c*s
发帖数: 2145 | 1 发信人: zzwh (头碰桌), 信区: Macromolecules
标 题: 怎么判断溶液是semidilute or dilute?
发信站: The unknown SPACE (Sun May 18 13:21:35 2003) WWW-POST
thanks!
发信人: wonderlich (左岸，遁去), 信区: Macromolecules
标 题: Re: 怎么判断溶液是semidilute or dilute?
发信站: The unknown SPACE (Sun May 18 13:24:38 2003) WWW-POST
ft...overlapping concentration..
(C*)*[eta]=1---->(C*)
发信人: zzwh (头碰桌), 信区: Macromolecules
标 题: Re: 怎么判断溶液是semidilute or dilute?
发信站: The unknown SPACE (Sun May 18 14:22:43 2003) WWW-POST
eta is the screening length?
if I |
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c*****e
发帖数: 238 | 2 I would suggest light scattering or SANS.
In semidilute solutions, the length scale is not the chain length, but the
correlation length, which should be smaller than the scale of a chain. |
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z**h
发帖数: 224 | 3 yes, I did SANS, I want to know if the solution is in semidilute or not. |
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c*****e
发帖数: 238 | 4 I never do experiments, so I'm not sure.
Theoretically, the scattering function for a dilute solution scales like
exp(-N^2k^2/6), in a semidilute solution, it scales as exp(-\psi^2k^2/6)
so there should be a crossover in the plot of S(k) vs. k |
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d*****w
发帖数: 124 | 5 Keep in mind C* is not a sharp but wide concentration regime. It gives a good
criteria from the estimation of isolated chain size base on the Kuhn length of
polymers. Only far below or above the concentration range you can say the
colution is dilute or semidilute.
fomula. |
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z**h
发帖数: 224 | 6 How about this, can I tell from the conformation of the polymer coil?
If the coil can be discribed as self-avoiding or random coil, then the
solution is not in semidilute region? or the conformation has nothing to do
with it?
gave
property. |
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z**h
发帖数: 224 | 7 I am trying to determine the critical concentration. I want to use a equation
that applies to the semidilute region, so i want to tell if my solution is in
it or not.
do
I
solutions. |
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a***n
发帖数: 578 | 8 I am curious what is the difference between semidilute and dilute? is there a
reason to seperate them? thanks.
not. |
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w********h
发帖数: 12367 | 10 ft...overlapping concentration..
(C*)*[eta]=1---->(C*) |
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z**h
发帖数: 224 | 11 eta is the screening length?
if I don't konw the screening lenght. |
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w********h
发帖数: 12367 | 12 [eta] is intrinsic viscosity.
you can get criteria for dilute solution from any polymer textbooks..
overlapping concentration C* can be also deduced using a simple fomula.
but this predicted one generally is lower than the real overlapping
concentration.
what's your polymer?
people already have MHS formula for different polymers in different solvents.
you can first use MHS to get [eta], then C*.
what's dilute solution?
just means the regime in which eta-eta(s) is linear with C. |
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z**h
发帖数: 224 | 13 where can i get the MHS formula? My polymer is diblcok.
solvents. |
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w********h
发帖数: 12367 | 14 then you can measure the viscosity to see which is the critical concentration
for the transition from dilute to semi-dilute regimes... |
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w********h
发帖数: 12367 | 15 why bother!
that's the basic idea of polymer solution. |
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w********h
发帖数: 12367 | 16 sure. but that's too complicated for verifying the overlapping concentration.
viscosity's concentration dependence offers all information.
the |
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z**h
发帖数: 224 | 17 where did you get the equations? Thanks
the |
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c*****e
发帖数: 238 | 18 You can get some results from de Gennes book.
Actually I just realized that there is an error in my post, the results I gave
are for Gaussian chains, which may not be applicable to polymer solutions.
A monograph on SANS of polymer solutions is
Polymers in solutions: their modelling and structures.
Anyway, wonderlich suggested an easy way to characterize the solution property.
you can also look at Doi&Edwards to find out how to do it that way. |
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w********h
发帖数: 12367 | 19 how far?
in fact, semi-dilute regime is really narrow. ~10% to C*.
and the critical concentration (empirical C*) is very clear (if not as sharp
as you expect) from the viscosity increment.
good
of
the
textbooks.. |
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w********h
发帖数: 12367 | 20 hehe..seems you are 舍简就繁，
probably that is what Science is...
like
exp(-\psi^2k^2/6) |
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w********h
发帖数: 12367 | 21 what's your concentration now?
equation
in
results
scales |
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w********h
发帖数: 12367 | 23 molecular weight of your PS-PIP?
if higher than 100K, for sure in semi-dilute.
