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

以表面活性剂为模板的二氧化硅及其他周期性多孔氧化物中力学性能的几何控制。Tolbert和Vijay Gupta，加州大学洛杉矶分校该研究涉及许多实验，旨在了解和利用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能。材料合成和自组装的进步现在允许通过溶液相自组织生产周期性的、高度规则的无机/有机复合材料。通过选择性地除去复合材料的有机部分，可以产生类似有序的多孔无机氧化物。通过改变有机模板的性质，可以将孔径从约2nm调整到超过20 nm，并且可以改变总体周期性。PI最近的实验表明，这些周期性材料的机械性能可能与无序无机/有机复合材料或无序多孔材料完全不同。有序材料似乎比无序复合材料更硬，更有弹性，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，我们使用金刚石压砧单元技术在流体静力学条件下压缩复合材料，目的是了解局部变形如何与纳米级扭曲联合收割机结合以控制体积模量。在第二组实验中，我们正在研究薄膜在张力下的机械性能，目的是测量宏观弹性模量，并了解在初步实验中观察到的高失效应变。在第一组实验中，我们使用流体静力学条件来压缩复合材料，同时使用散射光谱技术来询问它们，以了解在周期性二氧化硅/表面活性剂复合材料中观察到的高模量和优异的扭曲可逆性的基本原理。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尺度上的畸变。正在检查一系列具有不同周期性、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积，表面结构，长度尺度和连通性，以研究这些变量对局部和较长长度尺度的影响，以及周期性结构的变形。这些结果将使我们对纳米结构和原子尺度键合如何结合联合收割机来控制机械性能有一个详细的了解。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级结构如何产生各向异性的机械性能。拉伸模量和应变断裂值进行测量;周期性二氧化硅/聚合物复合材料的初步结果表明显着的应变断裂值50倍以上的散装二氧化硅所观察到的。我们正在探索一系列具有上述纳米级结构变化的样品，特别是利用复合膜的整体排列来测量各向异性弹性模量。正在使用断裂和应用力学概念对数据进行建模，以了解几何形状在控制开裂和断裂应变中的作用。这项工作的广泛影响是多方面的。周期性复合材料或多孔材料具有显著改善应用的潜力，其中低导热性、低介电常数或简单地低密度需要与高刚度和高应变相结合。通过开发框架来理解结构在控制弹性性能中的作用，我们为未来的广泛进展奠定了基础。 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，它们为跨学科科学和技术领域的研究生提供了良好的培训。

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.