Plasmonic Microgel Actuation Induced by Diffractively Excited Modes

Light-driven soft actuators at the microscale have gained significant interest, owing to their flexible and contactless manipulation of small objects. However, a major challenge in this field is the limited number of control parameters for deformation, resulting in relatively simple actuation modes. To achieve complex deformable actuators, it is crucial to increase the number of control parameters. We investigated the deformation of PNIPAM microgels induced by diffractively excited plasmons, chosen for their high controllability. Upon irradiation with 830 nm light, the microgel rapidly shrank by 53% in width, followed by a return to its original state. The photomechanical energy conversion using Au gratings was estimated to be 88 times higher than that of nonplasmonic Au thin films. This enhanced deformation was tunable by controlling not only the polarization angle of the excitation light but also the grating area. The deformation of the grating with an area of 30 μm2 was four times greater than that with an area of 15 μm2, despite the entire irradiated spot being confined within each grating area due to the superposition of the plasmonic waves.