Gellation in Nanoparticle/Clay Suspensions: Mechanisms and Applications

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

CBET-0827246 Walz Intellectual 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.