Gradient electric force-induced buckling of colloidal patches at droplet interface equilibrium.

Abstract

Active colloidal assembly has advanced the construction of patchy architectures and stimuli-responsive microsystems-yet structural diversity remains intrinsically limited by field-aligned polarization-that predominantly yield colloidal chains or aligned clusters. Here, we exploit curved liquid interfaces as geometric guidance to overcome orientation constraints via gravity-electric field interplay. The tilted interface amplified subcritical gradient electric forces (∼10^{-4} nN) against gravitational sedimentation and Brownian noise, enabling even low-density colloidal systems (2.5 wt %) to exhibit a buckling effect that generates counterintuitive assemblies. These processes are mechanistically distinct from well-known evaporation-induced buckling. Crucially, dielectrophoretic self-regulation under electric field confers frequency (10 kHz-1 MHz) and strength-independent buckling behaviors, enabling robust programmable architectures during colloidal spatial repositioning. These findings elucidate a principle where competing nonuniform and uniform fields enable expanding accessible configurations in orientation-agnostic assembly. This framework is generalizable to multimodal physical fields (magnetic, optical, and acoustic), providing promise for reconfigurable optical devices and the programmable patchy capsules.