Actuators made of soft matter are needed for a variety of fields ranging from biomedical devices to soft robotics to microelectromechanical systems. While there are a variety of excellent methods of soft actuation known, the field is still an area of intense research activity as new niches and needs emerge with new technology development. Here, a soft actuation system is described, based on a core-multi-shell particle, which moves via photothermal expansion. The system consists of a novel polystyrene-based thermally expandable microsphere, with a secondary shell of a silicate-silane graft copolymer, to which gold nanoparticles are covalently linked. The gold nanoparticles act as photothermal nano-transducers, converting light energy into the thermal energy necessary for microsphere expansion, which in turn results in material movement. Actuation is shown in isolated particles in thermal and photothermal regimes using metal ceramic heaters or 520 nm laser illumination, respectively. Macroscale actuation is demonstrated by making a composite material of particles suspended in the transparent elastomer polydimethylsiloxane. The sample demonstrates an inchworm-like movement by starting from an arched geometry. Overall, this work describes a new particle-based actuation method for soft materials, and demonstrates its utility in driving the movement of a composite elastomer.

Thermally expandable microspheres (TEMs) are liquid‐core, polymer‐shelled particles that are useful in both current industry and future manufacturing and basic research applications. Here, we systematically optimize TEMs for highest expansion ratio using a broad‐spectrum infrared head source. Microspheres are synthesized from a copolymer of 2‐hydroxyethyl methacrylate (HEMA), methyl methacrylate, and acrylonitrile as the shell, which is optimized for greatest expansion ratio. This represents the first time that HEMA is used in TEMs. The liquid blowing agent core is next optimized, followed by the prepolymerization emulsion time. It is found that particle morphology is greatly variable and influenced by kinetic and thermodynamic factors, with various phase‐separated and aniosotropic morphologies accessed.

Front Cover: In article number 2100222 by Rachel C. Steinhardt and co‐workers, a soft actuation system is described, based on a new core‐shell thermally‐expandable microparticle, made of isobutane core and polystyrene shell, linked to a photothermal nano‐transducer, gold nanoparticles, resulting in a core‐shell‐shell nanohybrid. The particles expand in photothermal and thermal milieus, and are able to power the movement of a composite elastomeric soft robot sample.