Gellation in Nanoparticle/Clay Suspensions: Mechanisms and Applications

CBET-0827246瓦尔兹智能优点建议合作研究圆盘状粘土颗粒和带电纳米颗粒在水溶液中的二元混合物的行为。这项研究的动机是最近在高岭石粘土颗粒和二氧化硅纳米颗粒的混合物中发现的一种独特的溶胶-凝胶转变。凝胶显示出一种非常开放的多孔结构，其中粘土颗粒以边对边的接触方式排列，同时具有显著的屈服应力。此外，凝胶在被剪切破坏后表现出显著的重复和可再生的能力。这些特性表明了各种有益的应用。该项目有两个主要目标。首先，将进行全面的实验研究，以确定驱动凝胶转变的基本机制。将解决的具体问题包括纳米颗粒和血小板之间可能存在的微尺度相分离，纳米颗粒沉积到血小板表面和/或边缘的重要性，以及观察到的粘土颗粒在凝胶中边缘到边缘排列的原因。我们还将探索凝胶的流变性能与微观结构发展之间的关系。使用的主要实验工具包括场发射和环境扫描电子显微镜、原子力显微镜和流变仪。其次，将进行各种实验测试，以测量干燥和烧结后得到的凝胶和二氧化硅/粘土复合材料的流变性、力学和材料特性。对这些特性的了解对于最终开发这些独特材料的应用至关重要。对于凝胶，将探讨它们对剪切和正应力的反应，包括它们在破裂后重复改革的能力。干燥和烧结这些凝胶将产生二氧化硅/高岭石复合材料，具有非常开放的多孔结构，由相对惰性的材料制成。除了研究实际的干燥和烧结过程外，还将进行测量以确定复合材料的微观结构、压缩强度、表面积和热性能。拟议工作的完成将提供对胶凝机理的透彻了解，以及对凝胶和由此产生的二氧化硅/粘土复合材料的关键微观结构和机械/功能特性的知识。这一知识对于理解其他二元胶体体系的行为也是有价值的。拟议工作的更广泛影响该项目将是一项合作努力，涉及来自化学工程系、材料科学和工程系的一名高级教员和一名初级教员。每一位PI在他们要执行的特定任务方面都有专业知识。所建议的材料具有广泛的潜在应用，包括催化剂载体、过滤器、膜和隔热材料。虽然这项工作将主要集中在二氧化硅/高岭石体系上，但结果将适用于任何显示出类似类型的凝胶转变或结构的体系。该项目将为两名研究生提供培训，并将积极推动本科生的参与。此外，PI还积极参与增加女性和少数族裔在工程学领域的入学人数，特别是在纳米技术等“前沿”领域。一个例子是我们与C-Tech2的合作，这是一个专注于科学和工程的项目，每年夏天将30到40名高中女生和少数族裔学生带到弗吉尼亚理工大学校园，为期两周。向到访的学生提供有关纳米技术对社会的重要性的示范和信息。拟议项目的结果将为这一重要方案提供大量额外资源。

CBET-0827246WalzIntellectual Merit A collaborative effort is proposed to investigate the behavior of binary mixtures of disk-shaped clay particles and charged nanoparticles in aqueous solutions. The study is motivated by a unique sol-to-gel transition that was recently discovered by one of the PI's in mixtures of kaolinite clay particles and silica nanoparticles. The gels display a very open, porous structure in which the clay particles are arranged in edge-to-edge contact, while at the same time possessing significant yield stress. In addition, the gels show a remarkable ability to rejuvenate repeatedly and reproducibly after breakage by shear. These properties suggest a variety of beneficial applications. The project has two primary objectives. First, a comprehensive experimental investigation will be performed to determine the fundamental mechanism driving the gel transition. Specific issues that will be addressed include possible micro-scale phase separation between the nanoparticles and platelets, importance of deposition of the nanoparticles onto the faces and/or edges of the platelets, and the cause of the observed edge-to-edge arrangement of the clay particles in the gel. We will also explore the relationship between the measured rheological properties of the gel and the development of the microstructure. Major experimental tools to be used include field emission and environmental scanning electron microscopy, atomic force microscopy, and rheometry. Second, a variety of experimental tests will be conducted to measure the rheological, mechanical, and material properties of both the gels and the silica/clay composites obtained after drying and sintering. Knowledge of these properties is critical for the eventual development of applications for these unique materials. For the gels, their response to shear and normal stress, including their ability to repeatedly reform after breakage, will be probed. Drying and sintering these gels will produce silica/kaolinite composites with a very open, porous structure made of relatively inert materials. In addition to studying the actual drying and sintering process, measurements will be performed to determine the composite's microstructure, compression strength, surface area, and thermal properties. Completion of the proposed work will provide a thorough understanding of the gellation mechanism, as well as knowledge of the key microstructural and mechanical/functional properties of both the gel and the resulting silica/clay composite. This knowledge will also be valuable in understanding the behavior of other binary colloidal systems. Broader Impacts of Proposed Work The project will be a collaborative effort involving one senior and one junior faculty from the Departments of Chemical Engineering, and Materials Science and Engineering. Each of the PI's has expertise in their specific tasks to be performed. There are a wide range of potential applications for the proposed materials, including catalyst supports, filters, membranes, and heat insulating materials. While the work will focus primarily on the silica/kaolinite system, the results would be applicable to any system displaying a similar type of gel transition or structure. The project will provide training to two graduate students, and undergraduate participation will be actively pursued. In addition, the PI's are heavily involved in increasing the enrollment of females and minorities in engineering, especially in "forefront" areas like nanotechnology. One example is our work with C-Tech2, a program focused on science and engineering that brings 30 to 40 high school female and minority students to the Virginia Tech campus for a two-week period each summer. The visiting students are provided with demonstrations and information on the importance of nanotechnology to society. The results of the proposed project will provide significant additional resources for this important program.