Light‐Actuated, Tunable Micromachines from Photo‐Swellable Colloidal Ionogels

Abstract

Active colloids that release ions hold potential for building micromachines capable of dynamically responding to environmental stimuli. Harnessing light to precisely regulate and fine‐tune their performance is essential for unlocking their versatility and expanding their range of applications. To address this challenge, light‐actuated, tunable micromachines are developed based on photo‐swellable colloidal ionogels—an azobenzene‐modified co‐polymer microsphere infused with azobenzene‐based ionic liquids (Azo‐ILs)—that undergo reversible cis‐trans isomerization under UV/visible light. UV irradiation increases the colloidal ionogel's hydrophilicity and causes it to swell by H2O, releasing Azo‐ILs into aqueous environments with a rapid photoresponse (milliseconds), while visible light irradiation stops the swelling. The dissociated ions lead to diffusiophoresis and diffusioosmosis, enabling two functionalities: isotropic ion release from the ionogel pumps water outward with exclusion zones up to 30 µm, while anisotropic release from partially coated ionogel microspheres leads to micromotors at speeds of ≈3 µm s−1 and a lifetime of ≈15 min. Importantly, the magnitude and range of these interactions are precisely modulated by light intensity and azobenzene content in co‐polymers. Finite element and Brownian dynamics simulations validate the electrokinetic mechanisms underlying the pump and motor's operation. This work establishes a platform for designing micromachines potentially useful in fluid manipulation, drug delivery, and soft robotics.