Herein, we report a biofriendly, air-operating electrochemical platform based on a unipolar coiled carbon nanotube (CNT) yarn artificial muscle that can operate either as an ionic actuator or as an ionotronic strain sensor. The device comprises two coiled CNT yarn electrodes coated with complementary ion-selective eutectogels, consisting of fixed-charge polymer networks swollen with a diluted deep eutectic solvent (DES), enabling selective ion transport. Under an applied potential difference, the complementary electrochemical responses of both electrodes produce synchronized unipolar contraction, whereas in sensing mode the device generates a strain-dependent open-circuit voltage (OCV) variation. In actuation mode, the device achieves a maximal reversible contractile stroke of 2.9% under a 90 mN pre-load. In sensing mode, it operates as a self-powered strain sensor with a sensitivity of 0.5 mV.%-1. Poisson-Nernst-Planck modelling is consistent with the proposed mechanism of strain-induced ion redistribution within the quasi-solid-state matrix. Two yarn artificial muscles were woven into a custom-made, bi-stretch auxetic structure with a folded zigzag geometry, enabling parallel actuation and strain monitoring, delivering peak-to-peak OCV signals of 4 mV at 10% extension. Finally, we demonstrate a wireless wearable armband for real-time motion monitoring, highlighting the potential of this platform for smart fabrics, wearable electronics, and adaptive soft robotics.

The growing demand for flexible electrochemical devices has prompted the development of safer and more mechanically compatible electrolytes. Conventional liquid electrolytes often fall short to meet these requirements, particularly in flexible or wearable applications, due to issues such as leakage, volatility and poor mechanical integration. In response, all-solid-state polymer electrolytes have emerged as a promising alternative, offering safety, mechanical robustness and processability. However, achieving high mechanical performance in these materials often comes at the expense of ionic conductivity. In this study, we report the synthesis and characterization of novel anionic poly(ionic liquid) (PIL)-based terpolymers, developed as flexible, self-standing all-solid electrolytes. The terpolymer design relies on the synergistic combination of three methacrylate-based monomers: an ionic liquid monomer that provides a high concentration of dissociated ions, poly(ethylene glycol) (PEG) methacrylate to enhance free volume and promote ion mobility, and ureidopyrimidinone (UPy) moieties capable of forming strong, reversible physical crosslinks, imparting elastomer-like mechanical properties and enabling reversible processability without compromising conductivity. The terpolymers were synthesized through a free radical polymerization (FRP) with various monomer ratios and their compositions were confirmed by 1H NMR spectroscopy. The optimized material demonstrated an ionic conductivity of 2.8 x 10-6 S cm-1, a Young's modulus of up to 2 MPa and a strain at break exceeding 150%, indicating a favourable balance between conductivity and mechanical properties. To evaluate practical performance, the terpolymer was integrated into a reflective electrochromic device consisting of a purple electrochromic polymer (as the active layer), the solid electrolyte, and a counter-electrode. Upon application of 0.7 V, the all-solid-state device demonstrated a maximal optical contrast in reflection of 32.6%, a coloration efficiency of 687 cm2 C-1 and a color switch time of 30 seconds. These results confirm the potential of UPy-functionalized PIL-based terpolymers as versatile solid electrolytes for next-generation flexible electrochemical devices.

This study describes the microwave solvothermal synthesis (MSS) of aluminum-doped ZnO nanocrystals (NCs) in a non-polar solvent, namely a hydrocarbon solvent. These NCs are compared with those obtained by the conventional solvothermal method. Both methods resulted in NCs with similar morphologies and IR absorption properties. However, the MSS method produced larger particles than the conventional one. These NCs were utilized to formulate an electrophoretic ink, then embedded in an electrophoretic display unit. Such a device is capable of modulating its emissivity and its apparent temperature observed by a long wave infrared (LWIR) camera. When the electrophoretic device was switched between its reflective and emissive states, the difference in apparent temperatures reached 4.2 degrees C, corresponding to an emissivity variation of 8.4 % in the LWIR.

