Seminar Abstract:
When granular materials flow, the particles rub against one another and other surfaces and become electrostatically charged. The electrostatic charge can be beneficial (e.g., in digital printing) or detrimental (e.g., disrupting industrial operations). This charging occurs by the same process that leads to the shock you feel when you touch a doorknob after shuffling across a carpeted floor. The culprit, known as triboelectric charging, is also responsible for phenomena as innocuous as a rubbed balloon that makes your hair stand on end, or as dramatic as a lightning strike. While it is familiar to every child, the fundamental understanding of triboelectric charging is so poor that even the most basic questions are still being debated, such as whether the transferred charge species are electrons or ions. Scientific progress is difficult because triboelectric charging is a non-equilibrium process (separated surfaces are neutral at equilibrium) that involves changes in electron states and occurs at a level of one electron per 100,000 surface atoms (physical and/or chemical defects at this low level likely control the behavior). This talk will describe our experimental and theoretical investigations of triboelectric charging, focusing on the charging that occurs in flowing granular materials.