Viscous Fluid Dynamics and Characterization of Nano-Structured Polymers

过去几年的理论工作表明，二维粘性流体的动力学是一种比迄今认为的和理论上描述的更丰富的现象。根据流体力学和扩散时间尺度的不同，相变粗化的标度不变性可以被打破，形成锯齿状的磁区。在初步实验中，对理论模拟中考虑的各种粘性区域进行了实验观察。将与理论进行详细的定量比较，并将通过实验确定从高度不相容到弱不相容的流体对的粘性流体(如聚合物熔体)的相分离。主要的模型体系是聚甲基丙烯酸甲酯/聚苯乙烯(PS)、PS/溴化PS和PS/聚甲基乙烯基醚。预计数据是在本模拟的适用性之外获得的，最明显的是具有不对称组成和体积分数以及不对称粘度的流体。二元粘性液体的一个有趣的扩展将是对其中一个相中含有小颗粒或珠子的体系的研究。最近的理论表明，硬粒子的加入显著改变了相分离的动力学和形态。为了产生真正的二维流体，将开发一种特殊的样品制备方法，将聚合物薄膜夹在Si3N4膜之间。对于所使用的聚合物，将对表面进行处理，使其处于中性或接近中性。在此过程中，将实现对聚合物薄膜粘度变化等约束效应的控制。近边X射线吸收精细结构(NEXAFS)显微镜将是一个重要的表征工具，与其他显微镜(AMF、VLM、SEM)相辅相成。-将改进对NEXAFS光谱的理论理解。将提高成分定量的准确性。学生将接受培训，执行位于物理、化学、材料和聚合物科学交界处的跨学科研究项目。将促进对聚合物薄膜的基本了解，这可能会改善半导体工业中的涂层、粘合剂、润滑剂、油墨和各种薄膜应用。这项努力的一部分是继续与陶氏化学的长期合作。

Theoretical work over the last years has shown that the dynamics of two-dimensional viscous fluids is a richer phenomenon than hitherto believed and described theoretically. Depending on the hydrodynamic and diffusive time scales, the scaling invariance of phase coarsening can break down and jagged domains can form. In preliminary experiments, the various viscosity regimes considered in the theoretical simulations have been experimentally observed. A detailed quantitative comparison to theory will be made and the phase separation of viscous fluids, such as polymer melts, will be experimentally determined for fluid pairs ranging from highly immiscible to weakly incompatible. The primary model systems will be poly(methylmethacrylate)/polystyrene (PS), PS/brominated PS, and PS/poly(vinyl methyl ether) above their glass transition temperature. It is expected that data is acquired outside the applicability of the present simulations, most notably fluids with asymmetric composition and volume fractions as well as asymmetric viscosities. An interesting extension to binary viscous liquids will be the investigation of systems that contain small particles or beads in one of the phases. Recent theory shows that the addition of hard particles significantly changes both the kinetics and the morphology of the phase separation. In order to generate truly two-dimensional fluids, a special sample preparation method that will sandwich the polymer films between Si3N4 membranes will be developed. The surfaces will be treated to make them neutral or near neutral for the polymers utilized. In the process, control over confinement effects such as changes of viscosity in thin polymer films will be achieved. Near Edge X-ray Absorption Fine Structure (NEXAFS) microscopy will be an important characterization tool, complemented by other microscopies (AMF, VLM, SEM). - Improvements in the theoretical understanding of NEXAFS spectra will be pursued. The accuracy of compositional quantitation will be improved.Students will be trained in executing interdisciplinary research projects situated at the interface of Physics, Chemistry, Materials and Polymer Science. Fundamental understanding of polymer thin films will be advanced, which might improve applications such as coating, adhesives, lubricants, inks and a variety of thin films applications in the semiconductor industry. Part of the effort continues a longstanding collaboration with Dow Chemical.