Definition
Surfactants are compounds that reduce surface and interfacial tensions by concentrating at the interface due to their amphiphilic nature.
Classification of Surfactant
Anionic Surfactants
Charge: Negative in water.
Functional Groups: Sulfate, sulfonate, or carboxylate.
Example: Sodium lauryl sulfate (SLS) - used in shampoos, toothpaste, detergents.
Characteristics: High detergency and foaming; can be skin irritants at high concentrations.
Applications: Oral, topical, and cleaning products for dirt and oil removal.
Cationic Surfactants
Charge: Positive in water.
Functional Groups: Quaternary ammonium groups.
Example: Cetyltrimethylammonium bromide - used in hair conditioners and antimicrobial agents.
Characteristics: Antimicrobial properties; conditions hair and skin but less effective as detergents.
Applications: Conditioners, fabric softeners, disinfectants.
Nonionic Surfactants
Charge: Neutral (no charge).
Functional Groups: Polyethylene glycol (PEG) chains.
Example: Polysorbates (e.g., Tween 80) - used as emulsifiers in food and pharmaceuticals.
Characteristics: Stable in varying pH and electrolyte conditions; mild and less irritating.
Applications: Creams, ointments, and injectables for solubility and stability enhancement.
Zwitterionic Surfactants
Charge: Both positive and negative, overall neutral.
Functional Groups: Quaternary ammonium and carboxylate groups.
Example: Betaines - found in mild shampoos and body washes.
Characteristics: Mild, excellent dermatological compatibility; act as good foamers and stabilizers.
Applications: Suitable for baby products and sensitive skin cleansers.
Properties
Critical Micelle Concentration (CMC): The concentration above which surfactants form micelles.
Micelle Formation: Aggregation of surfactant molecules in solution.
Solubilization Capacity: Ability to increase the solubility of hydrophobic compounds.
Applications
Emulsification: Formation and stabilization of emulsions.
Solubilization: Enhancing solubility of poorly soluble drugs.
Detergency: Cleaning action in pharmaceutical manufacturing.
Wetting Agents: Improve spread ability of liquids on solids.