A Systematic Study of Wetting as Influenced by Hydrocarbon Fluid Type

Hydrocarbon fluids and oils are commonly used as adjuvants to improve the wetting and spreading properties of a pesticide formulation. An improvement in wetting leads to an increase in the area of contact of a pesticide on a target and usually, although there are exceptions, translates to an increase in efficacy. Target coverage (area per drop) is controlled by a variety of physical and chemical properties of the fluid or oil; these include surface tension, viscosity, and specific gravity. In this study, the influence of these physical factors as well as the composition of the hydrocarbon fluids on the wetting of Sorghum halepense (johnsongrass) and other model substrates has been investigated.

The wetting properties, as measured by contact angle, of four different series of hydrocarbon fluids (normal paraffins, isoparaffins, mixed aliphatics containing iso-, cyclo- and normal paraffins, and aromatics) have been systematically examined on a variety of surfaces (johnsongrass, extracted johnsongrass wax, paraffin wax, Parafilm® and wax paper). It has been shown that hydrocarbon fluids are very good wetters (θ< 30°) of these substrates. Attempts to correlate contact angle measurements with the physical properties of hydrocarbon fluids were unsuccessful until the compositions of the fluids were considered. When the type of hydrocarbon fluid is taken into account, very good correlations are achieved for normal paraffinic, isoparaffinic and aromatic fluids. Mixed aliphatic fluids, as expected, show poorer correlations.