When deciding which adjuvants to use with active ingredients in a tank mix, it’s important to consider a few factors of the adjuvants. Before our products hit the market, extensive lab testing is conducted to understand how these adjuvants will behave and perform in real-world scenarios. These tests give valuable information to help users decide which adjuvants to include. One crucial test is measuring surface tension, which assesses how well a liquid can spread over a target, like a weed leaf or unwanted insect.
Since molecules are cohesive, a liquid wants to stay together, and the surface of a liquid allows it to resist an external force that prevents spreading over the target or breaking up into smaller droplets. A surface tension test measures that force. The surface tension measurement gives an idea of a formulation’s surfactant qualities. The lower the surface tension number, the better the formulation will spread.
At Exacto, Inc., we use a tensiometer to measure the surface tension. The process consists of the following steps:
To see the measurement in action, watch the video below.
Think about pulling your foot free from mud. It grabs you and doesn’t want to let go. The same thing happens with liquid on this plate, it just doesn’t hold on nearly as hard.
The same surface tension aids in the formation of emulsions, where substances like oil form small drops in water rather than mixing evenly. Lower surface tension helps create stable oil-water emulsions that last longer. In many tank mixtures, water is blended with oils and oil-based materials, making surface tension crucial to optimize a tank mix beyond just spreading on the intended target.
When a substance with a high surface tension is sprayed or dropped onto another surface, it beads up, causing it to roll off or sit on top of the surface without spreading out. This is often seen with pesticide tank mixes in both agriculture and turf. Pesticide spray droplets with high surface tension result in lower efficacy as more droplets roll off the target.
Adding a surfactant to a liquid can lower surface tension, encouraging wetting on grass and crop leaves, soil, and other surfaces. Better wetting means the droplet spreads out on the leaf, decreasing the likelihood that it will roll off target. Lower surface tension can also result in increased droplet size of spray fans.
Knowing the surface tension of a adjuvant is important because it tells its spreading capabilities. If the surface tension is under 50 newton meters per meter (Nm/m), the adjuvant has surfactant properties. Good surfactants at low concentrations (0.25%) can lower the surface tension of water to anywhere from 25 to 35 Nm/m, less than half the surface tension of plain water.
The surface tension test serves as a valuable tool for assessing adjuvant properties. When combined with other pertinent tests, such as contact angle and the Draves Test, it yields tangible data about the essential traits of a solution. Although these tests may not always show a direct one-to-one relationship with a solution’s ability to wet a surface, they do offer insights into the formulation’s characteristics. The process of wetting solid surfaces is intricate and influenced by a variety of factors, and measuring surface tension is a practical means of gauging the likelihood that an adjuvant will effectively cover a target
Understanding formulations starts in the lab. Knowing the specifications of a product can help users understand how they use may act and perform in the real-world. Exacto Chemist, Chris Walter, explains Contact Angle to help applicators better understand the chemistry behind surfactants, sticker spreaders, and wetting agents in this edition of the Research to Real-World series.
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