d**o
发帖数: 35 | 1 谁能讲讲？对于同一高分子，在高温结晶和在低温结晶是啥意思？不是一到熔点以下就开
始结晶了吗？ |
w********h
发帖数: 12367 | 2 熔点以下的温度也有高温和低温吧。比方说，从熔点以上淬冷至某温度结晶...
开
【在 d**o 的大作中提到】
: 谁能讲讲？对于同一高分子，在高温结晶和在低温结晶是啥意思？不是一到熔点以下就开
: 始结晶了吗？
|
b***e
发帖数: 115 | 3 对于这个问题，我觉得很难说清楚。我也在作关于高分子结晶方面的课题。我觉得你可以
看一下John D. Hoffman。关于三个结晶区域转变的文章。这样可能对这个概念比较清楚
。你也在做结晶吗？哪个学校的？？？
开
【在 d**o 的大作中提到】
: 谁能讲讲？对于同一高分子，在高温结晶和在低温结晶是啥意思？不是一到熔点以下就开
: 始结晶了吗？
|
b***e
发帖数: 115 | 4 这主要和他的结晶区域有关
就
【在 w********h 的大作中提到】
: 熔点以下的温度也有高温和低温吧。比方说，从熔点以上淬冷至某温度结晶...
:
: 开
|
r****r
发帖数: 14 | 5 The crystallization of polymer is different from those of small molecules in
which the Tm and Tc can be very close. For polymer, quite large supercooling
(the difference between Tm and Tc) is needed for the nucleation. The Tm is
determined by the Tc. You can check the Gibbs-Thompson equation to find the
relationship. Normally, larger Tc leads to larger Tm. Tc also determines the
morphology. At high Tc, for flexible and semi-rigid polymer, regular chain
folding lamellae structure can be formed fr
【在 d**o 的大作中提到】
: 谁能讲讲？对于同一高分子，在高温结晶和在低温结晶是啥意思？不是一到熔点以下就开
: 始结晶了吗？
|
b***e
发帖数: 115 | 6 very good!
spherulites,
就
【在 r****r 的大作中提到】
: The crystallization of polymer is different from those of small molecules in
: which the Tm and Tc can be very close. For polymer, quite large supercooling
: (the difference between Tm and Tc) is needed for the nucleation. The Tm is
: determined by the Tc. You can check the Gibbs-Thompson equation to find the
: relationship. Normally, larger Tc leads to larger Tm. Tc also determines the
: morphology. At high Tc, for flexible and semi-rigid polymer, regular chain
: folding lamellae structure can be formed fr
|
d**o
发帖数: 35 | 7 比如我想让橡胶结晶，先升温到熔点以上使它融化，开始降温，降到某一温度Tc时，一定
结晶度的结晶就应该形成了吧。那么通过什么来控制结晶温度变高变低呢？降温速度还是
什么？
spherulites,
就
【在 r****r 的大作中提到】
: The crystallization of polymer is different from those of small molecules in
: which the Tm and Tc can be very close. For polymer, quite large supercooling
: (the difference between Tm and Tc) is needed for the nucleation. The Tm is
: determined by the Tc. You can check the Gibbs-Thompson equation to find the
: relationship. Normally, larger Tc leads to larger Tm. Tc also determines the
: morphology. At high Tc, for flexible and semi-rigid polymer, regular chain
: folding lamellae structure can be formed fr
|
d**o
发帖数: 35 | 8 错了，不是橡胶，比如说尼龙吧
定
是
【在 d**o 的大作中提到】
: 比如我想让橡胶结晶，先升温到熔点以上使它融化，开始降温，降到某一温度Tc时，一定
: 结晶度的结晶就应该形成了吧。那么通过什么来控制结晶温度变高变低呢？降温速度还是
: 什么？
:
: spherulites,
: 就
|
r****r
发帖数: 14 | 9 Run a DSC with different cooling rate. You'll find the different onset
crystallization temperature. fast cooling leads to lower onset Tc. To controll
the onset Tc, you can try to find some nucleating agent to lower the
nucleation barrier (to decresase the surface free energy). I am not familar
with nylon, but as I know, some hydogen bonding will be formed inside the
crystal. So adding some additive that can affect the hydrogen bonding may have
chance to controll the kinetics thus the onset Tc.
【在 d**o 的大作中提到】
: 比如我想让橡胶结晶，先升温到熔点以上使它融化，开始降温，降到某一温度Tc时，一定
: 结晶度的结晶就应该形成了吧。那么通过什么来控制结晶温度变高变低呢？降温速度还是
: 什么？
:
: spherulites,
: 就
|
b*****h
发帖数: 29 | 10 From thermaldynamic point of view, you can not change the TC if you keep the
chemical unchanged.
As far as i known, the crystalization speed is controlled by the blance
between seed speed and growth speed. So I guess your question is related with
control the percentage of the crystalization.
Normally with glass material, you will find TTT graph is very helpful if your
objects are so pop that is available. Choose some speeds you can run even
metals right though the crystal phase letting them dire
【在 r****r 的大作中提到】
: Run a DSC with different cooling rate. You'll find the different onset
: crystallization temperature. fast cooling leads to lower onset Tc. To controll
: the onset Tc, you can try to find some nucleating agent to lower the
: nucleation barrier (to decresase the surface free energy). I am not familar
: with nylon, but as I know, some hydogen bonding will be formed inside the
: crystal. So adding some additive that can affect the hydrogen bonding may have
: chance to controll the kinetics thus the onset Tc.
:
|
r****r
发帖数: 14 | 11 Polymer crystallization is mostly a kintical problem. Thermodynamics only sets
a bound to it. Onset Tc can be easily changed by changing the cooling rate or
adding nucleating agent.
Talking about controlling the degree of crystallinity, it is related to the Tc
sometimes. Just imagine some entanglements will be trappped if the
crystallization rate is too fast and the disentanglement is only possible in
the case of low crystallization rate.
with
your
familar
，
度
Tm
find
determines
【在 b*****h 的大作中提到】
: From thermaldynamic point of view, you can not change the TC if you keep the
: chemical unchanged.
: As far as i known, the crystalization speed is controlled by the blance
: between seed speed and growth speed. So I guess your question is related with
: control the percentage of the crystalization.
: Normally with glass material, you will find TTT graph is very helpful if your
: objects are so pop that is available. Choose some speeds you can run even
: metals right though the crystal phase letting them dire
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