RUI: The Study of Molecular Motion in Simple Glass Forming Liquids

在这个由化学系化学结构、动力学和机制计划支持的项目中，圣约瑟夫大学的John Berberian教授和他的学生将探索玻璃形成系统的分子动力学，从它们的熔点到低于它们的玻璃化转变温度Tg。为本研究选择的示例性体系是相对简单的对称烷基卤化物(具体地说，3溴3甲基戊烷、3溴3乙基戊烷、1溴2乙基丁烷和1溴3乙基戊烷)，因为它们没有氢键和长程空间缠结。这个分子系统提供了碳链中特定位置的碳链长度的系统性变化。用调制差示扫描量热法和介电弛豫法研究了构型熵随温度的变化(所有分子体系都是介电活性的)，以检验Adam-Gibbs理论(协同重排区)中分子间相互作用的影响。此外，利用等温调制量热法和静态介电常数的测量，研究了这些体系在玻璃化温度以上的冷结晶动力学。这项研究的结果，以及以前类似体系的结果，将对导致玻璃形成性质的分子间相互作用以及总体上的相变提供更深层次的见解。反过来，在分子水平上了解材料的结构将使团队能够预测材料的机械、热和其他属性，如聚合物和聚合物混合物。这种结构性知识的重要性延伸到许多领域(制药业、建筑业、保健业等)。它们有可能提高生活质量。作为一个本科生研究机构(RUI)项目，参与该项目的本科生研究人员将获得坚实的物理化学基础经验，并有机会看到材料科学和其他领域的直接影响。

In this project supported by the Chemical Structure, Dynamics and Mechanisms Program of the Division of Chemistry, Professor John Berberian and his students at St. Joseph's University will explore the molecular dynamics of glass forming systems, from their melting points to below their glass transition temperatures, Tg. The exemplary systems chosen for this study are the relatively simple symmetrical alkyl halides (specifically, 3 bromo 3 methylpentane, 3 bromo 3 ethylpentane, 1 bromo 2 ethylbutane and 1 bromo 3 ethylpentane) since they are devoid of hydrogen bonds and long range steric entanglements. This molecular system provides a systematic change in the length of the carbon chain at specific sites in the chain. Both modulated differential scanning calorimetry and dielectric relaxation are used to assess the changes in the configurational entropy with temperature (all of the molecular systems are dielectrically active) to test effect of molecular interactions in the Adam-Gibbs theory (cooperative rearranging regions). Additionally, the kinetics of the cold crystallization above Tg for these systems are investigated using isothermal modulated calorimetry and the measurement of the static permittivity both as a function of time and as a function of temperature.The results of this study, along with previous results of similar systems, will provide deeper insights into the intermolecular interactions that give rise to the glass forming properties, and phase transitions in general. In turn, the understanding of the structure of materials on a molecular level will allow the team to predict the mechanical, thermal, and other properties of materials, such as polymers and polymer blend. The importance of such structural knowledge extends to a number of areas (drug industry, construction industry, health industry, etc.) which have the potential to increase the quality of life. As a Research at Undergraduate Institutions (RUI) project, the undergraduate researchers engaged in this project will receive a solid foundational experience in physical chemistry, as well as an opportunity to see direct implications in the materials sciences and beyond.