Anomalous Diffusion in Associative Networks of High-Sticker-Density Polymers
Anomalous Diffusion in Associative Networks of High-Sticker-Density Polymers
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DOI：
10.1021/acs.macromol.0c01892
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发表时间：
2021-01-27
期刊：
影响因子：
5.5
通讯作者：
Olsen, Bradley D.
中科院分区：
文献类型：
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作者：
Rasid, Irina Mahmad;Holten-Andersen, Niels;Olsen, Bradley D.
最近的实验表明，超扩散缩放假设起源于分子扩散机制，其中包括行走和跳跃的聚合物链的自扩散在关联网络。由于跳跃需要释放链上的所有粘着物，因此预期随着粘着物密度增加，行走模式将变得占主导地位，使得最终对于具有高于临界值的粘着物密度的聚合物将仅观察到菲克缩放。在这项工作中，一组共聚物的N，N-二甲基-丙烯酰胺和侧组氨酸基团的贴纸密度范围从4到IS贴纸每链使用可逆加成-断裂链转移（RAFT）聚合合成。在非缠结制度的凝胶中的聚合物链的自扩散，然后使用强迫瑞利散射（FRS）进行了研究。对于测量的长度尺度范围，在整个贴纸密度范围内观察到超扩散缩放。这表明分子跳跃是扩散的重要机制，即使对于具有最高粘着密度的聚合物也是如此。进一步的分析表明，跳跃的高贴纸密度的聚合物是促进的链内键的存在下，与结合到网络的熵罚，和固有的通过RAFT聚合合成的共聚物的贴纸密度的分布的显着分数。
Recent experiments on self-diffusion in associative networks have shown superdiffusive scaling hypothesized to originate from molecular diffusive mechanisms, which include walking and hopping of the polymer chains. Since hopping requires the release of all of the stickers on the chain, it is expected that as the sticker density is increased, the walking mode will become dominant such that eventually only Fickian scaling will be observed for polymers with sticker densities above a critical value. In this work, a set of copolymers of N,N-dimethyl-acrylamide and pendant histidine groups with sticker densities ranging from 4 to IS stickers per chain was synthesized using reversible addition-fragmentation chain-transfer (RAFT) polymerization. The self-diffusion of the polymer chains in the gels in the unentangled regime was then studied using forced Rayleigh scattering (FRS). For the range of length scales measured, superdiffusive scaling was observed across the entire range of sticker densities. This suggests that molecular hopping is an important mechanism for diffusion, even for the polymer with the highest sticker density. Further analysis shows that hopping of the high-sticker-density polymer is promoted by the presence of a significant fraction of intrachain bonds, the entropic penalty associated with binding to the network, and the distribution of sticker densities inherent to copolymers synthesized through RAFT polymerization.