Preparation of dye-loaded SiO2 nanoparticles

A room temperature method for the encapsulation of pyrene in SiO₂ nanoparticles is described. The relation between alkoxysilane surfactant chain length, reactant molar ratios and the uptake of dye, sample morphology, photophysical properties, and the ability of the silicate matrix to protect the encapsulated dye was examined. The synthesis can easily be adapted for the encapsulation of other hydrophobic and thermolabile substances, and used in the development of nanostructured optically active coatings, films and monoliths.     

High-temperature synthesis, single-crystal X-ray structure determination and solid-state NMR investigations of Ba7[SiO4][BO3]3CN and Sr7[SiO4][BO3]3CN

The novel alkaline earth silicate borate cyanides Ba₇[SiO₄][BO₃]₃CN and Sr₇[SiO₄][BO₃]₃CN have been obtained by the reaction of the respective alkaline earth metals M=Sr, Ba, the carbonates M^IICO₃, BN, and SiO₂ using a radiofrequency furnace at a maximum reaction temperature of 1350°C and 1450°C, respectively. The crystal structures of the isotypic compounds M^II₇[SiO₄][BO₃]₃CN have been determined by single-crystal X-ray crystallography (P6₃mc (no. 186), Z=2, a=1129.9(1) pm, c=733.4(2) pm, R₁=0.0336, wR₂=0.0743 for M^II=Ba and a=1081.3(1) pm, c=695.2(1) pm, R₁=0.0457, wR₂=0.0838 for M^II=Sr). Both ionic compounds represent a new structure type, and they are the first examples of silicate borate cyanides. The cyanide ions are disordered and they are surrounded by Ba²⁺/Sr²⁺ octahedra, respectively. These octahedra share common faces building chains along [001]. The [BO₃]³⁻ ions are arranged around these chains. The [SiO₄]⁴⁻ units are surrounded by Ba²⁺/Sr²⁺ tetrahedra, respectively. The title compounds additionally have been investigated by ¹¹B, ¹³C, ²⁹Si, and ¹H MAS-NMR as well as IR and Raman spectroscopy confirming the presence of [SiO₄]⁴⁻, [BO₃]³⁻, and CN⁻ ions.     

XRD and Si MAS-NMR spectroscopy across the β-Lu2Si2O7-β-Y2Si2O7 solid solution

Samples in the system Lu_2−xY_xSi₂O₇ (0?x?2) have been synthesized following the sol-gel method and calcined to 1300 °C, a temperature at which the β-polymorph is known to be the stable phase for the end-members Lu₂Si₂O₇ and Y₂Si₂O₇. The XRD patterns of all the compositions studied are compatible with the structure of the β-polymorph. Unit cell parameters are calculated as a function of composition from XRD patterns. They show a linear change with increasing Y content, which indicates a solid solubility of β-Y₂Si₂O₇ in β-Lu₂Si₂O₇ at 1300 °C. ²⁹Si MAS NMR spectra of the different members of the system agree with the XRD results, showing a linear decrease of the ²⁹Si chemical shift with increasing Y content. Finally, a correlation reported in the literature to predict ²⁹Si chemical shifts in silicates is applied here to obtain the theoretical variation in ²⁹Si chemical shift values in the system Lu₂Si₂O₇-Y₂Si₂O₇ and the results compare favorably with the values obtained experimentally.     

New trends in polylactide (PLA)-based materials: “Green” PLA-Calcium sulfate (nano)composites tailored with flame retardant properties

Starting from gypsum, a by-product of lactic acid fabrication process, novel “green” composites have been produced by melt-blending polylactide (PLA) and this filler after a previous specific dehydration to obtain anhydrite II (AII). Such a material is potentially interesting in biodegradable/rigid packaging and in technical applications requiring rigidity, heat resistance and dimensional stability. In order to obtain PLA-AII composites characterized by specific end-use flame retardant properties, the addition of selected organo-modified layered silicates (OMLS) was considered. Co-addition of AII and OMLS leads to PLA (nano)composites characterized by good (nano)filler dispersion, thermal stability and adequate mechanical resistance. The flame retardant properties as shown by cone calorimetry showed significant increase in the ignition time compared to neat PLA and a substantial decrease, i.e., ca. 40%, of the maximum rate of heat release, whereas the UL94 HB test was successfully passed revealing non-dripping effect and extensive char formation. The study represents a new approach in formulating novel PLA grades with improved characteristic features.     

