Neighbors Matter: Leveraging Collective Thermoplasmonic Effects for Smart Soft Actuators

In this work, we are exploring the collective thermoplasmonic properties of small spherical gold nanoparticles embedded into poly­(N-isopropylacrylamide) (pNIPAM) films, with a focus on their application as efficient light-driven nanoheaters for smart soft actuation systems. Uniform Au-pNIPAM hybrid films with adjustable thickness in the micrometer range (1–22 μm) and distinct concentrations of gold nanoparticles were fabricated by using a photopolymerizable pNIPAM-based resin containing Au-pNIPAM core–shell microgels as building blocks (15 nm diameter gold cores). Upon 520 nm light excitation, the Au-pNIPAM films exhibit a significant temperature increase of up to 75 °C above room temperature at a light irradiance of 116 mW/mm², as determined by thermal imaging. These results compare well with those obtained with an analytical model describing the rise in temperature produced by neighboring particles in a three-dimensional (3D) matrix under continuous illumination, with a relative margin of error of less than 7% for nearly all cases studied. Finally, light-guided swimming robots were fabricated by leveraging the collective photothermal properties of gold nanoparticles in the Au-pNIPAM films. Under light exposure, the trajectory and rotation of swimming robots floating at the air/water interface can be precisely controlled due to the light-induced Marangoni effect, with average speeds of up to 2.5 mm/s for triangular-shaped robots.