Thermodynamics and Dynamics of Mesophases from Novel Self-Assembling Building Blocks

新型自组装砌块的中间相的热力学和动力学

• 批准号: 1033349
• 负责人: Fernando Escobedo
• 金额: $ 25.72万
• 依托单位: Cornell University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-09-01 至 2013-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1033349&HistoricalAwards=false
• 关键词: Thermodynamics; Dynamics; Mesophases; Novel; Self

1033349EscobedoIntellectual Merit:Motivated by the growing ability to experimentally produce particles of almost any imaginable shape in the nano- to micro-size range, the goal of this proposal is to develop and apply novel molecular simulation methods to study the thermodynamic and dynamic properties of partially ordered phases (mesophases) of systems containing rigid colloidal particles of polyhedral shapes. This goal lies within the scope of nanotechnology that seeks to achieve greater control of orderly assembly of nanoscale objects; specifically, by elucidating how multifaceted building blocks form novel self-assembled structures. In this context, particle shape complementarity plays the role of an ?entropic bonding? that helps orient and position particles in regular patterns (even in the absence of chemical selectivity). The particle shapes to be investigated are convex space filling polyhedrons such as polygonal prisms, truncated octahedron, and rhombic dodecahedron.Selected binary mixtures of these particle types will also be studied, including mixtures of triangular and hexagonal prisms (which may template photonic band-gap materials), and mixtures of octahedra and tetrahedra (which would lead to model nano assembled 3D compounds). The models used are coarse grained representations of colloidal particles whose effective inter-particle interactions can be tuned by surface functionalization or by the composition of the solvent media. It is expected that many of these systems will exhibit a liquid crystalline phase or a plastic solid in between the isotropic phase (at low concentrations) and crystal phase (at high concentrations). To identify such mesophases, advanced Monte Carlo methods and order parameters will be used to outline their phase boundaries and characterize their structure. To elucidate how such mesophases form and melt, the kinetics and mechanism of isotropicmesophase transitions will be investigated via novel path sampling methods. To elucidate how particles and defects move in such phases, molecular dynamic simulations will be performed to track and characterize their motion at equilibrium conditions and under steady shear flow. Some of these mesophases may exhibit unusual shear response like flow directionality and yield stress.The methodological developments to be pursued are: (i) optimization of novel forward flux sampling to study the kinetics of order disorder phase transitions and to identify good orderparameters to characterize mechanism, and (ii) extension of expanded ensemble methods to simulate mesophase transitions in pure and binary systems using suitable order parameters. The proposed research can thus be seen as having a dual scope. The primary goal is to elucidate the thermodynamic and dynamic behavior of model rigid building blocks that have potential uses in the nanotechnology of self assembly. The secondary goal is to formulate novel numerical statistical mechanics techniques that have potentially widespread applications.Broader Impacts:This work is complementary to experimental efforts by collaborators who will try to realize the predicted novel phases and test their mechanical, optical, and rheological properties. In the long term, the results could impact the ceramic, plastics, and semiconductor industries by helping broaden the approaches available to develop strong nano composites with high particle loadings, sieves with regular topology, liquid armors, colloid based mesocrystals for light control in photonic materials, sensors and lubricants sensitive to stress directionality, and nanocrystal arrays for photovoltaics. Advances in simulation methods should also help materials modelers to improve product properties by predicting and exploiting meso-scale, entropy aided self-assembly.The graduate and undergraduate students involved with this project will get ample exposure to the physics and engineering of colloids while acquiring a significant expertise on multiple molecular and mesoscopic modeling techniques. They will also coordinate with the Cornell Centerfor Material Research (CCMR) to create a teaching module on Nano-Lego engineering: harnessing entropy to create order? for use in local high schools. Our scientific results will be disseminated through professional meetings and an industrial outreach program organized by CCMR. Results of this investigation will be used in at least two courses: a new course on molecular simulations and the advanced Chemical Engineering thermodynamics core course.

[33349escobedo10]智力优势：由于实验产生纳米到微尺寸范围内几乎任何可想象形状的颗粒的能力不断增强，本提案的目标是开发和应用新的分子模拟方法来研究含有多面体形状的刚性胶体颗粒的部分有序相（中间相）系统的热力学和动力学性质。这一目标属于纳米技术的范畴，纳米技术旨在更好地控制纳米级物体的有序组装；具体来说，通过阐明多方面的构建模块如何形成新颖的自组装结构。在这种情况下，粒子形状互补性起着一种？熵的结合?这有助于粒子以规则的模式定向和定位（即使在没有化学选择性的情况下）。要研究的粒子形状是凸空间填充多面体，如多棱体、截尾八面体和菱形十二面体。这些粒子类型的选择二元混合物也将被研究，包括三角形和六边形棱镜的混合物（可能模板光子带隙材料），以及八面体和四面体的混合物（这将导致模型纳米组装3D化合物）。所使用的模型是胶体颗粒的粗粒度表示，其有效的颗粒间相互作用可以通过表面功能化或溶剂介质的组成来调节。预计这些体系中的许多将在各向同性相（低浓度）和晶体相（高浓度）之间表现出液晶相或塑性固体。为了识别这样的中间相，将使用先进的蒙特卡罗方法和顺序参数来描绘它们的相边界并表征它们的结构。为了阐明这些中间相是如何形成和融化的，将通过新的路径采样方法研究各向同性中间相转变的动力学和机制。为了阐明颗粒和缺陷如何在这样的阶段中运动，将进行分子动力学模拟来跟踪和表征它们在平衡条件下和稳定剪切流下的运动。其中一些中间相可能表现出不寻常的剪切响应，如流动方向和屈服应力。方法学上的发展是：(i)优化新型正向通量采样，以研究有序无序相变动力学，并确定良好的有序参数来表征机理；（ii）扩展集成方法，以使用合适的有序参数来模拟纯系统和二元系统的中间相变。因此，拟议的研究可被视为具有双重范围。主要目标是阐明模型刚性构建块的热力学和动力学行为，这些构建块在自组装的纳米技术中具有潜在的用途。第二个目标是制定具有潜在广泛应用的新型数值统计力学技术。更广泛的影响：这项工作是对合作者的实验努力的补充，他们将试图实现预测的新相，并测试它们的机械、光学和流变特性。从长远来看，该研究结果可能会影响陶瓷、塑料和半导体行业，帮助拓宽开发高颗粒负载的强纳米复合材料、具有规则拓扑结构的筛子、液体盔甲、用于光子材料光控制的胶体基介晶、对应力方向性敏感的传感器和润滑剂以及用于光伏电池的纳米晶体阵列的方法。模拟方法的进步也应该帮助材料建模者通过预测和利用中尺度、熵辅助自组装来改善产品性能。参与该项目的研究生和本科生将充分接触到胶体的物理和工程，同时获得多种分子和介观建模技术的重要专业知识。他们还将与康奈尔材料研究中心（CCMR）合作，创建一个纳米乐高工程的教学模块：利用熵来创造秩序？供当地高中使用。我们的科学成果将通过CCMR组织的专业会议和行业外展计划进行传播。本研究结果将至少用于两门课程：一门新开设的分子模拟课程和高级化学工程热力学核心课程。