Conductive Architecture Design And Property Research Of Self-sensing Shape Memory Composites

Recently,shape memory polymers(SMPs)and their nano-composites as an important branch of emerging and intelligent electronics quietly promote the development of intelligent society.The researches in the combination of SMPs with conductive nano-materials have become one of the hot topics.Nano-materials enable SMPs responding to external stimuli such as light,electricity,moisture,etc.,and making the self-sensing actuations that could feedback the deformations in real time through resistance signals.In this dissertation,the self-sensing shape memory composites(SMCs)were mainly studied,of which shape memory polyurethanes(SMPUs)were served as flexible substrates and silver nanowires(Ag NWs),carbon nanotubes(CNTs),and graphene were utilized as the conductive nano-fillers.By designing conductive networks,the electric/light-responsive SMCs systems were constructed,of which the conductive structures,shape memory actuations and strain sensing performances were studied.The main researches are shown as following:(1)The aligned Ag NWs conductive network was constructed through interfacial self-assembly and then embedded into flexible SMPU substrate by transfer method to prepare the bi-layer electric-responsive SMCs.The morphologies and thermal properties were characterized by SEM and DSC.Contrast to the disordered Ag NWs composites,the aligned Ag NWs-SMPU composites exhibited the enhanced conductivity and Joule heat and possessed the good electro-thermal repeatability.Moreover,the composites with low nano-filler content(4.35 wt%)achieved the rapidly(25 s)low-voltage-triggered(2 V)actuation.The self-sensing resistance change(R_c)during actuation process was also studied.All the results indicated that through designing conductive networks,the rapidly low-voltage-triggered actuation of self-sensing electric-responsive SMCs could be achieved.(2)The CNTs and graphene were vacuum-deposited on electrospun SMPU nonwovens to prepare the near infrared ray-responsive(NIR)composites with 3D hierarchical structure.The morphologies and structure were characterized and analyzed through SEM,DSC and ATR-FTIR.The composites were provided for good conductivity and micro cracks-based strain sensing,which could be used as strain sensors to monitor human motions.The photo-thermal effects and shape memory actuations were further studied.As exposed to NIR,the R_c of the composite fixed at 50%strain were up to-1530,which indicated the highly sensitive self-sensing.The composites were utilized as self-sensing actuators to simulate actions such as dragging and lifting objects,which could be observed through resistance signals and achieved the integration of actuation and sensing.(3)The CNTs ultrasonically adhered to the electrospun SMPU fibers and then the Ag NWs-CNCs film was vacuum-deposited onto the porous nonwovens to prepare the NIR-responsive composites with the asymmetric conductive structure.Based on the specific structure,the AC-e SC composites possessed high stretchability(100%)and sensitivity(R_c=99576),which greatly solved the contradiction between strain range and sensing sensitivity.The morphologies and structure were characterized by SEM,DSC and Micro-FTIR.The sensing mechanism and asymmetric structure were studied and explained in detail.The double-side properties led to the distinct effects of metal and carbon layers in water contact angle,linear voltammetry and photo-thermal performance.Moreover,due to the asymmetric structure,the shape memory actuation exhibited differentiation,controllability and highly sensitive self-sensing.The asymmetric structure provides a novel research idea for the preparation of highly sensitive and stretchable actuators.