Electro-thermal responses polymer systems with continuous shape memory alloys: Merging rapid shape memory and color transitions

Abstract

Multi-responsive shape memory materials with on-demand programmability via external stimuli are highly desirable for many modern technologies-based applications, but have yet to be mixed with color-changing materials through a 3D-printing approach. To address this challenge, we engineered a blend of polylactic acid (PLA) and polyurethane (TPU), incorporated with thermochromic microcapsules (TMC), and fused these components through melt extrusion to create a 3D-printable, ternary filament. When combined with a shape memory alloy (SMA) wire using continuous fiber-reinforced 3D printing techniques, it gives rise to a PLA/TPU/TMC@SMA composite with exceptional conductivity, intelligent 3D structural adaptability, and superior mechanical characteristics, i.e., 3.29 % elongation at break and a 19.05 MPa tensile strength. Notably, our printed composite strip exhibits outstanding reversibility in electrochromic chromaticity parameters, swiftly recovering to its initial state after electrochromic heating and rapid cooling cycles, thus providing real-time reversible electrochromic responses. Furthermore, our composite strip displays rapid and simultaneous shape and color transformations upon exposure to predefined temperature thresholds, highlighting its dynamic functionality. Incorporating a highly efficient conductive network of continuous SMA wires enables swift electric and thermal shape memory responses, making our PLA/TPU/TMC@SMA composite an ideal candidate for high-performance electro-thermal actuators across diverse applications.