Collaborative research: Using electric field and capillarity for particle self-assembly into adjustable monolayers

合作研究：利用电场和毛细管现象将颗粒自组装成可调节的单分子层

• 批准号: 1067272
• 负责人: Shawn Litster
• 金额: $ 18万
• 依托单位: Carnegie-Mellon University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-05-01 至 2015-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1067272&HistoricalAwards=false
• 关键词: Collaborative; research; Using; electric; field

Award: 1067272/1067004 PI: Aubry/SinghA novel technique in which an electric field is applied normal to an interface is being developed for self-assembling monolayers of particles with virtually defect-free ordering and desired/adjustable lattice spacing. Experiments and numerical simulations are used to develop models for the electrostatic forces that act on particles at an interface and thus for the lattice spacing. This capability will be useful to form materials with superior mechanical, electrical and optical properties, and has the potential to revolutionize many fields of science and technology, including optoelectronics and medicine. Capillarity-driven clustering of particles, the main mechanism used for self-assembly of neutral particle at fluid interfaces, has the following deficiencies: (i) the formed monolayer lacks order, (ii) it is restricted to particle radii greater than about 10 m; and (iii) the lattice is packed and not adjustable. All of these deficiencies are overcome by a novel technique in which an electric field is applied normal to the interface. The dipole-dipole repulsive force amongst particles together with the buoyant weight and the electrostatic force induced capillary forces, leads to the formation of virtually defect-free monolayers with adjustable spacing. Experiments and numerical simulations are conducted to determine the dependence of the vertical electrostatic forces on spherical and prismatic particles for a broad range of parameters and develop models for the capillary and lateral electrostatic forces, which determine the lattice spacing. Similar investigations will be conducted for other particles (ellipsoids, rods, etc.) to determine their stable relative orientations. Conditions will be determined under which the vertical electrostatic force pushes particles away from the interface. This is a phenomenon which should be prevented for the purpose of self-assembly, but is desired if one seeks to clean interfaces of trapped particles.Intellectual Merit. While close-packed self-assembly of particles is well-developed, the self-assembly into defect-free, homogeneous, adjustable, non-close-packed arrays of electrically neutral particles has remained a challenge. The present novel self-assembly technique is easy to implement and can be applied to a broad range of particle sizes and types with a high level of controllability, which will be useful in many applications including anti-reflection coatings for high efficiency solar and thermophotovoltaic (TPV) cells, photonic materials and biosensor arrays. Such applications require highly-ordered crystals with a non-zero, specific lattice gap which can be adjusted, e.g., according to the wavelength of the light or radiation going through the crystal. The work presents great intellectual challenges as it involves non-linear coupling between multiphase flows, interfacial fluid dynamics and electrostatics. Broader Impacts. The technique will have a great impact on our capability to (i) fabricate new microstructured surfaces with a desired pore size and (ii) dynamically alter the formed monolayers and interfacial properties in time, with numerous applications in micro/nanotechnology and colloidal science. The research will be fully integrated with education and outreach, with the involvement of graduate and undergraduate students, particularly women and underrepresented minorities, who will be involved in state-of-the-art research. Research results, in turn, will be incorporated into courses and outreach activities.

奖：1067272/1067004 PI：Aubry/Singha正在开发一种将电场垂直于界面施加的新技术，用于自组装颗粒单分子层，具有几乎无缺陷的有序性和所需的/可调节的晶格间距。实验和数值模拟被用来建立作用在界面上的粒子上的静电力模型，从而建立晶格间距的模型。这种能力将有助于形成具有优异机械、电学和光学性能的材料，并有可能给包括光电子和医学在内的许多科学技术领域带来革命性的变化。用于中性粒子在流体界面上自组装的主要机制--毛细驱动粒子聚集具有以下缺陷：(I)形成的单分子膜缺乏有序性，(Ii)它被限制在大于约10&61549；m；的粒子半径内，以及(Iii)晶格是填充的且不可调节。所有这些缺陷都被一种新技术克服了，在这种技术中，电场垂直于界面。颗粒之间的偶极-偶极排斥力以及浮力和由毛细管力引起的静电力共同导致了几乎无缺陷、间距可调的单分子膜的形成。通过实验和数值模拟，在很大的参数范围内确定了垂直静电力对球形和棱柱状颗粒的依赖关系，并建立了决定晶格间距的毛细静电力和横向静电力的模型。将对其他粒子(椭球体、棒状物等)进行类似的调查。以确定它们稳定的相对取向。将确定垂直静电力将颗粒推离界面的条件。为了自组装的目的，这是一种应该防止的现象，但如果试图清理被捕获粒子的界面，则是所需的。虽然紧密堆积的粒子自组装已经发展得很好，但自组装成无缺陷、均匀、可调节、非紧密堆积的电中性粒子阵列仍然是一个挑战。这种新颖的自组装技术易于实现，可以应用于多种颗粒尺寸和类型，具有很高的可控性，将在许多应用中得到应用，包括用于高效太阳能和热光电(TPV)电池的减反射涂层、光子材料和生物传感器阵列。这种应用需要具有非零特定晶格间隙的高度有序的晶体，该晶格间隙可以例如根据穿过晶体的光或辐射的波长来调整。这项工作提出了巨大的智力挑战，因为它涉及多相流、界面流体动力学和静电学之间的非线性耦合。更广泛的影响。这项技术将对我们的能力产生巨大的影响，(I)制造具有所需孔径的新的微结构表面，(Ii)及时动态地改变所形成的单分子层和界面性质，在微/纳米技术和胶体科学中有着广泛的应用。这项研究将与教育和外联活动充分结合起来，研究生和本科生，特别是妇女和代表性不足的少数群体，将参与最先进的研究。反过来，研究成果将被纳入课程和外联活动。