How Does Anionic Surfactant Work?

23 Jun.,2025

 

An Easy Guide to Understanding How Surfactants Work | IPC

An Easy Guide to Understanding How Surfactants Work

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What is a Surfactant?

Surfactants are a primary component of cleaning detergents. The word surfactant means surface active agent. As the name implies, surfactants stir up activity on the surface you are cleaning to help trap dirt and remove it from the surface.

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Surfactants have a hydrophobic (water-hating) tail and a hydrophilic (water-loving) head. The hydrophobic tail of each surfactant surrounds soils. The hydrophilic head is surrounded by water.

How do surfactants work?

When there are a sufficient amount of surfactant molecules present in a solution they combine together to form structures called micelles. As the micelle forms, the surfactant heads position themselves so they are exposed to water, while the tails are grouped together in the center of the structure protected from water.

The micelles work as a unit to remove soils.  The hydrophobic tails are attracted to soils and surround them, while the hydrophilic heads pull the surrounded soils off the surface and into the cleaning solution.  Then the micelles reform with the tails suspending the soil in the center of the structure.

Types of Surfactants

The hydrophilic head of each surfactant is electrically charged. The charge can be negative, positive, or neutral. Depending on the charge of the hydrophilic head, the surfactant is classified as anionic, nonionic, cationic or amphoteric.

Anionic Surfactants

Anionic surfactants have a negative charge on their hydrophilic end. The negative charge helps the surfactant molecules lift and suspend soils in micelles. Because they are able to attack a broad range of soils, anionic surfactants are used frequently in soaps and detergents. Anionic surfactants create a lot of foam when mixed. While anionic surfactants are excellent for lifting and suspending particulate soils, they are not as good at emulsifying oily soils.

Sulfates, sulfonates, and gluconates are examples of anionic surfactants.

Nonionic Surfactants   

Nonionic surfactants are neutral, they do not have any charge on their hydrophilic end. Nonionic surfactants are very good at emulsifying oils and are better than anionic surfactants at removing organic soils. The two are frequently used together to create dual-action, multi-purpose cleaners that can not only lift and suspend particulate soils, but also emulsify oily soils.

Certain nonionic surfactants can be non-foaming or low-foaming. This makes them a good choice as an ingredient in low-foaming detergents.

Nonionic surfactants have a unique property called a cloud point. The cloud point is the temperature at which the nonionic surfactant begins to separate from the cleaning solution, called phase separation. When this occurs, the cleaning solution becomes cloudy. This is considered the temperature for optimal detergency. For low foaming cleaners, optimal detergency is at the cloud point; for foaming cleaners optimal detergency is either just below the cloud point or at the start of the cloud point. The agitation of low foaming cleaners is sufficient to prevent phase separation.

The temperature of the cloud point depends upon the ratio of the hydrophobic and hydrophilic portions of the nonionic surfactant. Some cloud points are at room temperature while others are very high. Some nonionic surfactants don’t have a cloud point because they have a very high ratio of hydrophilic to hydrophobic moieties.

Examples of some common nonionic surfactants include cocamide, ethoxylates, and alkoxylates.

Cationic Surfactants

Cationic surfactants have a positive charge on their hydrophilic end. The positive charge makes them useful in anti-static products, like fabric softeners. Cationic surfactants can also serve as antimicrobial agents, so they are often used in disinfectants.

Cationic surfactants cannot be used with anionic surfactants. If positively charged cationic surfactants are mixed with negatively charged anionic surfactants, they will fall out of solution and no longer be effective. Cationic and nonionic surfactants, however, are compatible.

Examples of some common cationic surfactants include alkyl ammonium chlorides.

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Amphoteric Surfactants

Amphoteric surfactants have a dual charge on their hydrophilic end, both positive and negative. The dual charges cancel each other out creating a net charge of zero, referred to as zwitterionic. The pH of any given solution will determine how the amphoteric surfactants react. In acidic solutions, the amphoteric surfactants become positively charged and behave similarly to cationic surfactants. In alkaline solutions, they develop a negative charge, similar to anionic surfactants.

Amphoteric surfactants are often used in personal care products such as shampoos and cosmetics. Examples of some frequently used amphoteric surfactants are betaines and amino oxides.

How Surfactants are used in Cleaners

Surfactants are a key ingredient in cleaning products. One thing that differentiates cleaning products is how they are made. Cleaners made from a single chemical, targeting a specific type of soil, are referred to as commodity cleaners. Cleaners that are blends of various chemical ingredients designed to work together to remove various types of soils are referred to as formulated cleaners.