This study introduces a novel class of bio-friendly, solid-state artificial muscles based on commercially available coiled carbon nanotube (CNT) yarns coated with eutectogel derivatives incorporating dilutions of deep eutectic solvents (DES). By combining polyanionic and polycationic gels based on DES, synchronized contraction of the two yarn electrodes is achieved via selective ion intercalation and enables unipolar actuation in solid-state CNT yarn actuators. The studies on the electrochemical properties of the actuator show that the contractile stroke and the stroke-to-charge ratio increase as the amount of ionic units in the polymers increases. At high ionic monomer content, evidence of an early scan-rate-enhanced-stroke (SRES) effect can also be observed. The solid-state actuator reaches a contractile stroke of 2.25% under a 90 mN load and remains stable over 300 cycles in ambient conditions. Textile integration through inlaying preserves actuator functionality, achieving up to 3.4% strain, demonstrating excellent compatibility with smart wearable platforms. These results highlight the potential of DES-based gel coatings for the scalable development of unipolar, high-performance, and environmentally sustainable artificial muscles suitable for e-textiles, soft robotics, and prosthetics.

The field of electrochromic materials has been the subject of extensive research, with a particular focus on the development of strategies for precise color tuning. To date, two principal routes of investigation have been pursued. The initial approach involves the synthesis of the electrochromic material with the desired color, employing chemical engineering to achieve the targeted color. The second approach involves utilizing the electrochromic material as a shutter, alternating between achromatic and black states, with the device color corresponding to that of the electrolyte when the polymer is in its achromatic states. In this study, we propose a novel approach that combines the two aforementioned technologies. This novel approach offers straightforward access to bi- and trichromatic devices. The electrochromic material utilized in this study is a conjugated polymer, poly (vinyltriphenylamine) (PVTPA), which exhibits three distinct colorimetric states depending on the applied potential: achromatic, ochre, and black. This study reports the synthesis of the monomer and the polymer, as well as the electro-optical characteristics of PVTPA. The easy integration of PVTPA into devices is demonstrated by the development of bi- and trichromatic displays using different colored membranes (white, turquoise, and orange). Additionally, the switching times and color coordinates of these displays are assessed. The combination of an easily accessible electrochromic polymer and the use of colored membranes provides easy access to trichromatic devices with multiple color options.

A contractile ionic electrochemical actuator was designed by incorporating two coiled carbon nanotube (CNT) yarns coated with a biofriendly ionogel. The working principle of such an actuator stands in capacitive ionic accumulation at the electrochemical double layer, which converts into linear contraction of the coiled CNT yarns. The prepared ionogel showed a good ionic conductivity of up to 1.9 mS cm-1 at room temperature and suitable mechanical properties (Young modulus <1 MPa and elongation at break at 75%). The ionogel/coiled CNT yarn actuator exhibited a maximum contractile stroke of 1.78% under electrochemical stimulation in open air. Such yarn actuators with safe components could open opportunities for application prospects in smart textiles and biomedical devices.

This work presents a comparison of ionic coatings (ICs) developed specifically for electroactive yarn actuators, able to operate in open-air. Six ionically conducting materials, previously reported in different studies from our group, were used and compared. Two all-solid-state crosslinked materials based on polymeric ionic liquids and four ionogels are described. They are all soft but differ from (i) their nature, i.e. all-solid polymeric ionic liquid vs "wet" ionogel, and from (ii) their ionic charge carriers, i.e. conventional ionic liquid vs biofriendly ionic liquid. As a result, they have conductivities ranging over two orders of magnitude. In spite of the different electrical stimulations applied on the yarn actuators and their electrochemical charging behavior, i.e. bipolar or unipolar, we achieved a conceptual understanding of the key characteristics that ICs should exhibit to induce optimal CNT yarn actuation through the establishment of a relationship between stroke rate-to-potential of coiled CNT yarn actuators' operation in open air.

Color reproduction through subtractive synthesis is achieved by combining the three primary colors cyan, magenta, and yellow (CMY). Three CMY electroactive polymers are selected, synthesized, and first, integrated into monochromatic electrochromic devices (pixels) similar to electrochemical cells. In order to develop innovative trichromatic devices, new pixel architectures are proposed and compared. In particular, the stacking of the three monochromatic CMY electrochromic devices in a single system is declined in the form of three different electrochemical cells, which differ in the nature and positioning of the counter-electrode. Overall performances are finally evaluated in terms of range and ease of assembly. The architecture with common counter-electrode is clearly the one that offers the best potential for the development of electrochromic devices to reproduce a wide range of colors. Color reproduction is achieved by combining three electroactive polymers cyan, magenta and yellow. In order to develop innovative trichromatic displays, new architectures of three stacked monochromatic pixels, which differ in the nature and positioning of the counter electrode, are proposed and compared. The architecture with common counter-electrode clearly shows the best potential to reproduce a wide range of colors.image

