y****u
发帖数: 50 | 1 in some sense
these academic masters are pop stars
and we students are fervid fans. |
|
c*******n
发帖数: 1648 | 2 Very good. Although you said you are not familar with the adhesion, you still
got the idea. What he talked about is the important basic theory for making
various polymer blends and adhesives.
separation)
.
bonding
种
意义
起
G(energy
同
最有趣得是他首先恭维了大家(这个lecture是chemistry的,所以大部分人也是chemistry
殊意 |
|
w********h
发帖数: 12367 | 3 来自主题: Macromolecules版 - Re: <> hehe...you guys...
高分子化学和物理两部分真的可以独立存在的。
PJ Flory的英文枯涩，
看起来是最头大的。
Odian的那本书基本上都已经被国内的高分子化学书给吸收重整了，
看看潘祖仁的那本就够了。
de Gennes的那本小书挺有意义，
但学化学的乃至是不做polymer dynamics的人来说仍然是艰深的，
哪怕他已经是用非常简单的语言阐述一些scaling的东西，
毕竟人家是诺贝尔奖得主。
Rubinstein和Colby最新要出版一本Polymer Physics的书，
偶已经看了，
等着它成为经典教材吧。 |
|
c*****e
发帖数: 238 | 4 今天讲的东西比较有趣,可惜没法和大家share,因为图片居多,而且他都是用
transparancy,所以我们也没有copy.
他以举例为主,介绍了soap film如何形成,生长,最后collapse.
这个东西是非常有趣的,但从某些方面说却很复杂,所以他也没有讲很多具体的细节. |
|
c*******n
发帖数: 1648 | 5 Very useful for polymer blends. Compatibilizers are surfactants basically.
However, small molecular surfactants are more complicated than block
copolymers.
Very interesting. |
|
z**h
发帖数: 224 | 6 Flory-Huggins interaction parameter 的演变 和de Genns 的screening length
or correlation length 的衍生。
不知大家以为如何？ |
|
c*****e
发帖数: 238 | 7 That's right. But I don't quite understand the most striking result obtained
by de Gennes, i.e. the connection between self avoiding walk and O(N) model.
The work done for flexible chains is quite a lot,
but I didn't learn the most beautiful parts yet and I still want to.
Nowadays most work on protein folding involves little physics, in my view.
Most work is based on old models and largely relies on computation.
A very excellent argument on the problem of conformations of protein is given
by de |
|
w********h
发帖数: 12367 | 8 Even for flexible, long homo-polymers, the picture is not fully clear.
Reptation model still faces some challenging problems. For very long
chain, de Gennes predicted Stokes-Einstein behavior recovers but nobody
verified yet.
After all, Zimm, Rouse, Reptation and some boundry conditions are the
most successful approach to explain linear monodisperse polymers.
clear |
|
c*****e
发帖数: 238 | 9 The infinite self avoiding walk is equilivant to the (\phi^2)^2 model
at the limit N goes to 0, where N is the dimension of \phi, the order parameter
I still don't quite understand why this is the case...
The most cited paper is de Gennes, Phys. Lett. 1972...
I think this letter is cited almost everywhere when this topic is discussed
and it should not be too difficult to find it if you search it by google.
I will give the full reference if you still need this tomorrow(now I don't have
it at hand |
|
c*****e
发帖数: 238 | 10 A very interesting question proposed in de Gennes book, soft matter and hard
science(maybe not accurate as I read the chinese translation) is as follows:
The polymer solution is usually viscous and the dissipation is more pronounced
than the pure solvent, but this is verified only for laminar flow when the
Reynolds number is not too large. Experiments show that adding very few polymer
chains to the turbulent flow can effectively reduce the energy loss in the flow
he gave the example that adding |
|
b*o
发帖数: 47 | 11 For complex systems such as polymers, I doubt that all details can be
clarified. However, I do think the big picture is there. For example,
Even for people like de Gennes, the importance of what he has been doing
recently,
such as polymers at interface, is not comparable with what he/his co-workers
did
in 1970/1980s. Most of the time, they just appllied the physics concepts into
more specific systems.
