Surfactants

Definition of Surfactants

• Surfactants are compounds that reduce surface and interfacial tensions by concentrating at the interface due to their amphiphilic nature.

Classification of Surfactant

1. 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.

2. 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.

3. 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.

4. 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 spreadability of liquids on solids.

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