NSF/DMR-BSF: Growth Induced Crystal Curvature

伟大的结晶学家舒布尼科夫说：“晶体闪现出它们的对称性。”他在这一精辟的评论中强调了水晶的特征，它们具有锋利的边缘和平坦的表面的醒目的多面体形状；根据定义，水晶是直的。有刻面的宝石或自然生长的石英就是明证。然而，人们在近一个世纪前就认识到，可以使各种各样的晶体以扭曲的螺旋状形态生长--这些形态肯定不是直的。值得注意的是，水晶王国的这一普遍特征在很大程度上被遗忘了，尽管它是阿司匹林等常见物质的特征。在固态和材料化学计划的支持下，研究小组旨在了解晶体在生长过程中是如何扭曲的。这些工艺是了解由分子制成的晶体机械性能的窗口，这些工艺是重要的工业操作的基础，如药品的压片。扭曲的晶体在光学对比的节奏带中非常生动，有望在微观和宏观手形之间架起一座桥梁。该研究团队与布朗克斯的几所公立高中合作，以提供科学认同建设的研究经验。技术摘要生长引起形变的原因可能在于混合晶体的超分子化学，以及这些力在固体的力学性能中的表现方式。该团队已经证明，添加剂在生长的晶体界面上以立体特异性的方式诱导扭曲。添加剂可能通过创建具有不同度规属性的混合结构域来扭曲晶体。分子水平上的不匹配会产生应变，而应变又会产生应力和扭矩。该策略包括三个方面：1.建立取代苯的混合或无序晶体扭转的条件，关于这些条件，我们已经从长期的单晶研究中了解了生长诱导菌株的来源。2.使用先进的显微镜精确描述具有生长诱导曲率的晶体的形状--这项工作是在材料研究部和美国-以色列双国科学基金会建立的合作安排下，与魏兹曼科学研究所的E.Efrati教授合作进行的。3.扭带微分几何领域的魏茨曼专家正在分析局部差异生长所编码的几何受挫的框架内的生长变形。这些研究将与原子力场和分子动力学模拟相匹配。

Non-Technical AbstractThe great crystallographer Shubnikov said that "crystals flash forth their symmetry." He was emphasizing in this pithy remark the characteristic feature of crystals, their striking polyhedral shapes with sharp edges and flat faces; crystals, by definition, are straight. Witness facetted gemstones, or naturally grown quartz. However, it was recognized almost a century ago that a wide variety of crystals can be made to grow with twisted, helix-like morphologies -- forms that are decidedly not straight. Remarkably, this general feature of the crystal kingdom was largely forgotten, even though it is characteristic of common substances such as aspirin. With support from the Solid State and Materials Chemistry program, the research team aims to understand how crystals twist themselves as they grow. These processes are windows into the mechanical properties of crystals built from molecules, processes that underlie important industrial operations such as the tableting of pharmaceuticals. Twisted crystals are vivid in their rhythmic bands of optical contrast, promising a bridge between microscopic and macroscopic handed forms. The research team is partnered with several Bronx public high schools in order to provide science identity-building research experiences. Technical AbstractThe origin of growth induced deformations of form presumably lie in the supramolecular chemistry of mixed crystals and in the manner in which these forces are manifest in the mechanical properties of solid bodies. The team has shown that additives induce twisting stereospecifically at growing crystal interfaces. Additives likely twist crystals by creating mixed domains with distinct metric properies. Mismatches at the molecular level produce strain that in turn can generate stress and twist moments. The strategy is threefold: 1. Establishing the conditions for twisting mixed or disordered crystals of substituted benzenes about which we already understand the origin of growth induced strain from long-standing studies of single crystals. 2. Using advanced microscopies to accurately describe the shapes of crystals with growth induced curvature -- this work is proceeding in collaboration with Professor E. Efrati at the Weizmann Institute of Science under the collaborative arrangement established by the Division of Materials Research and the US-Israel Binational Science Foundation. 3. Weizmann experts in differential geometry of twisted ribbons are analyzing growth deformation within the framework of geometric frustration encoded in local differential growth. These studies will be matched with atomistic force-field and molecular dynamics simulations.