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

1033349智能优点：由于在纳米到微米尺寸范围内实验生产几乎任何可以想象的颗粒的能力不断增强，该提议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体系的偏序相(中间相)的热力学和动力学性质。这一目标属于纳米技术的范畴，该技术寻求实现对纳米级物体有序组装的更大控制；具体地说，通过阐明多方面的构建块如何形成新颖的自组装结构。在这种情况下，颗粒形状的互补性起到了？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)。被研究的粒子形状是凸空间填充多面体，如多边形棱柱、截断八面体和菱形十二面体，还将研究这些粒子类型的精选二元混合物，包括三角形和六边形棱柱的混合物(可能形成光子带隙材料)，以及八面体和四面体的混合物(这将导致模型纳米组装三维化合物)。所使用的模型是胶体颗粒的粗粒表示，其有效的颗粒间相互作用可以通过表面官能化或溶剂介质的组成来调节。预计其中许多体系将在各向同性相(低浓度时)和晶相(高浓度时)之间显示液晶相或塑性固体。为了识别这些中间相，将使用先进的蒙特卡罗方法和序参数来勾画它们的相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，我们将通过新的路径采样方法来研究等温中间相转变的动力学和机理。为了阐明颗粒和缺陷在这些相中是如何运动的，分子动力学模拟将被用来跟踪和表征它们在平衡条件和稳定剪切流下的运动。其中一些中间相可能表现出异常的剪切响应，如流动方向性和屈服应力。方法学方面的进展是：(I)优化新的正向通量采样，以研究有序无序相变的动力学，并确定好的有序参数来表征机理；(Ii)扩展系综方法，使用合适的有序参数来模拟纯体系和二元体系的中间相转变。因此，拟议的研究可以被视为具有双重范围。主要目的是阐明在自组装纳米技术中具有潜在用途的模型刚性构建块的热力学和动力学行为。第二个目标是建立具有潜在广泛应用的新的数值统计力学技术。布罗德影响：这项工作是对合作者的实验工作的补充，他们将试图实现预测的新相并测试其力学、光学和流变性。从长远来看，这一结果可能会影响陶瓷、塑料和半导体行业，因为它有助于拓宽现有方法，以开发高颗粒负载的强大纳米复合材料、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介晶、对应力方向敏感的传感器和润滑剂，以及用于光伏发电的纳米晶体阵列。模拟方法的进步也应该帮助材料建模者通过预测和利用介观尺度、熵辅助的自组装来改善产品性能。参与这个项目的研究生和本科生将获得大量的胶体物理和工程知识，同时获得多分子和介观建模技术方面的重要专业知识。他们还将与康奈尔材料研究中心(CCMR)协调，创建一个关于纳米乐高工程的教学模块：利用熵创造秩序？供当地高中使用。我们的科学成果将通过专业会议和CCMR组织的产业推广计划进行传播。这项研究的结果将至少用于两门课程：一门新的分子模拟课程和一门高级化学工程热力学核心课程。

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.