Session: 01-04 Multifunctional Composites/Nanocomposites

Paper Number: 165532

165532 - Self-Folding Shape Memory Polymers Activated by Multiple Stimuli Using Conductive Carbon-Based Inks 

Shape memory polymers (SMPs) are smart materials capable of being programmed into a temporary shape and recovering their original form when exposed to a specific stimulus, such as heat, light, or magnetic fields. Their low cost and versatility make them promising candidates for applications in aerospace, soft actuators, and healthcare. The SMP can be deformed at a temperature higher than the glass transition temperature (T_g) and under an external force. When the SMP is cooled down below T_g and the external force is removed, the temporary pre-deformed shape will remain intact until the temperature of the polymer is increased back to T_g. At this point, the SMP returns to the initial from and the folding occurs.

Although the thermal actuation of SMPs have been extensively explored, previous studies have largely focused on single-stimulus activation, with limited research investigating multi-stimuli responses that could enhance shape recovery efficiency and functionality. Additionally, existing studies often rely on expensive materials like gold and silver for localized heating, limiting scalability.

This study explores the self-folding behavior of polystyrene (PS)-based shape memory polymers activated by multiple stimuli, utilizing cost-effective materials and scalable fabrication techniques. Conductive black hinge regions, composed of a polyvinyl alcohol (PVA) and carbon black, are patterned onto the PS-based SMP substrate to facilitate localized heating. The electrical resistance of the conductive ink is adjusted by varying the number of applied layers, allowing for controlled heat generation.

Two distinct activation methods were explored: Joule heating and infrared (IR) light exposure. In the first approach, an electric current was applied to the conductive ink patterns, generating localized heat through electrical resistance and initiating the self-folding process. In the second method, IR light was used to heat the black carbon-rich hinge regions, triggering shape recovery without direct electrical input. The ink patterns acting as hinges transfer heat locally to the SMP substrate and above the Tg, the substrate underneath the hinges shrinks back to the initial form, leading to a self-folding behavior towards a desired shape and application. The folding angles and rates, and overall efficiency of each method were analyzed and compared.

Experimental results demonstrated successful self-folding in both Joule-heated and IR-activated samples, with variations in actuation precision and efficiency. The ability to achieve shape transformation through multiple stimuli enhances the adaptability of SMP-based structures for use in reconfigurable devices, deployable systems, and autonomous soft robotics.

Future studies will focus on optimizing ink formulations and expanding the range of external stimuli to further enhance control and functionality in SMP-based systems.

Presenting Author: Leily Majidi California Polytechnic State University

Presenting Author Biography: Leily Majidi received her PhD in Mechanical Engineering from University of Illinois Chicago in 2021. She is currently an Assistant Professor at Mechanical Engineering department of California Polytechnic State University.