Motility of Inanimate Particles
“Motility” is a concept generally associated with living organisms, but there are mechanisms by which non-living particles can undergo directed motion driven by external stimuli. Here I discuss movement of particles suspended in fluids having gradients of chemical composition or voltage. These motions are controlled by dynamics at the surface of the particles in response to these gradients and are referred to “diffusiophoresis” or “electrophoresis”, respectively. If the particles are freely suspended in the fluid, they move in alignment with the gradients; however, if the particles are held fixed, the surrounding fluid moves, phenomena known as “diffusioosmosis” and “electroosmosis”. These transport mechanisms can move particles and fluids in a directed manner at micrometer to millimeter length scales, thereby creating a mechanism to target the location of small particles. I will discuss the basic concepts of diffusiophoresis and electroosmosis and highlight examples of their usefulness.
Bio: John L. Anderson was president of the National Academy of Engineering during 2019-2025. Before that position, his career spanned 48 years in academia. He has served as president of the Illinois Institute of Technology, provost and executive vice president at Case Western Reserve University, and dean of engineering at Carnegie Mellon University His first faculty appointment was in the Department of Chemical Engineering at Cornell University. He was elected to the National Academy of Engineering in 1992 for his contributions to the understanding of colloidal hydrodynamics and membrane transport phenomena. He is a fellow of the American Academy of Arts and Sciences and the American Association for the Advancement of Science, and he received the Professional Progress Award from the American Institute of Chemical Engineers. Anderson was a presidential appointment to the National Science Board for the period 2014-2020. He was elected to Academia Sinica (Taiwan) as an Honorary Academician in 2024. He received a bachelor’s degree from the University of Delaware and a Ph.D. degree from the University of Illinois at Urbana-Champaign, both in chemical engineering.