Modeling the Formation of Self-Ordered Nanoporous Anodic Oxides

该奖项的研究目标是开发合理设计高度有序的多孔阳极氧化物(PAO)薄膜的新方法。这些薄膜是在电化学电池中通过对铝和钛等金属施加电压来电化学形成的。这些薄膜包含覆盖宏观区域的纳米级孔的自排列六角形阵列。虽然人们的注意力主要集中在将PAO用作功能器件的模板上，但这些结构是在缺乏对控制薄膜生长的过程的充分了解的情况下凭经验开发的。这项研究的目标是开发一个完全预测孔隙形成和自有序化的模型。这项工作将遵循这样的概念，即氧化物材料是通过电场和机械应力的共同影响来运输的。实验应力测量将确定控制PAO薄膜中界面运动的粘性应力、静电应力和氧化诱导应力之间的平衡。利用这些知识，PAO的传输过程和驱动力的描述将被描述为预测的模拟PAO生长，揭示了电化学极化、溶液化学和自有序动力学之间的关系。如果成功，PAO形成的化学-力学模型将为基于模型的自组织多孔阳极膜的设计提供基础。因此，该模型可以合理地控制高速制备无缺陷薄膜的工艺条件，从而增强基于PAO的功能器件在太阳能转换、催化和生物医学应用中的商业潜力。学生培训将受益于该项目的独特方面：化学和力学的紧密结合；各种实验和建模方法的严格结合；以及与英国材料表征小组的现场合作。爱荷华州立大学的学生培训将利用研究生和本科生课程的强大影响力，在系和大学两级促进代表性不足的群体。

The research objective of this award is to develop new methods for the rational design of highly ordered porous anodic oxide (PAO) films. These films are formed electrochemically by applying voltages to metals such as aluminum and titanium, in electrochemical cells. The films contain self-ordered hexagonal arrays of nanoscale pores, covering macroscopic areas. While much attention has focused on the use of PAO as templates for functional devices, these structures have been developed empirically, in the absence of robust understanding of processes controlling film growth. The goal of this research is to develop a fully predictive model of pore formation and self-ordering. The work will be guided by the concept that oxide material is transported by the combined influence of the electric field and mechanical stress. Experimental stress measurements will determine the operative balances of viscous, electrostatic and oxidation-induced stress governing interface motion in PAO films. Using this knowledge, descriptions of transport processes and driving forces will be formulated as a predictive simulation PAO growth, revealing the relations between electrochemical polarization, bath chemistry, and the dynamics of the self-ordering.If successful, the chemical-mechanical model of PAO formation will provide a fundamental basis for model-based design of self-organized porous anodic films. Thus, the model may permit rational manipulation of process conditions for high-rate fabrication of defect-free films, thus enhancing the commercial potential of PAO-based functional devices for solar energy conversion, catalysis, and biomedical applications. Student training will benefit from the unique aspects of this project: close integration of chemistry and mechanics; rigorous combination of a variety of experimental and modeling approaches; and on-site collaboration with a materials characterization group in England. Student training at Iowa State will take advantage of the strong presence of graduate and undergraduate programs promoting underrepresented groups, both at the Department and University levels.