Mechanisms of Diffusion in Associative Polymer Networks: Evidence for Chain Hopping.
Mechanisms of Diffusion in Associative Polymer Networks: Evidence for Chain Hopping.
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DOI：
10.1021/jacs.8b07908
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发表时间：
2018-10-31
影响因子：
15
通讯作者：
Tirrell DA
中科院分区：
文献类型：
--
作者：
Rapp PB;Omar AK;Silverman BR;Wang ZG;Tirrell DA
由远旋聚合物可逆缔合而成的网络构成了一类常见的软材料。人们提出了联想网络中链式迁移的各种机制，但很少有定量的实验数据来区分它们。提出的链迁移机制包括多链聚合扩散以及单链机制，如“行走”和“跳跃”，其中扩散是通过相关链段的部分（“行走”）或完全（“跳跃”）脱离来实现的。本研究提供的证据表明，由于局部网络结构对桥的形成施加了很强的熵惩罚，跳跃可以支配联想网络中链的有效扩散；链在与两个或多个空间分离的结合位点结合时受到构象限制。这种限制降低了具有多个结合域的链的有效结合强度，从而增加了链跳跃的概率。对于远螺旋链，这表现为结合不对称，其中第一种结合比第二种有效地强。我们推导了一个简单的热力学模型，该模型预测了自由跳跃的链的比例，作为可调分子和网络特性的函数。对一系列模型缔合聚合物的自扩散率进行了大量的测量，结果与该模型吻合良好。
Networks assembled by reversible association of telechelic polymers constitute a common class of soft materials. Various mechanisms of chain migration in associative networks have been proposed, yet there remains little quantitative experimental data to discriminate among them. Proposed mechanisms for chain migration include multichain aggregate diffusion as well as single-chain mechanisms such as “walking” and “hopping”, wherein diffusion is achieved by either partial (“walking”) or complete (“hopping”) disengagement of the associated chain segments. Here we provide evidence that hopping can dominate the effective diffusion of chains in associative networks due to a strong entropic penalty for bridge formation imposed by local network structure; chains become conformationally restricted upon association with two or more spatially separated binding sites. This restriction decreases the effective binding strength of chains with multiple associative domains, thereby increasing the probability that a chain will hop. For telechelic chains this manifests as binding asymmetry, wherein the first association is effectively stronger than the second. We derive a simple thermodynamic model that predicts the fraction of chains that are free to hop as a function of tunable molecular and network properties. A large set of self-diffusivity measurements on a series of model associative polymers finds good agreement with this model.
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DOI：
10.1002/adma.201303680
发表时间：
2014-02-12
期刊：
Advanced materials (Deerfield Beach, Fla.)
影响因子：
--
作者：
McKinnon DD;Domaille DW;Cha JN;Anseth KS
通讯作者：
Anseth KS
影响因子：
4.4
作者：
JACOBSON, H;STOCKMAYER, WH
通讯作者：
STOCKMAYER, WH
影响因子：
5.5
作者：
BAXANDALL, LG
通讯作者：
BAXANDALL, LG
影响因子：
14
作者：
Li, Jun;Li, Xu;Leong, Kam W.
通讯作者：
Leong, Kam W.
影响因子：
4.4
作者：
DEGENNES, PG
通讯作者：
DEGENNES, PG