CL461 Colloids and interfacial technology: practice questions

Explain the physical significance of surface tesnion.

Present a molecular picture of how surface tension arises.

What are the dimensions and units of surface tension? Consider various systems of measurements, e.g., SI, cgs, and British system of measurement. Consider force/length as well as energy/area approaches.

Draw a diagram and show how the capillary-rise method would be used for a liquid with contact angle greater than 90 degrees. Note that in this case, it would really be a capillary-depression method. Note that there is the practical problem of taking measurements of the depression below the surrounding liquid, but ignore it for now.

Explain how the Wilhelmy plate method and the required measurements would change for a non-wetting liquid, i.e., with contact angle greater than 90 degrees.

Derive the Wilhelmy plate expression in which the plate is replaced by a circular rod.

Estimate the force with which two planes are drawn together when there is a drop of liquid with contact angle theta (between 0 and 90 degrees) and surface tension gamma inbetween them and in contact with both of them.