Ordered Mesoporous Materials with Closed Pores

非技术描述：材料化学的一个巨大挑战是在纳米尺度上控制材料的结构和性能。在努力满足这一挑战的焦点之一是在材料的结构中引入定义良好的纳米级空隙（孔）的能力。虽然过去二十年在具有可接近的（开放的）纳米孔的材料的设计方面带来了里程碑，但是在具有封闭的（隔离的）纳米级孔的材料的开发方面的进展是有限的，即使后者材料在电子工业中作为集成电路中的低介电常数片上绝缘介质具有重大意义。目前的项目集中在探索一种预测性的方法来合成闭孔材料，这是基于使用表面活性剂胶束作为模板来生成定义明确的孔阵列。表面活性剂模板化已经彻底改变了纳米多孔材料的合成，但是由于需要从孔中去除表面活性剂模板，因此它似乎天生适合于开孔而不是闭孔结构。最近，胶束模板法产生的闭孔材料的基础上确定的条件下，模板被删除之前的孔关闭。目前的研究工作集中在扩大这种强大的方法在新材料组合物的范围，并实现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，预计将使研究和应用多孔材料的广泛科学家和工程师受益。该项目涉及博士后研究员，研究生和本科生，特别关注少数民族本科生。技术优势：这项工作将探索一种新的和变革性的方法来合成具有封闭（孤立）纳米孔的良好定义的材料，这是基于最近发现的胶束模板介孔材料中的热诱导孔封闭现象。该方法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。正在探索获得具有直径为5 nm或更小的封闭球形孔的二氧化硅和有机二氧化硅的方法，这些方法最适合于作为低k材料的应用。寻求在尽可能低的温度（优选约300°C）下表现出孔闭合的材料。如何实现热致孔封闭与最小程度的收缩将划定。周期性介孔有机二氧化硅，这是固有的更适合于低k应用比二氧化硅，由于其较低的体积介电常数，正在探索作为闭孔材料的候选人。正在开发增加闭孔材料的孔体积从而降低介电常数的方法。具有封闭圆柱形孔的材料的合成途径正在探索中。该研究的重点是粉末形式的样品，由于缺乏方便的设施来表征薄膜，但研究的结论预计将扩展到薄膜形式的材料。该项目将生成用于合成具有定制框架组成、孔径、孔形状和孔体积的闭孔纳米多孔材料的知识库。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。该项目涉及对科学家和学生进行尖端纳米材料合成和表征方面的培训。

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.