Triboelectric charging is the process by which electrostatic charge develops after two surfaces come into contact. Examples of electrostatic charging are seen routinely in everyday life. For example, walking across a carpet and touching metal surface produces a small electrostatic discharge. Granular materials, which are collections of small particles, are especially susceptible to electrostatic charging. The particles are usually small, which means they have a high surface area to volume ratio, allowing large charge to accumulate in small volumes. Industrial processes often involve flowing granular materials, which promotes collisions among the particles leading to accumulation of charge. The accumulation of charge can disrupt the granular flow, can lead to deposition of material on container walls, and can create an important safety hazard. Despite the importance of charging in many systems, the mechanism of charging is still not well understood. Simple questions, such as whether charging reflects the transfer of ions or electrons, are still not resolved. This project will use a combination of theory and experiment to help uncover fundamentals of triboelectric charging. The project will involve students in the research, especially students from underrepresented groups. The research team will use project results in its course "Engineering Design Seminar" for local high-school students.
The goal of the project is to address the most important questions underlying triboelectric charging that remain unanswered - what are the species being transferred on contact (electrons, ions, material), what is the role of the nature of contact (e.g., rubbing or geometry of contact), and how can the direction of triboelectric charging be related to the material properties. The project comprises three major activities: measurements of particle charging in an integrated particle charging and characterization system, experiments on triboelectric charging between specific crystallographic faces of single crystals of quartz and sapphire, and experiments on the effects of materials strain on triboelectric charging. Measurements will be used to test predictions of a theory based on non-equilibrium dynamics of a charged species during many collisions, especially predictions of the theory for effects of particle size and environmental humidity on particle charging.
