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Measurement of Surface and Interfacial Tensions

  • Accurate Measurement of Surface and Interfacial Tensions is essential for understanding and controlling surface phenomena.

Measurement of Surface and Interfacial Tensions

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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