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Homework Help: A more complicated question on lipid phase diagrams

  1. Mar 29, 2015 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
    This is the final part of a past exam question. I've got through the first parts and can (thanks to a seperate question I asked here) read the phase diagrams and find melting points etc. However now it's asking for "composition trajectories", "phase morphology" and "domain size and internal structure" and I'm completely lost.

    I can work out the molar proportions and compostions by drawing a line down the diagram at 22% and figuring the ratio at 42 degrees. But I have no idea what to do for the above quoted terms.

    Any guidance would really be appreciated, I'm completely at a loss how you would derive this information from the phase diagrams given.
  2. jcsd
  3. Apr 1, 2015 #2
    How do you expect the size of the domains to compare when you cool rapidly compared to when you cool slowly? (Think nucleation rate)

  4. Apr 2, 2015 #3
    Thanks for the reply. I (think I) understand that kinetics influence the rate of transformation, i.e there is an additional barrier for cooling rapidly:


    So domains will form slower. Or have I misinterpreted the graph?

    thanks again
  5. Apr 2, 2015 #4
    I think that if you cool rapidly, you will get a lot more nucleation sites, so that, in the end, there will be many more domains, but they will all be smaller.

  6. Apr 2, 2015 #5
    Hmm, that would seem logical. The only 2 slides we have to solve this problem (not coursework, a past exam paper I'm working through for revision) are these:



    Slide 2 says they will eventually merge into 2 domains, so when the the question asks "domain size and internal structure" wont it eventually be the same whatever the cooling rate?

    Could you comment on whether you think the slides help with this question, because I've tried interpreting them but I'm still no closer to answering this question (especially giving 10 marks worth of description).
  7. Apr 2, 2015 #6
    I really don't know enough about this to comment. My experience on this type of thing relates to my experience with semi-crystalline polymers. Wish I could help further.

  8. Apr 2, 2015 #7
    That's no problem at all, thank you for your input!
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