What is the Difference Between Anionic and Nonionic Surfactants

What is the Difference Between Anionic and Nonionic Surfactants

The main difference between Anionic Surfactants and nonionic surfactants is that anionic surfactants have a negatively charged functional group, whereas nonionic surfactants have no net charge.

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Surfactants are chemical substances that reduce the surface tension of a particular liquid when added to it. They increase the spreading and wetting properties. They are known as surface active agents. Surfactant molecules together form micelles, which are spherical in shape. Surfactant molecules contain a hydrophilic head and a hydrophobic tail. Moreover, we can group surfactants according to the properties of the functional groups present in the surfactant molecules. Anionic surfactants and nonionic surfactants are two such groups.

Key Areas Covered

1. What are Anionic Surfactants
      – Definition, Nature, Features
2. What are Nonionic Surfactants
      – Definition, Nature, Features
3. Difference Between Anionic and Nonionic Surfactants
      – Comparison of Key Differences

Key Terms

Anionic Surfactants, Nonionic Surfactants, Surfactants

What are Anionic Surfactants

Anionic surfactants are surfactants that carry a negatively charged head in their molecules. This means their surfactant molecules have a negatively charged functional group as the head of the molecule. Examples of such functional groups are sulfates, carboxylates, phosphates, and sulfonates. In fact, anionic surfactants are the most popular surfactants. Some of the most popular anionic surfactants include sodium lauryl sulfate, ammonium lauryl sulfate, sodium laureth sulfate, ammonium laureth sulfate, potassium cocoate, and sodium stearate. Moreover, a wide range of oils and raw fats produce anionic surfactants.

Anionic surfactants are mostly used to remove oily residue. They are commonly found in every cleaning agent. They are also used in body washes, kitchen cleaners, and laundry detergents. However, these anionic surfactants can also cause skin irritations.

Anionic surfactants create a lot of foam when mixed. The negative charge helps to lift and suspend soils in micelles. Anionic surfactants are used in many different industries because of their unique properties. Some of these include solubilization, emulsification, dispersion, foaming, detergency, and wetting.

What are Nonionic Surfactants

Nonionic surfactants are surfactants that have got no net charge. Nonionic surfactants are very soluble. This solubility is due to their hydrogen bonding. Hydrogen bonding decreases with an increase in temperature; therefore, the solubility of nonionic surfactants decreases with increasing temperature. When the temperature is increased, a milky, cloudy emulsion called a cloud point is formed. This property is important for the determination of the optimum use of nonionic surfactants at high temperatures. We apply this concept to detergents.

Nonionic surfactants do not produce foam. They also do not contain dissociable ions. In other words, they do not separate into ions in water even though they contain a hydrophilic head and hydrophobic tail. They are available in a variety of chemical types. The main classes of nonionic surfactants are castor oil ethoxylates, amine ethoxylates, fatty acid esters and their ethoxylates, alcohol ethoxylates, and ethylene oxide propylene oxide copolymer. They are the second most used type of surfactant after anionic surfactants, but they are less effective than nonionic surfactants. Since they have no net charge on them, they are more stable than other surfactant types. Due to this feature, they are less susceptible to the effect of strong electrolyte inorganic salts, alkalis, and acids.

Difference Between Anionic and Nonionic Surfactants

Definition

Anionic surfactants are surfactants that carry a negatively charged head in their molecules, while nonionic surfactants are surfactants that have got no net charge on them.

Nature

Moreover, anionic surfactants are less mild in nature, whereas nonionic surfactants are comparatively milder than anionic surfactants. Generally, anionic surfactants are more effective than nonionic surfactants.

Foam Formation

Anionic surfactants produce a lot of foam, whereas nonionic surfactants do not produce foam.

Popularity

While anionic surfactants are the most popular surfactants in use, nonionic surfactants are the second most used type of surfactants.

