Surface Science: Foundations of Catalysis and Nanoscience

Chapter 5. Liquid Interfaces: Supplemental Material

Believe it or not, somebody else is trying to teach science with Sumi Nagashi. And now it seems everybody wants to get on the bandwagon. Try this for example. And here's another example of touchable digital painting. And if you would like to organize a workshop in it, I'm sure Frederica Marshall will help you out, though this offer may only pertain if you live in Maine or the Gulf Coast of Florida.

This from GE's web site: Non-reflecting glass - “Invisible Glass” (1918): A non-reflective glass that is the prototype for coatings used today on virtually all camera lenses and optical devices. It was invented by Katherine Blodgett, the first female scientist to join GE's Research Center. She, of course, is the same Blodgett of Langmuir-Blodgett films. Some of the first work on monomolecular films on water was performed by Agnes Pockels. (Noch mehr auf Deutsch) This fascinating story was brought to the scientific community's attention with the helpf of Lord Rayleigh, who transmitted some of her results to the journal Nature.

"I shall be obliged if you can find space for the accompanying translation of an interesting letter which I have received from a German lady, who with very homely appliances has arrived at valuable results respecting the behaviour of contaminated water surfaces. The earlier part of Miss Pockel's letter covers nearly the same ground as some of my own recent work, and in the main harmonizes with it. The later sections seem to me very suggestive, raising, if they do not fully answer, many important questions. I hope soon to find opportunity for repeating some of Miss Pockels' experiments." Lord Rayleigh, March 1891.

Much of electrochemistry occurs as the liquid/solid interface. In chapter 8, there is more focus on charge transfer and photovoltaics. Here we focus more on an introduction to the electrified interface. You can find basic refresher course in electrochemistry here. For more on the nomenclature, definitions and standards of electrochemistry, visit this site. You can find a application notes on electrochemical instrumentation and methods at this site maintained by Princeton Applied Research.

Questions and Exercises

  1. What is the collision rate with a surface held at 300 K if it is exposed to (a) water vapor with a pressure of 1 atm and (b) liquid water?
  2. If a clean Si(100) surface is exposed to pure liquid water at 300 K, how long does it take for the coverage to reach 0.1 ML, 0.5 ML and 1.0 ML if the sticking coefficient is one initially and follows Langmuir kinetics?
  3. Calculate the flux of ethanol onto a surface from a 5 wt% aqueous solution at 298 K.
  4. Calculate the flux of Fe(H2O)63+ onto a surface from a 0.05 M aqueous solution at 298 K.
  5. What is the difference between specific and non-specific adsorption of a solute?
  6. How does a change in the sign of the electric field at an electrode surface affect the water above it?
  7. Why is a sphere (or close to it) the natural shape of a drop of water in air?
  8. How does surface tension change with decreasing temperature?
  9. What is the Gibbs-Thompson effect?
  10. What are capillary waves? Are they more likely to have long or short wavelengths?
  11. Why does water on a hydrophobic surface tend to ball up into a number of small drops rather than one large drop?
  12. What is a Langmuir film?
  13. What is a Langmuir-Blodgett film?
  14. What forces are responsible for the ordering of a Langmuir film?
  15. (a) Calculate the Gibbs energy change that occurs when changing a cube to a sphere with the same volume at constant T and p. (b) Calculate the Gibbs energy change per atom in the sphere assuming constant number density when changing a sphere to a cube with the same volume at constant T and p. Discuss the implications and the relative importance for a nanoparticle with r = 1 nm compared to a microparticle r = 1 ┬Ám.
  16. (a) When is a nanoparticle buoyant in a liquid? (b) A Pt nanoparticle sinks to the bottom of a container and lands on an electrode. A reaction proceeds on the surface of the Pt nanoparticle that generates H2. The H2 forms a bubble that encapsulates the nanoparticle (assume a sphere within a sphere). How much H2 would have to be formed to make the nanoparticle buoyant in water?
  17. For a bubble that is growing in a quasi-static state in which momentum transfer can be neglected, detachment from a surface occurs when the forced provided by surface tension balances the net buoyancy of the bubble [1, 2].

    For a bubble that exhibits a contact angle a, Lubetkin has shown detachment occurs at
    Eq 5.16.1
    where Eq 5.16.2
    and the radius of the bubble is R, the radius of the attached circumference is Rd, the difference in densities is Eq 5.16.3, g is the surface tension of the liquid and g is the gravitational acceleration constant.
    Ex 5.16.3

    [1] S. D. Lubetkin, Journal of the Chemical Society-Faraday Transactions I, 85 (1989) 1753.
    [2] S. Di Bari, A. J. Robinson, Experimental Thermal and Fluid Science, 44 (2013) 124.

    Silver has a density of 10.50 g cm-3 compared to Pt with a density of 21.45 g cm-3 and the surface tension of water is 72.1 mN m-1. For a 10 nm particle with Eq 5.16.4, will it float before the H2 bubble detaches?

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