Systematic Variation of the Rheology of Wormlike Micelles - Experiment and Theoretical Description

本项目的目的是极大地提高我们对棒状(蠕虫状)胶束流动行为的理解，并根据体系的分子组成解释其流变性，特别是时空不稳定性的发生。为此，将对分子结构发生系统变化的表面活性剂体系进行全面的实验流变学研究。实验结果将与新发展的理论模型进行比较。流动行为由介观聚集体的结构和动力学决定，这些性质又由两亲性分子的组成控制，并将进一步通过添加助表面活性剂和两亲性共聚物以系统的方式进行调节(其中，这些疏水修饰的聚电解质和蠕虫状胶束的混合体系本身就已经是有趣的新体系)。这些系统的结构和动力学将通过光和中子散射(SANS，NSE)以及电双折射(EBR)来表征。将主要通过光学方法和粒子图像测速仪(PIV)来详细研究流变行为，特别是时空不均匀的发生。精确确定流场和时空变化(如剪切带的形成)是研究的重点。为了确定介观水平上的取向和结构，将进行互补的Rheo-SAXS和SANS测量。这些全面的实验研究将与新发展的宏观变量动力学理论模型的预测进行比较，特别是在Fiding-Olmsted模型框架下的粘弹性剪应力。特别是实验参数和观测结果与理论描述的直接比较，以及随后对这些理论模型的适应，将导致对这些粘弹性系统的系统和直接的理解。在这里，理论参数(特别是描述剪切引起的链长变化的指数，应力扩散系数)将与实验量直接相关，然后实验量又与体系的分子组成相耦合。通过这种方式，我们将在粘弹性体系的分子组成的基础上产生对流变行为的基本理解，因为粘弹性体系还不存在。如此深入地了解基于表面活性剂的粘弹性体系的性质不仅从基础物理化学研究的角度来看是重要的，而且也将是改进此类体系的应用的基础，因为该项目将提供基于分子理解的可靠的科学背景，这些体系被用于大量配方。

Aim of this project is a substantial improvement of our understanding of the flow behaviour of rod-like (worm-like) micelles, and to explain their rheological properties, especially the occurrence of spatio-temporal instabilities, on the basis of the molecular composition of the systems. For that purpose comprehensive experimental rheological investigations will be done on surfactant systems with a systematic variation of the molecular structure. The experimental results will become compared to newly developed theoretical models. The flow behaviour is determined by structure and dynamics of the mesoscopic aggregates and these properties are in turn controlled by the constitution of the amphiphilic molecules and will further be modulated in a systematic fashion by addition of cosurfactants and amphiphilic copolymers (where these hybrid systems of hydrophobically modified polyelectrolytes and wormlike micelles are already interesting novel systems by themselves). Structure and dynamics of these systems will be characterised by means of light and neutron scattering (SANS, NSE) as well as electric birefringence (EBR). The rheological behaviour and especially the occurrence of spatio-temporal inhomogeneities will be studied in detail, primarily via optical methods and particle image velocimetry (PIV). The precise determination of the flow field and of the spatio-temporal changes (e. g. formation of shear bands) are in the focus of the investigations. Complementary Rheo-SAXS und –SANS measurements will be done in order to determine orientation and structure on the mesoscopic level. These comprehensive experimental investigations will be compared to the predictions of newly developed theoretical models for the dynamics of macroscopic variables, especially the viscoelastic shear stress in the frame of Fielding-Olmsted model. Especially this direct comparison of experimental parameters and observations with the theoretical description and a subsequent adaption of these theoretical models shall lead to a systematic and direct understanding of these viscoelastic systems. Here the parameters from theory (especially exponents for describing shear-induced changes in the chain length, stress diffusion coefficient) will be put into direct correlation to experimental quantities, which then in turn are coupled to the molecular build-up of the systems. In this way, we will generate a fundamental understanding of the rheological behaviour on the basis of the molecular composition of the viscoelastic systems in a way as it does not yet exist. Such a much deepened understanding of the properties of surfactant-based viscoelastic systems is not only of importance from the point of view of fundamental physico-chemical research, but will also be the basis for improved applications of such systems, which are employed in a large number of formulations, as this project will deliver a sound scientific background based on a molecular understanding.