Liquid crystal elastomers (LCEs) with promising applications in the field of actuators and soft robotics are reported. However, most of them are activated by external heating or light illumination. The examples of electroactive LCEs are still limited; moreover, they are monofunctional with one type of deformation (bending or contraction). Here, the study reports on trilayer electroactive LCE (eLCE) by intimate combination of LCE and ionic electroactive polymer device (i-EAD). This eLCE is bi-functional and can perform either bending or contractile deformations by the control of the low-voltage stimulation. By applying a voltage of ±2 V at 0.1 Hz, the redox behavior and associated ionic motion provide a bending strain difference of 0.80%. Besides, by applying a voltage of ±6 V at 10 Hz, the ionic current-induced Joule heating triggers the muscle-like linear contraction with 20% strain for eLCE without load. With load, eLCE can lift a weight of 270 times of eLCE-actuator weight, while keeping 20% strain and affording 5.38 kJ·m-3 work capacity. This approach of combining two smart polymer technologies (LCE and i-EAD) in a single device is promising for the development of smart materials with multiple degrees of freedom in soft robotics, electronic devices, and sensors.

Doped zinc oxide nanocrystals (NCs) are halfway through semiconductors and metals. They exhibit unique optoelectronic properties from a high surface density of free-charge-carriers, which are responsible for localized surface plasmon resonance (LSPR). Here, a one-pot approach is presented to synthesize doped aluminum, gallium or indium zinc oxide NCs, making them all stable in non-polar media. The effect of doping on the growth mechanisms and the final crystalline structure were studied as a function of the aliovalent doping atom used. Doping atoms were integrated by substitution of Zn atom into the crystalline mesh of ZnO with a wurtzite phase identified as the primary crystalline phase for all samples by X-ray Diffraction (XRD). Typical aluminiun doped ZnO NCs (AZO) or Gallium doped NCs (GZO) nanoflowers were identified as a single crystalline structure by High-Resolution-Transmission Electron Microscopy (HR-TEM). Indium doped ZnO NCs (IZO) and pristine ZnO appeared significantly different with spherical and heart-like shapes, respectively. The doping level tendency was identified through Energy Dispersive X-ray (EDX) and increased form Al to Ga and In doping atoms. All plasmonic doped NCs have broadband infrared absorption in the Middle-wave (MWIR) and Long-wave infrared (LWIR) wavelengths, making them interesting for thermal regulation or thermal camouflage. As part of the latter application, dispersions of doped ZnO NCs were formulated as electrophoretic inks and their IR-absorbing performances determined by using a homemade setup including an infrared camera. AZO, GZO, and IZO NCs based inks achieved temperature contrasts of 15 degrees C and 6 degrees C in the MWIR and LWIR wavelengths.

The design of the electrochromic component of an instrumented contact lens capable of dynamically modifying its color is presented. The device is based on two electrochromic pi-conjugated polymers (CPs) deposited on two electrodes separated by an electrolyte medium. Yellow and cyan electrochromic CPs with two color states are combined to provide a tuneable tint of the eye iris, from green to cyan. The device can switch from green, in which both electrodes are colored, to cyan, in which only the cyan electrode is colored. The additive microsystem process with successive assembling steps allowing the realization of the bichromatic cell in the scleral contact lens is presented, as well as the characterization of the colorimetry and switching dynamics.

