Ideal Probe Single Molecule Imaging for the Study of Small Molecule and Polymeric Glass Formers

在这个由化学部门化学结构动力学和机制（CSDM-A）项目资助的项目中，哥伦比亚大学的劳拉·考夫曼教授正在使用先进的成像技术来研究一类被称为玻璃形成物的材料中的分子如何运动。玻璃形成物可能以过冷液体或玻璃的形式存在，这些材料在微观和宏观尺度上都表现出不寻常的和鲜为人知的行为。这些材料在自然界和现代技术中无处不在，存在于窗户玻璃、塑料和以药丸和片剂形式提供的药物中。了解分子在这些系统中的运动方式不仅可以解决基本问题，还可以增强对如何稳定这些材料以抵抗各种降解的理解。PI开发并使用单分子成像方法来详细描述这些系统中分子的旋转和平移，梳理出与这些环境中分子运动和弛豫相关的关键时间尺度和长度尺度。正在进行的过冷液体单分子成像实验采用了新设计和合成的理想探针分子；这些探测器不会在空间或时间上平均于玻璃质宿主的异质性。因此，这些探针直接询问这些系统中感兴趣的长度和时间尺度，并测试玻璃化转变理论的预测。实验详细描述了小分子和聚合物玻璃形成物中旋转动力学的弛豫和交换时间分布的动力学非均质性。此外，需要亚衍射定位的实验正在进行，以跟踪过冷液体中的平移动力学和结构重排，以解决有关旋转-平移解耦现象的问题。相关技术采用两种类型的探针来测量动态相关性，允许识别过冷液体的非均质长度尺度。理想探针单分子测量也在薄聚合物薄膜中进行，重点是确定假定的表面可移动层，这对薄膜器件和气相沉积玻璃的稳定性具有实际影响。为了补充通过冷却制备的玻璃系统的研究，通过膨胀制备的这种系统的研究也在进行中。这些研究既详细介绍了这些系统的动力非均质性，又直接可视化了这些系统长时间松弛下的结构重排。

In this project funded by the Chemical Structure Dynamics and Mechanism (CSDM-A) program of the Chemistry Division, Professor Laura Kaufman of Columbia University is using advanced imaging techniques to study how molecules move in a class of materials known as glass formers. Glass formers may exist as supercooled liquids or glasses, materials that demonstrate unusual and poorly understood behaviors at both the microscopic and macroscopic scales. These materials are ubiquitous in nature and in modern technology, present in window glass, plastics, and medications delivered as pills and tablets. Understanding how molecules move in these systems not only addresses fundamental questions but also enhances understanding of how to stabilize these materials against various types of degradation. The PI develops and uses single molecule imaging approaches to detail the rotations and translations of molecules in these systems, teasing out key time scales and length scales related to molecular motions and relaxations in these environments. The single molecule imaging experiments in supercooled liquids underway employ newly designed and synthesized ideal probe molecules; these are probes that do not average in space or time over heterogeneities in a glassy host. As a result, these probes directly interrogate length and time scales of interest in these systems and test predictions of theories of the glass transition. The experiments detail dynamic heterogeneity as manifested in relaxation and exchange time distributions of rotational dynamics in both small molecule and polymeric glass formers. In addition, experiments that require sub-diffraction localization are being performed to follow translational dynamics and structural rearrangements in supercooled liquids to resolve questions regarding the poorly understood phenomenon of rotational-translational decoupling. Related techniques employing two types of probes are employed to measure dynamic correlations, allowing identification of length scales of heterogeneity in supercooled liquids. Ideal probe single molecule measurements are also being performed in thin polymeric films, with a focus on identifying the putative surface mobile layer that has practical ramifications for the stability of thin film devices and vapor-deposited glasses. To complement studies of glassy systems prepared through cooling, studies of such systems prepared through swelling are also underway. These studies both detail aspects of dynamic heterogeneity and directly visualize structural rearrangements underlying long time scale relaxations in these systems.