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Dynamics of exchange within vitrimer networks are influenced by mobility of the chemical species involved in the exchange reaction, then it can be affected by the crystalline phase when boronic ester bond is introduced into the thermoplastic elastomers with crystalline phase as physical cross-links. In this work, the dynamic dioxaborolane cross-links were introduced into commercial poly(ethylene-α-octene) (POE) with crystalline phases as physical cross-links to prepare POE vitrimers. The results of stress relaxation show that relaxation time (τ) follows an Arrhenius law with the temperature at the melting range for not only POE vitrimers and thermally treated POE vitrimers with dynamic cross-links, but also neat POE with purely physical cross-links. The liquid-to-solid transition temperature can raise to 35.3 °C for POE vitrimers from -42.9 °C of the thermally treated one, due to the constrained mobility by residual crystalline phases. The resulted POE vitrimers maintain a stress at break of higher than 27.5 MPa and an elongation at break of higher than 800% at room temperature. With the temperature increasing, the crystal melting induced weakening of the physical cross-linking in POE decreases the strength, but the storage modulus and the stress at 300% and 500% elongation of POE vitrimers are improved. The properties of POE vitrimers can almost keep unchanged after recycling or healing. All these results show that the introduction of reversible boronic ester bonds is a promising strategy to improve the performances and recyclability of physically cross-linked POE materials. [ABSTRACT FROM AUTHOR]

A flexible strain sensor is developed via one-step in-situ construction of stiff PVDF nanospheres on the surface of TPU fibers via polymeric phase and morphology control technology. It enables tunable linear sensing to strain thanks to the restricting of quick crack propagation. [Display omitted] • Flexible fiber mat strain sensors of heterogeneous structures are developed. • The heterogeneous structure is consisted of stiff PVDF nanospheres on TPU fibers. • The structure can restrict quick micro-crack propagation throughout fiber surface. • The sensor with high-density nanospheres shows very good linearity. Wearable strain sensors with high sensitivity and linear resistance signal response to strain are urgently demanded for human–machine interface, which can be tuned by introducing uneven surface mechanics distribution onto fiber surfaces via structural heterogeneity for fibrous elastomer fiber mat sensors. Yet it is still of great challenge to build micro- or nano-scale heterogeneous structures on fiber surfaces in a facile and scalable way without using templates. Herein, we report a plastic nanosphere-decorated elastomer fiber mat strain sensor with a zoned surface strain energy release characteristic, designed based on analysis of material match and structural mechanics. Surface mechanics analysis confirms that the as-designed sensor shows a controllable strain energy release area, significantly improving sensing stability thanks to effective restriction of micro-crack propagation in conductive pathways. In particular, fibrous mat sensor with high-density nanospheres shows very low fluctuation in strain sensitivity variation (±0.05 for strain ≤ 30 %), i.e., good linearity in the resistance response to strain, while that for the control sensor is ± 10.0 for strain ≤ 16 %. Such a fiber mat strain sensor can not only be applied for real-time sensing of object deformations for human–machine interface and intelligent control, but also in hydrophobic porous elastomeric packaging materials and triboelectric devices. [ABSTRACT FROM AUTHOR]

Liquid metal (LM) based stretchable conductors have broad application due to their excellent conductivity and deformability. However, the poor interfacial interaction between LM and majority of elastic substrates because of the high surface tension of LM, limits the spread of LM on the substrate and the reconciliatory deformation of LM with underlying substrate. Herein, through the specific affinity between the immediately formed oxide layer on surface of eutectic gallium-indium (EGaIn) and carboxyl groups, an in-situ interfacial engineering for LM conductive coating on hydrogen-bonded poly(ethylene oxide)/poly(acrylic acid) (PEO/PAA) elastomers is presented. Particularly, EGaIn patterned on PEO/PAA elastomers can autonomously adapt to the mechanical deformation of substrates to form a stable interface conductive layer, and the slope of deformation ratio between EGaIn layer and PEO/PAA elastomers keeps nearly 1 even at strain of 800%. The design of interfacial interaction also ensures the simultaneous achievement of excellent stretchability and stable conductivity of LM based stretchable electronics, that is, the resistance of the EGaIn conductor will not change significantly and remain below 1 Ω even at a strain of 800%. This work provides guideline for the design of stretchable LM-based conductor. [Display omitted] • An in-situ interfacial engineering for LM on hydrogen-bonded PEO/PAA elastomers is presented. • Strong interaction occurs between oxide layer on surface of EGaIn and carboxyl groups. • The slope of deformation ratio between LM layer and PEO/PAA elastomers keeps nearly 1 even at strain of 800%. • The resistance of the LM-based conductor can remain below 1 Ω even at a strain of 800%. [ABSTRACT FROM AUTHOR]