Lithography on a nanosphere--an optical approach to arbitrarily patterned patchy particles

自组装——从更简单的组件自发形成定义良好的有序结构——是使生物体在规模和复杂性上发展和增长的关键机制。如果自组装技术能够被完全应用于解决技术问题，它将有可能创造出其他制造技术无法企及的材料和设备，并可能给材料科学、电气和化学工程以及其他领域的许多领域带来革命性的变化。阻碍这一点的障碍之一是难以制造足够复杂的起始部件，其质量要求足以进行有效的自组装。这个项目是由美国国家科学基金会固态和材料化学项目支持的，它实现了一种制造这种粒子的新技术。这些粒子的尺寸在几百纳米到几微米之间，具有几乎可以制成任何形状的表面特性。这些所谓的“片状粒子”是自组装启动组件的绝佳候选。维吉尼亚理工学院和州立大学的研究人员采用的技术是利用光对悬浮在液体中的球形颗粒进行图案设计，并且对球体上的图案的分布和结构几乎没有限制。在基础科学的层面上，这种研究斑点粒子的新途径允许对自组装进行更彻底的探索，这有助于揭示这种复杂且仅部分理解的现象背后的原理。因为同样的图案可以直接投射到任意数量的粒子上，它有可能使这项技术适用于未来在工业规模上生产片状粒子。因此，这项研究可能会影响广泛的领域，但项目的一些初始目标结构可能在柔性太阳能电池和微型机器人领域特别有用。除了所描述的科学和潜在的技术进步之外，学生们还可以通过直接参与项目和指导，或者通过对弗吉尼亚理工学院和州立大学新纳米科学课程的见解，从这项研究中受益。在这个由美国国家科学基金会固态和材料化学项目支持的项目中，弗吉尼亚理工学院和州立大学的研究人员开发了一种新的范例，用于合成具有几乎完全自由选择的斑块分布的斑块颗粒，并展示了这些颗粒的自组装成定义良好的结构，包括一些不易实现的现有斑块颗粒制造技术。该项目应用光学成像技术在任意数量的电介质纳米球和/或微球上投射相同的图案，其中含有光可切割保护基（PPGs）的配体的功能化确保光学图案被转移到功能基，如胺、硫醇、羧基等，然后可以进一步修改以产生具有所需功能的贴片。通过包含光学正交PPGs（包括邻硝基苯基、氨基香豆素和BODIPY基团）的功能化，可以通过一次暴露产生具有不同性质的多种贴片类型，这是完全实现贴片粒子概念所必需的。自组装的基本构建块是二氧化钛微球和纳米球，其中许多配体被开发以适应项目的需要，使用膦酸锚定与表面形成稳定的键。二氧化钛球在对社会有益的应用中特别有用，例如用于高效染料敏化太阳能电池的光子晶体。其他潜在的应用包括TiO2/Pt光控微电机，或者它们的光催化性能可以直接帮助表面斑块的形成。作为该项目的一部分，一个或多个贴片-贴片相互作用（如疏水吸引，静电结合，生物素-亲和素结合等）被用于实现几个目标结构，从相对简单的（线性链，四面体）到更具挑战性但已被证明的（Kagome晶格，五足体），再到尚未组装的高兴趣结构（二十面体，钻石结构胶体晶体）。图案可以应用于颗粒在散装悬浮液，因此具有潜在的可扩展性。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

PART 1: NON-TECHNICAL SUMMARYSelf-assembly -the spontaneous formation of well-defined ordered structures from simpler components- is a key mechanism that enables living organism to develop and grow in size and complexity. If self-assembly could be fully applied to technological problems, it would make it possible to create materials and devices that are well beyond the reach of other fabrication techniques, potentially revolutionizing many areas of materials science, electrical and chemical engineering, and other fields. One of the barriers preventing this is the difficulty in making starting components of sufficient complexity of the required quality for efficient self-assembly to take place. This project, which is supported by the Solid State and Materials Chemistry program at NSF, implements a new technique for making such particles. The particles are between a few hundred nanometers and a few micrometers in size and possess surface properties that can be patterned in nearly any configuration. These so-called "patchy particles" are excellent candidates for self-assembly starting components. The technique researchers at Virginia Polytechnic Institute and State University employ uses light to pattern spherical particles that are suspended in liquid, and it has very few restrictions of the distribution and configuration of the pattern fabricated on the spheres. On the level of basic science, this new route to patchy particles permits a more thorough exploration of self-assembly, which helps unravel the principles underlying this complex and only partially understood phenomenon. Because the same pattern can straightforwardly be projected onto any number of particles, it potentially makes the technique amenable to future production of patchy particle on an industrial scale. Thereby, this research may impact a wide range of fields, but some of the project's initial target structures may be particularly useful in the areas of flexible solar cells and in microrobotics. In addition to the scientific and potential technological advances described, students are benefitting from this research either by direct involvement in the project and mentoring, or through the insights it adds to the course curriculum of the new Nanoscience program at Virginia Polytechnic Institute and State University.PART 2: TECHNICAL SUMMARYWith this project, supported by the Solid State and Materials Chemistry program at NSF, researchers at Virginia Polytechnic Institute and State University develop a new paradigm for synthesizing patchy particles with a patch distribution that can be chosen with nearly complete freedom, and to demonstrate the self-assembly of these particles into well-defined structures, includes some that are not readily achievable with existing patchy particle fabrication techniques. The project applies an optical imaging technique to project identical patterns on any number of dielectric nanospheres and/or microspheres, where functionalization with ligands containing photocleavable protecting groups (PPGs) ensure that the optical patterns are transferred into functional groups such as amines, thiols, carboxyls, etc., which can then be modified further to produce patches with desired functionality. With functionalizations containing optically orthogonal PPGs (including o-nitrobenzyl, aminocoumarin, and BODIPY groups), multiple patch types with distinct properties can be produced through a single exposure, which is required for full implementation of the patchy particle concept. The basic building blocks for self-assembly are titania micro- and nanospheres for which a number of ligands are developed to suit the needs of the project, using phosphonic acid anchors to form stable bonds with the surface. Titania spheres are particularly useful for applications beneficial to society, such as photonic crystals for high efficiency dye-sensitized solar cells. Other potential applications include TiO2/Pt light-controlled micromotors, or their photocatalytic properties could be used to directly assist in the surface patch formation. As part of this project one or more patch-patch interactions (such as hydrophobic attraction, electrostatic binding, biotin-avidin binding etc.) are used to achieve several target structures ranging from relatively simple (linear chains, tetrahedra) to more challenging but previously demonstrated (Kagome lattices, pentapods) to structures of high interest that have yet to be assembled (icosahedra, diamond-structure colloidal crystals.) The patterning can be applied to particles in a bulk suspension and is therefore potentially scalable.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.