You can refer to Fetters' review article (Macromolecules 1994, 27:4642) to see
the /M values for PS and PIP.
0.675 for PIP, 0.434 for PS.
Suppose they are the same, say, 0.5.
It is almost half of PBD I am working on.
so, you can predict the overlapping concentration for PS-PIP is about 2.5
times that for PBD for the same Molecular weight.
From Colby's paper for PBD, (Macromolecules 1991, 24, 3873)
0.25 wt.% in g |
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z**h
发帖数: 224 | 24 Thanks, I am working on PS-PEO. Mw 58k-3k.
see
solution
then |
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w********h
发帖数: 12367 | 25 approximately 58K PS,
then 5 wt% is still in dilute regime considering PBD58K's C* should be higher
than 3 wt%. according to my experience.
//BTW: Why PS-PEO is so interesting?
So many people are working on that ;-)
a |
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d*****w
发帖数: 124 | 26 Oh, no. Actually for current polymers, i.e. N=1000-10000, the C* is about
10^-3,
and the semi-dilute regime crosses over about two decades. So most interests
of polymer solutions focus on this regime. Just my 2 cents.
length
not.
overlapping
different |
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d*****w
发帖数: 124 | 27 Macromolecules 1994, 27:4639 not 4642
Thanks anyway.
see
solution
then |
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w********h
发帖数: 12367 | 28 C*---M^(-0.5 or -0.6)
how can u say "N=1000-10000, the C* is about 10^-3"?
semi-dilute regime is from C* to ~10%.
refer to Colby's paper I mentioned.
And you said "most interests of polymer solutions focus on this regime",
but I think the theory in this regime is mostly undone.
de Gennes proposed something in 1971, Macromolecules,
but still not good enough.....
sharp
the
but
chain. |
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w********h
发帖数: 12367 | 30 dilute regime: C
entangled regime: C>Ce
both are almost clear in theory.
between C* and Ce, it is called semi-dilute.
de Gennes gave some prediction for this regime.
and many questions are undone in this regime.
hehe...later you will see my another paper on this subject,
although our interests are in dilute regime and entangled regime.
if you want to know further,
refer to de Gennes' books, or the new book of Rubinstein and Colby's.
a
but
chain. |
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c*****e
发帖数: 238 | 31 Generally there is a crossover between the two regime, in which the typical
length scale changes from the chain length to a partial chain length(correlation
length).
A most straightforward corollary is that the osmotic pressure scales as 9/4
power of the concentration, rather than 2 or 1. |
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d*****w
发帖数: 124 | 32 Let me make it clear. As you know, C* ~= N^(-4/5) for good solvent, where C* I
mean is volume fraction. If N = 10000 then C* = 10^-3.
See de Gennes' book at page 77 after equ. III.18 for details.
interests
a |
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w********h
发帖数: 12367 | 33 I knew the theoretical part.
But empirical overlapping is higher than predicted using that geometry
formula.
I
about
gives
say
or
length, |
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d****o
发帖数: 44 | 35 Rheological Properties. There must be entanglements in semidilated solutions
but not in diluted one. |
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w********h
发帖数: 12367 | 36 sorry, in semi-dilute regime, no entanglements. |
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w********h
发帖数: 12367 | 37 thanks
solvents.
concentration |
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a***n
发帖数: 578 | 38 good discussions although I just knew none about it. :) |
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c*****e
发帖数: 238 | 40 我记得好像de Gennes, M. Daoud, 等人好像发过一篇macromolecules,大概是1984年,
应该是总结了许多结果的(关于SANS测量polymer solution). |
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w********h
发帖数: 12367 | 41 Probably this paper will help about theory part.
for SANS, u need to check more papers.
Macromolecules, 2002, 35(24):9196,
JCP 1972, 57, 290,
PRL 1983, 51, 1983. |
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z**h
发帖数: 224 | 42 the papers are not correct.
, |
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w********h
发帖数: 12367 | 43 why?
等人好像发过一篇macromolecules,大概是1984年 |
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z**h
发帖数: 224 | 44 p9196 is in the middle of a paper, PRL 1983, talking about silicon |
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b***e
发帖数: 115 | 49 Although I did not use SANS, but the basic theory is the same as SAXS I think. |
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z**h
发帖数: 224 | 50 yes. The only difference is the contrast variation in SANS
think.
等人好像发过一篇macromolecules,大概是1984年, |
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