Examples

Sodium lauryl sulfate, sodium laureth sulfate, ammonium lauryl sulfate, ammonium laureth sulfate, potassium cocoate, and sodium stearate are some popular anionic surfactants, while castor oil ethoxylates, amine ethoxylates, and fatty acid esters are examples of nonionic surfactants.

Conclusion

In brief, surfactants are chemicals that reduce the surface tension in liquids. They are of different types depending on the nature and structure of the molecule. Anionic and nonionic surfactants are two of the most common types of surfactants. The main difference between anionic surfactants and nonionic surfactants is that anionic surfactants have a negatively charged functional group, whereas nonionic surfactants have no net charge.

Reference:

1. “Anionic Surfactant – Overview.” Science Direct.
2. “Non-ionic Surfactants.” Stockmeier.

Image Courtesy:

1. “Sodium stearate” By User:Innerstream – Own work (Public Domain) via Commons Wikimedia
2. “TensideHyrophilHydrophob” By Roland.chem (CC BY-SA 3.0) via Commons Wikimedia

“Breaking Down” Surfactants: What they are, how they work, and their role in the pandemic

We interact with surfactants every day without realizing it. Surfactants are in the toothpaste we use to brush our teeth, in creams and sunscreens to make emulsions of oil and water based ingredients, the pharmaceuticals we ingest, and – at the forefront of public attention due to the COVID-19 pandemic – the active component in the many cleaning products we use to keep our surroundings and ourselves clean. Industrial applications are equally varied, with surfactant applications ranging from agriculture to remediation.

Not only do we use surfactants on and around us – naturally occurring surfactants are produced inside us! (as well as other living organisms) In this article, we will define surfactants and explore how such a ubiquitous chemical works.

What are surfactants?

Surfactants are type of molecule that lowers the surface tension between two materials, either a gas and a liquid (e.g. water surface tension), two liquids (e.g. water and oil), or a liquid and solid (water and dirt particles).

The origin of the word surfactants describes just that: surfactants is a contraction of Surface Active Agents.

The word “surfactants” is a contraction of Surface Active Agents.

All surfactants are molecules that consist of a hydrophilic “water loving” (or water soluble) head, and a hydrophobic “water hating” (or oil-soluble) tail. In more technical terms, surfactants are amphiphilic molecules, meaning they are molecules that contain both a hydrophobic and hydrophobic region.

Digram of a generalized surfactant molecule.

Though the actual structure of this head and tail can vary widely between different types of surfactants (which results in different behaviours and chemical properties – discussed later), the core principle remains the same.

How do surfactants work?

Let’s start by considering what happens when we add surfactants to a container of water. Surfactants first gather on the surface of the water to form a layer at the water-air interface, with the water-loving (hydrophilic) heads towards the water, and the water repelling (hydrophobic) tails in the air. This results in a decrease in water surface tension – a key properties of surfactants.

Surfactants align at the water-air interface, reducing surface tension.

Critical micelle concentration (CMC)

As surfactant concentration increases, something interesting occurs: Micelles, or “balls” of surfactant form, with inward pointing tails away from the water. The surfactant concentration at which micelles begin to form is called the critical micelle concentration (CMC). This property varies by the type of surfactant, and affects efficacy and required concentration needed for a given application. Adding more surfactant beyond the CMC results in increased micelle formation, while surface tension at the water-air interface remains low.

The critical micelle concentration (CMC) is the concentration at which a surfactant begins to form micelles.

Micelle formation is crucial for many surfactant applications, as it facilitates the break down of substances like oil that are normally insoluble in water. In the presence of dirt and oils, micelle-structures form with hydrophobic and oil-like particles forming the centre, and hydrophilic head faces outwards towards the water filled environment. Surfactants with a low CMC need less surfactant to reduce the reduce surface tension and form micelles, and are thus more efficient.

Surfactants form micelles around oil-soluble particles, breaking it down and facilitating either emulsion or cleaning depending on the application.

