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

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.