Surfactants are chemicals that decrease the surface tension of liquids dramatically. Surfactants are common adjuvants to herbicides in formulations for improved performance. Surfactants increase the wettability of water so herbicides stick better to plant leaves, and are more effective against weeds.
Pesticide dissolution makes surfactant micelles more hydrophobic
Surfactants are essential for herbicides because they not only make herbicides effective but also help save the environment. The right type of surfactant (e.g., nonionic vs cationic) will depend on the herbicide formulation and use case. Nonionic surfactants are commonly used in agriculture and landscaping because they're broad compatible and less toxic.
Surfactants act by weakening the surface tension of water so that droplets of spray are more likely to permeate and coat plant leaves. The loss of surface tension makes the spray more wettable and dispersed, thus reducing the distance and length of time the herbicide contacts the plant.
Improve pesticide bioavailability and minimize environmental risk by surfactants
Surfactants also minimize rebound and evaporation so that the droplets get distributed more evenly on the plant surface. This is good for spray uniformity and also longer lasting on the leaves. Surfactants can also make the spray performance better by modifying the droplet shape and size to allow them to pass through the capillary systems of the leaves.
Surfactants improve the performance of herbicides by increasing the amount of contact of the herbicide on the surface of the plant, allowing it to permeate and absorb better. They're solvents that make herbicides bleed through the waxy skin of the plant and be more biologically active and effective. But the action of surfactants is also determined by their chemical composition and amount. Too much can result in a thin film that can diminish the residual herbicide.
Surfactants contribute to the herbicide formulations by reducing surface tension, increasing wettability and coverage, decreasing the size of droplets and spray time, and increasing the herbicide's permeability and absorption, all of which will greatly enhance herbicide performance.
Non-ionic surfactants are chargeless (they do not ionize in water, nor do they change the pH of the solution). Their hydrophilic part consists mostly of polyethylene glycol chains, and their hydrophobic portion contains saturated or unsaturated fatty acids, fatty alcohols or fatty oils. Non-ionic surfactants, being charge-free, are irritant and toxic less, so can be used in the biomedical and food markets. They are also stable in hard water and not easily influenced by calcium and magnesium ions.
Common non-ionic surfactants include polyethylene glycol esters (such as polyethylene glycol fatty acid esters), alkylphenol ethoxylates (such as nonylphenol ethoxylates), and fatty alcohol ethoxylates. These compounds are widely used in areas such as cleaners, emulsifiers, and solubilizers.
Non-ionic surfactants don't easily react to calcium and magnesium ions in hard water, so they are resilient in hard water.
Non-ionic surfactants can be used with different types of cationic and anionic surfactants and other chemicals which makes them ideal for mixed solutions.
Non-ionic surfactants are extensively used in agriculture, industry and cosmetics because of their chemical characteristics and wider use potential.
Non-ionic surfactants help herbicides break through cuticles in the plant leaf wax by dispersing water's surface tension. This helps the herbicide penetrate the plant more effectively and get absorbed faster. Non-ionic surfactants, for instance, can remove the waxy coat on leaves to help the herbicide get into the guts. Additionally, non-ionic surfactants can open up the area between spray drops and the leaves, increasing permeability of the herbicide.
Surfactant enhancing herbicide penetration and uptake
Non-ionic surfactants can help keep spray droplets more concentrated and longer linger on plants. Because they release the surface tension of the spray droplets, decreasing the probability of dropping and keeping the droplets on the plant surface longer, increasing the uniformity and efficiency of herbicide coverage. Non-ionic surfactants also slow down the evaporation of the spray droplets, increasing the herbicide's efficiency.
More practically, non-ionic surfactants are widely used in agriculture and landscaping for improving the efficacy of herbicides. In herbicide applications on US prairies and pastures, for instance, non-ionic surfactants optimise the absorption and efficacy of herbicides. In aquatic plants, non-ionic surfactants can also be used to maximize herbicide control on aquatic plants. A couple of researches have also demonstrated that non-ionic surfactants are highly effective when used in combination with other components (eg, silicone oils).
Ionic surfactants are surfactants that, when in solution, break down into charged ions. Depending on the charge-balancing effect of their molecular arrangement, ionic surfactants further divided into anionic, cationic and amphoteric (or zwitterionic).
These surfactants are negative after dissociation in water. Typical anionic surfactants are sulfates, sulfonates and carboxylates. These materials are often long-chain carbon chains and commonly present in soaps, detergents and cleaners.
These surfactants have a positive charge after they are dissociated in water. Almost all cationic surfactants contain a positively charged nitrogen atom (compact examples are quaternary ammonium salts and amine salts).
