Geometric and Size Control of Mechanical Properties in Surfactant Templated Silicas and Periodic Nanoporous Oxides

表面活性剂模板化二氧化硅中机械性能的几何与控制&及其他周期性多孔二氧化硅和维贾伊·古普塔，加州大学洛杉矶分校这项研究涉及许多实验，旨在了解和开发周期性纳米结构二氧化硅/表面活性剂复合材料和多孔无机固体的独特弹性性质。材料合成和自组装的进步使得通过溶液相自组织来生产周期性的、高度规则的无机/有机复合材料成为可能。通过选择性地去除复合材料中的有机部分，可以生成类似有序的多孔性无机氧化物。通过改变有机模板的性质，可以将孔径从大约2 nm调整到20 nm以上，并且可以改变总的周期性。PI最近的实验表明，这些周期性材料的力学性能可能与无序无机/有机复合材料或无序多孔材料截然不同。有序材料似乎既比无序复合材料更坚硬，又更具弹性，表现出非常高的破坏应变。因此，我们的目标是探索这些周期性复合材料和多孔材料的弹性性能，以了解纳米级结构如何影响机械性能。我们正在以两种不同的方式努力实现这一目标。在第一组实验中，我们使用钻石砧座技术在静压条件下压缩复合材料，目的是了解局部变形与纳米级扭曲如何结合来控制体积弹性系数。在第二组实验中，我们正在研究薄膜在拉伸下的机械性能，目的既是测量宏观弹性模量，也是为了了解在初步实验中观察到的高破坏应变。在第一组实验中，我们使用静压条件来压缩复合材料，同时使用散射光谱技术来询问它们，以了解周期性二氧化硅/表面活性剂复合材料中观察到的高模数和良好的可逆性扭曲的基础。我们通过结合低角X射线散射、拉曼散射和压力下的布里渊散射来探测原子和纳米长度尺度上的扭曲。正在检查一系列具有不同周期、壁和孔结构以及维度的样品。我们的目标是系统地改变表面面积、表面结构、长度尺度和连通性，以考察这些变量对局部和更长的长度尺度以及周期结构的变形的影响。这一结果将使我们能够详细了解纳米尺度的体系结构和原子尺度的键合是如何结合起来控制机械性能的。在第二组实验中，我们正在研究连续周期性模板薄膜的拉伸性能，以研究各向异性纳米结构如何产生各向异性机械性能。对周期性二氧化硅/聚合物复合材料的初步结果表明，其应变断裂值显著高于体相二氧化硅的50倍。我们正在探索一系列具有上述纳米尺度结构变化的样品，特别是利用复合膜的整体取向来测量各向异性弹性模数。正在使用断裂和应用力学概念对数据进行建模，以了解几何在控制开裂和应变到断裂中的作用。这项工作的更广泛影响是多方面的。周期性复合材料或多孔材料有可能极大地改善低导热系数、低介电常数或仅是低密度需要与高刚性和高应变相结合的应用。通过开发了解建筑在控制弹性特性中的作用的框架，我们为未来的广泛发展奠定了基础。更直接的是，这里提出的实验是化学家和工程师之间的真正合作，因此，它们为研究生在跨学科科学和技术领域提供了极好的培训。

GEOMETRIC & CONTROL OF MECHANICAL PROPERTIES IN SURFACTANT TEMPLATED SILICAS & OTHER PERIODIC POROUS OXIDESSarah H. Tolbert and Vijay Gupta, UCLA This study involves a number of experiments aimed at understanding and exploiting the unique elastic properties of periodic nanostructured silica/surfactant composite and porous inorganic solids. Advances in material synthesis and self-assembly now allow for the production of periodic, highly regular inorganic/organic composite materials through solution-phase self-organization. Similarly ordered porous inorganic oxides can be generated by selectively removing the organic fraction of the composite. By varying the nature of the organic template, the pore size can be tuned from approximately 2 nm to over 20 nm and the overall periodicity can be varied. Recent experiments by the PI suggest that the mechanical properties of these periodic materials may be quiet different from disordered inorganic/organic composites or disordered porous materials. Ordered materials appear to be both stiffer than disordered composites and more elastic, showing very high failure strain. Our goal is thus to explore the elastic properties of these periodic composite and porous materials to understand how nanoscale architecture influences mechanical properties. We are working on this goal in two different ways. In the first set of experiments, we are compressing composites under hydrostatic conditions using diamond anvil cell techniques with a goal of understanding how local deformation combine with nanoscale distortions to control bulk moduli. In the second set of experiments, we are examining the mechanical properties of thin films under tension, aiming both to measure macroscopic elastic moduli and to understand the high failure strain observed in preliminary experiments. In the first set of experiments, we use hydrostatic, conditions to compress composite materials while interrogating them using spectroscopic of scattering techniques in order to understand the basic for the high modulus and excellent reversibility of distortions observed in periodic silica/surfactant composites. We do this by combining low-angle X-ray scattering, Raman scattering, and Brillouin scattering under pressure to probe distortions on both the atomic and nanometer length scales. A range of samples with varying periodicity, wall and pore structures, and dimensionality are being examined. Our goal is to systematically vary surfaces area, surface structure, length scale, and connectivity to examine the effect of these variables on both local and longer length-scale, and deformations of the periodic structure. The results will allow us to develop a detailed understanding of how nanoscale architecture and atomic scale bonding combine to control mechanical properties. In the second set of experiments, we are examining tensile properties of continuous periodic templated thin films to examine how anisotropic nanoscale architectures can produce anisotropic mechanical properties. Tensile moduli and strain-to-break values are measured; preliminary results on periodic silica/polymer composites indicate remarkable strain-to-break values 50x greater than those observed for bulk silica. We are exploring a range of samples with variations in nanoscale architecture like those described above, particularly exploiting bulk alignment of the composite film to measure anisotropic elastic moduli. Data is being modeled using fracture and applied mechanics concepts to understand the role of geometry in controlling cracking and strain-to-break. The broader impacts of this work are multifold. Periodic composite or porous materials have the potential to dramatically improve applications where low thermal conductivity, low dielectric constant, or simply low density need to be combined with high stiffness and high strain. By developing the framework for understanding the role of architecture in controlling elastic properties, we lay the foundation for a broad range of future advances. More immediately, the experiments proposed here are a true collaboration between chemists and engineers and as such, they provide excellent training for graduate students in the area of in interdisciplinary science and technology.