Mechanisms of TL for production of the 230 °C peak in natural sodalite

The thermoluminescence (TL) peak in natural sodalite near 230 °C, which appears only after submitted to thermal treatments and to gamma irradiation, has been studied in parallel with electron paramagnetic resonance (EPR) spectrum appearing under the same procedure. This study revealed a full correlation between the 230 °C TL peak and the eleven hyperfine lines from EPR spectrum. In both case, the centers disappear at the same temperature and are restored after gamma irradiation. A complete model for the 230 °C TL peak is presented and discussed. In addition to the correlation and TL model, specific characteristics of the TL peaks are described.     

Improved DFT calculation of Raman spectra of silicates

Very accurate vibrational spectra of silicates are obtained from DFT calculations if the appropriate Hamiltonian is used. Theoretical considerations suggest that the Hartree-Fock component of ACM1 hybrid functionals should be 1/6 instead of 1/4 for this class of compounds. When applied to the PBE functional this removes the scaling error of the calculated vibrational frequencies. Calculations using this PBE(n = 6) functional in combination with optimized Gaussian basis sets result in very small remaining deviations between observed and calculated Raman shifts, with standard uncertainties of ≈3.5 cm⁻¹, maximum deviations of ≈10 cm⁻¹, and no significant systematic trends. This has been confirmed for a wide range of silicate structures, for which high-quality Raman spectra have been published: forsterite α-Mg₂SiO₄ (nesosilicate), γ-Y₂Si₂O₇ (sorosilicate), K₂Ca₃Si₃O₁₀ (oligosilicate), K₂Ca₄Si₈O₂₁ (phyllosilicate), and α-quartz SiO₂ (tectosilictae).     

Formation and stability of Gd, Y, Yb and Lu disilicates and their solid solutions

The synthesis and the phase stability regions of the disilicates of Y, Lu, Yb and Gd have been investigated at temperatures between 1300 and 1600 °C. The mean ionic radius of the rare-earth element ion including Y turns out to be the key parameter to govern the stabilities of polymorph types of both pure disilicates and their solid solutions. Both are predicted correctly by the phase stability diagram of Felsche [1] [J. Felsche, Struct. Bond. 13 (1973) 99-197]. Furthermore, it correlates with the reactivity, with increasing radius a faster reaction is observed at a given temperature. A fast reactivity is assumed to create difficulties in the densification of disilicates with ionic radius exceeding ∼0.88 Å. In the reaction from oxide powders monosilicates are formed in a first step. Disilicates are formed from those initially in the form of low-temperature modifications, which transform in a sequence to high-temperature modifications.     

Near- and mid-infrared spectroscopy of sol–gel derived ormosils: vinyl and phenyl silicates

The suitability of ormosils as photonic materials was investigated. Vinyl and phenyl silicates were synthesised below 100°C. A detailed assignment of mid-infrared vibrational absorption bands is given. This allowed assignment of overtone and combination bands in the near-infrared region and an assessment of residual water contamination, which is low and can be expelled by evacuation. These ormosils have low intrinsic and extrinsic optical absorption in the visible spectral region and at useful wavelengths in the near-infrared.     

Breakdown of the fractional Stokes–Einstein relation in silicate liquids

The fractional Stokes–Einstein relation postulates a direct relationship between conductivity and shear flow. Like viscosity, the electrical resistivity of a glass-forming liquid exhibits a non-Arrhenius scaling with temperature. However, while both viscosity and resistivity are non-Arrhenius, here we show that these two properties follow distinct functional forms. Through analysis of 821 unique silicate liquids, we show that viscosity is best represented using the Mauro–Yue–Ellison–Gupta–Allan (MYEGA) model, whereas the resistivity of the same compositions more closely follows the Avramov–Milchev (AM) equation. Our results point to two fundamentally different mechanisms governing viscous flow and conductivity and therefore cast doubt on the general validity of the fractional Stokes–Einstein relation.     

Effect of UV anneal on plasma CVD low-k film

Plasma-enhanced chemical vapor deposition (PE-CVD) low-dielectric (low-k) film was irradiated with ultra violet (UV) light of wavelength 172 nm to enhance mechanical strength and reduce dielectric constant (k value). The thickness measurement method for the UV annealed low-k film is discussed. The effects of UV irradiation on dielectric constant, shrinkage, stress, density, pore size, mechanical strength, and structure are clarified and the mechanism is discussed.