Using Capillary Forces to Manipulate Microscopic Objects

Abstract

Capillary interactions act between objects that deform a fluid-fluid interface. In recent decades, such interactions have been used to self-assemble objects at interfaces into complex structures. These assembly processes typically do not allow for direct control over individual particle trajectories. In this work, I describe machines and tweezers that use capillary interactions to manipulate small objects in programmable trajectories along fluid-fluid interfaces. Capillary machines are 3D-printed devices that can be used to manipulate millimeter-scale floating objects. I demonstrate that these machines can be used to braid, twist, and weave fibers that are too small to be manipulated with conventional machines. Capillary tweezers are a new kind of tweezer that can be used to manipulate single colloidal microspheres. I demonstrate that these tweezers can trap and translate a single particle and can be used to measure forces applied to the trapped particle.