MIT Scientists Throw an Electric Curveball

In many sports, throwing or hitting a ball with spin causes the rotating ball to travel in a curved path. This “Magnus effect” is well-known for macroscopic objects like baseballs but is not typically associated with microscopic objects like nanoparticles, proteins, and cells

In our recent paper, we show that charged and rotating nano- and colloidal-scale particles experience an analogous “electrokinetic Magnus (EKM) effect” and follow curved paths as they move through an electric field. Unlike throwing a curveball, getting nanoscopic objects to rotate can be quite challenging. However, when dispersed in electrolytes like salty water, we show that nanoparticles spontaneous rotate in electric fields due to an instability called “Quincke rotation”. Using detailed computer simulations and theoretical calculations, we develop accurate predictions that will allow us to leverage the EKM effect to tune the properties of electrolyte suspensions on the fly (for example, to improve the performance of batteries). The EKM effect can also be used to generate self-propulsion for “active” suspensions, where particles mimic living organisms by “swimming” through solution. These EKM swimmers can enhance mixing at the microscale and shuttle cargo for separations or drug-delivery applications.