Effect of heterogeneous particles and surfactants on the stability and rheology of fluid interfaces

流体-流体界面，如肥皂泡中的空气-水界面，在各种产品中都很常见，例如在家庭清洁、化妆品和药品中。通常，使用非常小的颗粒和一些特定的分子(称为表面活性剂)来稳定这种界面(以防止它们爆裂)。因此，这些界面的稳定性和强度取决于小颗粒和表面活性剂之间相互作用的类型和强度。本项目的目的是研究颗粒和表面活性剂对界面稳定性和流动行为的联合影响。这项研究将使用最先进的实验室实验和分子水平的计算机模拟。这将导致在广泛的技术应用方面的科学进步，从定向输送药物到回收地下储油罐中被困的石油。这个项目中描述的先进的实验和计算技术还将产生新的知识，用于通过调查人员提供的选修课来教育本科生和研究生。该项目还将支持将组织的K-12推广活动，向大学预科学生展示软材料的界面属性，以吸引他们学习STEM学科。拟议的项目将产生关于存在界面的异质胶体颗粒和表面活性剂分子相互作用的新的基础知识。使用异质胶体构建块调整组装过程可以促进创新材料和响应结构的设计。此外，流体界面的开放特性使其成为动态传输至关重要的应用的一个很有前途的平台，例如两相催化反应。因此，在由非均相胶体粒子和表面活性剂分子组成的复杂界面体系中，尤其是在阐明影响非均相粒子和表面活性剂在界面上协同作用的丰富物理机制方面，存在着一个关键的知识缺口。此外，流体界面不是静态的，它们经常受到外部干扰；因此，有必要研究这些界面系统在外加应力下的稳定性，以便更好地了解它们在与实际应用相关的条件下的动态行为和流变性。具有几种不均质性的微米和纳米颗粒？尤其是形状和表面化学异质性？将在没有表面活性剂的情况下对颗粒界面进行制造和实验分析。使用粗粒度技术的计算将被用来理解推动实验的分子相互作用。然后，实验工具和计算工具之间的协同作用将被用于涉及非均质颗粒和表面活性剂分子的更复杂的系统中，以便解决跨多个长度和时间尺度的现象(微米和纳米颗粒以及多流体系统之间的分子尺度相互作用)。预期成果植根于基本理解，包括具有定制的界面行为和流体/流体界面流变性的非均质胶体颗粒/表面活性剂系统的设计规则。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Fluid-fluid interfaces, such as air-water interface in a soap bubble, are commonplace in a variety of products such as in household cleaning, cosmetics, and pharmaceuticals. Oftentimes, very small particles and some specific molecules (called surfactants) are used to stabilize such interfaces (to prevent them from popping). Therefore, the stability and strength of these interfaces is dictated by the type and strength of interactions between the small particles and surfactants. The goal of this project is to investigate the combined effect of particles and surfactants on the stability and flow behavior of interfaces. State-of-the-art laboratory experiments and computer simulations at the molecular level will be used in this research. This will lead to scientific advances in a wide range of technological applications from targeted delivery of drugs to recovery of oil trapped in underground reservoirs. The advanced experimental and computational techniques described in this project will also generate new knowledge to be used in educating students at both undergraduate and graduate level through the elective courses that will be offered by the investigators. The project will also support K-12 outreach activities that will be organized to demonstrate interfacial properties in soft materials to pre-college students in order to attract them to STEM disciplines.The proposed project will generate new fundamental knowledge on the interaction of heterogeneous colloidal particles and surfactant molecules in presence of interfaces. Tuning the assembly process using heterogeneous colloidal building blocks can advance the design of innovative materials and responsive structures. Additionally, the open nature of fluid interfaces makes them a promising platform for applications in which dynamic transport is crucial, such as bi-phasic catalytic reactions. Therefore, a critical knowledge gap exists in complex interfacial systems comprised of both heterogenous colloidal particles and surfactant molecules, especially in elucidating the rich physical mechanisms that affect the synergism of heterogeneous particles and surfactants at interfaces. Furthermore, fluid interfaces are not static and they are constantly subject to external disturbances; thus, there is a need to study the stability of these interfacial systems in response to applied stresses in order to develop a better understanding of their dynamic behavior and rheology in conditions relevant to real applications. Micro- and nanoparticles with several types of heterogeneities ? particularly shape and surface chemical heterogeneity ? will be fabricated and experimental analysis of particle-laden interfaces will be conducted in the absence of surfactants. Computations using coarse-grained techniques will be employed to understand the molecular interactions driving the experiments. The synergy between the experimental and computational tools will then be employed in more complex systems that involve both heterogeneous particles and surfactant molecules in order to address phenomena across multiple length and times scales (molecular scale interactions between micro- and nanoparticles and multifluid systems). The anticipated outcomes, rooted in fundamental understanding, include design rules for heterogeneous colloidal particles/surfactant systems with tailored interfacial behavior and rheology at fluid/fluid interfaces.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.