z**h
发帖数: 224 | | c*****e
发帖数: 238 | 2 最好详细说说,当初好像记得这个,现在记不清了.
不过应该是说的morphology的演变吧,比如coarsening什么的?
【在 z**h 的大作中提到】
: Thanks
| c*******n
发帖数: 1648 | 3 Interdiffusion coeff. or selfdiffusion coeff?
If it's inter diffusion coeff. why it's surprising to know it's a negative
number at the phase seperation? If you say self diffusion, then I also want to
know the answer.
【在 c*****e 的大作中提到】
: 最好详细说说,当初好像记得这个,现在记不清了.
: 不过应该是说的morphology的演变吧,比如coarsening什么的?
| w********h
发帖数: 12367 | 4 I think it is interdiffusion bah..
I never heard of negative diffusion coefficient...//expect more details.
Here are some papers, I don't know if they are helpful or not:
(1)
Spontaneous Double Phase Separation Induced by Rapid Hydrodynamic Coarsening
in Two-Dimensional Fluid Mixtures
Physical Review Letters Volume: 81, Issue: 2, July 13, 1998. pp. 389-392.
Tanaka, Hajime; Araki, Takeaki
(2)
New mechanisms of droplet coarsening in phase-separating fluid mixtures
The Journal of Chemical Physics V
【在 c*******n 的大作中提到】
: Interdiffusion coeff. or selfdiffusion coeff?
: If it's inter diffusion coeff. why it's surprising to know it's a negative
: number at the phase seperation? If you say self diffusion, then I also want to
: know the answer.
| z**h
发帖数: 224 | 5 the question is a component diffuses from low concentration to high
concentration.
to
【在 c*******n 的大作中提到】
: Interdiffusion coeff. or selfdiffusion coeff?
: If it's inter diffusion coeff. why it's surprising to know it's a negative
: number at the phase seperation? If you say self diffusion, then I also want to
: know the answer.
| c*****e
发帖数: 238 | 6 I think that's related to coarsening..
Usually the region with high concentration also has small curvature, and thus
the chemical potential of the boundaries is lower.
【在 z**h 的大作中提到】
: the question is a component diffuses from low concentration to high
: concentration.
:
: to
| c*******n
发帖数: 1648 | 7 OK, that's interdiffusion. It's normal to see D<0 for any phase seperation
process. Because interdiffusion is totally different from the selfdiffusion.
It has two components, one is from the average mobility of the polymer pairs,
another is from the thermodynamic contribution(chi). At spinodal,actually D=0,
That's been called thermodynamic slowing down. D<0 simply means that two
components have tendency to demix.(chi>chi*) That's all. If you look at the
Fick's Law, you will find when D will be n
【在 z**h 的大作中提到】
: the question is a component diffuses from low concentration to high
: concentration.
:
: to
| z**h
发帖数: 224 | 8 How to explain the nucleation has positive diffusion coefficient while
spinodal has negative?
pairs,
D=0,
negative
【在 c*******n 的大作中提到】
: OK, that's interdiffusion. It's normal to see D<0 for any phase seperation
: process. Because interdiffusion is totally different from the selfdiffusion.
: It has two components, one is from the average mobility of the polymer pairs,
: another is from the thermodynamic contribution(chi). At spinodal,actually D=0,
: That's been called thermodynamic slowing down. D<0 simply means that two
: components have tendency to demix.(chi>chi*) That's all. If you look at the
: Fick's Law, you will find when D will be n
| c*******n
发帖数: 1648 | 9 Hoho, here is the big trap!
Personally, I never looked into this situation
However, based on my limited knowledge in crystallization
I guess in ur case, the nuclei are very pure particles initially
That means infinite sharp concentration gradient on interface
This concentration gradient relax with the time. That's the reason
【在 z**h 的大作中提到】
: How to explain the nucleation has positive diffusion coefficient while
: spinodal has negative?
:
: pairs,
: D=0,
: negative
| c*****e
发帖数: 238 | 10 It has something to do with the phase morphology.
I think the spinodal decomposition you referred to usually corresponds to
bicontinuous phases, in that case, the hydrodynamic effects dominate over
normal diffusion induced by the nuclei.
