161 research outputs found
Piezoresistive Elastomer Composites Used for Pressure Sensing
Pressure sensors with capability to detect small physical movements and mechanical deformations have been widely used in wearable and medical applications. However, devices that are commercially available currently require complex designs and fabrication and present only a limited force-range sensitivity. To simplify the design, a thermoplastic polyurethane (TPU)/ carbon nanotubes (CNTs) composite film has been developed using a melt extrusion technique followed by compression moulding. Pressure sensors were made from these films, whose piezoresistive response have been analysed as a function of the concentrations of CNTs, around the percolation threshold. The changes in the voltage of the device with applied pressure was continuously measured using a voltage divider system coupled with an electromechanical test machine that dynamically loaded the sensors under compression. The voltage divider system was tuned to obtain the best sensitivity and signal/noise (S/N) ratio for each device tested. The results showed that sensors containing a target of 2.5 wt.% CNTs had market leading sensitivity and repeatability during long-term stability testing and showed high durability during underwater testing indicating that such devices can be used as a promising robust pressure sensitive sensor in wearable devices
Highly stretchable and sensitive self-powered sensors based on the N-Type thermoelectric effect of polyurethane/Na_{x}(Ni-ett)_{n}/graphene oxide composites
The development of stretchable organic thermoelectric materials is prompted by fast evolving application fields like flexible electronic devices, soft robotics, health monitoring and internet-of-things. Stretchability in thermoelectric materials is usually obtained by using an insulating elastomer, either as a substrate or as a matrix in a blend or composite, which, unfortunately, leads to a compromise in thermoelectric performance. Herein, a potential solution is reported exploiting the addition of graphene oxide as a secondary (nano)filler in a polyurethane/poly nickel-ethenetetrathiolates film. Compared with traditional binary blends, our ternary composite shows an increased electrical conductivity (4 times), air-stability (âŒ20 times after 3 months), and stretchability (38% increase in strain at break). With a gauge factor (GF) of âŒ58, this new composite film shows high sensitivity to tensile strain. Thanks to its Seebeck coefficient of ⌠â40 ÎŒV K^{â1}, the composite film can generate a thermopower of âŒ0.25 pW when subjected to a small temperature difference (30 °C), which could be exploited by self-powered strain sensors. Therefore, the ternary polyurethane/poly nickel-ethenetetrathiolates/graphene oxide composite film can work as a stretchable strain sensor, providing a strategy to reconcile the compromise between thermoelectric performance and stretchability
The chiral 1:2 adduct (S)S(S)C(-)589-ethyl 2-phenylbutyl sulphide-mercury (II) chloride:(-)589[(S)S(S)C-Et(2-PhBu)S.(HgCl2)2]. Stereoselective synthesis, asymmetric oxidation, crystal and molecular structure and circular dichroism spectra
Optically active (-)589ethyl (S)-2-phenylbutyl thioether, (-)(S)C-Et(PhBu)S (I), and its new diastereoisomeric mercury (II) chloride adduct, 1:2, (-)[(S)S(S)C-Et(PhBu)S.(HgCl2)2]2, (II) were stereoselectively synthesized; the absorbance (UV) and circular dichroism (CD) spectra were measured and the crystal and molecular structure of complex (II) was determined by single-crystal X-ray diffraction. Two different Hg centres are present whose coordination environments are built by two short bonds to chloride ligands in one case, and to one chloride and one sulphur in the other one. These originate digonal units. Electroneutrality is achieved by a further chlorine, which can be considered prevalently ionic and bonded to the two Hg centres, forming square bridging systems nearly perpendicular to the digonal molecules. The coordination polyhedra can be interpreted as 2 + 4 tetragonally-compressed octahedra with the four longer contacts lying in the equatorial plane. IR spectroscopic data are consistent with the presence of one bent and one linear ClâHgâCl moiety. The absolute configurations at both stereogenic centres of the formed diastereoisomeric complex (II) are (S). The (S)S absolute configuration at the stereogenic sulphur atom bonded to the mercury(II) atom in complex (II) has been related with the negative Cotton effect assigned in its circular dichroism (CD) spectrum to a charge-transfer transition at ca. 230 nm. The stereoselective oxidation of (I) and (II) with hydrogen peroxide, induced by the stereogenic carbon atom (S)C of the enantiopure sulphide, gave (-)598ethyl (S)C-2-phenylbutyl(S)S-sulphoxide, (-)598[(S)S(S)C-Et(PhBu)SO], (III), having 18.1% de. Oxidations carried out in the presence of a 200 molar excess of mercury(II) chloride gave (-)598ethyl (S)C-2-phenylbutyl(R)S-sulphoxide, (-) 598[(R)S(S)C-Et(PhBu)SO], (IV) with 31% de, showing the cooperative influence of mercury(II) chloride on the selectivity of the oxidation reaction
