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Direct observation of a polymer chain in the vicinity of critical strain rate of coil-stretch transition

直接观察卷曲-拉伸转变临界应变率附近的聚合物链

基本信息

批准号：
14340117
负责人：
SASAKI Naoki
金额：
$ 3.9万
依托单位：
Hokkaido University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-14340117/
关键词：
flexible polymer chain elongational flow field coil-stretch transition critical strain rate flow birefringence fluorescent micrograph DNA molecule micro-cross slot 蛍光偏光顕微鏡 DNA DNA脂質複合体紡糸特性回転半径蛍光顕微鏡観測コイル・スレッチ転移臨海歪速度最長緩

项目摘要

It is well known that a flexible polymer chain in a solution manifests a coil-stretch transition (CST) at a critical strain rate ε_c as a response to an elongational flow field. ε_c has been determined by measuring flow induced birefringence as a function of strain rate. CST itself is an event of individual molecules, while flow birefringence averages over molecules in the solution. Deformation process of individual molecules by the elongational flow field has been known to depend on the conformation and orientation of each molecule in the vicinity of critical strain rate. It is unknown if macroscopically determined ε_c value actually reflects such molecular feature, that is, if an ensemble average of individual molecular deformation actually corresponds to ε_c. We aimed to make it clear this still unsolved question by comparing the macroscopic ε_c value with that determined by the molecular extension process observed using fluorescent micrograph. Elongational flow field under the microscope was generated by a micro-cross-slot fabricated by a photo etching of silicon wafer. Macroscopic observation was performed on a four roller mill. ε_c determined by fluorescent micrograph was one third of that determined by flow birefringence method. This difference in critical strain rate was attributed to a particular averaging procedure of detecting signals in the macroscopic flow birefringence method.

众所周知，溶液中的柔性高分子链在临界应变速率ε_c下表现出对拉伸流场的响应，即卷曲-拉伸转变（CST）。ε_c是通过测量作为应变率的函数的流动诱导双折射来确定的。CST本身是单个分子的事件，而流动双折射在溶液中的分子上平均。拉伸流场中单个分子的变形过程取决于临界应变速率附近每个分子的构象和取向。宏观测定的ε_c值是否真实地反映了这种分子特征，即单个分子形变的系综平均值是否真实地对应于ε_c值，尚不清楚。通过比较宏观ε_c值与荧光显微镜下观察到的分子伸展过程的ε_c值，阐明了这一尚未解决的问题。显微镜下的拉伸流场是由硅片光刻制作的微十字槽产生的。在四辊磨机上进行宏观观察。用荧光显微照相法测得的ε_c约为流动双折射法的1/3。临界应变率的这种差异归因于在宏观流动双折射方法中检测信号的特定平均过程。