w********h
发帖数: 12367 | |
y****q
发帖数: 16 | 2 没有最低，只有更低
【在 w********h 的大作中提到】
: 而且还要是amorphous,
: 是PDMS么？
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S*****n
发帖数: 6055 | 3 总之应该是polysiloxane这一类的吧
不知道有没有比PDMS更低的，呵呵
【在 w********h 的大作中提到】
: 而且还要是amorphous,
: 是PDMS么？
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w********h
发帖数: 12367 | 4 my question is "is there a theoretical minimum of Tg, given a certain length
to be called as polymer."
【在 S*****n 的大作中提到】
: 总之应该是polysiloxane这一类的吧
: 不知道有没有比PDMS更低的，呵呵
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S*****n
发帖数: 6055 | 5 I think the factor plays the role behind DP is # of Kuhn segments.
So think of flexibility or rigidity of the chain, and I think the limit could
be given when each chemical bond can rotate freely.
But the chemistry also affects Tg, considering small molecules also hold
different Tg. Tg of amorphous metal is even higher than any polymers.
Anyway, this is kind of Ban Men Nong Fu, since you know more dynamics than I
do......
【在 w********h 的大作中提到】
: my question is "is there a theoretical minimum of Tg, given a certain length
: to be called as polymer."
|
w********h
发帖数: 12367 | 6 对于固定某一聚合物，Tg和多少个库恩段有关系，或者表观和分子量有关系。
不同聚合物在这个临界分子量之上的Tg决定于骨架结构和侧链，
有没有人做过预测，所有possible的结构能产生的最低Tg应该是多少。。。。
could
【在 S*****n 的大作中提到】
: I think the factor plays the role behind DP is # of Kuhn segments.
: So think of flexibility or rigidity of the chain, and I think the limit could
: be given when each chemical bond can rotate freely.
: But the chemistry also affects Tg, considering small molecules also hold
: different Tg. Tg of amorphous metal is even higher than any polymers.
: Anyway, this is kind of Ban Men Nong Fu, since you know more dynamics than I
: do......
|
S*****n
发帖数: 6055 | 7 嗯，你要连侧链一起考虑，问题又复杂了。。。。。。
隐约有种印象，dendrimer没有Tg，很不确定的印象，呵呵
不知道有没有什么方法可以脱离高分子的载体，直接从自由体积的角度求解呢？
当然，这纯属瞎想了：）
【在 w********h 的大作中提到】
: 对于固定某一聚合物，Tg和多少个库恩段有关系，或者表观和分子量有关系。
: 不同聚合物在这个临界分子量之上的Tg决定于骨架结构和侧链，
: 有没有人做过预测，所有possible的结构能产生的最低Tg应该是多少。。。。
:
: could
|
c*******n
发帖数: 10 | 8 to be completely amorphous and in solid state, you should crosslink the chains
, just like in rubber.
You can plasticize the rubber with solvents to form gel to further reduce Tg.
Dynamics only determine what is the kuhn length, but no one can give a clear
definition of the critical DP to be called 'polymer'.
You may define a 'polymer' with DP above entanglment with typical Rouse and
Repetation behavior in G'-T (f) plot.
Or define a 'polymer' with DP above which Tg does not change with Mw.
Anywa |
S*****n
发帖数: 6055 | 9 Y. Ding, A. Kisliuk, A.P. Sokolov, When does a molecule become a polymer?,
Macromolecules 37, 161-166 (2004).
They developed a new critical condition to define a polymer, claiming its more
universal, hehe:)
chains
.
SOLID
for
【在 c*******n 的大作中提到】
: to be completely amorphous and in solid state, you should crosslink the chains
: , just like in rubber.
: You can plasticize the rubber with solvents to form gel to further reduce Tg.
: Dynamics only determine what is the kuhn length, but no one can give a clear
: definition of the critical DP to be called 'polymer'.
: You may define a 'polymer' with DP above entanglment with typical Rouse and
: Repetation behavior in G'-T (f) plot.
: Or define a 'polymer' with DP above which Tg does not change with Mw.
: Anywa
|
S*****n
发帖数: 6055 | 10 wonder......I don't think your question could have an answer since Tg is
really an ill-defined concept. It's even affected by the way you define it, or
by the way you measure it. Experimentally we have so many ways to get Tg, but
each method would give a different value, and theoretically what is the
definition of Tg? I think dynamics people are still arguing about this.
【在 w********h 的大作中提到】
: 对于固定某一聚合物，Tg和多少个库恩段有关系，或者表观和分子量有关系。
: 不同聚合物在这个临界分子量之上的Tg决定于骨架结构和侧链，
: 有没有人做过预测，所有possible的结构能产生的最低Tg应该是多少。。。。
:
: could
|
|
|
w********h
发帖数: 12367 | 11 enh...这个我记得Craig Hawker和Karen Wooley曾经在1994年发过一片JACS，
谈dendrimer的异常特性粘度行为，
他们对dentrimer的Tg vs Mn有另外一个类似于线性高分子的公式，
你们有兴趣可以去看看。。。。
前不久看到Akron的Forster和Quirk的一片大分子上，
引用了那个公式。
星型或者hyperbranched或者dendrimer或者环形的缠结行为和流变行为和线性有很大不同
，
具体参考Graessley或者Roovers或者Milner&McLeish的文章。。。。 |
w********h
发帖数: 12367 | 12 我知道这个Tg是个很不清楚地东东，
但就一般而言，一台机器，热历史相同，测试情况一致，
所能得到的可具可比性的Tg...
