Surfactants, a nickname for “surface active agents,” as coined by Antara Products in the 1950sa, are a type of molecule that contains both a water-loving (hydrophilic) and a water-fearing (hydrophobic) portion. This unique structure is why surfactants are major players in a variety of industrial and commercial applications including agrochemicals, home and personal care, industrial and institutional (I&I), oil and gas, and paints/coatings.
Types of Surfactants
So, how do surfactants work? Some surfactants possess an electrical charge on their hydrophilic (water-loving) moiety, and based on the identity of the electrical charge(s) – or lack of – surfactants are categorized within one of the four main classes including:
- nonionic (no charge)
- anionic (negative charge)
- cationic (positive charge)
- amphoteric (containing both a positive and a negative charge)
The type of surfactant chosen for a certain application heavily depends on the inherent solution properties and the intended end-use. Many of these compounds provide exceptional properties to a formulation for specific market, including low-foaming cleansers, rapid-wetting properties, water soluble compounds, and emulsification for water insoluble compounds.
Choosing the correct surfactant for your end-use application is a daunting task, but once you fully understand the differences between the four types of surfactants and how each surfactant works, the task of choosing the correct molecule(s) becomes much easier. So let’s dive into the four classes of surfactants and discuss what makes each type uniquely different.
What Is Nonionic Surfactant?
Nonionic surfactants are one of the more commonly used surfactants in industry, so let’s ask the simple question of ‘what is a nonionic a surfactant’?
A nonionic surfactant is a type of surfactant that does not carry a charge on its hydrophilic head group and is therefore milder in nature. Due to the mildness associated with nonionic surfactants, they are commonly used throughout the home and personal care markets, as well as the agrochemical industry.
Furthermore, the lack of charge contributes to nonionic’s ability to easily emulsify oils, making them a great player in removing grease and oils from soiled surfaces. Though this class of surfactants is commonly associated with cleaning products around the home or an industrial setting, they are widely used in other areas too. Nonionic surfactants are commonly used in the home, beauty, and personal care surfactants markets for products including shampoos (to aid in emulsification), perfumes (as solubilizing agents), cosmetics (to help disperse pigments in make-up), and to assist in the emulsification of oils for skin care products.
Nonionic surfactants are not limited the home and personal care markets, for instance, nonionic surfactants are used to help farmers within the agricultural surfactants industry, as these compounds are used in pesticide and adjuvant formulations to increase spreading, wetting, sticking, and penetration of the pesticide through the leaf’s surface. The refining and processing of oil and gas in the petroleum industry also utilizes nonionic surfactants. For instance, nonionics are used as a corrosion inhibitor in oil and gas for surfaces that come into contact with the petroleum products, as well as flow-back aids to help improve the flow of hydrocarbons. Due to their surface chemistry, nonionic surfactants are also widely used in coating applications, such as emulsifiers for latex paints and leveling agents for acrylic coatings.
Nonionic Surfactant List
Some common examples of nonionic surfactants are ethoxylated and alkoxylated fatty acids, ethoxylated amines, ethoxylated alcohol, alkyl and nonyl-phenol ethoxylates, ethoxylated sorbitan esters, and castor oil ethoxylate.
When choosing the correct surfactant, it is important to understand how the identity of the water-fearing portion, as well as, the ratio of the water-fearing to the water-loving portion can be tailored to provide better water solubility, wetting, detergency, emulsification, etc. To understand this phenomena, one must first understand the hydrophilic/lipophilic balance (HLB) theory, which is uniquely characteristic to nonionic surfactants.
Ranging in arbitrary units of 1-20, the HLB of a nonionic surfactant can be calculated and used to determine the propensity of a compound to work effectively in a given solution of oil and water. Lower HLB values (< 10) are commonly used for oil-rich solutions while surfactants with higher HLB values (> 10) are typically most efficient in oil-in-water emulsions.
Just as the identity of the hydrophobic portion of the ionic surfactant can be varied depending on the need of the final application, the length of the polyoxyethylene component (i.e. the hydrophilic portion) of the nonionic surfactant also provides this class of compounds with a wide assortment of water solubilities and detergency properties. Increasing the amount of ethylene oxide typically increases its water solubility, as well as increases the hydrophilic/lipophilic balance (HLB) of the compound. For a full list of nonionic surfactants, please visit our product brochure here.
What Is an Amphoteric Surfactant?
Amphoteric surfactants are zwitterionic, meaning they carry both a positive and a negative charge on their polar head-group, thereby making the overall net charge zero. Generally speaking, amphoteric surfactants have low toxicity, low eye and skin irritation, are tolerant to hard water, and exhibit excellent foaming and compatibility with other surfactants.
