Collaborative Research: Characterization of Functionally-Graded Sol-Gel-Derived Silica Films on Multiple Length Scales, from Single Molecules to Macroscopic Properties

摘要先进技术新材料的开发通常需要大量不同样品的合成和逐一测试，以找到最适合预期应用的样品。替代这一繁琐过程的另一种方法是生产一种包含化学梯度的材料，其中成分沿单个样品逐渐变化。因此，开发和确定最佳新材料的速度大大提高。这些化学梯度的快速通量筛选应用在开发用于生产药品、塑料、润滑剂和燃料的更好的催化剂以及为生物组织的附着和生长量身定制具有粘附特性的表面制造方面发现了可能的用途。化学梯度在从复杂的化学混合物中分离特定成分以及在小型化学装置和传感器中指导液体、化学前体和细胞的输送方面也有直接的用途。对于所有这些应用，所采用的梯度必须具有明确的化学和物理性质。理想情况下，它们将表现出从宏观尺度到分子水平的逐渐单调的组成和性质变化。在现实中，这种田园诗般的性格很少存在。意想不到的性质变化可能来自于制备过程中梯度组分的自发分离，产生的材料表现出逐步而不是渐进的性质变化，并限制了通常理想的合作相互作用的参与。这些特性使得梯度材料比单一组分材料或由相同前驱体制备的均匀非梯度薄膜更加复杂和有价值。这项活动强调探索有机硅烷梯度的化学和物理复杂性，这些梯度是由主要研究者小组最近开发的新型湿化学方法制备的。这些结果将导致具有更好理解和更好控制特性的梯度的发展，可以更有效地在先进材料中实施。合作小组之间的协同作用将导致在最先进的材料合成和先进的化学成像方法表征方面加强对各种本科生和研究生的培训。这些学生将受到两位研究人员的积极指导，并将参加两个校区之间的夏季交流计划和每周网络会议，以拓宽他们的教育、科学和职业视野。技术摘要：在材料研究部固态和材料化学项目的支持下，主要研究人员将(1)研究溶胶-凝胶法制备的多组分有机硅烷梯度中相分离和协同作用的程度，(2)评估所得结构域的大小和组成。要研究的材料将包括来自不同有机烷氧基硅烷前体的多组分极性、酸度、电荷和掺杂梯度。从长远来看，纳米到微米尺度的相分离和协同相互作用对这些梯度的宏观性质的影响将被探索。通过x射线光电子能谱、傅里叶变换红外能谱和拉曼作图，在多个长度尺度（微米到毫米）上对梯度成分进行表征。所有这三种方法都将产生关于梯度组成变化的距离尺度的定量数据，并将允许充分了解任何协同效应的化学起源。单分子超定位显微镜将用于探测纳米尺度上的梯度，并阐明梯度组分之间以及探针分子与薄膜组分之间的合作相互作用。通过对薄膜的局部介电常数进行独特的单分子水平测量，可以获得材料极性的定量数据。在所有情况下，梯度的结果将与均匀非梯度样本的结果进行比较。

Non-Technical AbstractThe development of new materials for advanced technologies usually requires that a large number of different samples be synthesized and tested one by one to find those best suited for the intended application. An alternative to this often-tedious process is to produce a material incorporating a chemical gradient in which the composition gradually varies along a single sample. The speed at which optimum new materials are developed and identified is thus greatly enhanced. These rapid-throughput-screening applications of chemical gradients find possible utility in the development of better catalysts for production of pharmaceuticals, plastics, lubricants and fuels and in the fabrication of surfaces with adhesion properties tailored for the attachment and growth of biological tissues. Chemical gradients also find direct utility in the separation of specific components from complex chemical mixtures and in guiding the delivery of liquids, chemical precursors and cells in miniaturized chemical devices and sensors. For all such applications, the gradients to be employed must have well defined chemical and physical properties. Ideally, they would exhibit gradual, monotonic compositional and properties variations extending from the macroscale down to molecule levels. In reality, such idyllic character seldom exists. Unexpected properties variations may arise from the spontaneous separation of the gradient components during preparation, producing materials that exhibit stepwise rather than gradual properties variations, and limit the participation of often-desirable cooperative interactions. These attributes make gradient materials uniquely more complex and valuable than either single component materials or uniform nongradient films prepared from identical precursors. This activity emphasizes exploration of the chemical and physical complexity of organosilane gradients prepared by novel wet-chemical methods recently developed by the principal investigator's groups. The outcomes will lead to development of gradients having better understood and better controlled properties that can be more effectively implemented in advanced materials. The synergy between the collaborating groups will lead to the enhanced training of a diverse body of undergraduate and graduate students in state-of-the-art materials synthesis and their characterization by advanced chemical imaging methods. These students will be actively mentored by both investigators and will participate in a summer exchange program between the two campuses and weekly web conferences to broaden their educational, scientific and career horizons. Technical AbstractWith the support from the Solid State and Materials Chemistry Program in the Division of Material Research, the principal investigators will (1) investigate the extent to which phase separation and synergistic interactions occur along multicomponent organosilane gradients prepared by the sol-gel process and (2) evaluate the sizes and compositions of the resulting domains. Materials to be investigated will include multicomponent polarity, acidity, charge and dopant gradients derived from different organoalkoxysilane precursors. Over the long term, the impacts of nanometer-to-micrometer scale phase separation and cooperative interactions on the macroscopic properties of these gradients will be explored. Gradient composition will be characterized on multiple length scales (micrometer-to-millimeter) by x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and Raman mapping. All three will yield quantitative data on the distance scales over which gradient composition varies and will allow for the chemical origins of any cooperative effects to be fully understood. Single molecule superlocalization microscopy will be used to probe the gradients on nanometer length scales and to elucidate cooperative interactions between the gradient components themselves as well as between a probe molecule and the film components. Quantitative data on materials polarity will be obtained through implementation of unique single molecule level measurements of the local dielectric constant of the films. In all cases, results from the gradients will be compared to those from uniform nongradient samples.