两亲性嵌段共聚物自组装体制备和稳定Pickering乳液的机理研究

Amphiphilic block copolymers can form self-assembles structure such as micelles, worm-like micelles and vesicles in solutions. Recently, those self organized structures have been used to prepare and stabilize Pickering emulsions which are usually stabilized by amphiphilic ultra-fine solid particles. However, there is no chemical bonds between those molecules, the micelles or vesicles at oil-water interfaces are not surface cross linked either. The molecules are bond to choose their conformation toward oil or water face at the interface. Can those self-organized structures formed in the bulk maintain their morphology at the oil-water interface? If so, how could they obtain their amphiphilic nature? If not, the block copolymers must have been re-organized and form new self-assembled structures which are surface amphiphilic. The bottle neck to answer this question lies in the characterization of the surface wetting of micelles or vesicles at oil-water interfaces. Yet it is extremely difficult to character the self-assembly in detail at the fluid oil-water interface. This project seeks to design and synthesis a type of new amphiphilic diblock copolymers, in which the components of hydrophilic block and hydrophobic block have significant difference that enables the direct observation of the organization of different blocks under cryo-TEM. Furthermore, the underlying mechanism of Pickering emulsions stabilized by amphiphilic block copolymers will be revealed. This project will not only provide scientific evidences for the better application of this new Pickering emulsifier, but also shed light on the understanding of fluid nano-scale interfaces.

两亲嵌段共聚物在溶液中能够形成胶束和囊泡等自组装体。这些自组装体已被证实可以用来制备通常由超细的两亲固体颗粒稳定的Pickering乳液。然而，两亲分子自组装体的形成是基于分子间的弱相互作用力，它们处在油水界面上时能否保持其在体相中的结构形貌？如果能，它们又是如何在油水界面赋予自组装体表面的两亲性呢？如果不能，这些分子必然在界面重组出表面具有两亲性的自组装体！回答该问题的瓶颈在于准确表征油水界面聚合物自组装体的润湿性，而油水界面的流动性又给直接表征自组装体的精细结构带来了困难。该项目拟设计合成一类两亲性嵌段共聚物，它们的亲水和亲油片段的组成具备较大差异，这种差异完全可以在冷冻蚀刻投射电镜下观察到。进而系统研究两亲嵌段共聚物的自组装体稳定Pickering乳液的基本原理，不仅为这类新型Pickering乳化剂的更好使用提供依据，也为认知纳米尺度的流动性界面提供借鉴。

分散体系是非均相体系，它稳定的物理根源在于界面能的降低和界面的稳定性。以油水界面为例，其稳定剂或乳化剂种类繁多，有小分子的表面活性剂、聚合物类两亲分子、超细固体粒子等。为了区别以表面活性剂的单分子层稳定的乳液体系，超细颗粒稳定的乳液在100多年前被称为Pickering乳液。两亲嵌段共聚物兼具表面活性剂和聚合物的功能，在溶液中能够形成胶束和囊泡等自组装体。这些自组装体已被证实可以用来制备Pickering乳液。然而，两亲分子自组装体的形成是基于分子间的弱相互作用力，溶剂的极性和环境有重要影响。它们处在油水界面上时能否保持其在体相中的结构形貌？如果能，它们又是如何在油水界面赋予自组装体表面的两亲性呢？如果不能，这些分子必然在界面重组出表面具有两亲性的自组装体！回答该问题的瓶颈在于准确表征油水界面上聚合物自组装体的稳定性，而油水界面的流动性又给直接表征自组装体的精细结构带来了困难和挑战。该项目利用共价键合成的手段，设计合成了一类两亲性嵌段共聚物，从化学组成上赋予该类两亲分子在亲水和亲油片段具备较大差异性。利用这种差异在冷冻蚀刻透射电镜下观察到了自组装体的形貌。然而冷冻蚀刻透射电镜制备样品复杂，操作困难，造价昂贵。我们发展了荧光增强激光共聚焦显微镜技术来表征乳液液滴表面两亲分子自组装体的存在条件，系统研究两亲嵌段共聚物的自组装体稳定Pickering乳液的基本原理，不仅为这类新型Pickering乳化剂的更好使用提供了依据，也为认知纳米尺度的流动性界面提供了借鉴。更重要的是，所发展的荧光增强激光共聚焦显微镜技术为乳液的表征提供了一种操作性强的实用手段。