Single Molecule Studies for Characterizing Dynamical and Mechanical Properties of Glassy Systems

在化学系化学结构、动力学和机理A(CSDM-A)计划的支持下，哥伦比亚大学的劳拉·考夫曼教授正在使用单分子显微镜方法研究玻璃聚合物的结构域。玻璃看起来是固体，但与晶体不同的是，它们具有更类似于液体的非晶态结构。聚合物，如塑料和橡胶，经常形成玻璃状固体。虽然它们在现代生活中无处不在，但它们仍然表现出鲜为人知的行为。例如，它们似乎是由小的结构域组成的，这些结构域在看似固体的材料中缓慢移动，通常以不同的速度移动。考夫曼教授和她的学生正在观察嵌入聚合物中的单个分子的荧光，以跟踪这些结构域的运动。他们的发现可能会为材料的设计提供指导，这些材料可用于从家居用品到太阳能电池和生物医学材料的广泛应用。参与这项研究的学生学习广泛的实验技术和分析方法，这些方法适用于许多科学和技术领域。考夫曼小组还定期通过讲座和演示与K-12学生接触，向学生介绍玻璃材料不同寻常的有趣特性。考夫曼教授将改进和扩展单分子成像。补充方法的增加有望提供对聚合物玻璃成型器中动态异质性的更详细的看法。从新型探针检测到的荧光信号将在从几分钟到几个小时的时间尺度上被跟踪，并被用于表征玻璃态聚苯乙烯中非均相区域的长度尺度、组织和机械性能。首先，通过一系列实验比较自由和束缚单分子探针在物理缠绕和化学交联聚合物中的行为，将阐明多相域的空间范围的各个方面。在此之后，将在该系统和类似系统中对低于其玻璃化转变温度的聚苯乙烯的整体和局部机械性能进行研究，包括以下扰动。使用模块化方法，考夫曼团队将进行集成的成像和流变学实验，以详细说明玻璃中块体机械性能、局部自由体积和时空局部动力学之间的联系。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

With support from the Chemical Structure, Dynamics, and Mechanisms A (CSDM-A) program in the Division of Chemistry, Professor Laura Kaufman of Columbia University is using single-molecule microscopy methods to study structural domains in glassy polymers. Glasses appear to be solid, but in contrast to crystals, they have amorphous structures that are more akin to liquids. Polymers, like plastics and rubbers, frequently form glassy solids. While they are ubiquitous in modern life, they still exhibit poorly understood behaviors. For example, they appear to be made up of small structural domains that slowly move through the seemingly solid material, oftentimes at different speeds. Professor Kaufmann and her students are watching the fluorescence from individual molecules embedded within polymers to track the movement of these domains. Their discoveries could inform the design of materials for use in a wide range of applications, from household goods to solar cells and biomedical materials. The students engaged in this research learn a broad range of experimental techniques and analysis approaches that are applicable to many areas of science and technology. The Kaufman group also regularly engages with K-12 students through talks and demonstrations that introduce students to the unusually interesting properties of glassy materials. Professor Kaufman will refine and extend single molecule imaging. The addition of complementary approaches is expected to provide for a more detailed view of dynamic heterogeneity in polymeric glass formers. Fluorescence signals detected from novel probes will be followed over time scales ranging from minutes to hours and used to characterize the length scale, organization, and mechanical properties of heterogeneous regions in glassy polystyrene. First, a set of experiments comparing the behavior of free and tethered single molecule probes in physically entangled and chemically cross-linked polymers will elucidate aspects of the spatial extent of heterogeneous domains. Following this, investigations into bulk and local mechanical properties in polystyrene below its glass transition temperature, including following perturbations, will be undertaken in this and similar systems. Using a modular approach, the Kaufman group will perform integrated imaging and rheology experiments to detail connections between bulk mechanical properties, local free volume, and spatiotemporally local dynamics in glasses.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.