Tensiometer is used for
-Surface and Interfacial tension - Dynamic Contact Angles (DCA)
-Powder Wettability - Adsorption Behavior of Solids
-Critical Micelle Concentration (CMC) - Free Surface Energy of Solids
Wetting studies usually in valve measurement of contact angles as primary data. Contact angles indicate the degree of wetting when a solid and liquid interact. The lower the contact angle the greater the wetting. Contact angles below 90ο indicate that the liquid wets the solid spontaneously (in a thermodynamic rather than kinetic sense). Contact angles above 90ο indicate that the liquid does not wet the solid.
Surface tension is a measurement of the cohesive energy present at an interface. The molecules of a liquid attract each other. The interactions of a molecule in the bulk of a liquid are balanced by an equal attractive force in all directions. Molecules on the surface of a liquid experience an imbalance of forces as indicated below
- Critical Micelle Concentration (CMC).
Surface tension may be used to measure CMC. A graph of surface tension versus log of concentration of surfactant added will appear as follows:
In this graph you can see three phases:
1. Slight change in surface tension is detected at very low concentrations of surfactant.
2. Additional surfactant decreases surface tension
3. Surface becomes fully loaded, no further change in surface tension.
- Dynamic Contact Angle
Contact angle is a quantitative measure of the wetting of a solid by a liquid. It is defined geometrically as the angle formed by a liquid at the three phase boundary where a liquid, gas and solid intersect as shown below