Extensional rheology and flow-induced structure formation of wormlike micelle solutions

蠕虫状胶束（WLM）的解决方案是巨大的技术兴趣，但也作为模型系统来研究聚合物物理的基本问题。这种溶液的结构、胶束动力学和流动行为之间的关系是非常重要的。WLM解的线性粘弹性性质现在已经得到很好的理解，研究集中在非线性流动性质，我们的知识仍然非常有限。特别是，流动引起的自组装和结构的WLM解决方案在拉伸流的变化是一个重大的挑战和更深入地了解这种现象是必要的先进的表面活性剂系统的有针对性的设计，用于各种重要的技术应用。例如，在过去几年中，由于全球石油需求的增加，使用表面活性剂溶液用于提高石油采收率（EOR）重新获得了极大的兴趣。从研究到油田实施的知识和产品的成功转移需要对这些受到拉伸流场的流体的结构和动力学的基本洞察。我们希望进行迄今为止第一次系统的研究，重点是流变学和拉伸流引起的WLM溶液结构变化之间的关系。将研究宽范围的表面活性剂浓度和盐表面活性剂比率，包括线性和支化胶束的稀溶液和浓溶液、缠结溶液。基于我们最近对毛细管破裂拉伸流变仪（CaBER）方法的技术改进，现在可以确定WLM溶液的真实拉伸粘度和流动活化能。对特定表面活性剂系统的初步测量表明，即使溶液的线性粘弹性性质相似，细丝寿命，即在这种类型的实验中流体对拉伸变形的阻力也可以变化几个数量级。这表明强烈的流动诱导的胶束结构的变化取决于表面活性剂的浓度和盐/表面活性剂的比例。胶束在拉伸流动中可能破裂或形成更大的聚集体。在双曲线流动通道中产生平面延伸流场的选定样品的结构调查（小角度光和中子散射，浊度，双折射和粒子图像测速）将定量揭示这种流动引起的结构变化作为伸长率和总变形的函数。拟议的研究项目将揭示哪些表面活性剂类型，表面活性剂以及作为盐的浓度，和流动条件下流动引起的偏离平衡胶束结构的发生，这些结构将被定量表征。实验结果将被用来建议修改的理论模型预测的流动行为的WLM解决方案考虑到流动引起的变化胶束的断裂和重组率。

Solutions of wormlike micelles (WLM) are of great technical interest but also serve as model systems to study fundamental issues of polymer physics. The relationship between structure, micelle dynamics and flow behavior of such solutions is of major importance. The linear viscoelastic properties of WLM solutions are now well understood and research focuses on non-linear flow properties where our knowledge is still very limited. In particular, flow-induced changes in self-assembly and structure of WLM solutions in extensional flows are a major challenge and a deeper understanding of this phenomena is necessary for a targeted design of advanced surfactant systems to be used in various important technical applications. For instance, using surfactant solutions for enhanced oil recovery (EOR) has re-gained great interest in the last few years stimulated by the increasing global oil demand. A successful transfer of knowledge and products from research to oilfield implementation requires fundamental insight into structure and dynamics of these fluids subjected to extensional flow fields.We want to perform the first systematic study focusing on the relationship between rheology and elongational flow-induced structural changes of WLM solutions so far. A broad range of surfactant concentrations and salt surfactant ratios will be investigated, including dilute and concentrated, entangled solutions of linear and branched micelles. Based on our recent technical improvements of the Capillary Breakup Elongational Rheometry (CaBER) method, the true elongational viscosity and flow activation energy of WLM solutions can now be determined. Preliminary measurements on specific surfactant systems have shown that filament lifetime, i.e. the resistance of the fluid to elongational deformation in this type of experiment can vary by orders of magnitude even if the linear viscoelastic properties of the solutions are similar. This indicates strong flow-induced changes in micellar structure depending on surfactant concentration and salt/surfactant ratio. Micelles may either break or form larger aggregates in extensional flows. The structural investigations (small angle light- and neutron scattering, turbidity, birefringence and particle image velocimetry) on selected samples in a hyperbolic flow channel generating a planar extensional flow field will quantitatively reveal such flow-induced structural changes as a function of elongation rate and total deformation. The proposed research project will disclose for which surfactant types, surfactant as well as salt concentrations, and flow conditions flow-induced deviations from the equilibrium micellar structure occur and these structures will be characterized quantitatively. Experimental results will be used to suggest modifications of a theoretical model predicting the flow behavior of WLM solutions taking into account flow-induced changes of micellar scission and recombination rates.