For heteropolymer physics, again, personally I think the late Tanaka had a
very
good begining, |
|
z**h
发帖数: 224 | 12 when talking about the polymer physics, people seems to talk their
specific research filed. However, what is important is the foundation of
polymer physics. some concepts are widely used to derive new things, to
expand a new field. I think that is the reason that some people like de Genns
can win Noble prize.
into
of
such |
|
c*****e
发帖数: 238 | 13 这次talk的内容与soap和foam有点关系.
所谓cellular adhesion指两个细胞或者一个细胞和另外一个平面拈连.
首先是patch,也就是一个versicle(相当于细胞膜)和另一个平面接触.
一般有两种方法:一是加入non-specific adhesive,可以将两者粘在一起;
另一种方法是使用比较重的heavy versicle,这样在重力作用下就会与水平的平面产生
接触.
接下来的过程是patch growth,也就是两者接触的平面逐渐扩张以降低能量.
具体的过程是细胞的表面和另外一个平面上的stickers之间不断产生binding.
内容就不详细讲了.
接下来他讲了一个general的问题,就是两个浸润的表面,从开始接触后,接触的面积
随时间的变化,涉及到表面张力和hydrodynamics.
Scaling的结果是
R(接触面积的线度)正比于时间的5/8次方.
最后一些更复杂的情形包括
1.非正常的adhesion,比如两者连接的平面并不是完全接触而是在中间形成一个dimple.
2.当两个平面带电的情况
3.在patch里面扩散很慢的情况
4.bind |
|
c*****e
发帖数: 238 | 14 Frustration effects in polymer systems
这个东西与我做的很有关系,所以听的比较认真.
所谓frustration,指的是体系有一个比较"喜欢"的低能量状态,但由于其他因素并
不能达到能量最低的状态.
一个简单的例子,如Ising magnet,或者不相容的polymer mixture,这种体系有相分离
(相变)的趋势,但在crosslink的A,B混合物中,相分离就不一定能顺利进行.比如
一般体系发生相分离的条件大概是
\chi * N～1,
在crosslink体系中,尽管总的趋势是满足这个条件的,但局部条件并不能得到满足
因为\chi *Ne(有效链长)<1.所以相分离不能顺利进行,体系就有可能被冻结在一个
metastable state.
具体的例子就是体系发生microphase separation的条件与具体的microphase structure
有关,并不能直接从mean field result来预言.
一般来说体系的相分离由concentration fluctuation诱发,但局部的fluctuation
有时并不一定 |
|
w********h
发帖数: 12367 | 15
structure
这个concentration fluctuation有实验直接证明么？
的block的平均长度决定,在这种近似下每一种segment的block的等效长度大概是N^(1/2) |
|
c*****e
发帖数: 238 | 16 这个只是一个一般的观点吧,实验可以测出concentration fluctuation,但不能确定
是否能引发phase separation/transition.
实际的情况是,在spinodal以后,任何微小的fluctuation都可以导致phase transition,
只要在q*有fluctuation.
但在亚稳区就不是一样了,通常需要比较大的fluctuation才能越过barrier.
所以要确定实际的phase transition point,就必须考虑fluctuation.
事实上,正是因为fluctuation任何体系才会回到equilibrium,或者到能量的最低态. |
|
w********h
发帖数: 12367 | 17
what I mean is:
can the idea (or theory) of "concentration fluctuation" be VERIFIED
experimentally? Though this idea is well accepted nowadays. |
|
c*****e
发帖数: 238 | 18 好像是有通过light scattering来测量structure factor的,在spinodal附近确实有peak
在q*,大概算是测定fluctuation的大小吧. |
|
z**h
发帖数: 224 | 19 neutron scattering
factor的,在spinodal附近确实有peak
定
transition,
. |
|
z**h
发帖数: 224 | 20 diblock copolymer phase separation happens when chiN>10.5 from mean filed
theory.
structure
的block的平均长度决定,在这种近似下每一种segment的block的等效长度大概是N^(1/2) |
|
c*****e
发帖数: 238 | 21 That is from accurate calculation.
Here we just estimate the limit. |
|
c*****e
发帖数: 238 | 22 Forgot to mention that this criterion is for symmetric diblock copolymers.. |
|
c*****e
发帖数: 238 | 23 I think dynamic/static light scattering is used for determination of the
structure factor for density fluctuation in phase transitions,
usually at the length scale of the wavelength of light.
