Hydrogels are investigated broadly in flexible sensors which have been applied into wearable electronics. However, further application of hydrogels is restricted by the ambiguity of the sensing mechanisms, and the multi-functionalization of flexible sensing systems based on hydrogels in terms of cost, difficulty in integration, and device fabrication remains a challenge, obstructing the specific application scenarios. Herein, cost-effective, structure-specialized and scenario-applicable 3D printing of direct ink writing (DIW) technology fabricated two-dimensional (2D) transition metal carbides (MXenes) bonded hydrogel sensor with excellent strain and temperature sensing performance is developed. Gauge factor (GF) of 5.7 (0 − 191% strain) and high temperature sensitivity (−5.27% °C−1) within wide working range (0 − 80 °C) can be achieved. In particular, the corresponding mechanisms are clarified based on finite element analysis and the first use of in situ temperature-dependent Raman technology for hydrogels, and the printed sensor can realize precise temperature indication of shape memory solar array hinge.

Shape memory poly(ε‐caprolactone) (PCL) networks with different molecular weights of PCL diol were prepared via thiol–ene reaction in this work. The highly efficient thiol–ene reaction ensured a uniform distribution of PCL chains between crosslinker, contributing well‐defined network architecture with good mechanical and shape memory properties. 1H NMR spectra were used to confirm that PCL diol was completely converted into acrylate‐terminated PCL. Gel content experiment and Fourier‐transform infrared showed that almost all samples exhibited virtually the complete crosslinking network due to the highly selective thiol–ene reaction between acrylate‐terminated PCL and tetrathiol crosslinker. Differential scanning calorimetry and X‐ray diffraction tests revealed that the melting temperature and crystallinity of the prepared PCL networks by using high molecular weight of PCL diol displayed a higher result compared to ones using low molecular weight. The dynamic mechanical analyzer results revealed that the storage modulus of the network dropped evidently across the thermal transition, these characteristics of the PCL network indicated that all exhibited a good shape memory effect. The shape fixing ability was kind of being affected by the PCL diol molecular weight, while the shape recovery ratio of all samples can almost reach 99% irrespective of the length of PCL diol. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47055.

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The research for self-healing epoxy vitrimers has attracted a lot of attention over the years. However, due to the special structure of the epoxy molecular chain, which limits its movement ability, epoxy vitrimers usually need to be healed under high temperature and pressure. So it is relatively difficult to healing. Here, a new type of cross-linked network is obtained by cross-linking hydrogenated bisphenol A epoxy resin and polypropylene glycol diglycidyl ether (PPGDGE) as hard and soft segments with an amine curing agent containing disulfide bonds. The addition of PPGDGE can improve the mobility of the molecular chains in the cross-linked network we designed, thereby obtaining a novel epoxy vitrimers with better healing properties. The effect of PPGDGE content on the mechanical properties and self-healing properties of the material was studied. The ideal sample HEP-3 has a good tensile strength (33.4 MPa) and a completely broken sample can achieve a good self-healing rate (71.5%) at 100 C for 3 h without high pressure. In addition, the ideal sample also has excellent shape memory properties (shape memory fixity ratio R f = 97.1%, shape recovery ratio R r = 94.9%). Moreover, due to the existence of the dynamic disulfide bond introduced by the curing agent 2-aminophenyl disulfide, compared with traditional thermosetting epoxy resins, epoxy vitrimers prepared by us can be reshaped or postprocessed like thermoplastic polymers under specific conditions. These characteristics will become the guarantee for expanding the application range of epoxy materials.

The resin matrix and CF fibers itself of CF/PEEK composites exhibit surface inertness, resulting in poor interface bonding between CF and PEEK matrix. This phenomenon seriously affects the mechanical properties of CF/PEEK composites especially the interlaminar shear strength (ILSS). In order to improve the interfacial properties of CF/PEEK composites, a novel sizing agent of CF fibers namely PPS‐NH2 was synthesized, and its influence on the fibers–matrix interface interaction and properties of CF/PEEK composites was investigated by using scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, atomic force microscopy. The results showed that the interface of CF/PEEK composite was improved by coating PPS‐NH2 sizing agent on the surface of CF. When the amination degree of PPS‐NH2 reaches 31.25%, the ILSS, flexural strength and modulus of CF/PEEK Composites reach 73.9 MPa (119%), 671.4 MPa (63%) and 32.8GPa (51%) and, respectively. At the same time, the main failure mechanism of CF/PEEK composites changes from fibers–matrix debonding into interface layer deformation and resin fracture. This method can effectively improve the interface defects between CF/PEEK composites.