Surface charge heterogeneity directed particle migration and assembly

Detecting and delivering colloidal particles to a spot with surface charge heterogeneity is important in many applications, such as coating quality control, surface modification, and cargo delivery. Since the location of the spot with surface charge heterogeneity is not known, it is challenging to map variations in the surface charge density in a large area simultaneously in an inexpensive way. Here we demonstrate a system to automatically assemble particles in areas with surface charge heterogeneity thus detecting and delivering particles to the target location at the same time. We utilize colloidal particles that self-emit solutes that interact with the non-uniformly charged surface to drive them diffusiophoretically. The physical mechanism for the particle motion is unveiled and a theoretical framework is laid out to predict the particle migration behavior with different types of surface charge density patterns. We have demonstrated experimentally that initially uniformly distributed colloidal particles on surfaces assemble and form patterns that conform to the surface charge density pattern. This unique system opens new avenues to sense the surface heterogeneity and harness it for targeted cargo delivery.