Dye Probe Studies of Spin Coating of Sol-Gel Solutions

9802334 Birnie Sol-Gel化学是一种流行的技术，可用于制造各种类型的新材料和高科技涂层。由于溶胶-凝胶合成的重要性与日俱增，而且由于需要用高通量的工业工艺来制备高质量的涂层，因此了解使用溶胶-凝胶溶液进行旋涂的基本原理是很重要的。该项目将实时监测和了解旋涂过程中溶胶-凝胶溶液的涂层形成和干燥过程。染料分子将被加入到溶胶-凝胶溶液中，以帮助感知旋涂过程中发生的化学和物理变化。在旋涂过程中，控制涂层形成的两个基本过程通常是关键的：1)粘性流动和2)蒸发。早期阶段以粘性行为为主，即相对平稳的流体在衬底上径向向外流动。当流体层变薄时，向外流动的速度减小，直到第二个过程(蒸发)成为主导过程。这一转变对应于涂层形成的“设定”点。当对溶胶-凝胶溶液进行旋涂时，会出现额外的复杂性，包括溶剂挥发引起的加速化学反应，以及溶液中的水解和缩合反应导致的粘度变化。因此，溶胶-凝胶溶液可能对旋涂工艺强加的条件特别敏感。将进行精心设计的光学测量，这将使我们能够深入研究旋涂过程中溶胶-凝胶溶液中发生的动力学和化学效应。在纺丝过程中，小浓度的染料分子将被加入到溶胶-凝胶溶液中，用作结构/化学探针。主要的焦点将是根据局部环境的特征改变其吸收光谱的分子。因此，将建立设备以允许在旋涂过程中测量吸收特性。此外，激光干涉法将被用来动态监测纺丝过程中发生的快速流体稀化过程。%预计，对这一重要工艺过程的更多了解将导致改进旋涂溶胶-凝胶层质量的新方法，从而使生产的材料具有更高的可靠性和更高的制造产量。例如，由于最易挥发的溶液成分的蒸发将在涂层形成过程中占主导地位，因此溶胶-凝胶科学家将学会特别密切地关注早期和快速去除该成分所造成的化学影响，特别是关于过早凝胶化的影响。反之，由于化学缩合反应会引起深刻的粘度变化，涂料开发商甚至在涂料质量问题出现之前，就会寻求更多地了解他们的溶胶-凝胶溶液的流变特性。***

9802334 Birnie Sol-gel chemistry is a popular technique for making new materials and high technology coatings of a wide variety of types. Because of the ever-expanding importance of sol-gel synthesis, and because of the need to make high quality coatings with a high- throughput industrial procedure, it is important to understand the fundamentals of spin coating when performed using sol-gel solutions. This project will monitor and understand, in real time, the coating formation and drying of sol-gel solutions during spin coating. Dye molecules will be incorporated into the sol-gel solutions to help sense the chemical and physical changes taking place during spin coating. Two fundamental processes are critical in controlling coating formation during spin coating in general: 1) viscous flow and 2) evaporation. Early stages are dominated by the viscous behavior, i.e. relatively smooth fluid flow radially outward on the substrate. As the fluid layer gets thinner the outward flow rate reduces until the second process (evaporation) takes over as the dominant process. This transition corresponds to a "setting" point for coating formation. When spin coating is performed on sol-gel solutions then extra complexities arise including accelerated chemical reaction caused by solvent evaporation and viscosity changes being driven by the hydrolysis and condensation reactions in solution. Thus, sol-gel solutions may be particularly sensitive to the conditions that are imposed by the spin coating process. Carefully designed optical measurements will be carried out which would allow in-depth study of the dynamical and chemical effects that are occurring in sol-gel solutions during spin coating. Small concentrations of dye molecules would be incorporated into the sol-gel solutions for use as structure/chemistry probes during the spinning process. The primary focus will be on molecules that change their absorption spectra depending on the characteristics of the local envir onment. Therefore, equipment would be set up to allow absorption characteristics to be measured during spin coating processing. In addition, laser interferometry would be used to dynamically monitor the rapid fluid thinning process occurring during spinning. %%% It is anticipated that increased understanding of this important technological process would lead to new methods for improving the quality of spin coated sol-gel layers, thus allowing the production of materials with higher reliability and increased manufacturing yield. For example, since the evaporation of the most volatile solution component will dominate during coating formation, then sol-gel scientists would learn to focus particularly close attention to the chemical effects caused by early and rapid removal of this component, especially with respect to premature gelation. And conversely, since the chemical condensation reactions can cause profound viscosity changes, then coating developers would seek to understand more about the rheological characteristics of their sol-gel solutions, even before coating quality issues arise. ***