Development of Polymer Molecule Manipulation by Means of Flow Field and Its Application to Polymer Dynamics

人们已经很好地确定了柔性聚合物在一个明确的延伸流场中表现出构象转变：线圈拉伸转变（CST）。我们研究了聚合物在不同条件下的CST，并尝试通过拉伸流场来操纵聚合物分子。通过四辊磨机系统产生拉伸流场，利用流动双折射监测聚合物分子对拉伸流场的响应。(1)采用延长流场双折射法结合荧光显微法研究了T4噬菌体DNA分子的螺旋球转捩。随机线圈被流场拉长并产生双折射信号，而球状分子被认为没有变形，不应该有双折射。经验表明，这种期望是正确的。通过双折射数据与荧光显微照片的比较，发现了一个双折射球状分子。用四辊磨机系统进行止流实验，发现这种双折射球状分子呈椭球状，具有光学各向异性。(2)聚电解质的柔韧性随溶液中盐浓度的变化而变化。通过CST观察，量化了聚电解质在拉伸流动中的柔韧性变化。通过改变DNA水溶液NaC1浓度，观察不同NaC1浓度下的CST。发生CST的临界应变率随NaC1浓度线性增加。这些事实表明，DNA分子是逐渐地被Na^+离子同时电中和的。由于现有流发生器产生的应变速率的限制，无法实现伸长流场对构象转变的调节。通过改进仪器，我们将重新进行实验。

It has been well established that flexible polymers manifest a conformational transition in a well-defined elongational flow field : a coil stretch transition (CST). We investigated the CST of polymers under various conditions and tried to manipulate a polymer molecule by stretching in the elongational flow field. The elongational flow field was generated by a four-roller mill system where the response of the polymer molecule to the elongational field was monitored by a flow birefringence.(1) Coil-globule transition of a T4 phage DNA molecule was investigated by means of the elongational flow field birefringence method in conjunction with a fluorescent micrograph method. A random coil is expected to be elongated by the flow field and generate birefringence signal while a globular molecule is considered not deformed and there should be no birefringence. The expectation was empirically revealed to be the case. A birefringent globular molecule was discovered by a comparison of the birefringence data with that of fluorescent micrograph. Such a birefringent globular molecule was found to be in the shape of an ellipsoid with an optical anisotropy by the stopped flow experiment using the four-roller mill system.(2) A polyelectrolyte changes its flexibility with the salt concentration in the solution. The flexibility change of the polyelectrolyte was quantified by the CST observation in the elongational flow. By changing NaC1 concentration of the aqueous DNA solution, the CST at each NaC1 concentration was observed. A critical strain rate where CST occurs increased linearly with NaC1 concentration. These facts indicate that the DNA molecule was electrically neutralized by Na^+ ions gradually and simultaneously whole through the molecule.The regulation of the conformational transition by the elongational flow field was not realized because of the limit of the strain rate generated by the present flow generator. By improving the apparatus, we will retry the experiment.