Adding surfactants or other adjuvants can increase the effectiveness of pesticides by positively affecting deposition, spreading, sticking or penetrating into the plant. Understanding the properties of adjuvants by measuring the contact angle of an adjuvant creates insight into the performance of adjuvants. Contact angle is a measurement taken in the lab that reveals a solution’s ability to spread out on and wet a surface.
Contact angle measures the angle of a liquid droplet when it is placed on a solid surface, emulating how a product will spread out on a leaf. The lower the contact angle, the more the adjuvant spreads out, the better wetting abilities it has. This measurement helps compare how well products can wet a surface.
1. A surfactant or adjuvant solution is prepared, loaded into a syringe, and placed into a contact angle goniometer.
2. The surface is prepared on the goniometer test platform. This can be glass, metal, quartz, or any other material so long as it is uniform and replicable.
In the Exacto lab, small pieces of Parafilm are used as our standard surface. This allows for a consistent surface that is both replicable as well as disposable to avoid contamination between tests. Parafilm is also an industry-accepted model for a waxy leaf surface, which makes the test more applicable to the real-world usage of Exacto formulations in agriculture, turf and ornamental or industrial vegetation management.
When an agricultural spray is applied to a plant, the droplets deposit onto the leaf surface. These droplets will either bead up or spread out. This is based on factors like temperature, how waxy the leaf is, how rough the leaf is, and the chemicals in the spray mixture. If a drop beads up, it is more likely to roll off the leaf surface together with the active. If a drop spreads out, it is more likely to stay attached to the leaf surface and keep the agricultural chemical on the plant. When a drop of liquid is put on a solid surface, there are three boundaries to consider – liquid – air, air – solid, solid – liquid. Contact angle is measured where these surfaces meet.
Contact angle measures where gas phase, liquid, and solid meet when a droplet is placed on a surface. A lower contact angle spreads the active over a larger surface.
When a droplet stretches out on a leaf, it increases the surface area it covers. The contact angle measures a liquid’s ability to stretch out over a leaf. A lower contact angle predicts more spread-out droplets, leading to better wetting capabilities.
A droplet that beads up on a surface has a very high contact angle. A droplet that spreads out across a surface has a low contact angle.
Water on Parafilm has a contact angle of roughly 93-95 degrees, which is high. Adding a surfactant or wetting agent can reduce the contact angle significantly depending on the type of surfactant and concentration. This also reduces the chance of droplets beading up and bouncing off the plants during an application.
Contact angle measures where gas phase, liquid, and solid meet when a droplet is placed on a surface.
While any liquid with a contact angle smaller than 90 degrees indicates a wetting capability, the lower the contact angle, the better the spreading is. Liquids with a zero-degree contact angle wet a surface completely and contact angles between 10 and 20 degrees are considered excellent wetters.
Contact angle is a very valuable measurement for comparing adjuvant properties. This test, combined with other useful tests like surface tension and Draves Test, provides concrete data on fundamental aspects of a solution. While they do not always correlate to a solution’s ability to wet a surface, they can provide insight to the characteristics of a formulation. Wetting of solid surfaces is a complicated process that depends on a multitude of other factors, and contact angle is a handy way to measure how adjuvants can help an active cover the target area more effectively.
Understanding formulations starts in the lab. Knowing how a substance might perform under certain conditions can help users understand how the products they use may act and perform in the real-world. Exacto Chemist, Chris Walter, explains the Draves Test to help applicators better understand the chemistry behind surfactants and wetting agents in this edition of the Research to Real-World series.
Surfactants are widely used across the world – in fact, you probably use surfactants every day in soaps, detergents, toothpaste, cosmetics, and countless other applications. Surfactants are just as important in agriculture and turf and understanding how and when to use the right surfactant can make or break a successful application.
Pre-emergence herbicide applications offer a valuable tool to prevent or reduce weed infestations early in the season. While these applications are helpful, it can be a challenge to achieve optimum results. Adjuvant use is increasing and studies continue to prove their effectiveness.
Leaders from Exacto and other companies recently took part in advocacy activities in Washington, DC, engaging in twenty-four meetings with congressional leadership, senators, and the Environmental Protection Agency (EPA). They addressed a major challenge related to the Endangered Species Act (ESA).
Failed weed control may resemble herbicide resistance, but it’s not always the culprit. Recent cases of HPPD-inhibitor (group 27) herbicide failures have shown that certain application errors are more common culprits than resistance. This research shows ways to overcome these application challenges.
Cutting-edge discussions on golf course maintenance, including adjuvants and wetting agents, took place at the 2024 GCSAA Conference. The Exacto team was in full swing, bringing spray adjuvants, wetting agents, and innovative formulations to the table.
Have you ever thought you prepared the perfect application, but gotten less-than-perfect results? As the largest component of a spray tank mix, water can significantly impact application quality with hardness, pH differences, or dirtiness. Water conditioners can help to mitigate these issues.
This site uses cookies and other tracking technologies to assist with navigation, monitor site usage, and web traffic, assist with our marketing efforts, customize and improve our services and websites, as set out in our Privacy Notice.