Gellation in Nanoparticle/Clay Suspensions: Mechanisms and Applications

CBET-0827246Walz智力价值 提出了一项合作研究，以研究圆盘状粘土颗粒和带电纳米颗粒的二元混合物在水溶液中的行为。这项研究的动机是由一位 PI 最近在高岭石粘土颗粒和二氧化硅纳米粒子的混合物中发现的独特的溶胶到凝胶转变。该凝胶呈现出非常开放的多孔结构，其中粘土颗粒以边对边接触的方式排列，同时具有显着的屈服应力。此外，凝胶在剪切断裂后表现出显着的反复且可重复恢复活力的能力。这些特性表明了多种有益的应用。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。将要解决的具体问题包括纳米颗粒和片晶之间可能存在的微观相分离、纳米颗粒沉积到片晶的面和/或边缘上的重要性，以及所观察到的凝胶中粘土颗粒边缘到边缘排列的原因。我们还将探讨测量的凝胶流变特性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测定法。其次，将进行各种实验测试来测量干燥和烧结后获得的凝胶和二氧化硅/粘土复合材料的流变学、机械和材料性能。了解这些特性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常应力的响应，包括它们在断裂后反复重新形成的能力。干燥和烧结这些凝胶将产生由相对惰性的材料制成的具有非常开放的多孔结构的二氧化硅/高岭石复合材料。除了研究实际的干燥和烧结过程之外，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。完成所提出的工作将提供对凝胶化机制的透彻理解，以及对凝胶和所得二氧化硅/粘土复合材料的关键微观结构和机械/功能特性的了解。这些知识对于理解其他二元胶体系统的行为也很有价值。拟议工作的更广泛影响 该项目将是化学工程系、材料科学与工程系的一名高级教师和一名初级教师的共同努力。每个 PI 都拥有其要执行的特定任务的专业知识。所提出的材料有广泛的潜在应用，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/高岭土系统上，但结果将适用于任何显示类似类型的凝胶转变或结构的系统。该项目将培养两名研究生，并将积极争取本科生的参与。此外，PI 积极参与增加工程领域女性和少数族裔的入学率，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，每年夏天都会有 30 到 40 名高中女生和少数族裔学生到弗吉尼亚理工大学校园学习两周。为来访的学生提供有关纳米技术对社会重要性的演示和信息。拟议项目的结果将为这一重要计划提供大量额外资源。

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.