Multiphase imaging of freezing particle suspensions by confocal microscopy

Ice-templating is a well-established processing route for porous ceramics. Because of the structure/properties relationships, it is essential to better understand and control the solidification microstructures. Ice-templating is based on the segregation and concentration of particles by growing ice crystals. What we understand so far of the process is based on either observations by optical or X-ray imaging techniques, or on the characterization of ice-templated materials. However, in situ observations at particle-scale are still missing. Here we show that confocal microscopy can provide multiphase imaging of ice growth and the segregation and organization of particles. We illustrate the benefits of our approach with the observation of particles and pore ice in the frozen structure, the dynamic evolution of the freeze front morphology, and the impact of PVA addition on the solidification microstructures. These results prove in particular the importance of controlling both the temperature gradient and the growth rate during ice-templating.     

Effect of Different Synthesis Approaches on Structural and Thermal Properties of Lanthanide(III) Metal–Organic Frameworks Based on the 1H-Pyrazole-3,5-Dicarboxylate Linker

Journal of Inorganic and Organometallic Polymers and Materials - The impact of different synthetic procedures such as: hydrothermal, mechanochemical and precipitation on the structure and thermal...     

Genetically targetable and color-switching fluorescent probe

Color bind: We have developed a probe TMR-para-MG that switches its fluorescence emission upon binding to a fluorogen-activating protein (FAP). In cells that express FAP, this dye labels target sites in one color and mitochondria in another color, thus it might be a suitable tool for monitoring changes in mitochondrial membrane potential.     

Mechanism of nanoparticle actuation by responsive polymer brushes: from reconfigurable composite surfaces to plasmonic effects

The mechanism of nanoparticle actuation by stimuli-responsive polymer brushes triggered by changes in the solution pH was discovered and investigated in detail in this study. The finding explains the high spectral sensitivity of the composite ultrathin film composed of a poly(2-vinylpyridine) (P2VP) brush that tunes the spacing between two kinds of nanoparticles-gold nanoislands immobilized on a transparent support and gold colloidal particles adsorbed on the brush. The optical response of the film relies on the phenomenon of localized surface plasmon resonances in the noble metal nanoparticles, giving rise to an extinction band in visible spectra, and a plasmon coupling between the particles and the islands that has a strong effect on the band position and intensity. Since the coupling is controlled by the interparticle spacing, the pH-triggered swelling-shrinking transition in the P2VP brush leads to pronounced changes in the transmission spectra of the hybrid film. It was not established in the previous publications how the actuation of gold nanoparticles within a 10-15 nm interparticle distance could result in the 50-60 nm shift in the absorbance maximum in contrast to the model experiments and theoretical estimations of several nanometer shifts. In this work, the extinction band was deconvoluted into four spectrally separated and overlapping contributions that were attributed to different modes of interactions between the particles and the islands. These modes came into existence due to variations in the thickness of the grafted polymeric layer on the profiled surface of the islands. In situ atomic force microscopy measurements allowed us to explore the behavior of the Au particles as the P2VP brush switched between the swollen and collapsed states. In particular, we identified an interesting, previously unanticipated regime when a particle position in a polymer brush was switched between two distinct states: the particle exposed to the surface of the collapsed layer and the particle engulfed by the swollen brush. On average, the characteristic distance between the particles and the islands increased upon the brush swelling. The observed behavior was a result of the anchoring of the particles to polymeric chains that limited the particles' vertical motion range. The experimental findings will be used to design highly sensitive optical nanosensors based on a polymer-brush-modulated interparticle plasmon coupling.     

Free‐volume structure of polyvinylpyrrolidone‐capped glassy As2Se3 nanocomposites prepared by mechanical milling

The method of positron annihilation lifetime (PAL) spectroscopy was first employed to study atomic‐deficient free‐volume structure of nanocomposites prepared by high‐energy mechanical milling of glassy g‐As₂Se₃ in water solution of polyvinylpyrrolidone (PVP). The formalism of x3‐x2‐CDA (coupling decomposition algorithm) describing conversion of bound positron‐electron (positronium Ps) states into positron traps was applied to identify free‐volume elements in pelletized PVP‐capped g‐As₂Se₃ nanocomposite in respect to parent dry‐milled g‐As₂Se₃. Under wet milling, the internanoparticle Ps‐decaying sites in preferential PVP environment were shown to replace free‐volume positron traps in dry‐milled g‐As₂Se₃ with defect‐specific positron lifetime of 0.352 ns, corresponding to diatomic/triatomic vacancies in g‐As‐Se matrix. POLYM. ENG. SCI., 59:2438–2442, 2019. © 2019 Society of Plastics Engineers     

Study on the binary intermetallic compounds in the Mg–Ce system

Electron-probe microanalysis (EPMA) and X-ray diffraction (XRD) studies conducted on Mg–38 wt%Ce and Mg–66 wt%Ce alloys demonstrated the existence of two distinct intermetallic phases, Mg_3.6Ce, Mg₃Ce, with the compositions Mg_3.6–3.7Ce, Mg_3.0–3.2Ce, respectively. XRD indicates that Mg_3.6Ce is likely a defect-vacancy structure of Mg₃Ce. The μ-Mg₃Ce phase, with the Mg_3.0–3.3Ce composition and a possible orthorhombic structure, has also been discovered, which is considered a metastable high-temperature form of the Mg₃Ce phase. Based on these results a version of the phase diagram is suggested for the Mg–Ce system in the composition range of 38–70 wt%Ce which correlates well with the solidification microstructures and phases of the two alloys.     

In Situ Fabrication of B4C–NbB2 Eutectic Composites by Spark–Plasma Sintering

This contribution reports, for the first time, the sintering, microstructure and properties of in situ synthesized/consolidated eutectic composites by spark–plasma sintering (SPS). SPS involves a number of processing parameters that may be used to tailor the composition of eutectic composites. It was shown that pressure may be used as a means of controlling the eutectic formation. By changing the pressure, temperature and composition, we propose a processing route that results in the in situ formation of strengthened eutectic composites, consisting of a matrix (B₄C, and B₄C–NbB₂ composite) and also containing regularly distributed whiskers of NbB₂. The composites with the eutectic composition of 35 mol.% NbB₂ obtained by SPS exhibit a high Vickers hardness (26–27 GPa) and indentation fracture toughness (~6 MPa·m^1/2).