Responsive materials operating outside of thermodynamic equilibrium

Resume : For almost 60 years ammonium sulfate (AS) has been known to exhibit ferroelectric properties below Tc at 223K. AS shows a unique dependence of spontaneous polarization (Ps ) versus temperature. Since Ps was not considered as the order parameter of the ferroelectric phase transition, AS has been classified as an improper or pseudo-proper ferroelectric. In ferroelectric phase AS belongs to polar Pna21 space group and in paraelectric phase its structure is described by centrosymmetric Pnam. Despite the variety of used experimental and theoretical approaches performed till now, the type of the phase transition and the mechanism of structural transformation is still not properly explained . In the present work the existing theories, which are often contradictory, were critically discussed and an attempt was made to investigate the structural changes by modern diffraction and spectroscopic methods. At first the series of single-crystal X-ray diffraction measurements were performed in the temperature range between 298 and 148 K. The significant modifications of the geometrical parameters for sulfate anion and two symmetrically independent ammonium cations as well as for the hydrogen bonds formed between them, were disscused in the view of previously discovered effects. We hope that the newly detected structural features will help to resolve the nature of the phase transition in ammonium sulfate.

Resume : The Sr2-хBaxFeMoO6-d system of a variable composition with a Curie temperature (Тс) higher than 300 K and almost 100% degree of spin polarization have been studied. A comparison of the results of magnetic and thermodynamic measurements data has made it possible to explain the phase transformations type. The investigations have been carried out in the mode of the discrete heat input on five samples having compositions Sr2-хBaхFeMoO6-d with х = 0; 0.4; 1.0; 1.6 and 2.0. Temperature dependences of the magnetization (М) for samples of all compositions are qualitatively identical. The value of М linearly decreases down to the paramagnetic state transition. The decrease of Тс is observed with an increase of Ba fraction which is caused by the change of the spin-spin interaction character. The revealed heat capacity anomalies relate to the second-order phase transitions of the λ-type, and the heat capacity does not obey the Debye Т3 – law in the temperature region 5 – 80 K. According to the magnetization measurements data, the anomalies of magnetic transformations correspond to the large enthalpy values. A considerably larger sensitivity of the adiabatic calorimetry method as compared with the magnetic measurements, makes it possible to detect the stated above phase transformations and confirms the existence of magnetically inhomogeneous areas in the compounds.

Resume : Polymetallic M9W6(M=Fe,Co,Ni,Mn) type clusters are currently extensively researched for the possibility of tuning their physical properties by varying the metal composition and organic ligand decoration. By rational choice of metallic composition, a multitude of mono- and polymetallic clusters has been obtained, with Fe9W6 and the FexCo9-xW6 series being the most prominent and unique by their temperature driven CTIST and spin state transition. Among other examples, SMM like behavior has been observed for Ni9W6(tetramethylphenanthroline)6 clusters and superparamagnetism in 1D cluster chains of Mn9W6 linked with di(pyridyl)ethylene ligands. The transitions in Fe9W6 and FexCo9-xW6 are reversible and accompanied by cluster and crystallographic cell compression and a thermal hysteresis loop, whose characteristics depend on cluster’s composition.

Resume : Broad visible light-responsive hybrid zeolites of polyoxometalate (POM)-encapsulated zeolite-supported AgNTiO2 nanochains (AgNTiO2@POM/Zeolite Y) were fabricated by binding AgNTiO2 nanochains on the outer surface of POM-encapsulated zeolite Y, and they were fully characterized by XRD, FESEM, TEM, XPS, DRS, and ICPAES analysis. Their photocatalytic activities for CO2 reduction with water were investigated under simulated solar illumination, and it was found that the solar photocatalytic reduction of CO2 produced CH3OH selectively with much higher conversion rate (240μmol/gcat/h) than that’s been reported to date. The photocatalytic water splitting over the hybrid zeolites was also observed to produce O2 with little H2. The incident-photon-to-electron conversion efficiency (IPCE) of the thin films of AgNTiO2@POM-Zeolite Y was enhanced, and its spectrum shiftstoward longer wavelength to be well resolved into two bands (450 nm, 650 nm) in contrast to the natural two photosynthetic systems competing for the nearly same photons. These results indicate that the hybrid zeolites are non-adiabatic systems harvesting two photons efficiently to induce the proton-coupled electron transfer by stepwise excitation of AgNTiO2 nanochains and POM. To the best of our knowledge, these hybrid zeolites provide a first case of totally inorganic artificial photosynthetic membrane with long-term photostability to fix CO2 selectively as CH3OH by a modified Z-schematic cooperative transport of [...]

Resume : One of the distinctive features of living systems is that they can follow external cues: cells, bacteria and some organisms exhibit chemotaxis, animals swarm and flock, while plants turn their flowers or leaves in the direction of the sun. This last process is called phototropism (or heliotropism, when sun is being tracked) and is associated with the mechanical deformation of the some plant cells upon sun exposure. Inspired by this mechanism, several technologies have been developed that use computer-controlled motorized systems to position solar panels towards the sun and thus harness maximum amount of light energy possible. Here, we also mimic key features of plants’ heliotropism but do so without using computer controllers/pre-programming, motors, or gears. Instead, we drive heliotropic motions by stimuli-responsive materials – in the designs we describe, these systems contain of a shape memory alloy, nitinol, and known materials such as solar panels. Finally, we achieve to get pronounced changes in response to light stimuli and the systems are capable of maintaining themselves in non-equilibrium dissipative states, in which they maximize light energy.

Resume : Bacteria are perfect example of flexible biomodels which respond to changes of external conditions. Here we present the results how bacteria become resistant and how they can adapt to nanomechanical stress. We exposed Escherichia coli to ZnO nanorods (ZnO NR) under stirring as an example of external stress. During cytotoxicity studies we observed that bacterial cells, which survived 24 hours of incubation with ZnO NR, acquired mechanical resistance. Such bacteria in second run of the experiment were almost unaffected by exposure to ZnO NR. Gram-negative E. coli bacterium appeared as a Gram-positive strain in standard Gram staining method after exposure to ZnO NR. Electron microscopy (TEM, SEM and Cryo-SEM with EDS) analysis revealed changes of morphology of survivor cells. Additional genetic and proteomic studies were performed.