Surface Tension

In this experiment you will explore the concepts of surface free energy, adhesion and wetting

Preparation

  1. Answer the following questions in writing:
    1. What is the measurement of "contact angle" and is it useful for?
    2. What is the meaning of a high or low contact angle result, regarding a liquid and its interaction with the solid surface?
    3. Predict the trends you are expected to observe in every part of the experiment. Explain your predictions.
    4. How is a change in surface tension of a liquid-solid interface possible?
    5. Explain the terms of hydrophobicity and hydrophilicity. Use examples from daily life.
  2. In order to extract the surface tension on a teflon surface using the Zisman plot, you are required to plan the relevant concentrations (X) of n-propanol in water. Use the following equation to calculate γLG:

    Remember that this equation is true only for 0.001 ≤ X ≤ 1, where X is the molar fraction of alcohol in water.
  3. For comparison to the experimental values, find the following values in literature:
    1. Contact angles of water on aluminium, copper, PVC, teflon and glass.
    2. Surface tension, γSG, of teflon and air.
    3. The critical concentration of TX-100 (CMC) for maximal wetting.