or
but
【在 S*****n 的大作中提到】
: wonder......I don't think your question could have an answer since Tg is
: really an ill-defined concept. It's even affected by the way you define it, or
: by the way you measure it. Experimentally we have so many ways to get Tg, but
: each method would give a different value, and theoretically what is the
: definition of Tg? I think dynamics people are still arguing about this.
|
w********h
发帖数: 12367 | 13 虽然有一些人试图用Kuhn length做点文章，试图把它作为使得高分子
链行为符合高斯链行为，但仍然不够清楚，或不够General。。。究其
原因，无非是因为在大部分polymer来说，Me挺低的，下面基本上没有
多少区间可供研究，也就PS和PDMS以及他们的一些改性的东东。。。
以我的看法，现在这个问题的重点应该先解决Me和Mc的区别的根本原因，
Fetters等人曾经有几片文章(Macromolecules, JPSB)讨论过用Packing
Length去说明之间的根本原因，好久没搞这冬冬了，不知道是否为众人
接受。。。。cashine，有没有什么input?
chains
.
SOLID
for
【在 c*******n 的大作中提到】
: to be completely amorphous and in solid state, you should crosslink the chains
: , just like in rubber.
: You can plasticize the rubber with solvents to form gel to further reduce Tg.
: Dynamics only determine what is the kuhn length, but no one can give a clear
: definition of the critical DP to be called 'polymer'.
: You may define a 'polymer' with DP above entanglment with typical Rouse and
: Repetation behavior in G'-T (f) plot.
: Or define a 'polymer' with DP above which Tg does not change with Mw.
: Anywa
|
S*****n
发帖数: 6055 | 14 前些天听Fetters讲Packing Length的时候睡着了，罪过罪过
【在 w********h 的大作中提到】
: 虽然有一些人试图用Kuhn length做点文章，试图把它作为使得高分子
: 链行为符合高斯链行为，但仍然不够清楚，或不够General。。。究其
: 原因，无非是因为在大部分polymer来说，Me挺低的，下面基本上没有
: 多少区间可供研究，也就PS和PDMS以及他们的一些改性的东东。。。
: 以我的看法，现在这个问题的重点应该先解决Me和Mc的区别的根本原因，
: Fetters等人曾经有几片文章(Macromolecules, JPSB)讨论过用Packing
: Length去说明之间的根本原因，好久没搞这冬冬了，不知道是否为众人
: 接受。。。。cashine，有没有什么input?
:
: chains
|
w********h
发帖数: 12367 | 15 星型主要是因为arm retraction导致的contour length fluctuation。。。这是
目前流行的说法, who knows对不对。。。。
星型多臂也不接近枝化罢。。。
枝化分好几种：短侧链，长侧链，高度枝化。。。。
星型一般在制备过程容易做到monodisperse，
而枝化控制起来就不是那么容易，反应到一定程度突破percolation就gelation乐。。。 |
c*****e
发帖数: 238 | 16 I know little about T_g in polymer melt, PS, for a simple example.
The reason is it is hard to relate a theoretical description with experimental
measurements.
The general motif here seems to be the free volume, which is caused by
geometric frustration (e.g. jamming) and slow dynamics.
Normally people believe glass transition occurs above the temperature when the
free volume vanishes, and that lower boundary of glass transition is somehow
termed the ideal glass transition temperature. But this i
【在 S*****n 的大作中提到】
: wonder......I don't think your question could have an answer since Tg is
: really an ill-defined concept. It's even affected by the way you define it, or
: by the way you measure it. Experimentally we have so many ways to get Tg, but
: each method would give a different value, and theoretically what is the
: definition of Tg? I think dynamics people are still arguing about this.
|
c*****e
发帖数: 238 | 17 Regarding packing length, my boss did some work very early on that.
Basically they are looking at the difference between ideal chains (gaussian)
and chains in the melt, still others are studying the difference between ideal
chains and theta solvent (yeah, I've earned a little more knowledge on this
and could probably resolve some of you guy's dispute on this).
Cutting short, chains in the melt has an extra constraint of volume
incompressibility and constant density, that is definitely not presen
【在 w********h 的大作中提到】
: 虽然有一些人试图用Kuhn length做点文章，试图把它作为使得高分子
: 链行为符合高斯链行为，但仍然不够清楚，或不够General。。。究其
: 原因，无非是因为在大部分polymer来说，Me挺低的，下面基本上没有
: 多少区间可供研究，也就PS和PDMS以及他们的一些改性的东东。。。
: 以我的看法，现在这个问题的重点应该先解决Me和Mc的区别的根本原因，
: Fetters等人曾经有几片文章(Macromolecules, JPSB)讨论过用Packing
: Length去说明之间的根本原因，好久没搞这冬冬了，不知道是否为众人
: 接受。。。。cashine，有没有什么input?
:
: chains
|