Due to this unique characteristic of amphoteric surfactants, they behave differently depending on the pH of the final formulation – in an acidic environment, amphoterics adopt more cationic characteristics, while in an alkaline environment, they behave more like an anionic surfactant. Because an amphoteric to an amphoteric surfactant’s structure, this class of molecules are compatible will all other classes of surfactants.
Amphoteric Surfactant List
Betaines and amine oxides are two of the more commonly used amphoteric surfactants. Betaines, contain both an anionic and a cationic group, such a carboxylate and a quaternary ammonium compound, respectively. Amphoteric surfactants are considered milder than their anionic counterparts such as alkyl ether sulfates and are therefore readily used in shampoos as either a direct or a partial replacement of sulfates. This is due to betaine’s ability to reduce the skin and eye irritation attributed to alkyl sulfates.
In a similar manner, lauramine oxides can mitigate the irritation effects of anionic surfactants. These surfactants can provide high foaming and thickening properties and is stable at most pH ranges, including, stability in peroxide and hypochlorite solutions. Major market segments for this product include home care, personal care, oil & gas, and agrochemicals.
What Is Cationic Surfactant?
Unlike anionic surfactants, cationic surfactants carry a positive charge on their hydrophilic head group, which makes them useful in antistatic products such as fabric softeners and hair conditioners. The positively charged polar head group is deposited onto the slightly negatively charged surfaces of hair or of fibers of textiles. Furthermore, the positive nature of cationic surfactants is known to aid in disrupting the bacteria cell membrane, making cationic surfactants useful as antimicrobial agents and are commonly found in hard-surface cleaners and disinfectants.
For the majority of formulations that involve cationic surfactants, an acidic solution is preferred, as this will keep the positive charge present on the cationic’s structure. When developing a new formulation, it is important for the formulator to know which types of surfactants can be mixed with one another. Unfortunately, due to the positive charge exhibited by cationic surfactants, it is best that a formulator does not combine cationic and anionic surfactants within their formulation unless they want goo – a sticky or slimy inhomogeneous substance.
What Is Anionic Surfactant?
Anionic surfactants carry a negative charge on their hydrophilic head, thereby providing excellent detergency properties due to their uncanny ability to bind to positively charged particles, such as dirt and oils, lifting and suspending these particles in a micelle-like structure. Once in the micelle, the dirt and grime can be swept away and down a drain via an aqueous solution, leaving your home and work place spick and span.
Anionic Surfactant List
Some common examples of anionic surfactants are alkyl ether sulfates, benzyl sulfonates, and phosphate esters. Anionic surfactants are known to foam under agitation, but this foam is not directly correlated to their ability to clean, as anionic surfactants are not great at removing, or emulsifying, oils compared to their nonionic counterparts. Specifically, anionic surfactants that contain phosphate ester moieties are versatile products that are effective coupling agents, fantastic hydrotropes and are stable and soluble in alkali conditions. These surfactants are widely used as compatibility agents in agrochemicals as well as corrosion inhibitors in the oil and gas industry.
Generally, anionic surfactants are best used in alkaline solutions, as some will precipitate from solution if they become protonated by an acid. When formulating, it is good to know that all anionic surfactants are compatible with nonionics, allowing the chemist to mix and match from a wealth of potential co-surfactants. However, in the case of the ‘goo’ (as mentioned earlier), it is most advisable to avoid mixing anionics with cationics.
Choosing the Correct Surfactant Types
Choosing the correct surfactant can seem like an overwhelming task when defining the scope of a formulation or project. As previously mentioned, the properties of these surfactants can be very specific, ranging from rapid wetting to strong detergency, often leaving the formulator with what appears to be a difficult decision to make in regards to his/her formulation.
Let’s take the example of a chemist who is building a laundry detergent. When selecting a surfactant for their product, this chemist may ask themselves…
‘Do I select a surfactant with rapid wetting or a surfactant with strong detergency to add to my product?’
Luckily, many of these surfactants are compatible with one another, allowing the formulator to combine surfactants from different classes to make a more efficient laundry detergent. Compatibility, however, is not the only benefit from using a two-surfactant-system, because, when mixed together, co-surfactants can boost one another’s performance. This is the reason that many formulators and chemists will often choose both a primary surfactant and secondary surfactant, when constructing a mixture, blend or formulation.
Using Primary Surfactants and Secondary Surfactants Together
One can equate formulating with surfactants to constructing a championship-winning football or basketball team. As the general manager, there are several important criteria that must be met when building your championship squad, including (1) deciding the roles of the individual players, (2) compatibility amongst the players, (3) the overall team chemistry and (4) cost of each player. If each of these criteria can be accomplished, then, as the general manager of the team (i.e. the chemist behind a formulation), you have achieved your goal of winning a championship (or selling your product to highest bidder!) In order to understand how these criteria affect a product’s stability and profitability, we will further break-down each individual step within this sports-related scenario.
