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

在这个由化学系化学结构动力学和机理(CSDM-A)计划资助的项目中，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分子如何在一种被称为玻璃成型器的材料中运动。玻璃成形器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、塑料以及以药丸和药片形式提供的药物中。了解分子如何在这些系统中运动不仅解决了基本问题，而且还加强了对如何稳定这些材料免受各种类型降解的理解。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的分子运动和松弛相关的关键时间尺度和长度尺度。正在进行的过冷液体中的单分子成像实验使用了新设计和合成的理想探测器分子；这些探测器不会在空间或时间上平均超过玻璃主体中的异质性。因此，这些探测器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。这些实验详细说明了动态异质性，表现在小分子和聚合物玻璃成形器中旋转动力学的松弛和交换时间分布。此外，为了跟踪过冷液体中的平移动力学和结构重排，正在进行需要亚衍射局域化的实验，以解决关于旋转-平移去耦合现象的鲜为人知的问题。采用了两种探头的相关技术来测量动态关联，从而可以识别过冷液体中不均匀的长度尺度。理想的探针单分子测量也在聚合物薄膜中进行，重点是识别对薄膜器件和气相沉积玻璃的稳定性具有实际影响的假定的表面移动层。为了补充通过冷却制备的玻璃体系的研究，通过溶胀制备的这类体系的研究也在进行中。这些研究既包括动态异质性的细节方面，又直接可视化了这些系统中长期时间尺度松弛背后的结构重新安排。

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.