Charged monosized droplet behaviour and wetting ability on hydrophobic leaf surfaces depending on surfactant-pesticide concentrate formulation

Concentration of surfactant and pesticide in aqueous solution influences droplet chargeability and impaction behaviour on leaf surfaces. The phenomenon was investigated in-situ by superposition of induction charges on droplets from surfactant L-77, pesticide EC and L-77 + EC solutions. With an exception of water (control), the conductivity and chargeability of these formulations increased with concentration, whereas surface tension (γ) decreased with an increasing concentration, which consequently minimized static contact angle (θ) on hydrophobic surfaces of Brassica campestris leaves. A reduction in γ- and θ-values enhanced deposition and wetted area per droplet of L-77, EC and L-77 + EC formulations. The wetted area per droplet of L-77 + EC concentration increased from 9.26 mm2 at θ-value of 65.29° in 2.5 mL/L plus 7.5 mL/L to 13.29 mm2 at θ-value of 43.1° in 10 mL/L plus 15 mL/L of water. Additionally, the degree of γ- and θ-values reduction was proportional to charged droplet sizes. For every 1 μL rise in droplet volume, γ-value of L-77, EC and L-77 + EC increased by approx. 5.2, 4.6 and 3.3 mN/m respectively, whereas θ-value reduced by approx. 28.45%, 28.24% and 27.23% respectively. The outcome of the experiment is useful for electrostatic spraying of pesticide in plant protection.