The synergistic effect of nano-Al2O3 size and concentration on the interfacial adhesion properties of SMA/PDMS composites and their enhancement mechanism

Soft actuators composed of shape memory alloy (SMA) wires embedded in polydimethylsiloxane (PDMS) matrix hold potential for shape-morphing structures and soft robots. However, SMA exhibits poor bonding with PDMS due to its smooth and nonpolar surfaces. Nanoparticles show promise in interfacial strengthening of polymer composites. In this work, KH590 was used to modify nano-Al₂O₃ particles and deposited on the SMA surface, creating a three-dimensional nanostructure bridging SMA and PDMS to enhance interface strength. The synergistic effects of particle size and content of nano-Al₂O₃ particles on the interface strength were investigated in detail. It founds that interfacial strength decreased exponentially with particle size at content of 1 wt%, while when the content exceeds 1 wt%, the interface strength firstly increases with the particle size and then decreases in a logarithmic trend. Specifically, the interface strength is enhanced by 110 % with 3 wt% 50 nm particles. The interface enhancement mechanism was also discussed. The proposed nanoparticle modification approach was to strengthen SMA/PDMS interphase by increasing and extending fracture path, consuming more fracture energy. Chemical cross-linking also contributed to interface enhancement. This work enhances understanding of interfacial bonding mechanisms and provides valuable guide for interfacial strengthening of SMA/PDMS.