QUESTION 0)           “I have read the special instructions and expectations outlined above. By

submitting this work, I certify that the work represents solely my own independent efforts. I confirm  that I am expected to exhibit honesty and use ethical behaviour in all aspects of the learning process. I confirm that it is my responsibility to understand what constitutes academic dishonesty under the        Academic Integrity Policy.”

If you agree, then for question 0, in your solutions, please write: the following statement:

I, (print your name) agree.

Signed (your name), and date.

CONCEPT QUESTIONS

(The following 8 questions are each worth 5 marks, for a total of 40.) The answers to the concept questions should be brief and in your own words:

1) Silly putty can fracture if we pull on it quickly, but if we hold the two fractured surfaces together the interface heals.  Why does the interface heal itself?

2) Imagine you have some liquid (oil, water, sugar solution, ketchup, honey etc), and have to measure the viscosity at home. How would you do this experiment with materialsyou might easilyfind?          Provide appropriate equations you might use.

3) You have a small droplet on the top and on the bottom of a sheet. The droplets are labelled as dt, and db , as shown and have the same contact angle. The droplets are small enough that gravity does not play a role. A small hole is suddenly opened up in the sheet. Is this a stable configuration? What happens     and why?

 4) When pulling or relaxing an elastic band, a change in the temperature can be observed when held up to your lip. Under which circumstances does the band feel warm or cool? Why is this? (give a simple    explanation)

5) The following plot is a schematic of a dilatometry experiment. Upon cooling a sample, the three different trajectories are obtained. Explain the three observations which result in T1, T2 , and T3 .

T1   T2       T3

6) If someone showed you microscopy images of two samples that phase separated through              “nucleation and growth” and “spinodal decomposition”, what distinguishing feature would you look for to determine which is which?

7) We frequently talk about the range of an interaction (long ranged, short ranged). The ‘range of         interaction’ is a rather vague concept.  For example, the range of a power law 1/d2 or 1/d6 interaction is strictly infinite.  However, when we talk about the range of an interaction, we understand what this      means.  What is a reasonable practical definition for the range of an interaction for the systems that we have been studying? (again, be brief!)

8) Jean-Christophe is doing experiments where he makes tiny droplets of oil in a water bath. He uses  conical pipettes as shown below. Despite his best efforts he cannot apply enough pressure to get the   droplets to come out. Why might he be able to push the fluid partway, but at some point he cannot get the fluid any further. What is going on?

PROBLEMS:

*The last page has formulas that may be useful to you

(The following 4 questions are each worth 10 marks, for a total of 40)

9) I have gold wire on a spool. I am standing on a tall tower. I unroll the spool of wire. How long can the wire be before it snaps? (assume that the gold wire snaps with a smooth fracture perfectly             perpendicular to the vertical, assume that vdW’s is all that matters, density of gold is 2.0 x 104 kg/m3, A = 2.5 x 10- 19 J).

10) There is a cylindrical rod of length H, radius r, density p, that

is falling with a constant speed, v, through a hole with radius R, in

a slab of material with thickness h. The gap thickness, R – r, is

very thin and filled with a fluid with viscosity  . Derive an

expression for the speed of the rod. After testing several fluids

with this setup, the experimentalists plot the data on a log-log plot

of speed (y axis) as a function of viscosity (x axis). What would

the plot look like? Now on a linear plot they show v as a function

of H. What would the plot look like for a Newtonian fluid, what

would it look like for a fluid that is shear thinning?

11) We have a diblock-copolymer that forms lamella with constant thickness. There is a small hole in the topmost lamella, as shown in the diagram. In an experiment it is found that small holes shrink in  size and close back up, while larger holes grow.

Explain what might drive a small hole to collapse. Assume that there is some reduction in the free     energy associated with the creation of a hole which scales like the area of the hole. Ignore the change in volume. Calculate the free energy of the system, defining clearly whatever parameters you need.   Draw the free energy as a function of radius, what is the critical radius.

P(x) =  exp 1 2  3

0 to some distance  ee   =  .