Linear and Nonlinear Rheology of Thread-like Micelles: Multi-scale Simulations, Theory, and Experiments

含水表面活性剂（即肥皂）溶液非常广泛地用于消费者护理产品，包括洗发水、沐浴露、凝胶、清洁产品，以及工业产品，包括乳液和粘合剂。溶液中的表面活性剂自组装成称为“胶束”的球形或圆柱形聚集体，其形状和大小控制着表面活性剂溶液的性质。胶束的大小和形状依次由表面活性剂的分子结构和添加的盐和其他成分的浓度控制。预测和控制这些依赖关系的能力是快速设计表面活性剂产品的关键。因此，该项目将开发多层次的分子模拟工具，这些工具将共同深入了解控制表面活性剂自组装的能量和力，从而实现表面活性剂产品的预测设计。在这个项目下开发的软件工具将被公开，我们希望它能被宝洁等公司使用，就像以前在国家科学基金会资助下开发的软件一样。这个新项目将通过与宝洁公司的互动，包括可能的实习机会，来培养博士生。我们将使用分子动力学（MD）模拟和加权直方图分析方法（WHAM）来提取断开线状胶束所需的断裂自由能，以及去除胶束分支所需的自由能。这些信息将与更大尺度的模拟相结合，使用？指针算法?它跟踪胶束断裂，融合和分支形成的速率以及胶束在缠结路径上的滑动速率。这些方法将用于预测线性和分支胶束系的流变性。这些预测工具将通过测量CTAC（十六烷基三甲基氯化铵）与NaCl或水杨酸钠（鼻）以及其他表面活性剂溶液混合的明确胶束溶液的流变学数据进行测试。我们还将开发一种模拟方法和本构理论，用于描述线状胶束的非线性流变特性，包括断裂/融合、非线性变形和缠结。这种模拟方法将是珠簧链断裂/融合的布朗动力学模拟的新颖混合，并使用Likhtman的滑移弹簧模型来解释缠结，为线状胶束的非线性特性提供了第一种模拟方法。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Aqueous surfactant (i.e., soap) solutions are very widely used in consumer-care products including shampoos, body washes, and gels, cleansing products, as well as in industrial products, including emulsions and adhesives. Surfactants in solution self-assemble into spherical or cylindrical aggregates called "micelles", whose shape and size control the properties of the surfactant solutions. The micelle sizes and shapes are in turn controlled by the molecular structure of the surfactant and by the concentrations added salts and other ingredients. An ability to predict and control these dependencies is the key to the rapid design of surfactant products. The project will therefore develop molecular simulation tools at multiple levels of scale that, together, will produce a deep understanding of the energies and forces that control surfactant self-assembly allow for predictive design of surfactant products. Software tools developed under this project will be made public and we expect it to be used by companies such as Procter and Gamble, as has been the case with software developed under the previous NSF funded grant. The new project will train Ph.D. students, aided by interactions with P&G, including possible internships there. We will used molecular dynamics (MD) simulations and the Weighted Histogram Analysis Method (WHAM) to extract the scission free energy required to break a thread-like micelle, and the free energy for removal of a micellar branch. This information will be combined with simulations at a coarser scale, using the ?Pointer Algorithm,? which tracks rates of micellar breakage and fusion and branch formation along with rates of sliding of micelles along entanglement pathways. These methods will be used to predict the rheology of ensembles of linear and branched micelles. These predictive tools will be tested by measuring rheological data for well-defined micellar solutions of CTAC (cetyl trimethylammonium chloride) mixed with either NaCl or with sodium salicilate (NaSal), and other surfactant solutions. We will also develop a simulation method and constitutive theory for the nonlinear rheological properties of thread-like micelles that accounts for breakage/fusion, nonlinear deformation, and entanglements. This simulation method will be novel hybrid of Brownian dynamics simulations of breakage/fusion of bead-spring chains, with the slip-spring model of Likhtman to account for entanglements, providing the first simulation method for the nonlinear properties of thread-like micelles.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.