1. Deciding on the Roles for the Individual Players
This may seem obvious, but when building a championship-caliber basketball team, for instance, it might be easy to say that, ‘an entire squad of Michael Jordans would work!’ This scenario of an all ‘Jordan-esque’ team would never work in reality, as his skill-set (while very impressive) cannot fulfill every need of the team.
While Jordan scored the majority of the points, who helped with the assists or the rebounds? This is why Michael needed Scottie Pippen (and possibly why Scottie needed Michael). For these same reasons, a single surfactant cannot perform all of the duties needed of surfactancy in a blend or formulation. Most often a chemist will choose a secondary surfactant (in this case Scottie Pippen) to fulfill the weakness of the primary surfactant (e. Michael Jordan).
Let’s take our example of a laundry detergent, the primary surfactant will act to as the detergent, thus serving the main purpose of the formulation. A good option for the primary surfactant in this scenario could be an anionic due to its strong detergency properties that remove dirt from a garment. The secondary surfactant will be present to boost the performance of the final product (in this case, rapid wetting of the textile).
In this part of the formulation, a nonionic (HLB ~ 10) would be a good choice for a secondary surfactant as it can particulate the oil and dirt from the textile, allowing the primary surfactant to remove the soil. The secondary surfactant in the case of a laundry detergent is able to enhance the function of the primary surfactant as it wets the surface of the soiled garment, bringing the dirt into wash solution and finally allowing the primary surfactant to emulsify the dirt away from the substrate.
By combining a primary with a secondary surfactant, one can achieve properties of a formulation that cannot be ascertained through the use of a single surfactant. See, Jordan really did need Scottie!
2. Player Compatibility
Whether in sports or in a business setting, it is a necessary component to have your team members be compatible with one another, as strife, disagreements and conflict can disrupt the objective of the group. A team works best when each individual is working harmoniously with everyone. In football, would Tom Brady and Bill Belichick have six Super Bowl rings (as of August 2019) if they did not see eye-to-eye?
The answer is an emphatic NO, as the two of them are in-sync and their football-decision-making-abilities complement one another perfectly. For this reason, selecting for compatibility between a primary and secondary surfactant can be just as rewarding for product development. Below are some general guidelines for surfactant compatibilities.
- Nonionic surfactants are generally compatible with anionic, cationic and amphoteric surfactants.
- Anionic surfactants are NOT compatible with cationics (and vice versa).
- Amphoteric surfactants are generally compatible with nonionic, anionic and cationic surfactants.
3. Team Chemistry
The term ‘team-chemistry’ is often used to describe how well a team understands and accepts their role within the larger scope of an entire team and sport. Players may fit their roles perfectly and get along well with one-another (fulfilling criteria 1 and 2), but for some unforeseeable reason do not mesh well on the playing field. Coaches can help the situation by having practices and passing along years of knowledge to the players. However, unless the general manager has properly constructed a squad that has a unique team chemistry, the entire group will miss out on that championship ring.
Likewise, primary surfactants and secondary surfactants must not only be compatible with one another, they must have the right ‘chemistry’ within a formulation to promote product stability, while continuing to have the optimal application properties. For instance, primary and secondary surfactants that have the uncanny ability to emulsify a paraffin wax, may not be as useful when emulsifying naphthalenic oils. The chemist in this scenario, is like the coach, and will need to rely on their experience to select surfactants that will provide the most stable and viable option during the development of a product.
Additionally, practicing surfactant blends and mixing techniques with a variety of surfactants that range in their HLB values will aid in determining the choice of primary, secondary and sometimes tertiary surfactants. As the saying goes in sports and chemistry… practice makes perfect!
4. Cost of the Players
Achieving the first three criteria for building a championship team can come at a cost. The Michael Jordan’s and Tom Brady’s of the world do not come cheap, but even with the most expensive players, a championship team needs cultivation, practice and guidance. In a similar manner, choosing the most expensive surfactant will not solve all of the issues of a product’s stability, usefulness or applicability on the market.
As a US surfactant manufacturer, Oxiteno not only has a broad selection of surfactants to choose from, but our seasoned team of experts are available to guide you on product costs, technical information and regulatory issues that you may face.
Feel free to contact us online today to discuss any of your product formulation needs. We’re here to help guide you on your way to your championship.
a- Rahman, Pattanathu KSM, and Kamaljeet K. Sekhon Randhawa. “Microbiotechnology based surfactants and their applications.” Frontiers in microbiology 6 (2015): 1344.