Direct measurements of the colloidal Debye force

Abstract

The Debye interaction is defined as the attraction between a polar molecule and a nonpolar molecule, which governs many self-assembling processes in materials. Here, Lee et al. design a like-charged colloidal model at the water-oil interface to characterize the Debye interaction for the first time. Colloids often behave in a manner similar to their counterparts in molecular space and are used as model systems to understand molecular behavior. Here, we study like-charged colloidal attractions between a permanent dipole on an interfacial particle and its induced dipole on a water-immersed particle caused by diffuse layer polarization. We find that the scaling behavior of the measured dipole-induced dipole (D-I) interaction via optical laser tweezers is in good agreement with that predicted from the molecular Debye interaction. The dipole character propagates to form aggregate chains. Using coarse-grained molecular dynamic simulations, we identify the separate roles of the D-I attraction and the van der Waals attraction on aggregate formation. The D-I attraction should be universal in a broad range of soft matter, such as colloids, polymers, clays, and biological materials, motivating researchers to further conduct in-depth research on these materials.