Molecular Control over the Mechanism of Crystal Growth

摘要：晶体结构的控制对材料的应用至关重要，无论是控制药物的活性还是控制先进材料的电子导电性。然而，破译决定特定晶体结构生长的物理/化学过程是复杂的。本项目系统测量分子形状和分子间相互作用强度对晶体生长动力学的影响，研究熔体结晶机理的分子水平控制。除了推进基础科学之外，这项工作对于晶体生长至关重要的所有科学领域都是无价的，例如聚合物、制药、食品、地质学和大气科学。此外，北卡罗莱纳州还为高中化学教师提供专业发展培训。这种基于学科的专业发展帮助教师将课程从基于标准化测试的内容/算法重点转向基于批判性思维/解决问题的教学和学习。技术摘要：该奖项支持的研究独特地提出了一种熔体结晶策略，直接探讨了分子形状和分子间力的内在因素对晶体生长机制的影响。实验测量了低聚芳烃和烷基铵金属卤化物盐的结晶动力学，分别作为芳香环数和烷基链长度的函数，以探讨分子各向异性和晶体尺寸对结晶速率的影响。利用各向同性和取向液晶熔体的比较动力学测量来阐明分子预取向对结晶速率的影响。此外，整个取代苯家族的结晶动力学创造了一个几何和能量矩阵，用于评估官能团效应。PI最近发现的过渡区理论，即艾灵过渡态理论的凝聚态模拟，使结晶反应的熵和焓激活参数的识别成为可能。该奖项有助于继续提供暑期教师研讨会，并支持聘请一名高中化学教师在暑期与PI一起编写和发布这一专业发展的组成部分，从而提供更多的传播解决问题/发现基础材料。

Non-technical Abstract:Control of crystalline structure is important to the application of materials, whether to control the activity of pharmaceuticals or the electronic conductivity of advanced materials. However, deciphering the physical/chemical processes that determine growth of specific crystal structures is complex. This project systematically measures the influence of molecular shape and the strength of intermolecular interactions on the kinetics of crystal growth to investigate molecular level control of the mechanism of melt crystallization. In addition to advancing the fundamental science, this work is invaluable to all fields of science for which crystal growth is critical, such as polymers, pharmaceuticals, food products, geology, and atmospheric science. In addition, professional development for high school chemistry teachers is made available across the state of North Carolina. This discipline based professional development helps teachers shift curricula from a standardized test-based content/algorithm focus to critical-thinking/problem-solving based teaching and learning.Technical Abstract:The research supported by this award uniquely presents a melt crystallization strategy that directly probes the influence of intrinsic factors of molecular shape and intermolecular forces on the mechanism of crystal growth. Experimental measurement of the crystallization kinetics of oligoacenes and alkylammonium metal halide salts, as a function of the number of aromatic rings and length of alkyl chains, respectively, is being used to probe the impact of molecular anisotropy and crystal dimensionality on the rate of crystallization. Comparative kinetic measurements from isotropic vs. oriented melts of liquid crystals is utilized to articulate the impact of molecular pre-orientation on the rate of crystallization. Also, the crystallization kinetics across the family of substituted benzenes creates a geometric and energetic matrix with which to evaluate functional group effects. The PI's recent discovery of Transition Zone Theory, the condensed matter analog of Eyring's transition state theory, enables for the identification of entropic and enthalpic activation parameters of crystallization reactions. This award facilitates a continuing offering of the summer teacher workshops, and also supports hiring a high school chemistry teacher to work with the PI during summers to write and publish components of this professional development, which affords greater dissemination of the problem-solving/discovery based materials.