Surfactant Applications and Key Benefits
What are Surfactants?
Whoever said oil and water can’t mix had perhaps never heard of surfactants. A surfactant or a surface-active agent is a compound that lowers the surface tension at the interface of two liquids, a liquid and a gas or a liquid and a solid. It has an amphiphilic molecular structure which means that the molecule is water-loving (hydrophilic) at one end and fat-loving (lipophilic) at the other. The surfactant molecules align themselves such that their hydrophilic groups (heads) are in the water phase whereas the lipophilic end (tails) extend out into the oil or gas (usually air) phase. Surfactants are classified as follows based on the charge of the head group.
- Anionic Surfactants: The head group has a negative charge
- Cationic Surfactants: The head group has a positive charge
- Amphoteric Surfactants: The head group may simultaneously carry both anionic and cationic hydrophilic groups. Cations or anions are formed depending on ambient conditions such as pH.
- Non-ionic Surfactants: The head group carries no charge
Surfactant Applications in Cosmetics
Detergency
Surfactants are an essential part of all cleansing formulations. Dirt can bind to skin and hair through natural skin oils or oily contaminants picked up from the environment. Surfactants combine oil and water to lift the contaminants off the surface which can then be washed away with water. The choice of a suitable surfactant depends on the preferred chemistry, method of delivery, and desired user experience.
Wetting
Wetting is the ability of a liquid to spread on a solid surface. Products with poor wetting properties tend to ball up on the surface. Surfactants also act as wetting agents, making the product easier to spread while also helping lift oil from the surface for removal. Surfactants are incorporated as wetting agents in the formulation of creams and lotions.
Foaming
Bubbles are formed when air is incorporated into a liquid as a result of working the product on the skin or hair. A small amount of surfactant, added to a product, reduces surface tension between the liquid and air phases thereby reducing the work needed to generate foam. The surfactant also increases the stability of the foam by inhibiting the coalescence of bubbles. Although foaming does not contribute to dirt removal, it is an important part of a pleasing user experience.
Emulsification
Creams and lotions are formulated to deliver beneficial lipid (oily) materials to skin or hair. The lipid material is combined with water and other ingredients to formulate an easy-to-apply product. Surfactants are used as emulsifiers to produce semi-stable oil-in-water (lotions) or water-in-oil emulsions (creams).
Choosing the best surfactants
Many companies offer a wide range of surfactants to meet the diverse requirements of various types of cosmetic formulations. The different range includes cationic, anionic, amphoteric, and non-ionic surfactants suitable for all major cosmetic applications.
Some important features of high-quality surfactants:
Low irritancy
Harsh surfactants interact with proteins and lipids in the outermost layer of the skin, called the stratum corneum. They may cause this protective barrier to break down leading to redness, irritation, dryness, and itching. Anionic surfactants generally offer the best foaming and cleansing properties for cosmetic applications but they are also the harshest towards human skin.
Narrow Range Ethoxylation:
Narrow-range ethoxylation can obtain alkylene oxide adducts having a narrow distribution of the number of alkylene oxide adduct moles.
Excellent foaming properties
Foams are generally easier to generate and maintain under alkaline conditions. As the pH is lowered, the foam-forming potential of surfactants is reduced. An ideal surfactant gives good foaming properties even in a weak acidic medium. The surfactants should be able to generate stable, fine, rich, and soft foams suited to various applications.
Easily bio-degradable
With the advancement of the cosmetics industry following the sustainable trends, the surfactants should be easily bio-degradable which can help cosmetics manufacturers formulate products that are eco-friendly and sustainable.
The other benefits can be low odor, prevention of excessive de-greasing, excellent solubility and detergency, compatibility with other surfactants, non-neutralized products, and compliance with safety and health regulations.