CAREER: Interactions between 2D particles at fluid-fluid interfaces

二维(2D)材料具有独特的特性，因为它们在原子上很薄。与“块状”材料相比，这些材料的导电性、机械强度和光学透明度等性能可以显著提高。2D材料的种类越来越多，最常见的例子是石墨烯、二硫化钼(MoS2)和六方氮化硼(h-BN)。这些材料和其他材料广泛用于包括电子设备和复合材料在内的各种消费产品。利用2D材料的挑战之一是它们的制造，这通常是通过在微观尺度上组装2D颗粒的集合来创建具有所需性能的更大材料来实现的。这个项目将有助于理解当2D粒子被限制在流体-流体界面时如何相互作用，这种类型的限制可以用于组装2D粒子“边到边”。该项目还将开发制造大小和形状可控的模型2D粒子的技术，这将推进理解这些系统所需的实验工作。该项目的结果将为科学家和工程师提供关于2D颗粒相互作用的基本见解，以便科学家和工程师将2D颗粒加工成先进的薄膜、涂层和复合材料。此外，该项目团队将与科罗拉多矿业学院的夏季多元文化工程培训计划(Summet)合作，向高中高年级学生介绍本科研究的机会。其目的是提高对本科研究的认识，将其作为这些传统上代表较少的科学和工程专业学生的机会，并最终鼓励他们参与科学、技术、工程和数学(STEM)领域。通过直接观察颗粒轨迹和颗粒组合，将测量在空气-水界面上大小、形状和厚度可控的2D颗粒之间的相互作用势。模型2D粒子将在内部制造，使用光刻技术在铜箔上选择性地对通过化学气相沉积生长的2D材料薄膜进行图案设计。将铝箔放置在流体-流体界面处，并在亚相交换池中用蚀刻液去除，剩下的颗粒将用干涉反射显微镜观察。颗粒周围的接触线波动将通过各种形式的凝胶捕获结合电子显微镜来探测，以了解颗粒-颗粒相互作用上的毛细管力的性质。颗粒-颗粒相互作用对宏观膜结构和强度的影响将用界面流变仪进行研究。该项目的总体目标是了解限制在流体-流体界面上的2D粒子之间相互作用的性质，特别是2D粒子的低维形态如何发挥作用。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。

Two-dimensional (2D) materials have properties that are unique because they are atomically thin. Properties such as electrical conductivity, mechanical strength, and optical transparency can be significantly enhanced in these materials compared with their “bulk” material counterparts. There is a growing list of 2D materials, the most common examples being graphene, molybdenum disulfide (MoS2), and hexagonal boron-nitride (h-BN). These materials and others are used in a wide range of consumer products including electronic devices and composite materials. One of the challenges of utilizing 2D materials is their fabrication, which is often accomplished by assembling a collection of 2D particles at the microscopic scale to create a larger material with the desired properties. This project will help understand how 2D particles interact with each other when confined to a fluid-fluid interface, a type of confinement that can be used to assemble 2D particles “edge-to-edge”. The project will also develop techniques for fabricating model 2D particles of controlled size and shape, which will advance the experimental work needed to understand these systems. Results from the project will provide fundamental insight about the interactions of 2D particles that scientists and engineers can use to process 2D particles into advanced films, coatings, and composites. In addition, the project team will work with the Summer Multicultural Engineering Training Program (SUMMET) at the Colorado School of Mines to introduce high school seniors to opportunities in undergraduate research. The goal is to increase awareness of undergraduate research as an opportunity available to these traditionally underrepresented students in science and engineering, and ultimately to encourage their participation in science, technology, engineering, and mathematics (STEM) fields.The interaction potential between 2D particles of controlled size, shape, and thickness at air-water interfaces will be measured from direct observation of particle trajectories and particle assemblies. The model 2D particles will be fabricated in-house using photolithography to selectively pattern 2D material films grown via chemical vapor deposition on copper foil. The foil will be placed at the fluid-fluid interface and removed with etchant solution in a sub-phase exchange cell, and the remaining particles will be visualized with interference reflection microscopy. Contact line undulations around particles will be probed with various forms of gel trapping in conjunction with electron microscopy to understand the nature of capillary forces on the particle-particle interactions. The influence of particle-particle interactions on the macroscopic film structure and strength will be investigated with interfacial rheological tools. The overall goal of the project is to understand the nature of the interactions between 2D particles confined to a fluid-fluid interface, and in particular how the low-dimensional morphology of 2D particles plays a role.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.