Direct Observation of Polymer Chains in Solutions

我们对固体薄膜中的聚合和化学反应进行了研究，得到了许多新的发现。然而，化学香料通常在溶液中反应，因此通过分子分辨成像来观察溶液中的化学反应是可取的。为了直接观察溶液中的化学反应，本项目旨在提供一种观察溶液中聚合物等有机分子的新技术。由于聚合物的形状较长，期望通过电子显微镜观察它们的图像变得容易和方便。虽然目前的透射电子显微镜具有分解材料中的分子甚至原子的能力，但样品必须在真空中保存。这样，用传统的电子显微镜就不能观察到溶液中的分子。在本研究中，将标本冷冻并在冷冻电子显微镜下观察。将溶液在100K的温度下放入液态丙烷中快速冷冻，并在专门设计的冷冻转移系统下用低温透射电子显微镜观察。冷冻后的试样在4K左右观察，以免在显微镜下观察时改变溶液中的结构。作为该技术的应用，研究了吡咯与离子聚合物的化学聚合反应。观察了离子聚合物从形成胶束到最终在水溶液中形成球形聚吡咯颗粒的聚合过程。另一个例子是细金属颗粒与一些表面活性剂在水溶液中。结果，发现金属颗粒在任意位置形成，但它们被表面活性剂包裹起来。因此，它们以纳米微粒的形式分散在溶液中。通过冻结溶液，对金属形成过程进行了一步一步的成像。

We have investigated polymerization and chemical reactions in thin solid films and many new findings on the reactions have been obtained. However, chemical spices are reacted usually in solutions, so that it is desirable to observe chemical reactions in solutions by molecularly resolved imaging. In order to observe directly the chemical reactions in solutions, this project was aimed to provide a new technique to observe organic molecules like polymer molecules in solutions. Since polymers are long in shape, it is expected to be easy and convenient to observe their images by electron microscopy.Though present transmission electron microscope has ability to resolve molecules or even atoms in materials, the specimen should be kept in vacuum. Then, molecules in solution could not be observed as they are in solution by conventional electron microscope. In this study, the specimen was frozen and observed with a cryo-electron microscope. The solution was quickly frozen by plunging it into liquid propane at 100K and observed with a cryo-transmission electron microscope with a specially designed cryotransfer system. The frozen specimen was observed at about 4K so as not to change the structure in solution during the microscopic observation.The chemical polymerization of pyrrole with a ionic polymer was investigated as an application of the technique. The polymerization process to form spherical polypyrrole particles was observed from micelle formation of ionic polymer to the final spherical product in water solution. The other example is the fine metal particles with some surfactants in water solution. As a result, the metal particles were found to be formed arbitrary places, but they are encapsulated with the surfactants. Accordingly they are dispersed as fine nano-particles in solution. The metal formation process was imaged step-by-step by freezing the solution.