Abstract:

The effects of pH value, emulsification temperature and electrolytical ions on the the stability of metolachlor emulsion in water which was stabilized by emulsifier triethanolamine tristyryiphenol polyoxyethy-lene ether phosphate (SCP) were studied by means of average size analysis and Zeta potential measurement. It has been found that: pH value affected the ionization of SCP in water, at pH=9, the stability of emulsion in water was best on account of strong electrostatic exclusion which was provided by completely ionizing of the molecules; when the emulsification temperature was lower, the stability of the emulsion in water was poor because of the slow strength of interfacial film and the less negative charge of the droplets, which was due to the slow diffusion of SCP moleculars to the oil-water interface and the incomplete stretch of SCP moleculars; with the emulsification temperature rising, the viscosity of water phase decreased and the Brownian motion of the droplets were enhanced, which led to the increased probability of the droplets coalescence, and the SCP moleculars were easier to escape from the interface because of thermal motion, which caused the weaken electrostatic repulsion between the droplets, what was more, the hydrophile of SCP would decrease, therefore the stability of emulsion in water became worse;electrolytical ions were able to decrease Zeta potential by compre- ssing the electronic double layer thickness of droplets interface, which could lead to droplets aggregation due to the reduction of electric quantity, the higher the concentration of electrolytical ions and charge number were, the worse the stability of metolachlor emulsion in water were, and ultimately made the the stability of emulsion in water worse. If the electrolytical ions concentration were the same, the capacity of compressing the electro-nic double layer thickness of droplets interface by Ca²⁺ was stronger than Mg²⁺, the stability of metolachlor emulsion were worse after adding Ca²⁺.

Key words: Metolachlor, Emulsion in water, Average diameter, Zeta potential, Emulsion stability