不同拓扑结构高分子链在拉伸流场下如何穿过柱状纳米小孔?

How Do Polymer Chains with Different Topologies Pass Through a Cylindrical Pore under an Elongational Flow Field?

在流场剪切下发生形变的高分子穿过比自身尺寸还小的纳米孔的现象被称为高分子的超滤.阐明该现象是高分子物理研究中的一个重要课题,它的研究与许多其它领域相关,如高分子研究中常用的体积排除色谱,石油开采用的高分子助剂,DNA、mRNA和蛋白链的跨膜传输.然而,因缺乏合适的理想高分子样品及纳米孔中超滤流场的不确定性,直到21世纪初人们仍未系统地在实验上对高分子的超滤行为进行本质探究.为揭示其物理本质及验证相关理论,近十年来我们课题组合成了一系列具有不同拓扑结构的模型高分子,解决了在纳米孔道中形成理想拉伸流场等一系列技术难题,成功开展了对高分子链在柱状纳米小孔中超滤行为的系统研究.本文回顾了高分子链穿过纳米小孔的经典理论,并综述了我们所取得的研究成果,即(1)首次成功观测到了线形高分子链穿越柱状纳米小孔的"coil-to-stretch"转变行为,并发现过孔临界流量的确与高分子链长无关,但与小孔直径相关,与de Gennes经典理论的预测不相符;(2)结合实验观测结果,建立了不同拓扑结构高分子链穿过柱状纳米小孔的统一理论描述;(3)通过高分子模型样品,系统地在实验上研究了过孔临界流量与高分子链拓扑结构、小孔结构之间的关系;(4)根据实验研究结果和新发展的理论描述,成功实现了不同拓扑结构高分子链混合物的分离以及高分子聚集结构之间的快速转变.

Translocation of polymer chains through nanopores （uhrafihration behavior） is not only a basic problem in polymer physics and biophysics, but also related to many physical and chemical processes, such as gene transfection, protein transportation, and separation of polymer chains by size exclusion chromatography. However, due to the lack of appropriate polymer model samples as well as ideal elongational flow fields, the ultrafihration behavior of polymer chains has not been systematically explored experimentally for a long time. To deeply understand the ultrafiltration behavior of polymer chains and verify relevant theory, we have made much effort on this subject in the past decade. In this article, we＇ 11 first review the classic theory of polymer chains passing through nanopores, and then provide an overview of our recent theoretical and experimental research achievements in this field, more specifically, we have （1） successfully observed the ＂coil-to-stretch＂ first-order transition of polymer linear chain passing through nanopores, and found that the critical flow rate （qc） is indeed independent on the chain length, but dependent on the pore size, inconsistent with de Gennes＇ prediction; （2） developed a unified theoretical description of polymer chains with different topologies passing through a nanopore; （3） systematically studied the effects of polymer chain topology and pore structure on the ultrafiltration behavior of polymer chains; and （4） successfully applied the ultrafiltration method into the separation of polymer chain mixtures and the rapid transition between various polymeric aggregated structures.