layer of surfactant is adsorbed on the neutralized particles, it can be well dispersed.
If a surfactant of the same charge is used, it is difficult for the particles to adsorb the surfactant, and again only at high concentrations is there sufficient adsorption to stabilize the dispersion. In practice, the ionic dispersants used often contain multiple ionic groups and are distributed throughout the surfactant molecule, while the hydrophobic groups contain unsaturated hydrocarbon chains with polar groups such as aromatic rings or ether bonds.
