Simon Tricard

Molecular actuators driven by cooperative spin-state switching

Molecular switches have great potential to convert different forms of energy into mechanical motion; however, their use is often limited by the narrow range of operating conditions. Here we report on the development of bilayer actuator devices using molecular spin crossover materials. Motion of the bilayer cantilever architecture results from the huge spontaneous strain accompanying the spin-state switching. The advantages of using spin crossover complexes here are substantial. The operating conditions used to switch the device can be manipulated through chemical modification, and there are many existing compounds to choose from. Spin crossover materials may be switched by diverse stimuli including light, temperature, pressure, guest molecules and magnetic field, allowing complex input combinations or highly specific operation. We demonstrate the versatility of this approach by fabricating actuators from four different spin crossover materials and by using both thermal variation and light to induce motion in a controlled direction.

Highly Stable Water‐Soluble Platinum Nanoparticles Stabilized by Hydrophilic N‐Heterocyclic Carbenes

Controlling the synthesis of stable metal nanoparticles in water is a current challenge in nanochemistry. The strategy presented herein uses sulfonated N-heterocyclic carbene (NHC) ligands to stabilize platinum nanoparticles (PtNPs) in water, under air, for an indefinite time period. The particles were prepared by thermal decomposition of a preformed molecular Pt complex containing the NHC ligand and were then purified by dialysis and characterized by TEM, high-resolution TEM, and spectroscopic techniques. Solid-state NMR studies showed coordination of the carbene ligands to the nanoparticle surface and allowed the determination of a (13)C-(195)Pt coupling constant for the first time in a nanosystem (940 Hz). Additionally, in one case a novel structure was formed in which platinum(II) NHC complexes form a second coordination sphere around the nanoparticle.

Re-Appearance of Cooperativity in Ultra-Small Spin-Crossover [Fe(pz){Ni(CN)4}] Nanoparticles†

A reverse nanoemulsion technique was used for the elaboration of [Fe(pz){Ni(CN)4}] nanoparticles. Low-temperature micellar exchange made it possible to elaborate ultra-small nanoparticles with sizes down to 2 nm. When decreasing the size of the particles from 110 to 12 nm the spin transition shifts to lower temperatures, becomes gradual, and the hysteresis shrinks. On the other hand, a re-opening of the hysteresis was observed for smaller (2 nm) particles. A detailed (57)Fe Mössbauer spectroscopy analysis was used to correlate this unusual phenomenon to the modification of the stiffness of the nanoparticles thanks to the determination of their Debye temperature.

Polypyrrole and graphene quantum dots @ Prussian Blue hybrid film on graphite felt electrodes: Application for amperometric determination of l-cysteine.

A novel polypyrrole (PPy) and graphene quantum dots (GQDs) @ Prussian Blue (PB) nanocomposite has been grafted on a graphite felt (GF) substrate (PPy/GQDs@PB/GF), and has been proven to be an efficient electrochemical sensor for the determination of l-cysteine (l-cys). GQDs, which were fabricated by carbonization of citric acid and adsorbed on GF surface ultrasonically, played an important role for promoting the synthesis process of PB via a spontaneous redox reaction between Fe(3+) and [Fe(CN)6](3-). The PPy film has been electro-polymerized to improve the electrochemical stability of the PPy/GQDs@PB/GF electrode. The as-prepared electrode was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), infrared spectroscopy (IR), X-ray diffraction (XRD) and electrochemical methods. It exhibited an excellent activity for the electrocatalytic oxidation of l-cys, with a detection sensitivity equal to 0.41 Amol(-1) L for a concentration range of 0.2-50 μmolL(-1), and equal to 0.15 Amol(-1) L for a concentration range of 50-1000 μmolL(-1). A low detection limit of 0.15 μmolL(-1), as well as a remarkable long-time stability and a negligible sensitivity to interfering analytes, were also ascertained.

Prussian blue @ platinum nanoparticles/graphite felt nanocomposite electrodes: Application as hydrogen peroxide sensor

In this study, we report a triple-component sensor fabricated by freestanding graphite felt (GF), platinum nanoparticles (Pt) and Prussian blue (PB). Pt is ultrasonically-electrodeposited on GF to increase the conductivity and to render the catalysts to the chemical deposition of PB. Cyclic voltammetric and amperometric measurements show that the double porous PB@Pt/GF sensor exhibits two pairs of well-defined redox peaks and a prominent electrocatalytic activity toward H2O2 reduction. This resulting sensor displays impressive results with regard to a low detection limit of 1.2×10(-9)M and very high detection sensitivity of 40.9Acm(-2)M(-1), using a potential work of 0.0V.

Noncontact orientation of objects in three-dimensional space using magnetic levitation.

