A light-driven soft actuator based on liquid-gas phase transition composites integrated with optical force sensors

We present a light-driven soft actuator based on a liquid–gas phase transition composite integrated with an optical fiber force sensor. The actuator is composed of low-boiling-point organic solvents and iron oxide particles embedded within a soft elastomer matrix. To enable real-time force and position monitoring, an optical fiber sensor is embedded inside the actuator for precise manipulation. Inspired by the geometry of blooming flowers, the actuator features a tri-chambered design fabricated from elastomer. An inextensible paper layer is attached to the underside of the actuator to constrain its elongation during operation. Laser irradiation is employed as the thermal stimulus to trigger the phase transition. As the temperature reaches the boiling point of the organic solvent, evaporation occurs, generating gas that induces deformation in the actuator. The inclusion of iron oxide particles significantly enhances the photothermal response, resulting in an actuation speed 1.2 times faster than actuators without these particles. The integrated optical fiber sensor offers direct measurement of the actuator’s bending angle, with a sensitivity of 0.366 nm/°. A strong linear correlation is observed between spectral shift and bending angle, achieving a linearity of 97.719%. By calibrating the relationship between bending angle and output force, the system enables accurate real-time force estimation through spectral wavelength monitoring. This advancement in actuation speed and integrated sensing marks a significant step forward for phase-transition-based soft actuators, expanding their potential in precise and responsive soft robotics applications.