Self-powered ultrasensitive and highly stretchable temperature-strain sensing composite yarns
With the emergence of stretchable/wearable devices, functions, such as sensing, energy storage/harvesting, and electrical conduction, should ideally be carried out by a single material, while retaining its ability to withstand large elastic deformations, to create compact, functionally-integrated and autonomous systems. A new class of trimodal, stretchable yarn-based transducer formed by coating commercially available LycraÂź yarns with PEDOT:PSS is presented. The material developed can sense strain (first mode), and temperature (second mode) and can power itself thermoelectrically (third mode), eliminating the need for an external power-supply. The yarns were extensively characterized and obtained an ultrahigh (gauge factor âŒ3.6 Ă 105, at 10â20% strain) and tunable (up to about 2 orders of magnitude) strain sensitivity together with a very high strain-at-break point (up to âŒ1000%). These PEDOT:PSS-Lycra yarns also exhibited stable thermoelectric behavior (Seebeck coefficient of 15 ÎŒV Kâ1), which was exploited both for temperature sensing and self-powering (âŒ0.5 ÎŒW, for a 10-couple module at ÎT ⌠95 K). The produced material has potential to be interfaced with microcontroller-based systems to create internet-enabled, internet-of-things type devices in a variety of form factors
Structure and dynamics of pentacene on SiO2: From monolayer to bulk structure
We have used confocal micro Raman spectroscopy, atomic force microscopy (AFM), and x-ray diffraction (XRD) to investigate pentacene films obtained by vacuum deposition on SiO2 substrates. These methods allow us to follow the evolution of lattice structure, vibrational dynamics, and crystal morphology during the growth from monolayer, to TF, and, finally, to bulk crystal. The Raman measurements, supported by the AFM and XRD data, indicate that the film morphology depends on the deposition rate. High deposition rates yield two-dimensional nucleation and quasi-layer-by-layer growth of the T-F form only. Low rates yield three-dimensional nucleation and growth, with phase mixing occurring in sufficiently thick films, where the T-F form is accompanied by the "high-temperature" bulk phase. Our general findings are consistent with those of previous work. However, the Raman measurements, supported by lattice dynamics calculations, provide additional insight into the nature of the TFs, showing that their characteristic spectra originate from a loss of dynamical correlation between adjacent layers
Flexible and Stretchable Self-Powered Multi-Sensors Based on the N-Type Thermoelectric Response of Polyurethane/Na-x(Ni-ett)(n) Composites
Flexible and stretchable electronic devices have a broad range of potential uses, from biomedicine, soft robotics, and health monitoring to the internetâofâthings. Unfortunately, finding a robust and reliable power source remains challenging, particularly in offâtheâgrid and maintenanceâfree applications. A soughtâafter development overcome this challenge is the development of autonomous, selfâpowered devices. A potential solution is reported exploiting a promising nâtype thermoelectric compound, poly nickelâethenetetrathiolates (Na_{x}(Niâett)_{n}). Highly stretchable nâtype composite films are obtained by combining Nax(Niâett)n with commercial polyurethane (Lycra). As high as 50 wt% Na_{x}(Niâett)_{n} content composite film can withstand deformations of â500% and show conductivities of â10^{-2} S cm^{-1} and Seebeck coefficients of approx. â40 ”V K^{-1}. These novel materials can be easily synthesized on a large scale with continuous processes. When subjected to a small temperature difference (<20 °C), the films generate sufficient thermopower to be used for sensing strain (gauge factor â20) and visible light (sensitivity factor â36% (kW m^{-2})^{-1}), independent of humidity (sensitivity factor â0.1 (%RH)^{-1}. As a proofâofâconcept, a wearable selfâpowered sensor is demonstrated by using nâtype Na_{x}(Niâett)_{n}/Lycra and PEDOT:PSS/Lycra elements, connected in series by hot pressing, without employing any metal connections, hence preserving good mechanical ductility and ease of processing
