Dequan Chi,Haoyu Gu,Jingfeng Wang,Chao Wu,Ruijie Wang,Zhongjun Cheng,Dongjie Zhang,Zhimin Xie,Yuyan Liu
Complex and controlled reversible actuation inevitably relies on changing thermal fields (direct or indirect) for semi-crystalline reversible shape memory networks. Unfortunately, the non-tunability of thermal signals often brings potential limitations to actuators’ applications. In practice, a wide response temperature range (T-range) formed by Thigh and Tlow in the remarkable reversible actuation is an obvious fact. Herein, we demonstrate the tunability of the transition temperatures while stably maintaining excellent actuation abilities. We further verified that the narrow T-range (24 °C) that had not been reported could present more than 17% reversible strain. Special parameter optimization provides opportunities for potential non-implantable biomedical applications. Therefore, based on target 2W-SMP, a vehicle concept with the drug release and vehicle recovery ability was proposed, proving our approach's feasibility.
Semi-crystalline shape memory polymers exhibit two-way shape memory effect (2W-SME) under constant stresses through crystallization-induced elongation upon cooling and melting-induced constriction upon heating. The applied constant stress influenced the prediction and usability of 2W-SME in practical applications without any external force. Here the reversible shape transition in EVA-shaped memory polymer was quantitative analyzed under a suitable temperature range and external stress-free condition. The fraction of reversible strain increased with increasing upper temperature (Thigh) within the temperature range and reached the maximum value of 13.62% at 70 °C. However, reversible strain transition was almost lost when Thigh exceeded 80 °C because of complete melting of crystalline scaffold, known as the latent recrystallization template. The non-isothermal annealing of EVA 2W-SMP under changing circulating temperatures was confirmed. Moreover, the orientation of crystallization was retained at high temperatures. These findings may contribute to design an appropriate shape memory protocol based on application-specific requirements.
Xiaoming Qi,Wenjun Wang,Hongbo Dai,Yaofeng Zhu,Yubing Dong,Shao-Yun Fu,Qingqing Ni,Yaqin Fu
Shape memory polymer fibers (SMPFs) coated with conductive layers are attracting increasing attention in soft robots and wearable electronics. However, the thickness and poor stretchability of the conductive layer hinder its applications. Here, the multifunctional two-way shape memory reduced graphene oxide (RGO)/ethylene–vinyl acetate copolymer (EVA) composite yarn is designed following the “swelling-ultrasonicating” and one-step twisting procedures. These RGO/EVA composite fiber conductive paths connected with each other by constructing the helical conductive network. The RGO/EVA composite yarn presents excellent electro-thermal conversion performance and outstanding load-bearing capability, enabling controlled electro-driven reversible strain (more than 10% reversible strain) and high energy density (72.5 J/kg). Additionally, the composite yarn has great stretchability (130% strain), high strain sensing sensitivity (gauge factor of 7.3), large linear working range (up to 70% strain). This work provides an innovative manufacturing strategy for the RGO/EVA composite yarn with two-way shape memory, electro-driven actuation, and strain sensing performance.
危险品化学品经营许可证（带存储）