How Does It Work?
It may seem contradictory, but water does not always “wet” well. This is because water (H20) is a polar molecule. It has both positive and negative ends. When these ends are linked by an electrical charge, a chain forms and droplets occur. This is called hydrogen bonding and is the cause of surface tension.
Surface tension isn’t easily visible when viewing a glass of water or a farm pond. It is evident, however, when water is placed on a water-repellant surface such as a waxy plant leaf. The water is NOT SOLUABLE in the wax and remains on the surface of the leaf. The water molecules form chains within themselves, beading into tiny droplets.
Surfactants overcome the effects of beading or surface tension. One end of the surfactant molecule is soluble in oily or waxy substances, and the second end is water soluble. When a surfactant is added to water and oil, its molecules align themselves at the appropriate ends of the interface and pull the layers together, reducing the beading or surface tension.
Figure 2 demonstrates what happens when the same two solutions are sprayed on the leaf surface (common lamb’s-quarters). The leaf at the left has been sprayed with plain water. Distinct droplets occur resulting in spotty coverage of the leaf surface. The leaf on the right has been sprayed with water containing APSA-80® Adjuvant (5oz./20gal. water). It’s evenly covered with the spray solution and will resist runoff, thus saving costly herbicide.
Figure 1 shows drops of water. On top is just water, on the bottom is a solution with Nutriplant APSA-80® All-purpose Spray Adjuvant concentrate (5oz./20gal. Water). Both form drops, but the drop containing the APSA-80® Adjuvant has spread more, has lower height, and will tend to run off the leaf less.
Since water is a carrier for pesticides, when you increase its “wetability” and cause it to spread more evenly, the result is much better pesticide coverage. Air pockets are reduced or eliminated. The pesticide stays on the leaf and penetrates the surface faster and more evenly.
This is visible on the leaf surface as the surfactant molecules pull the water and the wax (on the leaf surface) together, causing the droplet to spread out.
In technical terms, water’s normal surface tension is about 72 dynes/cm. When APSA-80® Adjuvant is added at a rate of 5oz/20gal. Water (equivalent to about 2,000 parts per million [ppm]), the water’s surface tension is reduced by more than half to less than 29 dynes/cm.