Optimizing the Thermodynamics and Kinetics of Nanoparticle Crystal Assembly

纳米粒子是具有纳米级尺寸的材料，它们可以组装成更大的材料。纳米粒子的形状和表面化学性质可以被调整，这是原子或分子无法做到的。虽然具有一种表面覆盖或片状覆盖的球形纳米颗粒已经被广泛研究，但其他可以制备的颗粒形状，如多面体和框架，却很少被探索。该研究项目旨在设计和验证通用计算方法，以指导研究人员选择任意形状部件的关键特性，从而使其有效地自组装成目标材料。这项研究的结果可能会影响先进材料和半导体行业，为设计和制备光子学、光伏和催化应用的材料提供原理。这项研究的结果将通过在专业会议上的演讲、康奈尔大学组织的工业推广计划以及化学与生物分子工程系研究生创建的播客来传播。该研究项目是研究生进行前沿研究的训练基地。将招募一名本科生创建一个关于纳米级工程自组装的多媒体模块，通过面向农村高中女生的CBE妇女小组外展计划进行传播。这项研究的结果也将用于康奈尔大学的两门研究生统计力学课程。该研究项目包括制定和验证变分原理，以增强热力学和动力学装配行为。研究人员将实施有效的模拟方法来测试和改进变分原理，将它们应用于包含：(i)核心组件，（ii）与互补DNA链嫁接的纳米颗粒，有利于物种间键合，（iii）非凸形状，可以发生非加性混合，以及（iv）形成开放晶格的构建块。要研究的粒子形状包括球体、多面体和框架。这项研究是基于这样一个假设，即自由能值的最小化可以确定粒子-粒子相互作用应该如何调整，以增强它们在目标超晶格中的生产组装。在热力学行为方面，假设为了使纯组分晶体和取代有序化合物的稳定性达到最佳，有序-无序相变时的自由能应最小化。在动力学行为方面，假设在一定的过饱和程度下，粒子间相互作用导致无序到有序转变的自由能势垒高度降低，与自组装的最佳动力学能力相关。将自由能映射为系统哈密顿量参数的函数的先进方法将用于确定这些参数的最优值。在测试这些变分原理的过程中，许多具有科学意义的系统的相和动力学行为将被绘制出来，有可能揭示新的相和成核机制。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。

Nanoparticles are materials that have dimensions on the nanometer scale, and they can be assembled into larger materials. The shapes and surface chemistries of nanoparticles can be tailored in ways that atoms or molecules cannot. While spherical nanoparticles with one type of surface coverage or patchy coverage have been studied extensively, other particle shapes that can be prepared, like polyhedra and frames, have been much less explored. This research project aims to devise and validate general computational methods to guide investigators in selecting the key characteristics of arbitrarily-shaped components that lead to their efficient self-assembly into target materials. The outcomes of this research could impact the advanced materials and semiconductor industries by providing principles to design and prepare materials for photonics, photovoltaics, and catalysis applications. The results of this research will be disseminated through presentations at professional meetings, an industrial outreach program organized by Cornell, and a podcast created by graduate students of the Chemical and Biomolecular Engineering (CBE) Department. The research project serves as a training ground for graduate students to perform cutting edge research. An undergraduate student will be recruited to create a multimedia module about engineering self-assembly at the nanoscale to be disseminated through the CBE Women's group outreach initiatives that target rural High School girls. Results from this investigation will also be used in the curriculum of two graduate statistical mechanics courses at Cornell.This research project involves formulating and validating variational principles for enhancing thermodynamic and kinetic assembly behavior. The researchers will implement efficient simulation methods to test and improve the variational principles by applying them to systems containing: (i) hard-core components, (ii) nanoparticles grafted with complementary DNA strands that favor inter-species bonding, (iii) nonconvex shapes where non-additive mixing can occur, and (iv) building blocks that form open lattices. The particle shapes to be investigated include spheres, polyhedra, and frames. The research is based on the hypothesis that the minimization of a free-energy figure of merit can identify how particle-particle interactions should be tuned to enhance their productive assembly into target superlattices. In terms of thermodynamic behavior, it is hypothesized that the free-energy at the order-disorder phase transition should be minimized for optimal stability of pure-component crystals and substitutionally ordered compounds. In terms of kinetic behavior, it is hypothesized that inter-particle interactions that lead to a reduced free-energy barrier height for the disorder-to-order transition, at a fixed degree of supersaturation, correlate with optimal kinetic ability to self-assemble. Advanced methods to map such free-energies as a function of parameters of the system's Hamiltonian will be used to identify optimal values of such parameters. In testing these variational principles, the phase and kinetic behavior of many systems of scientific interest will be mapped out, potentially unveiling new phases and nucleation mechanisms.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.