Understanding what Nonionic surfactants really do in a spray tank and on leaf surfaces

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Understanding what Nonionic surfactants really do in a spray tank and on leaf surfaces

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It can be challenging at times to conceptualize/imagine what a surfactant is doing from a spray tank mixture to a leaf surface. By the time a spray tank mixture (water, herbicide, Adjuvant/surfactant, etc.) is sprayed on to a leaf surface as liquid droplets, they are relatively small and indistinguishable from rain droplets to the naked eyes, and that which is taking place within the liquid droplet because of the surfactant is not always obvious. Our goal is to paint a clear picture of what the Nonionic surfactant functions within the mixture and its impact on the leaf surface.  

Surfactant increases the spray tank droplet spreading on leaf surface (Schematic)

As you may have heard many times over, a surfactant is a surface-acting-agent, and yes, this is true. You may have also heard that surfactant is a chemical substance that reduces the surface tension of a liquid, also true. The application of these definitions in relation to herbicide spray applications can be summarized as the ability of a chemical (called surfactant) to help liquid spray droplets spread across leaf surface. In addition to spreading, surfactants have features that allow for water and oil/oil-like chemicals to mix well. These features of surfactant are critical to why they are mandated on herbicide labels, so that there is reduction in over-using herbicides that possess the ability to significantly impact environment and those living within them.  

The term surfactant is generally used interchangeably with the term Adjuvants. Although, it should be noted that not all adjuvants are made up of surfactants, though most are. Within the Adjuvant formulation, surfactant make up, what is called, the Principal Functioning agent. Principal Functioning Agents (PFAs) are chemicals within an adjuvant formulation that play an important role in determining the features of the adjuvant. Many adjuvants have stated on their labels several Principal Functioning Agents. It is the combination of these PFAs that determines the features and overall classification of Adjuvants, such as Nonionic surfactants, Methylated Seed oil concentrates, High Surfactant Oil concentrates, etc. Hopefully we are not confused with the term nonionic surfactant which is also used to represent a type of surfactant. For the remainder of the article, we will use the term NIS when referring to the classification of adjuvants, and nonionic surfactants when referring to the type of surfactant based on its chemistry.  

Whenever an adjuvant is classified as a NIS, the typical claim is that the nonionic surfactant within the formulation is responsible for the predominant feature, among the other listed PFAs, of that adjuvant. The adjuvant classified as a NIS is primarily responsible for increasing the ability of the liquid spray droplet to spread and maintain contact with the leaf surface. This is crucial to increasing the probability that the herbicide active ingredients get maximum contact with the leaf surface and increases the chance of the herbicide active ingredient reaching the active site of the target weed.

There are many groups of nonionic surfactants within NIS adjuvant. For example, alcohol ethoxylates, alkylphenol ethoxylates, fatty acid ethoxylates, alkyl polyglucosides, polyethylene sorbitan fatty acid ester are a few common groups of nonionic surfactants. The reason they are called nonionic surfactants is because there is no formal charge within the chemical structure of these surfactants. These types of chemicals are beneficial because when a surfactant has a charge (positive or negative) they can potentially react either favorably or unfavorably with the herbicide active ingredients. When nonionic surfactants are used, there is no reaction with the herbicide active ingredients which allows the herbicide to be delivered as intended.

It should be noted that there are two other type of surfactant worth mentioning, called Ionic and amphoteric surfactants, and these are sometimes used within the different types of Adjuvants, even Adjuvants that are classified as NIS. Some common ionic and amphoteric surfactants are Alkyl sulfates (anionic), alcohol ethoxylates phosphates (anionic), tallow amine ethoxylates (cationic) and lecithin/phosphatidylcholine (amphoteric). The different groups of surfactants, whether ionic or nonionic, are typically stated on Adjuvant labels.

Additionally, It is also important to be aware that other classifications of Adjuvants, other than NIS, may also contain nonionic surfactants in their formulations. However, the primary feature may not be because of the type of surfactant but due to the features of another component of the PFAs. For example, MSO concentrates, which is a type of adjuvant, are so called because ‘methylated seed oil’ provides the most important feature, among the PFAs that are present, to the MSO concentrate classification.

When choosing an adjuvant, the overall feature of the adjuvant along with the label recommendation classification should assist you in choosing an adjuvant to be used in your tank mix. For example, if spraying in relatively windy conditions and the label recommends using a NIS, a good choice would be a NIS that also has drift reduction features. Or if spraying in hot climate and a NIS is recommended, using a NIS with the added ability to reduce the rate of spray droplet evaporation would be a better choice.  

In summary, NIS causes your spray droplet to mix well in a tank and to spread well on a leaf surface. Both features are important to increasing the efficacy of herbicides where a NIS is recommended by the herbicide label. Brewer International supplies a variety of NIS surfactants: Big Sur 90 (APE-free/low foam), 90-10 surfactant (APE-free/low foam), Cide-Kick (penetrant/fragrant), Cide-kick II (penetrant/fragrant), Cide-kick II methylated (penetrant/fragrant), Sun Control (penetrant/buffer), PolyFilm R (APE-free/penetrant/fragrant), AquabupH (Sequestrant/Fragrant/buffer), Sun Control (APE-free/buffer/penetrant), SilNet200 (Premium APE-free NIS/low foam/slow drying), SilEnergy (low foam/slow drying). 

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