Fabrication, Nanomechanical Properties, and Surface Functionality of Polymer Nanocomposites

纳米制造的进展在很大程度上取决于对如何控制材料构件的基本理解。近年来，由于生物技术和微电子学的迅速兴起，聚合物引起了人们的极大关注。然而，对聚合物表面性质的基本知识，往往比整体性质对组分功能的影响更深远，以及对纳米级潜在变形机制的深入了解非常稀少。这项研究的中心主题是通过对旋转铸造制造的微米厚的聚合物样品进行纳米机械测试和表面化学分析来弥合这一差距。选择进行研究的模型聚合物是聚氨酯弹性体，由两种玻璃化转变温度相对较低和较高的不溶单体组成，分别称为软段和硬段。主要目的是考察在固定伸长率下，聚合物组成、接触载荷、伸长应变和时间等方面的表面纳米机械性能和粘着(摩擦)特性。用原子力显微镜和表面力显微镜研究预应变纳米复合材料试件的表面织构和材料性能，用和频产生振动光谱分析不同应变水平和恒定伸长时间下的表面化学行为。从这项研究中获得的信息将有助于对聚合物纳米复合材料的化学机械行为进行工程设计，并直接影响到具有定制性能的纳米器件的制造，以及具有亲水或疏水化学行为的多阵列/生物植入物的制造，具体取决于表面组成和施加的应变。此外，该项目将为两名研究生提供机会，使他们有机会参与涉及聚合物力学性能评估和亚微米级化学分析的跨学科研究，使用特定于表面的最先进的微孔和光谱技术。这种表面敏感仪器的结合是这一提议的优势之一。这项研究的结果将被纳入PI每年教授的一门研究生课程的内容中，该课程目前只涉及本体聚合物的行为。这一举措还将促进与参与聚合物生物材料研究和开发的行业开展合作，从而扩大所获得的关于加强聚合物纳米复合材料表面机械性能和化学特性演变的基本知识的应用范围。

Advances in nanomanufacturing greatly depend on basic understanding of how to control building blocks of materials. Polymers have attracted significant attention in recent years, largely due to the rapid emergence of biotechnology and microelectronics. However, basic knowledge of the surface properties of polymers, often affecting component functionality more profoundly than bulk properties, and in-depth understanding of underlying deformation mechanisms at the nanoscale is very sparse. The central theme of this research is to bridge this gap by performing nanomechanical testing and surface chemical analysis on micrometer-thick polymer specimens manufactured by spin casting. The model polymers selected for study are polyurethane elastomers, comprising two insoluble monomers of relatively low and high glass transition temperatures, referred to as soft and hard segments, respectively. The principal objective is to examine the surface nanomechanical properties and adhesion (friction) characteristics in terms of polymer composition, contact load, elongation strain, and time under fixed elongation. The surface texture and material properties of pre-strained nanocomposite specimens will by studied by atomic force and surface force microscopy, while the surface chemical behavior at different strain levels and time under constant elongation will be analyzed by sum frequency generation vibrational spectroscopy. The information derived from this research will enhable enginnering of chemomechanical behavior of polymer nanocomposites, with direct implications to the manufacturing of nanodevices exhibiting tailor-made properties and multi-arrays/bio-implants possessing either hydrophilic or hydrophobic chemical behaviors, depending on the surface composition and applied strain. In addition, this project will provide the opportunity to two graduate students to become invovled with interdisciplinary research dealing with polymer mechanical property evaluation and chemical analysis at submicron scales using surface-specific state-of-the-art microsocpy and spectroscopy techniques. Such combination of surface-sensitive instrumentation is one of the strengths of this proposal. Results from this research will be incroporated in the content of a graduate course taught annualy by the PI, which currently addreses only bulk polymer behavior. This initiative will also enable the development of collaborations with industry involved with polymer biomaterials research and development, thereby increasing the application range of the obtained basic knowledge regarding the evolution of surface mechanical properties and chemical characteristics of strecthed polymer nanocomposites.