Measurement of Surface and Interfacial Tensions
- S-3-PHYSICAL-PHARMACEUTICS
- Mar 1
- 1 min read
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Accurate Measurement of Surface and Interfacial Tensions is essential for understanding and controlling surface phenomena.
Capillary Rise Method
Principle: Measures the height a liquid rises or falls in a capillary tube due to surface tension.
Equation:
where:
γ is the surface tension.
ρ is the liquid density.
g is the acceleration due to gravity.
h is the height of liquid rise.
r is the radius of the capillary.
Limitations: Suitable only for liquid-air interfaces.
Du Noüy Ring Method
Principle: A platinum ring is immersed in the liquid and the force required to detach it from the surface is measured.
Application: Can measure both surface and interfacial tensions.
Wilhelmy Plate Method
Principle: A thin plate is partially immersed, and the force due to surface tension is measured.
Advantages: Simpler calibration compared to the Du Noüy method.
Drop Weight and Drop Volume Methods
Principle: Based on the weight or volume of drops formed at the end of a capillary.
Equation:
where:
m is the mass of the drop.
r is the radius of the capillary.
Pendant Drop Method
Principle: Analyzes the shape of a liquid drop suspended in another liquid or gas.
Application: Useful for measuring low interfacial tensions.
Importance in Pharmaceuticals
Formulation Development: Helps in selecting appropriate surfactants.
Quality Assurance: Ensures consistency between batches.
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