Non-Classical Mechanisms of Solution Crystallization Studied Using Colloidal Experiments and Simulations

非技术摘要：结晶是一种广泛遇到的相变，影响了许多科学和技术领域。从浓缩相，晶体通过添加单体成核和生长，并通过经典的单步过程很好地描述。然而，从稀溶液中，控制结晶的因素仍然存在激烈的争论。这种缺乏了解阻碍了电子和光学应用的单晶材料的生产以及化学品和药物的沉淀，这是两个例子。它还对涉及蛋白质和大分子结晶的疾病的治疗提出了重大挑战，包括肾结石、痛风和血红蛋白CC疾病。虽然溶液中的晶体通常使用多步而不是单步途径成核和生长，但决定给定系统所使用的途径的因素尚未得到很好的理解。该项目开发了由悬浮在液体中的微米级胶体颗粒组成的实验和计算模型系统，并确定了随着颗粒之间的相互作用的变化，溶液中晶体成核和生长的途径。从这些研究中获得的知识将提供控制溶液结晶和自组装所需的基本理解。教育推广工作传达这些结果及其对社会的重要性，以K - 12学生和公众，包括在休斯顿大学的科学夏令营和在休斯顿市中心举行的科学节的活动。技术摘要：晶体在溶液中被广泛报道成核和增长使用多步骤的途径，偏离经典的机制，其中涉及单步过程。虽然已经报道了许多非经典组装的例子，但对控制成核和生长途径选择的因素的物理理解仍然有限。该项目的目标是部署胶体成像实验和计算模型，以了解分子间相互作用如何决定溶液中晶体的经典（单步）与非经典（多步）成核和生长机制的选择。驱动假说是相互作用势的形状控制晶体成核和生长的路径选择。该团队通过整合粒子合成和共聚焦显微镜，光散射和先进模拟技术的互补专业知识，在分子的类似物，亚微米胶体颗粒的悬浮液中测试这一假设，以解决两个具体目标：（1）确定非特异性相互作用在从直接相互作用转变为直接相互作用中的作用。（经典）成核到多步成核，通过在实验和模拟中调整粒子之间的长程排斥和短程吸引相互作用，和（2）研究粒子相互作用对非经典生长机制的影响，通过表征在模板上或溶液中生长的晶体中添加团簇。该项目的智力价值是对非经典成核和生长机制如何影响溶液中有序晶体组装体形成的基本见解，这为开发新策略铺平了道路，以快速可控地组装大规模晶体并生成具有精确放置成分的良好控制结构。这个项目也对社会产生了广泛的影响：结晶是无数工业和病理过程的基础。该项目继续了该团队的持续努力，通过为从休斯顿大学多元化研究机构招募的本科生和研究生提供指导性研究机会，一个指定的西班牙裔服务和亚裔美国人和美国土著太平洋岛民-该奖项反映了NSF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。

Non-technical abstract:Crystallization is a widely-encountered phase transition that affects many areas of science and technology. From concentrated phases, crystals nucleate and grow through the addition of monomers, and are well described by classical single-step processes. From dilute solutions, however, the factors controlling crystallization remain hotly contested. This lack of understanding hinders the production of single-crystal materials for electronic and optical applications and the precipitation of chemicals and pharmaceuticals, as two examples. It also poses a significant challenge for the treatment of diseases that involve crystallization of proteins and large molecules, including kidney stones, gout, and hemoglobin CC diseases. Whereas crystals in solution often nucleate and grow using multi-step rather than single-step pathways, the factors that determine the pathway used by a given system are not well understood. This project develops experimental and computational model systems consisting of micron-sized colloidal particles suspended in liquids and identifies the pathways for crystal nucleation and growth from solution as the interactions between the particles are varied. The knowledge gained from these studies will provide the fundamental understanding needed to control crystallization and self-assembly from solution. Educational outreach efforts conveying these results and their importance for society to K – 12 students and the general public include activities at science camps at the University of Houston and at science festivals held in downtown Houston.Technical abstract:Crystals in solution are widely reported to nucleate and grow using multi-step pathways that deviate from classical mechanisms, which involve single-step processes. Although many examples of non-classical assembly have been reported, physical understanding of the factors controlling the choice of nucleation and growth pathways remains limited. The objective of this project is to deploy colloid-imaging experiments and computational models to understand how intermolecular interactions dictate the choice of classical (single-step) versus non-classical (multi-step) nucleation and growth mechanisms for crystals in solution. The driving hypothesis is that the shape of interaction potentials controls the choice of pathways by which crystals nucleate and grow. The team tests this hypothesis in analogues for molecules, suspensions of submicron colloidal particles, by integrating complementary expertise in particle synthesis and confocal microscopy, light scattering, and advanced simulation techniques to address two specific aims: (1) identify the role of nonspecific interactions in the transition from direct (classical) nucleation to multistep nucleation, by tuning both long-range repulsive and short-range attractive interactions between particles in experiment and simulation, and (2) investigate the effects of particle interactions on mechanisms of non-classical growth, by characterizing addition of clusters to crystals grown on a template or in solution. The intellectual merit of this project is fundamental insight into how non-classical nucleation and growth mechanisms affect the formation of ordered crystalline assemblies in solution, which paves the way for the development of novel strategies to rapidly and controllably assemble large-scale crystals and generate well-controlled structures with precisely placed constituents. This project also has significant broader impacts for society: crystallization underlies myriad industrial and pathological processes. The project continues the team’s ongoing efforts to broaden participation in science through mentored research opportunities for undergraduate and graduate students recruited from the diverse study body at the University of Houston, a designated Hispanic-Serving and an Asian American and Native American Pacific Islander-Serving Institution.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.