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Liquid crystal elastomers (LCEs) are anisotropic polymeric materials. When subjected to an applied stress, liquid crystalline (LC) mesogens within the elastomeric polymer network (re)orient to the loading direction. The (re)orientation during deformation results in nonlinear stress‐strain dependence (referred to as soft elasticity). Here, we uniquely explore mechanotropic phase transitions in elastomers with appreciable mesogenic content and compare these responses to LCEs in the polydomain orientation. The isotropic (amorphous) elastomers undergo significant directional orientation upon loading, evident in strong birefringence and x‐ray diffraction. Functionally, the mechanotropic displacement of the elastomers to load is also nonlinear. However, unlike the analogous polydomain LCE compositions examined here, the isotropic elastomers rapidly recover after deformation. The mechanotropic orientation of the mesogens in these materials increase the toughness of these thiol‐ene photopolymers by nearly 1300 % relative to a chemically similar elastomer prepared from wholly isotropic precursors. [ABSTRACT FROM AUTHOR]

We report the pressure-induced crystallographic transitions and optical behavior of MAPbI3 (MA=methylammonium) using in situ synchrotron X-ray diffraction and laser-excited photoluminescence spectroscopy, supported by density functional theory (DFT) calculations using the hybrid functional B3PW91 with spin-orbit coupling. The tetragonal polymorph determined at ambient pressure transforms to a ReO3-type cubic phase at 0.3 GPa. Upon continuous compression to 2.7 GPa this cubic polymorph converts into a putative orthorhombic structure. Beyond 4.7 GPa it separates into crystalline and amorphous fractions. During decompression, this phase-mixed material undergoes distinct restoration pathways depending on the peak pressure. In situ pressure photoluminescence investigation suggests a reduction in band gap with increasing pressure up to ≈0.3 GPa and then an increase in band gap up to a pressure of 2.7 GPa, in excellent agreement with our DFT calculation prediction. [ABSTRACT FROM AUTHOR]

Silatrane prepared from fumed silica and triethanolamine was used as a precursor for SBA-1 synthesis at room temperature using cationic surfactants, derived from alkyltrimethylammonium bromides, C nTMAB ( n=14, 16, and 18), as templates in dilute solutions. The influence of acidity, alkyl chain length of the surfactant, and synthesis temperature was studied. The shape of the SBA-1 crystals was dependent on the alkyl chain length of the surfactant. At a high surfactant concentration and an elevated reaction temperature (50°C), three-dimensionally ordered mesopores were invariably produced. Both X-ray diffraction and transmission electron microscopic results showed characteristics of the three-dimensional cubic structure. Scanning electron microscopic images of SBA-1 indicated the crystalline-like appearance of an octadecahedron (18-hedron) consistent with six square {100} and 12 hexagonal {110} planes with a cubic symmetry. The surface area of the product was as high as 1000–1500 m2/g with an adsorption volume of 0.6–1.0 cm3/g. [ABSTRACT FROM AUTHOR]

Environmental chlorapatites, of the form A10(B xC1− xO4)6Cl2, where A=Ca, Cd, or Pb; B/C=P, V, or Cr and 0≤ x≤1, were synthesized by solid-state reactions. Crystal structure variations, primarily lattice parameters, were examined through powder X-ray diffraction methods, while performance and long-term durability of these waste form apatites were assessed by a combination of the toxicity characteristic leaching procedure (TCLP) and the American Nuclear Society (ANS) method. As expected, an overall dilation of unit cell edges was observed with increasing ionic substitutions. However, a discontinuity in linearity was often observed, generally forx≥0.5. The correlation of microstructural changes and leach testing shows that lead chlorapatite is found to be more suitable for waste stabilization than calcium and cadmium analogues. [ABSTRACT FROM AUTHOR]

