Decomposition of plastics

giovle

Hi everybody,

I'm currently studying for my exams and one of the exams I've got is about plastics. Now in my notes there's something about spinodal decomposition and binodal composition due to nuclei. I wrote it down myself but I seem to have forgotten what it means. Can anybody help me? It's kinda important since I've seen questions of last years exam and there was a question: 'Explain binodal and spinodal decomposition.'

Thx

Bikerman

http://pruffle.mit.edu/3.00/Lecture_32_web/node3.html
http://math.gmu.edu/~sander/movies/spinum.html
http://sbcb.bioch.ox.ac.uk/oliver/research/Lattice-Boltzmann/spinodal.html
http://www.mate.tue.nl/mate/research/index.php/7
http://en.wikipedia.org/wiki/Spinodal_decomposition

giovle

Alright thanks Bikerman!

Let's see if I get this right:
If you have two materials and you make a mixture of them you've got three things that can occur (I assume that you are at a temperature at which these three cases can occur):

1) The composition lies on the outside of the two binodal points (which are found through the tangent method)

this is the stable region so your mixture will not decompose.

2) The composition lies between the binodal point and the spinodal point (so there are two regions in which this can occur), the spinodal points being the points where the second derivative of the free energy curve equals zero

this is a metastable region, decomposition will start only in supercritical nuclei since you've got to have a large difference in composition. Therefor it will only nucleate at several location and not throughout the global mixture.

3) The composition lies between the two spinodal points

the material is unstable now and will globally decompose due to slight differences in composition and not just at the nuclei.

Bikerman

I'm afraid I know nothing about the subject so I'm not the right person to ask - I just gave you some references from my database of science links which have been vetted by others who DO know something about it.
If you want to discuss it with people who are more likely to be expert then I could suggest;
http://www.sciencefile.org/cgi-bin/yabb2/YaBB.pl