Surface Tensions

Surface tension is the force per unit length existing at the interface between a liquid and a gas (usually air), arising from the imbalance of intermolecular forces at the surface layer of the liquid.
Molecules at the surface experience a net inward force, leading to minimized surface area.
Units: Dynes per centimetre (dyn/cm) or Newtons per meter (N/m).
Equation:
- - - - $\gamma = \frac{F}{2L}$
where:
γ is the surface tension.
F is the force required to break the surface.
L is the length over which the force acts.

Interfacial tension is the force per unit length existing at the interface between two immiscible liquids or between a liquid and a solid.
Similar in concept to surface tension but involves two liquid phases.
Influences the formation and stability of emulsions.
Factors Affecting Surface and Interfacial Tensions
- Temperature: Generally, decreases with increasing temperature.
- Presence of Surfactants: Surfactants lower surface and interfacial tensions by accumulating at the interface.
- Impurities: Can either increase or decrease tensions depending on their nature.
Applications in Pharmaceuticals
- Emulsion Stability: Lower interfacial tension promotes emulsification.
- Dosage Form Development: Affects the design of topical formulations and aerosols.
- Quality Control: Measurement of tensions can indicate purity and consistency.