Hydrogen bonding exists in all hybrid organic-inorganic lead halide perovskites MAPbX3 (X = Cl, Br, or I). It has a strong influence on the structure, stability, and electronic and optical properties of this perovskite family. The hydrogen-bonding state between the H atoms of the methylammonium (MA) cation and the halide ions is resolved by combining ab initio calculations with temperature-dependent Raman scattering and powder X-ray diffraction measurements on MAPbBr3 hybrid perovskites. When the compounds are cooled, the H-bonding in the NH3 end of the MA group shows sequential changes while the H atoms in the CH3 end form H bonds with only the Br ions in the orthorhombic phase, leading to a decrease in the degree of rotational freedom of MA and a narrowing for MA Raman modes. Hydrogen bonding drives the evolution of temperature-dependent rotations of the MA cation and the concomitant tilting of PbX6 octahedra with the consequent dynamical change in the electronic band structures, from indirect bandgap to direct bandgap along with ~60-fold PL emission enhancement upon cooling. We experimentally and theoretically reveal the evolution of hydrogen bonding during polymorphic transformations and how the different types of hydrogen bonding lead to specific optoelectronic properties and device applications of hybrid perovskites. [ABSTRACT FROM AUTHOR]

There are demands to form nanolayered coating consisting of different materials in order to enhance the coating mechanical properties. However, poor structure control may lead to the formation of second phase and various defects. In this work, we endeavored to use cathodic arc deposition (CAD) method to fabricate TiN/Ti X Al 1 − X N nanolayered coatings with periods (Λ) ranging from 8 to 45 nm, which has great influences on coating microstructures and properties. X-ray diffraction (XRD), electron microscopy, nanoindentation and tribometry were employed to correlate coating microstructure and Λ with mechanical properties and wear resistance. The nanolayered coatings consisted of columnar grains with [111] texture, where individual grains contained low-angle grain boundaries without voids and amorphous phases. As Λ decreased, superlattices were generated, and reducing Λ from 45 nm to 13 nm yielded coatings with superior mechanical properties. The hardness peaked at 38.9 ± 3.6 GPa with a Young's modulus at 502.5 ± 40.4 GPa at 13 nm, however, when the Λ decreased to 8 nm the hardness and the Young's modulus deteriorated. It was concluded that wear resistance improved as the Λ decreased due to the greater interface population that impedes crack propagation. [ABSTRACT FROM AUTHOR]

Wireless transduction of light into mechanical work manifested as shape-changing surfaces, adaptive structures, or actuators is a topic of considerable recent interest. In the work reported here, the photomechanical responses of a new series of crosslinked azobenzene-functionalized polyimides prepared with increasing backbone rigidity over a range of crosslinker concentrations are examined. The baseline properties of the materials were characterized with X-ray diffraction, thermal analysis, and photomechanical examination including cantilever bending experiments and tensile tests. Increasing the rigidity of the backbone repeat unit reduces the magnitude of the shape change (observed as cantilever deflection) but increases the magnitude of photogenerated stress (in tensile tests). The promise of these materials as wireless actuators was examined in photoinitiated snap-through experiments. [ABSTRACT FROM AUTHOR]

Abstract: (Ba,Sr)2TiSi2O8 fresnoite powders were prepared via a Pechini process in which citric acid and ethylene glycol were used as complexing agents. The resulting gel contained a homogeneous distribution of the metal ions that suppressed the formation of (Ba,Sr)TiO3 perovskite as a secondary phase during calcination. Phase development was examined as by isochronal and isothermal reaction analysis. A combination of thermo- and differential gravimetric analysis (TGA–DGA), quantitative X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) confirmed that calcination at 900°C/12h yielded finely crystalline (∼70nm) Ba2TiSi2O8 (BTS) and Sr2TiSi2O8 (STS). The endmembers and compositional intermediates crystallized directly from the Pechini resin and indirectly through reaction of (Ba,Sr)CO3, (Ba,Sr)TiO3 and a silica-rich glass intermediates. This new method for preparing fresnoite yields materials suitable for consolidation as dense monolithic dielectrics or for use as high surface area catalytic powders. [Copyright &y& Elsevier]