X-ray scattering is used to determine the crystal lattice constants.
Neutron scattering could be used to determine the correlation functions of
deutrium, mostly used to characterize the conformation of a single chain,
what I know about SANS is it can be used to measure Rg. |
|
z**h
发帖数: 224 | 24 no, it is not only for symmetric. for symmetric diblock copolymer, lamellae
morphology will form after phase separation. with the change of volume
fraction of two blocks, the morphology will change also.
filed
的block的平均长度决定,在这种近似下每一种segment的block的等效长度大概是N^(1/2) |
|
z**h
发帖数: 224 | 25 the difference between the light anb x-ray or neutron is the length scale
they can measure. they all can measure the correaltion. just use small angle
scattering. usulay people use neutron because the contrast is bigger than
x-ray. |
|
c*****e
发帖数: 238 | 26 For asymmetric diblock copolymer melts, the phase transition point from
mean field approximation is not \chi*N>10.495, but is higher.
The 10.495 limit is only at the critical point which is for symmetric diblock
copolymers. |
|
c*****e
发帖数: 238 | 27 It's correct that these methods are only different in the length scale.
But I never heard of using SANS to measure the parameters of microphases,
they are not of the same length scale. |
|
z**h
发帖数: 224 | 28 yes. for asymmetric it is bigger than 10.495
diblock
lamellae
copolymers..
的block的平均长度决定,在这种近似下每一种segment的block的等效长度大概是N^(1/2) |
|
z**h
发帖数: 224 | 29 nuetron reflecticity can measure the lamellae spacing.
the length between 10A and 1000A or bigger can be measured by neutron
angle
of
chain, |
|
c*******n
发帖数: 1648 | 30 FAINT，DON‘T DO THAT，YOU WILL BE BEATED BY DE GENNES【 在 zzwh (钻石小程) 的大作中提到: 】 |
|
c*****e
发帖数: 238 | 31 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. |
|
c*****e
发帖数: 238 | 32 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. |
|
w********h
发帖数: 12367 | 33 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. |
|
d*****w
发帖数: 124 | 34 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 |
|
c*****e
发帖数: 238 | 35 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). |
|
w********h
发帖数: 12367 | 36 There are two people I admire to death,
de Gennes and him....
one is the most admirable theory physicist,
one experimental physicist.
However,
of
nomadic
at
Queens
factor
not
and
When
MDs,
degree.
black
high
a
remember.
steps. |
|
w********h
发帖数: 12367 | 37 come on...de Gennes cannot speak Chinese either...
why this is the criterion for admiring one people?
he is famous for his nobel prize in laser trap,
but he is also well-known in polymer community for his application of laser
twizer in single chain polymer dymamics studies....
also, it is related to bio...
what I mean is:
only if you have a strong background in PHYSICS,
you can achieve a lot in Macromolecular Science.
//sorry, I have to say, Polymer Chemistry is nothing but Chemistry. |
|
w********h
发帖数: 12367 | 38
block copolymer根据组成比不同会有miscrophase separation。
从sphere结构cylinderical结构到lamellae结构的变化，
再细致观察，在cylindrical与layer结构之间，
有两个复杂的结构，
一个叫做Bicontinuous,
一个叫做perforated layers (HPL)结构。
其中bicontinuous结构又叫double gyro phase,
也因结构复杂被称为“水管工的噩梦”。
大分子如何运动。
通常三种理论：Zimm, Rouse, and Reptation.
在polymer chain 高于一个临界分子量Mc的时候，
粘度的分子量依赖关系由M^1变化到M^3.4.
Mc通常和一个叫做entanglement molecular weight Me的量有关系，
Mc--2~3 Me.
对于不同种类的聚合物，Me不同。
在形容M>Me的聚合物，通常用Reptation理论，
由de Gennes首先提出tube model and snake-like motion,
Doi and Edwards |
|
b*o
发帖数: 47 | 39 I am very interested in this and looking forward to your publication. In
Edwards' derivation, I think the attraction part has the physical origin of
the monomer space packing entropy de Gennes mentioned. The polymer chain in
melt (supposedly polymer good solvent, i.e., kai=0) and in theta solvent both
shrink from that in good monomer solvent, but with different physical driving
force: entropy in the melt case while enthalpy in the theta solvent case, I
think.
off.