Types of surfactants

There are as many different surfactants as there are applications! These differ in their chemical structure and properties, which affects strength, foaming properties, compatibility with other chemicals, toxicity, and biodegradability.

Surfactants can be broadly fall into two categories, based on the charge of the head group.

Ionic Surfactants

Ionic surfactants have a charged (positive or negative) head, and can be further classified into 3 sub-groups:

• Cationic Surfactants: Head possesses a positive charge
• Anionic Surfactants: Head possesses a negative charge
• Zwitterionic (Amphoteric) Surfactants: Head has both a negative and positive charge

Non-ionic Surfactants

Non-ionic surfactants have a neutral head (no positive or negative charge). This class of surfactants can be either hydrophilic (more water loving) or lipophilic (more oil loving) depending on the relative strength of the head and tail. This is called the Hydrophilic-Lipophilic Balance (HLB), an important characteristic for non-ionic surfactants for which the optimal behaviour is highly application dependent.

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Major types of surfactants; the optimal surfactant type is highly application dependent.

Bacteria and viruses: How surfactants can kill (to protect you)

All cells are encased by fat-based (lipid) membranes, in which other molecules like proteins are embedded. The lipids that make up the cell membrane are called phospholipids, which consist of a water-loving (hydrophilic) head, and two long water-hating (hydrophobic tails).

Sound familiar?

Indeed, the phospholipids that surround living cells are surfactants themselves! Surfactants used in cleaning can kill bacteria by interfering with and breaking up the cell membrane components such as lipids and proteins. The hydrophobic surfactant tail embeds itself in the lipid layer surrounding cells, and causes it to break apart, which can be easily washed away with water.

This review article (Falk , J Surfactants Deterg) discusses surfactants as antimicrobials in much greater detail.

Surfactants in hand soap can break down the lipid membranes surrounding bacteria and enveloped viruses like those causing COVID-19 and the flu, simultaneously destroying the microbes while facilitating their removal from your hands.

What about viruses?

Viruses are diverse infectious particles that can only replicate inside of a cell. They fall into one of two broad categories:

• Enveloped Viruses: Common examples include coronaviruses (e.g. causing COVID-19) and influenza viruses (causing the flu)
• Non-Enveloped Viruses: Norovirus (causing stomach flu) and polioviruses

Anti-viral capacity depends on the type of surfactant, as well as the type of virus. Surfactants can break down enveloped viruses in much the same way as cell walls are broken down – by attacking and breaking down the lipid membrane that surrounds and protects the virus. Non-enveloped viruses can be more difficult to inactivate due to the stable protein shell (capsid), some surfactants are capable of destroying the protein capsid as well.

Regardless, particularly in the case of hand-washing, viral inactivation is not the only way to rid yourself of viruses – the combination of surfactant activity and mechanical agitation (such rubbing hands together) helps lift viruses from surfaces so they can be easily removed with water.

This video summarizes how soap (or more accurately, the surfactants in soap) break down viruses such as COVID-19.

Viruses can be either enveloped or non-enveloped (naked), depending on whether or not it is encased in a lipid envelope. Enveloped viruses in particular, like that causing COVID-19, are easily broken down by the surfactants used in hand soap, however

Summary

Surfactants are a fascinating group of molecules that play an important role across many areas of industry and our personal lives. Though varying widely in chemical properties, safety, and capabilities, the basic principles of how surfactants work remain the same.

What Are Surfactants

What is a surfactant?

Surfactants are unique organic molecules that are made up of a polar hydrophilic and a non-polar hydrophobic component. The action-end of the molecule is the polar head group which is often anionic or cationic in nature.  The hydrophobic portion of the molecule is generally a long-chain hydrocarbon. 

Types of surfactants: how are they classified?

There are two types of surfactants: ionic and non-ionic.  

