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

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.