MRI: Development of a Colloidal Force-Distance-Adsorption Apparatus for Particle Science Research and Education

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

With this award from the Major Research Instrumentation program Virginia Polytechnic Institute and State University will develop a new experimental tool for measuring colloidal forces. An understanding of these forces is important in materials science, cell biology, soil science, waste disposal and water purification, ceramic engineering, the development of personal products, and in quality control in the microelectronics industry. The instrument will combine capabilities of atomic force microscopy (AFM) and total internal reflection microscopy (TIRM), while overcoming most of the drawbacks for each technique. The instrument will provide a new capability: the ability to measure adsorption isotherms during particle collisions. The atomic force microscope is currently the most widely used method for measuring colloidal forces. A major problem with this application is that the separation between the particle and the surface is not measured; it is derived indirectly. With this apparatus, the separation will be obtained directly, from the scattering intensity from an evanescent wave produced by totally reflecting a laser beam at the substrate/fluid interface. This approach is based on the TIRM technique. The TIRM technique will be improved through modulation of the scattered evanescent wave. The adsorption of material to surfaces is the main method by which colloidal forces can be modulated, so it is useful to determine adsorption during particle interactions. We will develop a technique for measuring adsorption during collisions using fluorescent tags on the adsorbates. Graduate and undergraduate students will participate in this instrument development project. Many of the objects that we encounter in everyday life actually consist of very fine particles. For example, bricks, paper, clothing, china, soil, most foods, cosmetics, and even humans are composed of small particles. The physical properties (e.g. stiffness, flow, and workability) of these objects depends on the forces between the particles. Part of the process of creating new and improved products is the manipulation of the forces between particles to obtain desirable material properties. The first stage of manipulating these forces is to measure them. With this award from the Major Research Instrumentation program Virginia Polytechnic Institute and State University will develop a new experimental tool for measuring the forces acting on particles. The new apparatus will combine existing techniques, the force probe from Atomic Force Microscopy and the distance probe from Total Internal Reflectance Microscopy, and incorporate improvements through the use of signal modulation and fluorescent tagging of molecules. A graduate student and undergraduate students will participate in this instrument development project.