=
correlation
of
interaction
i |
|
p******s
发帖数: 137 | 40 中国某院士和另一院士认为有。
另一新近的院士用light-scattering在JPS-Phys.上曾经发了篇文章“证实”有。
查，发现主要由中国作者引用，共15次。
又看到某些中国的高分子学界的领袖人物们编了本书：高分子物理，
有subtitle曰：跨世纪的高分子科学。
书中正文第一章（引言blah blah若干不算）中谈到高分子溶液，
何其重要的内容，居然参考文献几乎全部是中国人的工作、甚至中文、会议论文。
在这章中的Introduction部分，
高度评价了某院士和另一院士的工作---de Gennes的overlap浓度下还有个浓度呐！
恕我无知，从未从权威的英文教科书中获得如此的信息，
请教于大家，
在分子链互相接触的overlap C*以前究竟有什么重要物理意义的临界浓度？ |
|
o****e
发帖数: 1011 | 41 大概是觉得有区别于“de Gennes的overlap浓度”的“overlap浓度”吧。
这一种“接触”(如果有的话)应该就是其物理意义。 |
|
b*o
发帖数: 47 | 42 Just had a long vacation. I remeber that I read it somewhere saying
entanglement length, as estimated from viscoelasticity measurment and
theoretical models, is usually several times longer than the correlation
length of polymer solutions of the same concentration as measured by
light/neutron scattering (?) experiment. Forget the original literature and
the details, just this conclusion vaguely in my memory. These two concepts
seem easy to understand with de Gennes' drawing in his book.
As for t |
|
w********h
发帖数: 12367 | 43 de Gennes decribes the scaling concept without introducing the accurate
prefactors. it focuses on the relationship between two or more important
parameters. for example, tube diameter "a" with concentration "fi",
a---fi^(-2/3). while the correlation length ---fi^(-1) in theta condition.
and
it. |
|
w********h
发帖数: 12367 | 44 that's what I mentioned about "Constraint Release" and "Contour Length
Fluctuations" corrections to the initial Tube model designed by de Gennes.
significant
not
motion
the
one
effects.
chains,
(as
to
simple
SANS
approach.
they
are
people
references
identical.
see
length
polymers?
entangled
might |
|
c*****e
发帖数: 238 | 45 Grubbs definitely is very promising, but he is doing almost pure chemistry, we
may count him in as one like Zigler or Natta. This is my feeling, I'm not sure
about this.
The other people we usually count as polymer scientist, Flory, de Gennes,
A.J. Heeger all bring in new concepts to chemistry and physics, sometimes even
introduce new fields and ideas. Maybe Grubbs can do the same. |
|
w********h
发帖数: 12367 | 46 there is not one person to appear per nanosecond..
you must be a sperm now...hoho
Gennes应该
but |
|
c*****e
发帖数: 238 | 47 You are only talking about physics...
for math, more and more geniuses are appearing...
Well, for scientists, no one cares
I guess the scaling needs to be corrected, i.e., from Archimedes to Newton
it takes 2000 years, from Newton to Einstein, it takes 300, next should take
even shorter time.
Fermi, Heisenberg, Witten...are all above Flory/de Gennes level, although F/G are
definitely above a lot of others. |
|
w********h
发帖数: 12367 | 48 Basically I think the second choice would be better when one cannot be
that great as de Gennes, Edwards, or Freed (though I don't think Freed
is parallel to the former two as to their contributions...:-(). Currently
Muthukumar and Rubinstein are more precisely defined as polymer physicists in
US.
Yes, I do agree on your conclusion that Bio-field currently seems isolated
from polymer physics though many biophysicists are doing some experiments
on the single chain of DNA or protein. To me, those e |
|
t*******n
发帖数: 4445 | 49 内容还不太过时么，如果是非专业人士瞎看的话。
“Introduction to Polymer Dynamics”
by P.G. de Gennes
57 pages, Lezioni Lincee series
Cambridge University Press 1990 |
|
w********h
发帖数: 12367 | 50 de Gennes' books are all classical, never out of date. |
|
