CNTs' Effect on the Light-Responsivity of Soft Robotic Two-Way Bilayer Polymer Actuators Having Two Morphing...

This work investigates the influence of carbon nanotubes (CNTs) incorporation into poly(polyhedral oligomeric silsesquioxane) (polyPOSS) nanocomposites, serving as the active layer in two-way shape memory polymer Kapton/polyPOSS bilayer actuators. Four types of actuators, containing up to 0.5 wt % CNTs, were studied for their light-responsivity. While CNTs had only a modest effect on mechanical properties, their impact on optical absorption was pronounced, producing a linear increase with concentration. Consequently, CNTs-containing actuators reached temperatures nearly 3-fold higher than CNTs-free counterparts, enabling up to 3-fold larger and faster motions during irradiation heating and beam obscuration cooling. Consecutive heating-cooling cycles revealed a secondary shape-change mechanism, previously unreported for this material system, arising from the coefficient of moisture expansion (CME) mismatch between the polyPOSS and Kapton layers. This CME-based mechanism operates independently of CNTs presence and competes with the primary coefficient of thermal expansion (CTE)-based mechanism. During initial heating, desorption of yet-absorbed moisture from the polyPOSS drives contraction, while thermal expansion promotes elongation, with dominance shifting from CTE- to CME- and back to CTE-based responses across the heating range. These findings highlight the dual nature of shape-change mechanisms in polyPOSS-based actuators and emphasize the critical role of ambient moisture conditions, while demonstrating CNTs as effective enhancers of light-driven actuation performance.