Ionic surfactants are known by the charge on their polar head-groups, and they include both anionic (negative charge) and cationic (positive charge) surfactants.  The non-polar hydrophobic tail is typically a long-chain hydrocarbon, often derived from natural products such as fatty acids and alcohols.  

The largest category of surfactants is anionic, which dissociate in water into negatively charged head-groups.  Examples of anionic surfactants include sulfates (-SO4-), sulfonates (-SO3-), carboxylates (-CO2-), and betaines (-N+R2-R’SO3-). The counter ions are usually ammonium, sodium, or potassium cations.  

Conversely, cationic surfactants dissociate in water to positively charges head-groups such as quaternary ammonium salts (-R’N+R3-).  Amphoteric surfactants have a dual charge, both positive and negative, on the head position of a hydrophobic molecule end, such as sulfo-betaines (-N+R2-R’SO3-). The positive and negative charges neutralize each other, creating a net-zero charge.  If the hydrophilic end has no charge, the surfactant is called non-ionic.  Non-ions are often used as cosurfactants.

What are the main functions of surfactants in emulsion polymerizations?

At concentrations above their critical micelle concentration (CMC) in water, surfactants form micelles, which are entities capable of solubilizing vinyl and acrylic monomers.  The monomer polymerizations take place in the surfactant stabilized spherical micelles.

The surfactant must enable a fast rate of polymerization, minimize coagulum in the process, control viscosity during polymerization, and contribute to the performance of the final polymer. Emulsion polymer performance attributes include stability, gloss, physical properties, and water resistance. Anionic surfactants are the preferred type of surfactant in emulsion polymerizations, with lauryl (dodecyl) sulfates, alpha-olefin sulfonates, and fatty acids being among the most common and economical.

What are key performance indicators (KPIs) for surfactants?

KPIs for anionic surfactants used in emulsion polymerizations include the following:

1. Required Critical Micelle Concentrations (CMC)

2. Rates of polymerization (high rates are desirable)

3. Complete monomer conversions 

4. Control of micelle particle size and polymer MWD uniformity

5. Latex stability and coagulum control 

6. Film forming characteristics of the emulsion polymer

7. Polymer performance properties including water resistance, clarity, and adhesion

Surfactant-stabilized emulsion polymerization is an important technique for preparing waterborne latexes, which are the basis for many paint and coating systems, adhesives and sealants, and inks. The main functions of surfactants in CASE applications are to emulsify water-insoluble, hydrophobic monomers to facilitate polymerizations in an emulsion state, and to stabilize suspensions of the resulting synthetic polymers so they can be stored, formulated and applied.  

In conventional emulsion polymerizations, selection of the correct surfactant type is critical. Gantrade, in collaboration with Tiarco-RST, offers a broad range of surfactants that exhibit excellent stabilization properties in the manufacture of acrylic, vinyl, vinyl-acrylic, styrene-acrylic, and many other polymer systems, and contribute to improved end product performance.

What is the Gantrade-Tiarco value proposition for surfactants?

Our surfactants portfolio has a product for a wide range of applications in the emulsion polymerization, paints and coatings, adhesives and sealants, inks and related applications. The emulsion polymer experts and chemists at Tiarco are always available to assist customers with any formulation challenges and new product developments. Combining technologies from across their leading-edge chemistry portfolios can offer products with distinctive performance properties.

Tiarco employs a unique sulfation technology based on chlorosulfonic acid (CSA).  This environmentally-friendly, advanced manufacturing technology yields higher-quality sulfated surfactants, with excellent consistency and minimal waste and clean-up requirements.  In addition, Tiarco’s CSA sulfation technology enables short turnaround times and greater flexibility in manufacturing.  Accordingly, our partners can custom-synthesize or blend a wide variety of unique formulations to meet your special requirements, within strict quality limits.  Production capacities span small and large quantities.

Whatever your specialty surfactant requirements, we welcome the opportunity to work jointly to enhance the performance of your products. Contact Gantrade today to get started.