Stability of etofenprox in water emulsion induced by block copolymer and surfactant

Abstract

Effect of block copolymer polyalkoxylated butyl ether (LQ) and anionic surfactant polyoxyethylene styrenated phenol ether phosphonate (P) on stability of etofenprox in water emulsion was systematically investigated by measuring creaming stability, droplet size, viscosity, and crystallization temperature. Addition of P (LQ) enhanced markedly stability of emulsions prepared with polyoxyethylene (40) castor oil ether (EL-40) and polyoxyethylene (20) castor oil ether (EL-20). On the basis of it, we prepared the EL-40+EL-20+P+LQ (1) and EL-40+EL-20+P+LQ (2) emulsions at the fixed concentrations of EL-40 and EL-20, P and EL-20, respectively. The emulsions displayed the excellent stability, observed only a little turbid layer on the surface with time prolong. The distinct trends of droplets size and viscosity in two kinds of emulsions were well analyzed by the structural properties of surfactants (including block copolymer) and the interaction between them. Furthermore, differential scanning calorimetry (DSC) technology was first introduced to study freeze–thaw stability of pesticide emulsions. The data indicated that the freezing point shifted evidently with P and/or LQ concentration, however, the melting point had almost no change. It revealed that the EL-40+EL-20+P+LQ emulsions had good stability at low temperature. Combination of droplets size and viscosity measurements with DSC technology can be helpful to examine comprehensively the emulsion stability, and select surfactants and obtain pesticide emulsions with good storage and freeze–thaw stability.