4D printing of electro-activated thermochromic composites for dynamic 3D displays

• 4D printing embeds FeCrAl wires in thermochromic PLA for dynamic color changes via Joule heating. • Achieved ∼78.5s response time for 80% color change with localized, efficient heating. • Optimal parameters: 1.5mm thickness, pulsed current for fast, precise color transformations. • Functional 7-segment display fabricated, showcasing low-power, adaptive thermochromic applications. • Advances thermochromic material use in smart displays, sensors, and anti-counterfeiting technologies. This paper introduces a novel 4D printing approach for dynamic displays, using thermochromic-PLA composites embedded with FeCrAl wires activated by Joule heating. Previous studies struggled with high energy consumption, heat bleed, and slow activation. By embedding continuous resistance wires directly within the thermochromic-plastic matrix, localized, efficient heating is achieved, improving response speed and energy efficiency. The study optimizes color change by focusing on specimen thickness, current intensity, and pulse duration. A customized G-code workflow allowed for precise wire integration into 3D-printed specimens fabricated using a composite dual-nozzle co-extrusion printer, enabling controlled color changes upon activation. Experiments identified 1.5 mm as the ideal specimen thickness, balancing rapid response time (∼78.5 s for 80 % color change) with effective wire concealment. A water medium significantly accelerated recovery time compared to air, emphasizing the benefits of faster heat dissipation. The color change was found to be linearly proportional to pulse-on time and the square of the current. Shorter pulses at higher currents resulted in more efficient and predictable color transformations than constant current inputs. A functional 7-segment display was fabricated, demonstrating the practical application of this technology for smart displays, sensors, and other 4D-printing applications.