Formulated cleaners usually contain four basic elements: surfactants, hydrotropes, builders and carriers. Hydrotropes are chemicals that keep the otherwise incompatible surfactants and builders stable in a solution. The carrier is either water or a solvent. These elements work together to create mechanical actions to remove soils. The end result is a product that can attack dirt on surfaces with a variety of cleaning mechanisms including emulsifying, lifting, dispersing, sequestering, suspending and decomposing soils of various types. The type of surfactants used in a cleaning product largely determines which soils they will be best at removing.

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What are surfactants and how do they work? - Biolin Scientific

Surfactants are highly versatile products in the chemical industry, used across various sectors from household detergents to drilling muds, and from food products to pharmaceuticals. The term "surfactant" is derived from "surface active agent." These molecules are amphiphilic, meaning they have both hydrophobic and hydrophilic parts, and they naturally align at the air-water interface. In this alignment, the hydrophobic part extends into the air while the hydrophilic part remains in the water, leading to a reduction in surface or interfacial tension.

Surfactants are classified based on their head group

Surfactants are amphiphilic molecules with distinct hydrophobic and hydrophilic components. The hydrophobic tail can be a hydrocarbon, fluorocarbon, or siloxane. Surfactants are generally categorized based on their polar head groups, as the hydrophobic tails are usually similar.

Anionic surfactants are surfactants with a negatively charged head group, making them highly effective at removing dirt and grease. They are widely used in household cleaning products such as laundry detergents, dishwashing liquids, and shampoos due to their excellent foaming and cleaning properties. Anionic surfactants are also utilized in industrial applications, including textile processing and emulsification in agriculture. Common examples of anionic surfactants include Sodium Lauryl Sulfate (SLS) and Sodium Laureth Sulfate (SLES), both known for their ability to create rich lathers and effectively break down oils and fats.

Cationic surfactants possess a positively charged head group, which gives them unique properties such as antimicrobial activity and the ability to bind to negatively charged surfaces. These surfactants are commonly used in fabric softeners, hair conditioners, and antistatic agents due to their conditioning effects and ability to reduce static cling. In addition, cationic surfactants are utilized in disinfectants and sanitizers because of their effectiveness in killing bacteria and viruses. Examples of cationic surfactants include benzalkonium chloride and cetyltrimethylammonium bromide, both of which are frequently used in personal care and cleaning products.

Non-ionic surfactants are characterized by their lack of electrical charge in the head group, which makes them particularly useful in applications where compatibility with various substances is important. They are commonly used in stabilizing emulsions, such as oil-in-water and water-in-oil emulsions, and are prevalent in cosmetic products designed for sensitive skin, baby care, and everyday skin care. Additionally, non-ionic surfactants are used in household cleaning products like laundry detergents, toilet bowl cleaners, and dishwashing detergents due to their resistance to water hardness. Examples of non-ionic surfactants include Tween 20 and Triton X-100.

Zwitterionic surfactants contain both positive and negative charges within the same molecule, allowing them to exhibit unique properties such as high solubility and low irritation potential. These surfactants are particularly useful in personal care products like shampoos and body washes, where mildness and compatibility with the skin are important. They are also employed in the formulation of pharmaceuticals and cosmetics due to their ability to stabilize proteins and emulsions. Examples of zwitterionic surfactants include cocamidopropyl betaine and sulfobetaine, both of which are valued for their gentle cleansing and foaming capabilities.

Surfactants absorb at interfaces

Due to their amphiphilic nature, surfactants are absorbed in the air-water or oil-water interface. At these interfaces, surfactants align such that the hydrophobic part is in the air (or oil) and the hydrophilic part is in the water.

Focusing on the air-water interface, the strong cohesive forces between water molecules result in high surface tension. When surfactants are absorbed, they disrupt these interactions. The intermolecular forces between surfactant and water molecules are weaker than those between water molecules, leading to a reduction in surface tension. At high surfactant concentrations, micelles form, with the concentration at which this occurs known as the critical micelle concentration.

The primary function of surfactants is to reduce surface and interfacial tension and stabilize interfaces. Without surfactants, tasks like washing laundry would be challenging, and products like mayonnaise and ice cream might not exist. Therefore, optimizing surfactants for various applications is crucial, with surface and interfacial tension measurements playing a key role in this process.

If you would like to read more about how surfactants are utilized in the industry, please download the overview below.