Vortex flows impart chirality-specific lift forces

Around the turn of the 21st century, reports of macroscopic vortex flows discriminating between and forming chiral molecular assemblies sparked considerable scientific interest indeed, the prospect of simple rotary evaporation inducing chiral selection could have profound implications for separations technologies and, above all, could shed new light on the origins of biological homochirality. Subsequently, however, these early results were put into question and attributed to either instrumental artifacts or even poor experimental control. After a decade of controversy, the question remains unresolved how do vortex flows interact with different stereoisomers? Here, we implement a model experimental system to show that chiral objects placed in a vortex flow can indeed experience a chirality specific lift-force. Remarkably, this force is parallel to the shear plane which is in contrast to previous studies in which helices, bacteria, and chiral cubes in shear flows were reported to experience forces perpendicular to the shear plane. In addition to experiments with macroscopic particles, we present a quantitative, hydrodynamic model that explains the origins of the chiral lift force and how it depends on particle size, shape, position, and flow velocity. The scaling laws derived here suggest that rotating flows can provide physical means of chiral separations at the micro- and nanoscales