4D printing of shape memory polymer nanocomposites for enhanced performances and tunable response behavior

The emergence of four-dimensional (4D) printing introduces a novel approach to the design and manufacturing of high-performance multifunctional shape memory polymers (SMPs). Herein, two types of nanomaterials were blended or embedded into SMPs matrix to enable 4D printing of shape memory polymer composites (SMPCs) via photocuring. The incorporation of hexagonal boron nitride (HBN) nanoparticles enhanced the thermal stability and mechanical properties of SMPs, and accelerated their thermally responsive shape recovery speed. HBN nanoparticles also significantly improved the performance stability of SMPs, even after undergoing multiple shape memory cycles. Electrically responsive shape memory behavior in SMPCs was achieved by embedding a spray-coated polyaniline: polystyrene sulfonate /graphene (PANI: PSS/GR) electrothermal layer (ETL). The applied voltage, ETL resistance, HBN blend content, and sample thickness had a significant regulation effect on electrically responsive shape recovery behavior and shape recovery force. PANI: PSS improved adhesion between ETL and SMPCs matrix, filled the gaps between graphene platelets, which resulted in rapid, uniform, and stable heating upon energization. The presented electrically responsive gripper was capable of grasping objects of various shapes and sizes. This strategy broadens the potential applications of 4D printed SMPCs in challenging environments while propelling the advancement of 4D printing.