【在 z**h 的大作中提到】
: How to explain the nucleation has positive diffusion coefficient while
: spinodal has negative?
:
: pairs,
: D=0,
: negative
| | | w********h
发帖数: 12367 | 11 yes.
refer to the papers I listed before...
seperation
selfdiffusion.
spinodal,actually
the
【在 c*****e 的大作中提到】
: It has something to do with the phase morphology.
: I think the spinodal decomposition you referred to usually corresponds to
: bicontinuous phases, in that case, the hydrodynamic effects dominate over
: normal diffusion induced by the nuclei.
| c*******n
发帖数: 1648 | 12 hard to follow, more detail?
【在 c*****e 的大作中提到】
: It has something to do with the phase morphology.
: I think the spinodal decomposition you referred to usually corresponds to
: bicontinuous phases, in that case, the hydrodynamic effects dominate over
: normal diffusion induced by the nuclei.
| c*****e
发帖数: 238 | 13 You can read the papers listed by wonderlich.
Or you can read two papers by P.G. de Gennes and P. Pincus in JCP
the title is Dynamics of spinodal decomposition(?), 1980
Very excellent scaling argument.
【在 c*******n 的大作中提到】
: hard to follow, more detail?
| c*******n
发帖数: 1648 | 14 Thanks a lot. Maybe you guys concentrated on the internal reasons. Actually
from the first principle of interdiffusion, the change of concentration
gradient profile with time near the interface tells all.
to
over
【在 c*****e 的大作中提到】
: You can read the papers listed by wonderlich.
: Or you can read two papers by P.G. de Gennes and P. Pincus in JCP
: the title is Dynamics of spinodal decomposition(?), 1980
: Very excellent scaling argument.
| z**h
发帖数: 224 | 15 we are trying to explain this physically. If you plot the free energy vs
compositon , you get two minimums.The nucleation and spinodal lies between
the two minimums. when the second derivative of free energy is negative , the
spinodal happens. My question was for nucleation or spinodal, we finally got
A-rich phase and B-rich phase. The initial composition lies between this two.
So if A from initial mixture goes to A-rich phase we have negative diffusion.
If A from initial mixturre goes to B-rich
【在 c*******n 的大作中提到】
: Thanks a lot. Maybe you guys concentrated on the internal reasons. Actually
: from the first principle of interdiffusion, the change of concentration
: gradient profile with time near the interface tells all.
:
: to
: over
| c*******n
发帖数: 1648 | 16 Actually what I was talking about is a physical picture in people's mind
When spinodal happens, the tiny amplitude of composition fluctuation wave
exists initally, the composition fluctuation is getting bigger and bigger
with the time. The concentration gradient is getting bigger and bigger as the
result. That's exactly what negative diffusion coeff. means!
When nucleation happens, following your way, let's say tiny amount of
B nucleat into almost 100% pure particles. As this particle grows into
【在 z**h 的大作中提到】
: we are trying to explain this physically. If you plot the free energy vs
: compositon , you get two minimums.The nucleation and spinodal lies between
: the two minimums. when the second derivative of free energy is negative , the
: spinodal happens. My question was for nucleation or spinodal, we finally got
: A-rich phase and B-rich phase. The initial composition lies between this two.
: So if A from initial mixture goes to A-rich phase we have negative diffusion.
: If A from initial mixturre goes to B-rich
| c*****e
发帖数: 238 | 17 Since the normal diffusion is usually pure entropic, when the enthalpic
contribution to the free energy becomes pronounced, it can dominate over the
entropy, then there might appear this negative diffusion, which is related the
concentration difference, but the real difference is governed by the chemical
potential, which still favors aggregation of similar components(A or B)
As for the difference between spinodal decomposition and nucleation, the
macroscopic difference is mainly the difference i
【在 z**h 的大作中提到】
: we are trying to explain this physically. If you plot the free energy vs
: compositon , you get two minimums.The nucleation and spinodal lies between
: the two minimums. when the second derivative of free energy is negative , the
: spinodal happens. My question was for nucleation or spinodal, we finally got
: A-rich phase and B-rich phase. The initial composition lies between this two.
: So if A from initial mixture goes to A-rich phase we have negative diffusion.
: If A from initial mixturre goes to B-rich
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