Interaction of Water with Polymer Surfaces: Consequence on Wetting, Adhesion, and Friction

非技术概要：水与聚合物表面的相互作用在不同的技术领域具有重要的意义。其影响是深远的：从能量收集设备、生物医学植入物、耐腐蚀涂层，延伸到任何受水环境润湿性影响的表面创新。该项目的目标是了解聚合物表面在与水接触后如何在分子水平上自我重组。聚合物被广泛用作粘合剂和润滑剂，了解这些材料如何与水相互作用是非常重要的。这种理解将通过先进的专业表面和光谱技术获得，其中一些是在PI实验室开发的。计划中的研究开发的基本理解将有助于设计更好的材料，这些材料可以适应或抵抗与水接触时的变化。PI将在表面科学领域培养两名研究生，这是开发或制造粘合剂或涂料行业的关键要求。除了这些直接整合的教育方面，PI还将参与面向初高中学生和社区大学的更广泛的外展活动。技术总结：人们普遍认为，当我们使水与表面接触时，极性基团可以在接触界面迁移或重新定向，从而降低界面能。这种表面重排导致接触角迟滞。例如，当两个固体表面接触时，这种界面重排导致附着滞后和更高的摩擦。但对这些结构重排的直接观察是难以捉摸的。表面敏感和频率产生光谱（SFG）已被用于研究与水接触时的表面重排，固体-固体接触和滑动接触期间的变化。然而，与水接触的表面重排的动力学尚不清楚，特别是动力学效应如何与聚合物的Tg甚至表面Tg相关。PI将进行SFG实验，研究聚（烷基甲基丙烯酸酯）和聚（α -羟甲基取代丙烯酸酯）在表面与水、湿度和蒸汽接触后，表面重排的动力学与时间和温度的关系。这将允许PI将这些表面变化与水下接触角迟滞和附着迟滞联系起来，并研究干湿摩擦系数之间的差异。最近，PI和他的合作者已经证明，分子动力学（MD）模拟能够重现聚甲基丙烯酸甲酯表面的SFG光谱。在这里，PI将用聚合物-水界面的MD模拟来补充SFG实验。拟议的研究将在分子水平上协同努力，以了解水与聚合物表面的相互作用。

NON-TECHNICAL SUMMARY:The interaction of water with polymer surfaces has significant implications in diverse technological areas. The impacts are far-reaching: from energy-harvesting devices, biomedical implants, corrosion-resistant coatings, and extending to any innovation with surfaces that is influenced by wettability in aqueous environments. The goal of this project is to understand how polymer surfaces restructure themselves on a molecular level after coming in contact with water. Polymers are widely used as adhesives and lubricants and the knowledge of how these materials interact with water is of great importance. This understanding will be obtained using advanced specialized surface and spectroscopic techniques, some developed in the PI's laboratory. The fundamental understanding developed by the planned research will help in designing better materials that either adapt or resist changes upon contact with water. The PI will be training two graduate students in the area of surface science, which is a key requirement of industries developing or manufacturing adhesives or coatings. In addition to these directly integrated educational aspects, the PI will also be involved in broader outreach activities to middle and high school students as well as to community colleges. TECHNICAL SUMMARY:It is well accepted that when we bring water in contact with surfaces, polar groups can migrate or reorient at the contact interface and reduce the interfacial energy. This surface rearrangement results in contact angle hysteresis. For example, when two solid surfaces come in contact, this interfacial rearrangement leads to adhesion hysteresis and higher friction. But the direct observations of these structural rearrangements are elusive. Surface-sensitive sum frequency generation spectroscopy (SFG) has been used to study surface rearrangements upon contact with water, changes during solid-solid contact, and during sliding contact. However, the kinetics of the surface rearrangements in contact with water are not well understood, particularly how dynamical effects are related to the Tg of the polymer or even surface Tg. The PI will conduct SFG experiments to study the kinetics of surface rearrangements for poly(alkyl methacrylates) and poly(alpha-hydroxymethyl substituted acrylate) as a function of time and temperature after bringing the surfaces in contact with water, humidity, and steam. This will allow the PI to relate these surface changes with contact-angle hysteresis and adhesion hysteresis underwater, and to study the differences between wet and dry friction coefficients. Recently, the PI and his collaborators have shown that molecular dynamics (MD) simulations are able to reproduce the SFG spectra of the poly(methyl methacrylate) surface. Here, the PI will complement the SFG experiments with MD simulations for polymer-water interfaces. The proposed research will be a concerted effort at the molecular-level to understand the interaction of water with polymer surfaces.