高分子一本鎖力学計測の現在過去未来

摘要

Past, present and future of single polymer chain mechanics based on atomic force microscopy were reviewed, which is generally called as single molecule force spectroscopy (SMFS). Static SMFS can provide information such as persistent length and contour length appearing in a worm-like chain model. Thiol-terminated Poly(N-isopropylacrylamide) was used as an example study and its behavior change near its LCST was investigated. The temperature dependence of the plateau force at the low-extension region agreed well with the prediction by the pearl-necklace model developed by Prof. F. Tanaka. Two types of dynamic SMFS methods were also reviewed. The first noise-analysis SMFS may need future instrumental improvement The second forced-oscillation SMFS measurements have resulted in a lot of interesting insights. As an example, the relaxation time of the polystyrene chain in N,N-dimethylformamide was measured and its dependence on the degree of polymerization was investigated. The Kirkwood model reproduced well the experimental results, while the necessity for a new concept of effective viscosity is proposed.%ゴムやプラスチックの応力ひずみ曲線を測定するように、高分子一本鎖を伸長し、そのときの力と伸長距離の関係を調べる方法がある。高分子一本鎖に限らず、基板と原子間力顕微鏡（AFM)の探針の間に挟まれた分子にかかる力学計測を行う手法は、単一分子力分光(Single Molecule Force Spectroscopy、SMFS)と一般に呼称されている。その亜種として溶媒中で高分子一本鎖を伸長する手法を筆者らはナノフィッシングという愛称で呼ぶことにしている。SMFSを謳っている論文の中にも必ずしも単一分子レベルの現象を扱えていないケースも存在するので注意が必要である。過去にはAFMファミリーとして化学力顕微鏡（CFM)という手法があって、それとSMFSの切り分けは難しい。ただし最近はCFMという言葉はほとんど聞かない。SFMSの最近の例として化学結合の開裂を扱った論文を参考文献に挙げておく。