Think about answers for the following problems. Draw on all the material you have learned so far. Make the answers as complete as possible, looking at all aspects of the phenomena. Think about ways that you might be able to make detailed calculations applying equations such as the Y-L eqn., Young’s equation, the Kelvin eqn. and Gibbs’ eqn., or any other relationship in the material covered.

1. Consider the following.
   1. An fcc metal crystal is cut into a perfect cube with no damage to the surfaces. The cube is annealed so that it relaxes into a stable structure. What do you think that the structure will be? (You eventually should derive Wulff’s principle)
   2. Now consider a crystalline mineral. Take a big odd-shaped chunk from a mine and smack it with a hammer. Examine a piece that falls out from the inside. What might it look like?

    

2. Predict whether each of the following components in the given system will show a surface excess or depletion:
1. KH₂PO₄ in water
2. Benzene dissolved in solid anthracene
3. Hg in an alloy with Au
4. Water dissolved in benzene liquid

 

3. Predict the molecular configurations at the following surfaces:
1. an aqueous solution of n-octanol in air
2. pure liquid phenol

From these observations derive a general principle (Irving Langmuir did this over 50 years ago).

 

4. Which should show the larger contact angle in the following sets?
1. Hg(l) on:
   1. Pt
   2. A hydrocarbon
   3. Au
2. An aromatic polymer with benzene rings with a drop of:
   1. water
   2. octane
   3. ethanol

 

5. A thin glass plate, 10 cm x 1 cm, is hung vertically by a string and the weight recorded. Then the plate is immersed into a beaker of liquid water, with the 1 cm edge just slightly under the liquid surface, enough to form a meniscus. The weight of the plate is again measured. This weight is more that the weight befor immersion. Neglecting buoyancy effects, what has occurred? How could this measurment lead to a calculation of the surface tension of water? Would anything else need to be measured?

 

6. A glass rod is bent until it breaks. The force required in a vacuum is observed to be considerably larger than in typical room air. Why? Why might engineers in the telecommunications industry be vitally interested in this phenomena?