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An isotactic polypropylene (iPP) nanocomposite with low percolation threshold, ultrahigh dielectric permittivity and toughness by controlling the dispersion of multi-walled carbon nanotubes (MWCNTs) through ethylene-α-octene block copolymer (OBC), is reported. A special ‘sosatie’ structure, i.e. finely dispersed long MWCNTs inserted in OBC phase uniformly distributed in the continuous iPP matrix, was constructed through simple melt compounding process. The percolation threshold of the prepared iPP/OBC/MWCNT nanocomposites was ca. 0.5 vol%, lower than that of iPP/MWCNT nanocomposites. The iPP/OBC/MWCNT nanocomposites exhibited an ultrahigh dielectric permittivity (ca. 9000) at 100 Hz and a very low dielectric loss (ca. 1.5). MWCNTs also improved the compatibility between iPP and OBC components, leading to a high impact strength of iPP/OBC/MWCNT nanocomposites (about 13 times higher than pure iPP when the content of MWCNT was 1.49 vol%). Thus, the approach reported in this work can provide a new and convenient route to prepare high-performance polymer nanocomposite dielectric materials with low percolation thresholds and balanced mechanical properties. [ABSTRACT FROM AUTHOR]

Continuous monitoring of physical signals such as stress and strain plays a crucial role in Internet of Thing and artificial intelligence, thus flexible mechanical sensors gain increasing attention due to their enormous application potential in wearable electronics, soft robots, human-machine interfaces, etc. Recently, significant progress has been made in mechanical sensors for trading off high sensitivity and wide range for low dimensional strain/force sensors, yet it is still of significant challenge to discriminate complicated three-dimensional (3D) mechanical signals in practical applications. Herein, a novel wearable film sensor capable of sensing multi-directional mechanical stimuli is developed by coating MXene onto low-entropy structured piezoelectric poly(vinylene fluoride-trifluoroethylene) (PVDF-TrFE) mat composed of aligned nanofibers. The resultant functional fiber mats give rise to an anisotropic in-plane conductive network for 2D in-plane strain sensing, and oriented ferroelectric crystals in nanofibers with piezoelectricity allow for out-of-plane dynamic pressure detection. Besides, the all-in-one flexible anisotropic sensor shows linear sensing properties and high sensitivities both in the plane strain and out of the plane pressure due to piezoresistive and piezoelectric mechanisms, respectively. Such sensors can effectively distinguish multi-directional mechanical stimuli for potential applications in human machine interfaces, healthcare, entertainment and other systems. [Display omitted] • MXene coated low-entropy structured PVDF-TrFE nanofiber mat enables 3D mechanical sensing due to piezoresistive-piezoelectric hybrid effect. • The low-entropy structure of PVDF-TrFE gives rise to better piezoelectric response than commercial piezoelectric PVDF film and quartz sensors. • The sensor shows linear and sensitive response of electrical signals to mechanical stimuli both in-plane strain and out-of-plane pressure. • The as-designed 3D mechanical sensor is applicable for office staff sitting posture monitoring and international chess game control. [ABSTRACT FROM AUTHOR]

Wearable flexible electronics are experiencing rapid development for smart life assistance, rehabilitation, and even human enhancement. Owing to the complexity and diversity of wearable and implantable applications, strain sensors with customizable sensing ranges and sensitivities have aroused great interest, while it is still challenging to simultaneously achieve high sensitivity and stretchability. In this work, we report a novel crack design strategy to fabricate sensors for targeted detections via formation of nanocrystal titanium oxide (TiO 2) by means of Ti 3 C 2 T x MXene surface oxidation and typical micro- and through-crack pattern sensors for stable large and accurate subtle motion detections are fabricated, respectively. An efficient crack pattern control strategy based on strain localization induced fracture mechanism is proposed. Two typical sensors with a stable sensitivity in a wide sensing range (GF = 1.3 for 0–100% strain) and high sensitivities in small sensing ranges (GF = 530, 3380, 4650, and 75000 in the strain ranges of 0–0.175%, 0.175%–0.45%, 0.45%–3.6%, and 3.6%–5%, respectively) are obtained for large and subtle human motion detection, respectively. This work introduces a new way to fabricate and combinedly use customizable strain sensors for full-range human motion monitoring, addressing the sensitivity-stretchability contradiction issues for conventionally fabricated and solely used strain sensors via strain localization dominated crack control strategy. MXene-based strain sensors with customizable sensitivities and sensing ranges are fabricated by strain localization directed crack control strategy for full-range human motion monitoring. Image 1 • A concept of designing customizable crack patterns on strain sensors is proposed. • In-situ formed TiO 2 from oxide MXene are harnessed for strain localization control. • A crack control strategy based on strain localization control is developed. • Typical micro- and through-crack patterns are fabricated for full-range monitoring. • Matching the sensor abilities to requirements avoids paying for an overkill. [ABSTRACT FROM AUTHOR]

Stretchable electrodes play a crucial role in wearable electronics for high-efficiency carrier transport in the information communication, yet it is challenging to achieve high electrical conductivity at large strain for stretchable and porous conductive composites. Here, a simple yet efficient strategy is proposed to fabricate highly conductive, porous and stretchable composites via seeding hydrophilic carbon nanotube (CNT) oil-in-water microemulsions in elastomer films prior to growing silver nanoparticles (AgNPs) in situ. It aims at forming a dual heterogeneous structure of CNT microspheres in the elastomeric films containing conductive networks of AgNPs, which allow to guarantee the overall good electrical conductivity. Unlike the rapid propagation of cut-through microcracks in conventional conductive network of AgNPs under strain, the mechanical and electrical dual hetero-structured CNT microspheres in the conductive networks can sustain high electrical conductivity at large strains by blocking and cutting off microcrack propagation. Therefore, the porous composite electrodes show electrical conductivity above 103 S/cm at 200% strain thanks to the efficient dissipation of strain energy by dual hetero-structured CNT microspheres, which is controlled by CNT concentration in the oil-in-water microemulsions. Besides, the as-fabricated porous composites sustain high yet stable electrical conductivity at various kinds of mechanical deformations, such as tension, bending, twisting and a combination of them, allowing for the promising application in stretchable and wearable electrodes. [Display omitted] [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]