Preparation And Properties Of Shape Memory Polymer Composites Based On Liquid Metal

Shape memory polymer(SMP)is an important smart material.SMP can recover its original(permanent)shape when subjected to environmental stimulus(temperature,electric field,light,magnetic field,or p H).Based on this unique characteristic,SMP has been widely used in various fields,including flexible electronics,soft robotics,biomedicine and aerospace.Direct heating is the tranditional method to activate SMP,which was restriced by low heating efficiency and uncontrollable heat.Electrical driven SMPs have received extensive attention due to their unique electrical deformation behavior.Besides,electrical driven SMPs can be actuated through Joule heating,which achieved the requirement of remote control.Some electrical-driven SMPs currently developed are usually polymer composites based on solid metals or carbon(such as carbon black and carbon nanotubes).These SMPs suffer from low flexibility,poor deformability and require high-voltage to drive.How to improve the conductivity of SMPs and develop SMPs that can be activated under low voltages without affecting the shape memory performance still has great challenges.In this study,liquid metal(LM)was introduced into the typical shape memory polymer,polycaprolactone(PCL).The electrical driven SMP based on LM was obtained through solvent casting method.The mechanical properties,electrical properties and shape memory behavior of LM-SMP were investigated,the main results were included as follows:LM and PCL had good compatibility and the resulted LM-SMP exhibited high flexibility.The effect of LM content on the mechanical properties of LM-SMP composites was studied.The mechanical properties of LM-SMP composite were decreased after LM was incorporated.However,the mechanical properties of LM-SMP were better compared with traditional CNTs-SMP.The electrical properties of LM-SMP with different LM content were studied.LM-SMP exhibited a strain-related conductivity.The resistance of LM-SMP decreased uopon stretching.Interestingly,when the volume fraction of LM was 30%,LM-SMP showed a unique transition from insulator to conductor after been stretched.The effect of LM content on the melting and crystallization properties of LM-SMP was studied.The crystallinity of LM-SMP was about 64% which proved that the introduction of LM had little effect on the melting and crystallization properties of the polymer matrix.LM-SMP composite had excellent shape memory behavior,the shape fixation rate was 95% and the shape recovery rate was99%.The electrical driven shape memory performance of the LM-SMP was studied.The pre-stretched LM-SMP-50% could recover the original shape within 18 s under the applied voltage of 2 V.In addition,we fabricated a reversible actuation based on bilayer LM-SMP films.The bending deformation and shape recovery could complete within 130 s at 2 V,which showed the potential applications in soft robots and advanced electronics.