NIRT: Directed Assembly of Nanostructures: Theory, Simulations, and Experiments in Hard and Soft Materials

本提案是对NSF 03-043 NIRT类纳米科学与工程倡议的响应。定向自组装和聚集为制造纳米尺度的结构提供了巨大的可能性。挑战在于要求原子、分子或粒子组装成直径几厘米的复杂且高度有序的纳米大小结构。这种结构的潜在应用出现在广泛的技术中，包括纳米和分子电子学、用于数据存储的高密度图案化介质、光电子学和纳米传感器阵列等。使用外加磁场来控制和指导微结构和纳米结构的进化是实现这种精确控制聚集的一条非常有前途的途径。外场与物质相互作用的实际应用将需要基本的理解和工程设计方法来创造纳米级的有序聚集体。虽然在微尺度和纳米尺度系统中许多新的相行为的最初发现都是纯粹的实验研究，但越来越明显的是，建模和预测微结构演变的能力对于在纳米尺度上实现有效和实用的控制将是至关重要的。拟议的研究旨在通过大量的建模和理论工作，结合最先进的硬材料和软材料系统实验来实现这一目标，这两种实验都提供了互补的优势。硬(或原子)系统，例如晶体材料中的纳米沉淀物，无论从实验还是理论上都很难完全表征。另一方面，胶体或软系统在设置控制粒子-粒子相互作用的“微观”属性和进行直接实验观察方面提供了更大的灵活性，特别是在依赖时间的现象的情况下。这项研究的结果将是一个基于物理的框架，用于在硬系统和软系统中实现定向聚合。在这两种情况下，统一的主题将是外部应用领域对运输的诱导和控制。例如，硬材料中的应力，软材料中的熵场，以及两者中的化学势。场辅助定向组装的概念并不是特定于材料的，所提出的研究将作为在非常广泛的材料范围内进行定向纳米尺度聚集的建模和实验设计的一般基础。它可能提供对聚集机制的全新见解，并揭示几乎所有材料共同的方面。同时，通过利用共同的基本特征，加深了解将能够在不同的技术应用之间转移方法。这种统一的概念至关重要，因为高科技材料正变得越来越复杂，表面上看起来并不相关。最后，预计本研究对研究生教育的影响将是深远的。越来越明显的是，需要新一代科学家和工程师来领导纳米技术的发展，这需要在化学工程、材料科学和材料力学方面进行综合培训。这一紧密结合的项目将为这种跨学科培训提供一个理想的框架。这项研究由化学和运输系统司的热运输和热加工计划、化学和运输系统司的界面、运输和热力学计划、土木和机械系统司的材料力学和结构计划以及设计、制造和工业创新司的纳米制造计划共同资助。

This proposal was received in response to Nanoscale Science and Engineering initiative, NSF 03-043, category NIRT. Directed self-assembly and aggregation offers tremendous possibilities for making structures at the nanoscale. The challenge lies in the requirement that atoms, molecules, or particles be assembled into complex and highly organized nanometer-sized structures across centimeters. Potential applications for such structures arise in a wide range of technologies, including nano and molecular electronics, high-density patterned media for data storage, optoelectronics, and nanosensor arrays to name a few. The use of externally applied fields to control and direct micro- and nanostructural evolution is a very promising avenue for achieving such precise control of aggregation. The practical application of external-field interactions with matter to create nanoscale, ordered aggregates will require both fundamental understanding and engineering design methodologies. While many of the initial discoveries of novel phase behavior in microscale and nanoscale systems have arisen from purely experimental investigations, it is increasingly apparent that the ability to model and predict microstructural evolution will be of central importance for achieving effective and practical control at the nanoscale. The proposed research aims to accomplish this goal with a substantial modeling and theoretical effort in conjunction with state-of-the-art experiments in both hard and soft material systems, each of which offers complementary advantages. Hard (or atomic) systems, e.g. nanoprecipitates in crystalline materials, are very difficult to completely characterize either experimentally or theoretically. Colloidal or soft systems, on the other hand, offer greater flexibility both in setting the "microscopic" properties that control particle-particle interactions and in the ability to make direct experimental observations, particularly in the case of time-dependent phenomena. The outcome of this research will be a physically based framework for achieving directed aggregation in both hard and soft systems. In both cases, the unifying theme will be the induction and control of transport by externally applied fields. Examples include stresses in hard materials, entropic fields in soft materials, and chemical potentials in both. The concept of field-assisted directed assembly is not material specific and the proposed research will serve as the general foundation for modeling and experimental design of directed nanoscale aggregation in a very broad range of materials. It may provide entirely new insights into the mechanisms of aggregation and reveal aspects that are common to practically all materials. At the same time, by exploiting common underlying characteristics, a deeper understanding will enable transfer of methodologies among different technological applications. Such unifying concepts are of paramount importance as high-tech materials are becoming more complex and ostensibly unrelated. Finally, the impact of this research on the education of graduate students is expected to be far reaching. It is increasingly apparent that a new generation of scientists and engineers is needed to lead the development of nanotechnology, which requires combined training in chemical engineering, materials science, and mechanics of materials. This closely-knit project will provide an ideal framework for this type of cross-disciplinary training. The research is being funded jointly by the Thermal Transport and Thermal Processing Program of the Chemical and Transport Systems Division, the Interfacial, Transport and Thermodynamics Program of the Chemical and Transport Systems Division, the Mechanics and Structures of Materials Program of the Civil and Mechanical Systems Division, and the Nanomanufacturing Program of the Design, Manufacturing and Industrial Innovation Division.