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

1033349 Escobedo智力优点：由于实验生产几乎任何可以想象的纳米至微米尺寸范围内的颗粒的能力不断增长，该提案的目标是开发和应用新的分子模拟方法来研究包含多面体形状的刚性胶体颗粒的系统的部分有序相（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围，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，颗粒形状的互补性发挥作用的？熵键这有助于以规则的图案定向和定位颗粒（即使在没有化学选择性的情况下）。研究的粒子形状是凸空间填充多面体，如多边形棱柱、截顶八面体和菱形十二面体。还将研究这些粒子类型的选定二元混合物，包括三角形和六棱柱的混合物（可能是光子带隙材料的模板），以及八面体和四面体的混合物（可能导致模型纳米组装的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官能化或溶剂介质的组成来调节。预期这些系统中的许多将在各向同性相（在低浓度下）和结晶相（在高浓度下）之间表现出液晶相或塑性固体。为了识别这样的中间相，先进的蒙特卡罗方法和顺序参数将被用来勾勒出它们的相边界和表征它们的结构。为了阐明这些中间相是如何形成和熔化的，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相中移动，将进行分子动力学模拟，以跟踪和表征它们在平衡条件下和稳定剪切流下的运动。这些中间相中的一些可能会表现出不寻常的剪切响应，如流动方向性和屈服stress.The方法的发展将追求：（i）优化新的前向通量采样研究有序无序相变的动力学和识别良好的有序参数表征机制，和（ii）扩展系综方法模拟纯和二元系统中的中间相转变，使用合适的序参数。因此，拟议的研究可被视为具有双重范围。主要目标是阐明在纳米技术的自组装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。第二个目标是制定新的数值统计力学技术，具有潜在的广泛应用。更广泛的影响：这项工作是补充实验工作的合作者谁将试图实现预测的新阶段，并测试其机械，光学和流变性能。从长远来看，这些结果可能会影响陶瓷，塑料和半导体行业，有助于拓宽可用于开发具有高颗粒负载的坚固纳米复合材料，具有规则拓扑结构的筛，液体装甲，用于光子材料中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，以及用于光子学的纳米阵列的方法。模拟方法的进步也将帮助材料建模者通过预测和利用介观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胶体的物理和工程，同时获得多个分子和介观建模技术的重要专业知识。他们还将与康奈尔大学材料研究中心（CCMR）合作，创建一个关于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专业会议和CCMR组织的工业推广计划进行传播。这项研究的结果将用于至少两门课程：一门新的分子模拟课程和先进的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.