Electroactive liquid crystal elastomers (eLCEs) are used to make actuators and soft robotics. However, most eLCEs are monofunctional with one type of deformation (bending or contraction). Recently, a trilayer eLCE are reported by combining ion-conducting LCE and ionic electroactive polymer device (i-EAD). This i-EAD-LCE is bifunctional and performs either bending or contractile deformation by controlling low-voltage stimulation. Nevertheless, it has a Young's modulus of only 1.63 MPa. To improve the mechanical performance, the i-EAD-IPN-LCE is prepared here, whose central membrane is composed of interpenetrating LCE and ionogel (i-IPN-LCE) instead of a single ion-conducting LCE. This i-EAD-IPN-LCE with a typical thickness of 0.5 mm can function not only as linear and bending actuators, but also as a sensor. As a linear actuator, its Young's modulus, actuation stress, and strain are 51.6 MPa, 0.14 MPa and 9%, respectively, reaching skeletal muscles' values. As a bending actuator, its bending strain difference Delta epsilon is 1.18% with 3 mN output force. It can also operate as a sensor producing 0.4 mV Open-Circuit-Voltage to respond to bending deformation (Delta epsilon = 9%). Therefore, this i-EAD-IPN-LCE is a promising system for the fabrication of robust electroactive devices and sensors with multiple degrees of freedom. The trilayer device i-EAD-IPN-LCE has mechanical properties reaching those of mammalian skeletal muscles. It can function not only as linear and bending actuators under low-voltage electrical stimulation, but also as a sensor in response to bending deformation. image

The low power consumption of electrochromism makes it widely used in actively shaded windows and mirrors, while flexible versions are attractive for use in wearable devices. Initial demonstration of stretchable electrochromic elements promises good conformability to complex surfaces. Here, fully integrated intrinsically stretchable electrochromic devices are demonstrated as single elements and 3 × 3 displays. Conductive and electrochromic ionic liquid-doped poly(3,4-ethylenedioxythiophene) polystyrene sulfonate is combined with poly(vinyl alcohol)-based electrolyte to form complete cells. A transmission change of 15% is demonstrated, along with a reflectance change of 25% for opaque reflective devices, with <7 s switching time, even under 30% strain. Stability under both electrochemical and mechanical strain cycling is demonstrated. A passive matrix display exhibits addressability and low cross-talk under strain. Comparable optical performance to flexible electrochromics and higher deformability provide attractive qualities for use in wearable, biometric monitoring, and robotic skin devices.

Polymeric ionic liquids (PILs) are an emerging class of materials which have attracted considerable attention as solid‐state electrolytes because they combine the attractive properties of ionic liquids with the mechanical features of polymers. This paper presents a new method for the synthesis and characterization of stretchable and highly ionically conducting membranes and their subsequent use in truly all‐solid‐state, flexible, and soft electroactive devices. Linear conductive PIL and reinforcing poly(ethylene oxide) (PEO) network are first intimately entangled during the synthesis of a semi‐interpenetrating polymer network (semi‐IPN). Polymerization kinetics, thermomechanical properties, as well as ionic conductivity measurements reveal that for the 60:40 wt ratio of PEO:PIL a true synergy of the properties of both polymer partners is achieved, with ionic conductivities up to 8.7 × 10 −5 S cm −1 at 30 °C and elongations at break greater than 100%, being both superior to each partners taken separately. The performances of these semi‐IPNs as central membranes in all‐solid‐state electrochemical microdevices, composed of three self‐supported and flexible layers, namely poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/semi‐IPN membrane/PEDOT:PSS, are successfully demonstrated. Their testing as liquid‐free ionic actuators and liquid‐free piezoionic sensors undoubtfully proves that electromechanical and mechanoelectrical responses of these all‐solid‐state microdevices can reach performances identical to that of “classical” ionic liquid‐filled systems.

Artificial muscles, or soft actuators, that could exhibit contractile stroke and operate in open-air, would be crucial for many applications, such as robotics, prosthetics, or powered exoskeletons. Amongst the different artificial muscle technologies, electrochemical carbon nanotube (CNT) yarn muscles, transducing capacitively ionic accumulation at the electrochemical double layer into linear contraction, are amongst the most promising candidates. However, their performances are either limited by an undesired bipolar behaviour or short lifetime due to the inevitable drying of water-based electrolytes. In this paper, we present here the fabrication of air-operating contractile linear artificial muscles from commercially available CNT yarns exhibiting outstanding performance. The synthesis and the junction of two ionogels based on cationic and anionic polyelectrolyte have been designed for the coating process on CNT yarns, and for selectively orienting the ionic flow allowing optimal electromechanical energy conversion. The dual-electrode CNT yarn actuators showed air-stable unipolar contractile stroke, reaching 9.7% without loss of performances after 2000 cycles.

Ionogels are composed of ionic liquid percolated within a polymer network. Here, endowed with vitrimer properties to conceive sustainable solid-state electrolytes working in open air, they keep their performance after healing or welding.