Depending on environment pH, these surfactants are anionic or cationic. Typically, they are amphipathic, that is, with both hydrophilic and lipophilic parts.
| Type of Surfactant | Properties | Examples |
|---|---|---|
| Anionic Surfactants | High foaming, used as emulsifiers and dispersants in cleaners | Sodium dodecylbenzenesulfonate (SDBS), fat acid salts, alkyl sulfates, etc. |
| Cationic Surfactants | Usually antimicrobial, used in disinfectants and sterilizing products; cationic in acidic conditions, anionic in alkaline conditions | Benzalkonium chloride (BZK), cetyltrimethylammonium bromide, etc. |
| Amphoteric Surfactants | Change charge depending on pH; effective in emulsification, solubilization, and wetting | Lecithin, betaine compounds, etc. |
Ionic surfactants are charge-sensitive and multifunctional, so they can be found in a host of industrial and personal use cases, from cleaning agents to medicines and cosmetics.
Anionic surfactants are negatively charged and ionize in water to make anions. They aid herbicide absorption by decreasing the surface tension of water, allowing the herbicide to be easily absorbed and spread on the plant surface. Contact herbicides are often formulated with anionic surfactants, which act directly on the plant surface instead of passing into the plant system. But because of their negative charge, anionic surfactants are rarely used together with cationic surfactants, as they would precipitate in water, becoming useless.
Cationic surfactants are positive charge that ionizes in water which cations. They are more surface soluble, and also less solvent soluble which means they can be able to better adhere to plants, and they are able to penetrate the wax layer of the plant. This is why cationic surfactants can improve the cationic adhesion and permeability of the herbicide. But the chemical is stronger and less used for agriculture.
Advantages: Anionic surfactants will be effective in moistening and spreading herbicides so that they will spread more uniformly over plant surfaces and thus be better absorbed and effective. And they keep herbicides from getting washed away by rain or irrigation, optimizing herbicidal efficacy.
Disadvantages: With anionic surfactants in conjunction, they precipitate and detract from herbicidal action. Also some anionic surfactants can be toxic, so be careful with your choice.
Advantages: Cationic surfactants are extremely adherent and permeable, and can be a means to prolong herbicides' time on plant surfaces and to make them penetrate deeper into plant wax. Which makes them, in some situations, more effective.
Disadvantages: Because of their toxicity and potential environmental effects, cationic surfactants are not typically approved for use in herbicide formulations. They can also precipitate when combined with anionic surfactants, and they lose functionality.
Ionic surfactants can make herbicides much more absorbed and effective. Anionic surfactants, for instance, make water easier to absorb into the plant's tissue, by reducing its surface tension. But in its incorrect use, over-addition or accidental admixture with other non-compatibility chemicals could diminish herbicidal activity or produce unwanted side effects.
Ionic surfactants can also react with other substances in herbicides or in the environment. For example, some cationic surfactants react with calcium and magnesium ions in hard water to create precipitates that can interfere with herbicide action.
The ionic surfactants provide an essential herbicidal benefit, though these must be used with care so as not to cause harm or pollution.
Depending on the herbicide, you might need different surfactants to make them work better. For instance, some herbicides may require cationic or anionic surfactants and others nonionic.
There are many different herbicide sensitivity of plants, therefore a surfactant which is suitable for that particular plant can have a higher herbicidal action. Some surfactants will also work better against particular types of weeds, for example.
Surfactant selection can also be influenced by environmental factors like water hardness, pH, etc. In the case of certain surfactants, for instance, use in hard water can precipitate or cause less effectiveness.
Non-Ionic Surfactants: Non-ionic surfactants are generally safe and a general choice, suitable for most applications where there is a concern not to impact non-target plants. Non-ionic surfactants do not change the pH of the herbicide and are therefore usually a good choice.
Ionic Surfactants: The surface activity and solubility of cationic and anionic surfactants are higher but are more reactive to plants or environments. Therefore, they must be properly vetted before being applied.
Read Product Labels: Before choosing and using a surfactant, be sure to check the product label to get the proper concentration and usage guidelines. This means that the surfactant you use will work perfectly well to boost the herbicide performance.
Test and Adjust: Small-scale trials are recommended before a larger scale application to make sure that the chosen surfactant does not cause any negative effects on crops or the environment. Modify surfactant concentration and form according to test results.
Consider Environmental Factors: Select a surfactant based on local climate, soil type, and water hardness. A low-concentration non-ionic surfactant, for instance, could work better in hard water.
With such considerations and selection of the right surfactant depending on the specific application requirements, herbicide performance can be enhanced with little risk of toxicity to the environment or untarget plants.
Following these best practices, herbicides using surfactants can have the greatest possible efficiency with the least amount of harmful impact on the environment.
Enhanced oil recovery by injecting oleic acid as a surfactant into the porous medium
With such tools and indicators, the effectiveness of surfactants in various application scenarios can be fully analyzed and improved.
References
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