Surfactants in Cleansing and Conditioning Products

Surfactants and Their Functions

• Surfactants, or surface active agents, are crucial in various cleansing and conditioning products.
• They function by wetting, emulsifying, solubilizing, and dispersing oils.

Wetting

• The initial function of a surfactant is wetting, which allows the shampoo to surround the hair, overcoming the hair's natural oiliness that repels water.
• Oily hair repels water, causing it to bead instead of enveloping the hair.
• Sometimes, multiple applications of shampoo are needed for proper wetting of very oily hair.
  • This is because the initial layer of shampoo may primarily work on breaking down the surface oils, requiring subsequent applications to penetrate deeper and fully wet the hair.

Emulsification and Solubilization

• Surfactants create a foam that removes oils when massaged into the hair.
• The oils become solubilized and are surrounded by surfactant molecules, which then disperse into the water and are washed away.
  • Emulsification is the process where oil droplets are broken down into smaller droplets and stabilized in water, preventing them from coalescing.
  • Solubilization refers to the ability of surfactants to increase the solubility of oils in water, facilitating their removal.

Surfactant Behavior in Water

• When a surfactant is added to water, its molecules quickly align at the surface.
• Polar head groups are exposed to the water, while non-polar tails stick out into the air.
• The surface of the water rapidly becomes covered with surfactant molecules.
  • This alignment reduces the surface tension of the water, allowing it to spread more easily.

Micelle Formation

• When there are more surfactant molecules than can fit on the surface, micelles start to form.
• Micelles are ball-like structures with non-polar tails pointing inward and polar heads outward.
• The critical concentration is the concentration at which the surface is full, and micelles begin to form.
  • The critical micelle concentration (CMC) is a key parameter for surfactant performance.
  • Micelle formation is essential for the solubilization and removal of oils and dirt.

Micelles and Oil Transport

• Micelles can encapsulate oils and transport lipophilic active ingredients into the skin in cosmetic formulations.
• They also surround oil and dirt on the hair, allowing them to be washed away.
  • This encapsulation is crucial for delivering beneficial ingredients in skincare products.

Products Containing Surfactants

• Surfactant-rich formulas include foaming cleansers, eye makeup removers, body washes, shampoos, dish detergents, and hair colors.
• In hair color, surfactants aid in dye penetration by breaking down lipids and provide a foamy quality during the rinse.
• Conditioners also contain surfactants.
  • Different surfactants are used in these products based on the desired function, such as cleansing, foaming, or conditioning.

Shampoo vs. Conditioner

• Surfactant formulas are classified as either shampoos or conditioners.
• The type of surfactants included (anionic, cationic, amphoteric, or nonionic) determines the product's function.

How Shampoo Works

• Hair collects sebum oils, dirt particles, and shed skin over time.
• Shampoo cleans hair through wetting, emulsification, and dispersion.
• Water and surfactants align with sebum droplets, and micelles form around the oil.
• Massaging the shampoo emulsifies the sebum and dirt, which are then dispersed and rinsed away.

Mixture of Surfactants in Shampoos

• Shampoos often contain a mixture of surfactants to enhance cleaning action.
  • This mixing strategy ensures a balance between effective cleaning and minimizing irritation.

Anionic Surfactants

• Anionic surfactants have a negative charge that enhances emulsification and dispersion because hair and skin are also negatively charged.
• The negative charge repels the hair, helping to lift off sebum.
• They have good foaming qualities, which are desirable in shampoos.
  • Common examples include sodium lauryl sulfate (SLS) and sodium laureth sulfate (SLES).

Nonionic Surfactants

• Nonionic surfactants are milder.
• They often constitute the bulk of surfactants in a formula.
  • They are less likely to cause irritation compared to anionic surfactants.

Amphoteric Surfactants

• Amphoteric surfactants are even milder and can increase the overall mildness of a formula while boosting foaming.
  • They can act as either an acid or a base, depending on the pH of the solution.

Synergistic Effect

• A mix of surfactants provides richer lathering and reduces irritancy.
  • This is because different surfactants have different properties and can complement each other.

How Conditioners Work

• Conditioners primarily use cationic surfactants, which have a positive charge.
• The positive charge attracts to the negative charge of the hair, making the surfactants substantive to the hair.
• Conditioners leave hair feeling silky and smooth, providing antistatic qualities and reducing frizz.
  • They also help to detangle hair and improve manageability.

Cationic Surfactants

• Cationic surfactants are attracted to the negatively charged hair and remain even after rinsing, providing a conditioning effect.
• They can also deliver active ingredients that improve hair health.
  • Examples include cetrimonium chloride and behentrimonium chloride.

Identifying Shampoo vs. Conditioner in a Formula

• Cationic surfactants indicate a conditioner, while anionic surfactants indicate a shampoo or other foaming cleanser.

Kitchen Science Experiment: Surfactant Action

• Water soluble food coloring in water demonstrates surfactant action.
• Adding a drop of dishwashing detergent (a surfactant) causes a film to form and pushes the color to the side.
• The churning of the color indicates micelle