Significance We describe several noncontact methods of orienting objects in three-dimensional (3D) space using Magnetic Levitation (MagLev), and report the discovery of a sharp geometry-dependent transition of the orientation of levitating objects. An analytical theory of the orientation of arbitrary objects in MagLev explains this transition. MagLev is capable of manipulating and orienting hard and soft objects, and objects of irregular shape. Because controlling the orientation of objects in space is a prerequisite for assembling complex structures from simpler components, this paper extends MagLev into 3D self-assembly, robotic assembly, and noncontact (stiction-free) orientation of hard and soft objects for applications in biomimetics, soft robotics, and stimulus-responsive materials, among others. This paper describes several noncontact methods of orienting objects in 3D space using Magnetic Levitation (MagLev). The methods use two permanent magnets arranged coaxially with like poles facing and a container containing a paramagnetic liquid in which the objects are suspended. Absent external forcing, objects levitating in the device adopt predictable static orientations; the orientation depends on the shape and distribution of mass within the objects. The orientation of objects of uniform density in the MagLev device shows a sharp geometry-dependent transition: an analytical theory rationalizes this transition and predicts the orientation of objects in the MagLev device. Manipulation of the orientation of the levitating objects in space is achieved in two ways: (i) by rotating and/or translating the MagLev device while the objects are suspended in the paramagnetic solution between the magnets; (ii) by moving a small external magnet close to the levitating objects while keeping the device stationary. Unlike mechanical agitation or robotic selection, orienting using MagLev is possible for objects having a range of different physical characteristics (e.g., different shapes, sizes, and mechanical properties from hard polymers to gels and fluids). MagLev thus has the potential to be useful for sorting and positioning components in 3D space, orienting objects for assembly, constructing noncontact devices, and assembling objects composed of soft materials such as hydrogels, elastomers, and jammed granular media.

A simple two-dimensional model system to study electrostatic-self-assembly

This paper surveys the variables controlling the lattice structure and charge in macroscopic Coulombic crystals made from electrically charged, millimeter-sized polymer objects (spheres, cubes, and cylinders). Mechanical agitation of these objects inside planar, bounded containers caused them to charge electrically through contact electrification, and to self-assemble. The processes of electrification and self-assembly, and the characteristics of the assemblies, depended on the type of motion used for agitation, on the type of materials used for the objects and the dish, on the size and shape of the objects and the dish, and on the number of objects. Each of the three different materials in the system (of the dish and of the two types of spheres) influenced the electrification. Three classes of structures formed by self-assembly, depending on the experimental conditions: two-dimensional lattices, one-dimensional chains, and zero-dimensional ‘rosettes’. The lattices were characterized by their structure (disordered, square, rhombic, or hexagonal) and by the electrical charges of individual objects; the whole lattices were approximately electrically neutral. The lattices observed in this study were qualitatively different from ionic crystals; the charge of objects had practically continuous values which changed during agitation and self-assembly, and depended on experimental conditions which included the lattice structure itself. The relationship between charge and structure led to the coexistence of regions with different lattice structures within the same assembly, and to transformations between different lattice structures during agitation.

Using Magnetic Levitation for Non-Destructive Quality Control of Plastic Parts

Magnetic levitation (MagLev) enables rapid and non-destructive quality control of plastic parts. The feasibility of MagLev as a method to: i) rapidly assess injection-molded plastic parts for defects during process optimization, ii) monitor the degradation of plastics after exposure to harsh environmental conditions, and iii) detect counterfeit polymers by density is demonstrated.

Amperometric detection of hydrogen peroxide utilizing synergistic action of cobalt hexacyanoferrate and carbon nanotubes chemically modified with platinum nanoparticles

In this study, a novel composite of cobalt hexacyanoferrate nanoparticles (CoNP) and platinum nanoparticles (Pt) on carbon nanotubes (CNTs) is obtained by ultrasonically mixing CoNP synthesized in a microemulsion with CNTs chemically modified with platinum nanoparticles (Pt/CNTs). Cyclic voltammetric and amperometric measurements on a glass carbon electrode showed that the composite (called CoNP–Pt/CNTs) exhibits a well-defined pair of redox peaks and a prominent electrocatalytic activity toward hydrogen peroxide (H2O2) reduction. Besides, the current response of CoNP–Pt/CNTs is 2 orders of magnitude higher than the response of CoNP alone and 1 order of magnitude higher than the response of Pt/CNTs or CoNP/CNTs alone. This higher efficiency can be attributed to a remarkable synergistic effect between CoNP, Pt and CNTs. This sensor shows a linear response to H2O2 concentrations ranging from 0.2 μM to 1.25 mM with a detection limit of 0.1 μM, a maximum sensitivity of 0.744 A·M−1 and a fast response time below 2 s.

Well separated trion and neutral excitons on superacid treated MoS2 monolayers

Developments in optoelectronics and spin-optronics based on transition metal dichalcogenide monolayers (MLs) need materials with efficient optical emission and well-defined transition energies. In as-exfoliated MoS2 MLs, the photoluminescence (PL) spectra even at low temperature consist typically of broad, overlapping contributions from neutral, charged excitons (trions) and localized states. Here, we show that in superacid treated MoS2 MLs, the PL intensity increases by up to 60 times at room temperature. The neutral and charged exciton transitions are spectrally well separated in PL and reflectivity at T = 4 K, with linewidth for the neutral exciton of 15 meV, but both transitions have similar intensities compared to the ones in as-exfoliated MLs at the same temperature. Time resolved experiments uncover picoseconds recombination dynamics analyzed separately for charged and neutral exciton emissions. Using the chiral interband selection rules, we demonstrate optically induced valley polarization for bot...