Understanding Acid-Base Interactions using Interface-Sensitive Spectroscopy

技术摘要：本国家科学基金项目的目标是利用红外-可见和频产生光谱（SFG）的界面灵敏度来测量固-固界面的酸碱相互作用。对极性相互作用的理解在粘附、摩擦和润湿方面是很重要的。在分子水平和动力学条件下（例如，在滑动和机械接触过程中），酸碱相互作用及其在这些涂层粘附中的作用的原位表征对科学家来说是一个艰巨的挑战。首席研究员Dhinojwala教授建议直接探测与无机蓝宝石衬底接触的聚合物或带有酸性或碱性端基的自组装单层修饰的蓝宝石的酸碱相互作用，以在分子水平上了解这些相互作用。SFG仪器可以直接监测酸性基团和碱性基团的振动峰位移，并将其与相互作用能联系起来，研究聚合物-固体界面上的交换动力学随时间、温度和成分的变化。本研究探讨了由酸碱相互作用驱动的表面偏析的动力学和热力学。此外，本文还以共混物和共聚物为研究对象，研究了这些相互作用能对近固-固界面的偏析以及滑动和剥离过程中的动力学的作用。相互作用能的研究及其实验结果对理解摩擦和粘滞具有重要意义。这些相互作用能量将与使用Johnson-Kendall- Roberts （JKR）几何的粘附测量值进行比较。除了这些实验，PI还将进行原子分子动力学模拟（MD）和量子计算，以了解频移的幅度及其对偏析的影响。这些实验的SFG、MD和量子计算将结合使用，以了解表面浓度、空间约束和表面粗糙度对酸碱相互作用的影响及其对粘附能的影响。对酸碱相互作用的基本理解有助于预测聚合物与基质的粘附性，并有助于开发下一代增强涂层和粘合剂，用于多个领域，包括但不限于电子、生物矿化、肽基表面识别、纳米复合材料和太阳能电池。该项目将支持两名研究生，他们将与表面科学、MD模拟和工业研究领域的专家组成一个小组。与这个广泛的多学科小组一起工作的学生将接受团队合作的培训。此外，研究生也将有机会在夏季指导NSF-REU的学生。作为第5区科学日的志愿者总监，PI将继续在阿克伦大学（UA）举办地区科学日。PI还发起了一项指导计划，他将来自工业界和学术界的科学家聚集在一起，指导科学项目。这项指导计划始于俄亥俄州哈德逊市，PI计划将这项计划推广到第五区的所有学校。在与UA商学院和奥斯汀生物创新研究所的合作下，PI正在帮助开发一个多学科的生物设计课程，提供给UA物理科学，商业和医学的学生，目标是观察或基于实验的方法来解决问题。本课程将与UA商学院和医学院的教授合作教授。

TECHNICAL SUMMARYThe objective of this NSF project is to exploit the interface sensitivity of infrared-visible sum frequency generation spectroscopy (SFG) to measure acid-base interactions at solid-solid interfaces. An understanding of polar interactions is important in the areas of adhesion, friction, and wetting. In-situ characterization of acid-base interactions and their role in adhesion of these coatings at the molecular level and under kinetic conditions (for example: during sliding and mechanical contact) pose a formidable challenge to scientists. The principal investigator (PI), Professor Dhinojwala, proposes to directly probe the acid-base interactions for polymers in contact with inorganic sapphire substrate or sapphire modified with self-assembled monolayers with acidic or basic end groups to understand these interactions at the molecular level. SFG instrumentation is used to directly monitor the shifts in the vibrational peaks of the acidic and basic groups and correlate them with interaction energies to study exchange kinetics at polymer-solid interface as a function of time, temperature, and composition. This proposal explores the kinetics and thermodynamics of surface segregation driven by acid-base interactions. In addition, this proposal focuses on blends and copolymers to study the role of these interaction energies on the segregation of near solid-solid interfaces and dynamics during sliding and peel-off. The study of interaction energies and its experimental results have important implications in understanding friction and adhesion hysteresis. These interaction energies will be compared with adhesion measurements using the Johnson-Kendall- Roberts (JKR) geometry. In addition to these experiments, the PI will also conduct atomistic molecular dynamics simulations (MD) and quantum calculations to understand the magnitude of the frequency shift and its effect on segregation. The SFG, MD, and quantum calculations of these experiments will be used in conjunction to understand the influence of surface concentration, steric constraints, and surface roughness on acid-base interactions and the consequences on adhesion energies. NON-TECHNICAL SUMMARYThe fundamental understanding of acid-base interactions helps in predicting the adhesion of polymers to substrates and in developing the next generation of enhanced coatings and adhesives for applications in multiple areas, including, but not limited to, electronics, bio-mineralization, peptide-based surface recognition, nano-composites and solar cells. This project will support two graduate students who will work together as a group with experts in the areas of surface science, MD simulations, and industrial research. The students working with this broad multidisciplinary group will be provided training to work as a team. Additionally, the graduate students will also have the opportunity to supervise NSF-REU students during the summer. As a volunteer Director of District 5 Science Day, the PI will continue his outreach to host District Science Day at The University of Akron (UA). The PI has also initiated a mentorship program where he brings together scientists from industries and academia to mentor the science projects. This mentorship program was started in the city of Hudson, Ohio, and the PI plans to make this program available to all schools in District 5. In collaboration with UA's business school and Austen Bio-innovation Institute in Akron, the PI is helpping in developing a multidisciplinary Bio-design class offered to UA students in physical sciences, business, and medicine with a goal of observation or experimental based approach to solve problems. This class will be taught in collaboration with professors from UA's business and medicine schools.