Cloaking Anisotropic Capillary Interactions Through Tunable Nanoscale Surface Topography

新型材料，如太阳能光伏、减反射涂层、合成膜和生物传感器，可以通过纳米和微米尺度的小颗粒有序来改进性能。这些技术的下一代版本需要有序的二维结构，这些结构具有方向相关的组织。在这个项目中，研究小组将研究一种新的方法，使用拉伸的聚合物球体来创建这种有序的粒子集合，这种球体被称为“椭球体”。这种颗粒不可逆地固定在空气-水界面上，方便地形成二维层；然而，颗粒之间的力会导致形成无组织的集合体。在这个项目中，这一障碍将通过设计颗粒之间的相互作用来克服，通过新的颗粒合成技术，使颗粒表面具有可控的粗糙程度。该项目将专注于如何设计颗粒粗糙度来决定颗粒之间的作用力，并导致它们在空气-水界面上的最终有序组装。通过这项基础科学的研究，将建立开发适用于各种领域的二维材料的基础范例，包括等离子激元、太阳能光伏、涂层、膜和生物传感器。此外，该项目还纳入了几项教育和外联活动。来自当地社区学院的本科生将通过招聘暑期研究经验获得STEM的机会。PI还将为初中生和高中生开发积极的学习研讨会，旨在通过让学生接触到粒子在界面上令人兴奋的真实世界应用来提高对STEM领域的兴趣。该项目将研究纳米级表面形貌(粗糙度或孔隙度)如何决定各向异性聚合物椭球粒子在流体界面上的毛细相互作用和组装。这项工作的动机是由于各向异性胶体的二维有序化而产生了过多的新型材料(如减反射涂层、合成膜、分层表面、仿生材料)。然而，流体界面上颗粒之间强烈的毛细吸引决定了颗粒的各向异性聚集。中心假设是，通过合理设计具有可控孔隙率或粗糙度的颗粒，可以通过改变被钉扎的微粒周围流体界面的曲率来调节毛细作用力。该研究小组寻求应用一种新的合成方法来创建具有可调粗糙度和孔隙率的聚合物椭球，定量表征此类颗粒之间的毛细相互作用，并最终控制其有害的毛细相互作用已通过其表面形貌有效地“掩盖”的颗粒的微观结构组织。首先，种子乳液聚合将被用来产生两相的、化学上斑驳的聚合物胶体，这些胶体可以转化为粗糙的、多孔的椭球。其次，颗粒间的毛细相互作用能将通过监测两个颗粒的接近轮廓和使用Mirau干涉测量纳米级精度的颗粒-液体接触线上的起伏相结合来确定。最后，将使用相互作用能量很有希望的粒子来创建有序的组件。通过将纳米颗粒的表面特性与界面相互作用联系起来，我们将能够确定纳米尺度表面形貌的设计原则，该设计原则将最大限度地减少(即“披上”)强烈的毛细相互作用，以解锁由各向异性颗粒组成的有序2D微结构。这些定义明确且无法获得的单层组件与能量收集、光子学、粒子稳定乳剂、生物界面、膜和/或分级材料等领域的应用直接相关。该项目将包括为K-12教育工作者和学龄儿童开发专注于界面材料和自组装概念的积极学习研讨会，以及通过与当地社区大学的协调，为代表不足的群体扩大获得工程研究机会的机会。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Novel materials, such as solar photovoltaics, antireflective coatings, synthetic membranes, and biosensors, may be engineered for improved performance through the nano- and micro-scale ordering of small particles. Next generation versions of these technologies require ordered two-dimensional structures that have direction-dependent organization. In this project, the research team will investigate a new approach to creating such ordered assemblies of particles using stretched polymer spheres, termed “ellipsoids”. Such particles irreversibly pin to air-water interfaces to conveniently create a two-dimensional layer; however, forces between the particles cause disorganized assemblies to form. This hurdle will be overcome in this project by engineering the interactions between the particles through novel particle synthesis techniques that give the particle surface a controlled degree of roughness. The project will focus on how particle roughness can be designed to dictate the forces between the particles and lead to their ultimate ordered assembly at the air-water interface. By doing this fundamental science, the foundational paradigm to develop two-dimensional materials applicable to a variety of fields, including plasmonics, solar photovoltaics, coatings, membranes, and biosensors, will be established. In addition, several educational and outreach activities are integrated into the project. Undergraduate students from local community colleges will be exposed to opportunities in STEM by recruitment for summer research experiences. The PI will also develop active learning workshops for middle and high school students aimed at increasing interest in STEM fields by exposing students to the exciting real-world applications of particles at interfaces. The project will investigate how nanoscale surface topography (roughness or porosity) dictates the capillary interactions and assembly of anisotropic polymer ellipsoidal particles at fluid interfaces. This work is motivated by the plethora of novel materials (e.g., antireflective coatings, synthetic membranes, hierarchical surfaces, biomimetic materials) enabled from the two-dimensional ordering of anisotropic colloids. However, strong capillary attraction between particles at fluid interfaces dooms anisotropic particle assembly. The central hypothesis is that the capillary forces can be tuned by altering the curvature of the fluid interface surrounding pinned microparticles through the rational design of particles with controlled porosity or roughness. The research team seeks to apply a novel synthetic approach to create polymer ellipsoids with tunable roughness and porosity, quantitatively characterize the capillary interactions between such particles, and ultimately control the microstructural organization of particles whose detrimental capillary interactions have effectively been “cloaked” via their surface topography. First, seeded emulsion polymerization will be used to create biphasic, chemically patchy polymer colloids which can be transformed into rough and porous ellipsoids. Second, the capillary interaction energy between particles will be determined via a combination of monitoring two-particle approach profiles and using Mirau interferometry to measure undulations in particle-liquid contact line with nanometer scale precision. Finally, ordered assemblies will be created using particles with promising interaction energies. By linking the nanoscale particle surface characteristics with interfacial interactions, we will be able to identify design principles for nanoscale surface topography that minimize (i.e., “cloak”) strong capillary interactions to unlock ordered 2D microstructures comprised of anisotropic particles. These well-defined and otherwise inaccessible monolayer assemblies are directly relevant to applications in the fields of energy harvesting, photonics, particle-stabilized emulsions, biological interfaces, membranes, and/or hierarchical materials. The project will include the development of active learning workshops focused on interfacial materials and self-assembly concepts for K-12 educators and school-aged children, as well as expanding access to engineering research opportunities for underrepresented groups through coordination with local community colleges.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.