Influence of the hydrophilic moiety of polymeric surfactant on their surface activity and physical stability of pesticide suspension concentrate

Abstract

Polymeric surfactant has explored as an efficient dispersant for improving the physical stability of pesticide suspension concentrate. However, the influence of the hydrophilic monomer on the surface-active property of polymeric surfactant and its application performance in pesticide formulation is rare investigated. Herein, three kinds of random polymers were designed and synthesized via polymerization reaction of styrene (St), methacrylic acid (MAA) with 2-hydroxyethyl acrylate (HEA), 2-hydroxypropyl acrylate (HPA) and vinyl sulfonate sodium (VS), respectively. A series of surface-active parameters, including critical aggregation concentration (CMC), saturation surface excess concentration (Γmax), minimum area per molecule (Amin) and standard Gibbs free energy ΔGm0 values were obtained from surface tension measurement. The results showed that CMC increased and ΔGm0 decreased with the increase of the hydrophilicity of the third monomer. The results of foamability measurement indicated that the polymeric surfactant with VS as the third monomer had the best foam producing ability and foam stability. When HPA served as the third monomer, the surfactant had the lowest hydrophile lipophile balance (HLB) value and the O/W emulsion prepared by it had the worst stability. Besides, the influence of synthesized polymeric surfactants as dispersant on zeta potential, viscosity and suspension rate of 430 g/L tebuconazole suspension concentrate were investigated. The results showed that poly(styrene-co-methacrylic acid-co-2-hydroxypropyl acrylate) performed best in improving the physical stability of the formulations. From SEM imagines of tebuconazole particle, it was found the increase of particle size in tebuconazole suspension concentrate were caused by aggregation or Ostwald ripening after thermal storage.