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

此外，我们实验室最近的结果表明，粒子形状对电场中各向异性粒子的无序到有序转变具有令人惊讶的丰富作用。这些建议的新途径，形成复杂的，更高阶的结构，从分散体通过自组装。虽然球形颗粒在AC电场中快速且可逆地形成有序的六方密堆积阵列，但胶体椭球体和双胶体，类似于两个熔融球体的颗粒，可以形成独特的聚集体几何形状（与场成角度的链，具有交替取向的颗粒链）和具有中心矩形对称的开放有序阵列。然而，颗粒形状也可以发挥关键作用的自组装动力学，通过挫败的路径的无序到有序的过渡。 例如，最初在场方向上形成的双胶体颗粒链之间缺乏配准阻碍了组装成居中的矩形阵列。然而，这也表明了使用类似于分子化合物的球形和各向异性胶体的混合物来创建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同质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颗粒间相互作用、堆积和自组装动力学。我们将利用大的参数空间来创造新的，复杂的胶体结构。这包括改变颗粒叶之间的分离程度，从轻微的非球面到吻球，以及改变颗粒的体介电、表面化学或表面导电性，甚至使用吸附的聚合物、表面活性剂或颗粒单体化学来制造Janus双胶体。 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率的机制以及双电层、体电导率、粒子介电性质和粒子表面电导率的作用。 结合我们以前在球形颗粒之间直接胶体相互作用测量方面的工作所提供的物理见解，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，以定制颗粒自组装。此外，通过混合具有不同极化率的颗粒，其控制场中的颗粒取向，可以获得具有甚至更大复杂性的自组装结构。其他新颖的方面的领域定向组装将开发，包括脉冲场退火结构和辅助组装使用全息opticaltweezer.Intellectual优点：溶液相自组装有望成为技术和经济上最佳的方法在实现工业规模的纳米材料和器件。从本质上讲，利用自组装技术进行人造应用，模仿了自然界形成功能性纳米结构的途径。这项工作的目标是开发和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基本机制有基本的了解。后者将导致我们的研究结果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，成分（介电性质），表面化学和溶液条件。 除了广泛的技术影响，拟议的工作将开发所需的人力资源，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性。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（NSF）赞助的自然激励工程研究经验的教师（NISE-RET）计划。

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.