Ordered Mesoporous Materials with Closed Pores

非技术描述：在纳米尺度上控制材料的结构和性能是材料化学的一大挑战。在应对这一挑战的努力中，焦点之一是在材料结构中引入定义良好的纳米级空隙（孔隙）的能力。虽然在过去的二十年中，具有可访问（开放）纳米孔的材料的设计取得了里程碑式的进展，但具有封闭（隔离）纳米孔的材料的开发进展有限，尽管后者作为集成电路中的低介电常数片上绝缘介质在电子工业中具有重要意义。目前的项目重点是探索一种预测合成闭孔材料的方法，该方法基于使用表面活性剂胶束作为模板来生成定义良好的孔阵列。表面活性剂模板已经彻底改变了纳米多孔材料的合成，但由于需要从孔中去除表面活性剂模板，它似乎天生就适合开孔而不是闭孔结构。近年来，基于确定在孔隙闭合之前模板被移除的条件，开发了胶束模板制备闭孔材料的方法。目前的研究重点是将这种强大的方法扩展到新材料成分的范围，并获得更有益的闭孔材料的结构特性。因此，该项目将为开发具有设计结构和性能的闭孔材料提供知识基础，并有望使广泛的研究和应用多孔材料的科学家和工程师受益。该项目涉及博士后、研究生和本科生，特别关注少数民族本科生。技术细节：这项工作将探索一种新的和转型的方法来合成具有封闭（孤立）纳米孔的明确定义的材料，这是基于最近在胶束模板介孔材料中发现的热诱导孔闭合现象。该工艺有望成为合成闭孔纳米多孔二氧化硅的预测途径，并有望应用于有机二氧化硅。人们正在探索获得最适合作为低钾材料应用的直径为5nm或更小的闭孔球形二氧化硅和有机二氧化硅的方法。寻求在尽可能低的温度下（最好在300°C左右）表现出孔隙关闭的材料。在最小化收缩的情况下实现热致闭孔的方法将被描述。周期性介孔有机硅，由于其较低的体积介电常数，本质上比二氧化硅更适合低k应用，正在被探索作为闭孔材料的候选材料。目前正在开发增加闭孔材料孔隙体积从而降低介电常数的方法。人们正在探索具有封闭圆柱形孔的材料的合成途径。由于缺乏易于获得的表征薄膜的设施，该研究的重点是粉末形式的样品，但该研究的结论有望扩展到薄膜形式的材料。该项目将为合成具有定制框架组成、孔径大小、孔型和孔容的闭孔纳米多孔材料提供知识库。这一努力有助于通过探索低介电常数材料的新途径来克服电子器件处理速度的限制。该项目包括在尖端纳米材料的合成和表征方面对科学家和学生进行培训。

NON-TECHNICAL DESCRIPTION: A grand challenge in materials chemistry is to control the structure and properties of materials at nanoscale. One of the focal points in the effort to meet this challenge is the ability to introduce well-defined nanoscale voids (pores) in the structure of materials. While the last two decades brought milestones in the design of materials with accessible (open) nanopores, advances in the development of materials with closed (isolated) nanoscale pores were limited, even though the latter materials are of significant interest in electronics industry as low-dielectric-constant on-chip insulating media in integrated circuits. The current project is focused on exploring a predictive way to synthesize closed-pore materials, which is based on the use of surfactant micelles as templates to generate well-defined pore arrays. The surfactant templating has revolutionized the synthesis of nanoporous materials, but because of the need to remove the surfactant template from the pores, it seemed to be inherently suitable for open-pore rather than closed-pore architectures. Recently, the micelle-templating approach to generate closed-pore materials was developed which was based on identifying conditions at which the template is removed before the pores close. The current research effort is focused on extending the scope of this powerful approach on new material compositions and on achieving more beneficial structural properties of the closed-pore materials. Thus, the project will provide a knowledge base for the development of closed-pore materials with designed structures and properties and is expected to benefit a broad range of scientists and engineers that study and apply porous materials. The project involves postdoctoral fellows, graduate students and undergraduate students, with a special focus on minority undergraduate students.TECHNICAL DETAILS: This work will explore a new and transformational approach to the synthesis of well-defined materials with closed (isolated) nanopores, which is based on recently discovered thermally-induced pore closure phenomenon in micelle-templated mesoporous materials. This process promises to be a predictive pathway for the synthesis of closed-pore nanoporous silicas and is expected to be applicable for organosilicas. Ways to obtain silicas and organosilicas with closed spherical pores of diameter 5 nm or lower, which are most appropriate in applications as low-k materials, are being explored. Materials that exhibit the pore closure at as low temperatures as possible (preferably around 300°C) are sought. Ways to achieve the thermally-induced pore closure with minimized extent of shrinkage will be delineated. Periodic mesoporous organosilicas, which are inherently more suitable than silicas for low-k applications due to their lower bulk dielectric constant, are being explored as closed-pore materials candidates. Ways to increase the pore volume of closed-pore materials, thus reducing the dielectric constant, are being developed. Synthetic pathways to materials with closed cylindrical pores are being explored. The study focuses on samples in powder form due to the lack of readily accessible facilities to characterize thin films, but conclusions of the study are expected to extend to materials in the thin-film form. The project will generate the knowledge base for the synthesis of closed-pore nanoporous materials with tailor-made framework composition, pore size, pore shape and pore volume. This effort contributes to the current quest to overcome limitations in the processing speed of electronic devices by exploring a new avenue to the low dielectric constant materials. The project involves the training of scientists and students in the synthesis and characterization of cutting-edge nanoscale materials.