Plasmonic nanoparticle monomers and dimers: From nano-antennas to chiral metamaterials
We review the basic physics behind light interaction with plasmonic
nanoparticles. The theoretical foundations of light scattering on one metallic
particle (a plasmonic monomer) and two interacting particles (a plasmonic
dimer) are systematically investigated. Expressions for effective particle
susceptibility (polarizability) are derived, and applications of these results
to plasmonic nanoantennas are outlined. In the long-wavelength limit, the
effective macroscopic parameters of an array of plasmonic dimers are
calculated. These parameters are attributable to an effective medium
corresponding to a dilute arrangement of nanoparticles, i.e., a metamaterial
where plasmonic monomers or dimers have the function of "meta-atoms". It is
shown that planar dimers consisting of rod-like particles generally possess
elliptical dichroism and function as atoms for planar chiral metamaterials. The
fabricational simplicity of the proposed rod-dimer geometry can be used in the
design of more cost-effective chiral metamaterials in the optical domain.Comment: submitted to Appl. Phys.
Smart and repeatable easy-repairing and self-sensing composites with enhanced mechanical performance for extended components life
Structural composites with smart functionalities of self-healing and self-sensing are of particular interest in the fields of aerospace, automotive, and renewable energy. However, most of the current self-healing methodologies either require a relatively complex design of the healing network, or sacrifice the initial mechanical or thermal performance of the carbon fibre composite system after introducing the healing agents. Herein, an extremely simple methodology based on commonly used thermoplastic interleaves has been demonstrated to achieve repeatable easy-repairing and self-sensing functionalities, alongside enhanced mechanical performance in comparison with unmodified carbon fibre/epoxy system. Moreover, due to the high glass transition temperature of the thermoplastic, the repairable composites are shown to have an unchanged storage modulus up to 80 °C, solving the previous limitation of repairable epoxy matrix systems with thermoplastics. High retention of peak load (99%) and a decent recovery of interlaminar fracture toughness (34%) was achieved. Most importantly, the mechanical properties remained greater than the unmodified system after four consecutive cycles of damage and healing. Repeatable in-situ damage sensing was achieved based on the piezoresistive method. This ânewâ discovery based on an âoldâ approach, which is fully compatible with current composite manufacturing, may overcome existing conflicts between mechanical performance and healing functions, providing a new solution to extend componentsâ service life towards a more sustainable development of the composite sector
Microcellular epoxy/graphene nanocomposites with outstanding electromagnetic interference shielding and mechanical performance by overcoming nanofiller loading/dispersion dichotomy
With the rapid evolvement of wireless communication technologies, the ever increasing needs to prevent electromagnetic waves (EMWs) pollution have urged the development of lightweight materials with excellent electromagnetic interference (EMI) shielding property. However, achieving desired EMI shielding performance often requires high loadings of conductive nanofillers, like graphene, which poses challenges to control the nanoparticle dispersion and the mechanical performance of the nanocomposite. Herein, we demonstrate a method to fabricate highly-loaded (>30 wt%) graphene in microcellular epoxy nanocomposites, successfully overcoming the long-lasting dichotomy in the field of nanocomposites of high filler loading and dispersion. By utilizing supercritical CO2 foaming method, modified thermosetting epoxy-based nanocomposite was foamed with multiple interfaces and tunable microcellular cells. In addition, a rearrangement of nanofillers during foaming process is favorable for more intense conductive network, leading to enhanced EMWs attenuation by repeated reflections and absorptions. An optimal combination of electrical conductivity (314 S mâ1), EMI shielding effectiveness (86.6 dB and 156.3 dB/(g/cm3)), compressive strength (27.4 MPa) and density (0.55 g cmâ3) has been achieved for foamed nanocomposite with 32.26 wt % graphene content. This versatile method opens up an easy route to fabricate lightweight structural foams with high nanofiller contents, which could be used in many applications such as electronics, robotics, and aircrafts
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