Interactions and self-assembly of anisotropic colloidal particles in electric fields

[09:30549]我们实验室最近的研究结果表明，粒子形状对电场中各向异性粒子的无序到有序跃迁具有惊人的丰富作用。这提示了通过自组装从分散形成复杂的高阶结构的新途径。当球形粒子在交流电场中快速可逆地形成有序的六边形紧密排列阵列时，胶体椭球和二胶体，类似于两个融合的球体的粒子，可以形成独特的聚集几何形状（与电场成一定角度的链，粒子链具有交替的方向）和开放的有序阵列，具有中心矩形对称。然而，粒子形状也可能在自组装动力学中发挥关键作用，阻碍无序到有序转变的路径。例如，最初在磁场方向上形成的二胶体颗粒链之间缺乏注册，阻碍了组装成中心矩形阵列。然而，这也暗示了利用类似分子化合物的球形和各向异性胶体的混合物创造复杂胶体结构的独特可能性。在这项工作中，我们将研究具有对称叶的双胶体粒子的场定向自组装。即使这种相对简单的各向异性形状也会导致复杂的粒子间相互作用、堆积和自组装动力学。我们将利用大参数空间来创造新的、复杂的胶体结构。这包括改变颗粒裂片之间的分离程度，从轻微的非球形到亲吻球形，改变颗粒的整体介电、表面化学或表面电导率，甚至使用吸附聚合物、表面活性剂或颗粒单体化学来制造双面胶。我们将研究有序无序转变，包括自组装结构和动力学的表征，以及各向异性粒子之间的场诱导相互作用。后者将阐明粒子极化机制和双层、体积电导率、粒子介电性能和粒子表面电导率的作用。结合我们之前对球形粒子之间直接胶体相互作用测量的物理见解，这将使我们能够在分子水平上理解和控制场诱导的胶体相互作用，以定制粒子自组装。此外，通过混合具有不同极化率的粒子，可以控制粒子在场中的取向，从而可以获得更复杂的自组装结构。场定向组装的其他新方面将得到发展，包括脉冲场退火结构和使用全息光学镊子辅助组装。智力优势：溶液阶段自组装有望成为实现工业规模纳米材料和器件的技术和经济最佳方法。从本质上讲，利用自组装的人造应用模仿了自然形成功能纳米结构的途径。这项工作的目标是开发并从根本上验证使用胶体构建块和外部场的自组装结构的新方法。我们将发现形成复杂自组装结构的新途径，并对电场中粒子相互作用和自组装的潜在机制有一个基本的了解。后者将导致我们的发现在物理化学条件的巨大参数空间中具有广泛的可扩展性，包括颗粒尺寸，形状，组成（介电性质），表面化学和溶液条件。更广泛的影响。除了广泛的技术影响外，拟议的工作将发展所需的人力资源，以维持和发展国家在胶体和纳米颗粒悬浮液的科学和工程方面的卓越水平。通过赞助一名中学科学、技术、工程和数学（STEM）教师作为我们实验室的暑期研究员，与特拉华州？美国国家科学基金会资助的教师自然启发工程研究体验项目（NISE-RET）。

0930549FurstRecent results in our laboratory demonstrate the surprisingly rich role particle shape has on the disorder to order transition of anisotropic particles in electric fields. These suggest new routes to forming complex, higher order structures from dispersions via self assembly. While spherical particles rapidly and reversibly form ordered hexagonal close packed arrays in AC electric fields, colloidal ellipsoids and dicolloids, particles resembling two fused spheres, can form unique aggregate geometries (chains at an angle with the field, particle chains with alternating orientations) and open, ordered arrays with a centered rectangular symmetry. However, particle shape may also play a critical role in the self assembly kinetics by frustrating the path of the disorder to order transition. For instance, the the lack of registry between chains of dicolloid particles initially formed in the field direction frustrates assembly into centered rectangular arrays. However, this also suggests unique possibilities for creating complex colloidal structures using mixtures of spherical and anisotropic colloids that resemble molecular compounds. In this work, we will study the field directed self assembly of homo-dicolloid particles with symmetric lobes. Even this relatively simple anisotropic shape leads to complex interparticle interactions, packing, and self assembly kinetics. We will exploit the large parameter space to create new, complex colloidal structures. This includes varying the degree of separation between the particle lobes, from slightly aspherical to kissing spheres, and altering the bulk dielectric, surface chemistry or surface conductivity of the particles, even making Janus dicolloids, using adsorbed polymers, surfactants or particle monomer chemistries. We will study the order disorder transition, including the characterization of self assembled structures and kinetics, as well as the the field induced interactions between anisotropic particles. The latter will elucidate the mechanisms of the particle polarizability and the roles of the double layer, bulk conductivity, particle dielectric properties and particle surface conductivity. Combined with the physical insight provided by our previous work on direct colloidal interaction measurements between spherical particles, this will enable us to understand and control the fieldinduced colloidal interactions on the molecular level to tailor particle self assembly. Furthermore, by mixing particles with different polarizabilities, which controls particle orientation in the field, self assembled structures with even greater complexity may be attainable. Other novel aspects of field directed assembly will be developed, including pulsed fields to anneal structures and assisted assembly using holographic optical tweezers.Intellectual Merit: Solution phase self assembly promises to be the technologically and economically optimal approach in the realization of industrial scale nano materials and devices. In essence, harnessing self assembly for man made applications mimics nature's route to the formation of functional nanostructures. The goal of this work is to develop and fundamentally validate novel approaches to self assembled structures using colloidal building blocks and external fields. We will discover new routes to forming complex self assembled structures and gain a fundamental understanding of the underlying mechanisms of particle interactions and self assembly in electric fields. The latter will lead to broad scalability of our findings across a vast parameter space of physico chemical conditions, including particle size, shape, composition (dielectric properties), surface chemistry and solution conditions.Broader impacts. In addition to the broad technical impacts, the proposed work will develop the human resources needed to sustain and grow national excellence in the science and engineering of colloidal and nanoparticle suspensions. The education and outreach impact will be amplified by sponsoring a secondary school Science, Technology, Engineering, and Mathematics (STEM) teacher as a summer research fellow in our laboratory, in coordination with the Delaware?s NSF sponsored Nature InSpired Engineering Research Experiences for Teachers (NISE-RET) program.