Casimir forces exerted by epsilon-near-zero hyperbolic materials

The Casimir force exerted on a gold dipolar nanoparticle by a finite-thickness slab of the natural hyperbolic material namely, the ortorhombic crystalline modification of boron nitride, is investigated. The main contribution to the force originates from the TM-polarized waves, for frequencies at which the parallel and perpendicular components of the dielectric tensor reach minimal values. These frequencies differ from those corresponding to the Lorentzian resonances for the permittivity components. We show that when the slab is made of an isotropic epsilon-near-zero absorbing material the force on the nanoparticle is larger than that induced by a hyperbolic material, for similar values of the characteristic parameters. This fact makes these materials optimal in the use of Casimir’s forces for nanotechnology applications.

Crystalline Modification of Isotactic Polypropylene with a Rare Earth Nucleating Agent Based on Ultrasonic Vibration

In this paper, the crystalline modification of isotactic polypropylene (PP) with a rare earth β nucleating agent (WBG) with different ultrasound conditions was investigated by scanning electron microscopy (SEM), wide-angle X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The relationship between the ultrasound conditions and the crystalline structure, as well as the mechanism for the behavior, were revealed. SEM showed that the dispersion of the nucleating agent in the PP matrix was better at shorter ultrasound distances. In addition, the higher the water cooling temperature, the better the nucleating agent was dispersed in the PP matrix. The results of XRD and DSC showed that the crystallinity and the relative content of the β-crystal were increased with nearer ultrasound distance, as well as increased in higher water cooling temperatures. In particular, under the same conditions, the crystallinity and the relative content of the β-crystal after ultrasonic treatment were much higher than those without ultrasound.

Crystal structure, synthesis and thermal properties of bis(acetonitrile-κN)bis(4-benzoylpyridine-κN)bis(isothiocyanato-κN)nickel(II)

In the crystal structure of the title compound, [Ni(NCS)2(CH3CN)2(C12H9NO)2] or Ni(NCS)2(4-benzoylpyridine)2(acetonitrile)2, the NiII ions are octahedrally coordinated by the N atoms of two thiocyanate anions, two 4-benzoylpyridine ligands and two acetonitrile molecules into discrete complexes that are located on centres of inversion. In the crystal, the discrete complexes are linked by centrosymmetric pairs of weak C—H...S hydrogen bonds into chains. Thermogravimetric measurements prove that, upon heating, the title complex loses the two acetonitrile ligands and transforms into a new crystalline modification of the chain compound [Ni(NCS)2(4-benzoylpyridine)2], which is different from that of the corresponding CoII, NiII and CdII coordination polymers reported in the literature. IR spectroscopic investigations indicate the presence of bridging thiocyanate anions but the powder pattern cannot be indexed and, therefore, this structure is unknown.

Thermal Stability of Shear-Induced Precursors and Their Effect on the Crystalline Structure of β-Nucleated Isotactic Polypropylene

The thermal stability and lifetime of shear-induced precursors under various annealing temperatures, as well as the influence of their relaxation on the crystalline modification in β-nucleated isotactic polypropylene (iPP), are investigated using an ARES rheometer. The wide-angle X-ray diffraction results show that the β-crystal content of sheared β-nucleated iPP samples gradually increases with thermal treatments. The relaxation of shear-induced precursors during annealing which caused the decrease of shear nuclei may restrain the counteraction effect between the shear flow and β-nucleation agent as well as result in the increase of β-crystal content. At the early stage of relaxation, the relaxation degree is closely related to the increase of β-crystals, for which the deeper relaxed shear-induced precursors result in the more restoration of β-crystals. However, when the relaxation degree exceeded a certain limitation, where the β-crystals reached the maximum, the relaxation of shear-induced precursors will no longer influence the crystal structure of β-nucleated iPP.

Synthesis, crystal structure and Hirshfeld analysis of a new crystalline modification of the radical ion salt octamethylenetetrathiafulvalenium triiodide (OMTTF)I3

The reaction between 4,5,6,7-tetrahydro-2-(4,5,6,7-tetrahydro-1,3-benzodithiol-2-ylidene)-1,3-benzodithiole (common name: 4,4′,5,5′,6,6′,7,7′-octahydrodibenzotetrathiafulvalene, OMTTF) and an excess of iodine in tetrahydrofuran (THF) yielded the respective radical organic polyiodide salt, C14H16S4 +·I3 −. The asymmetric unit contains one and a half formula unit of both the cation and the anion, with the half-ions completed through inversion symmetry. The (OMTTF^\bullet+) positive charge can be assigned by the bond distances and the planar structure of the C2S2C=CS2C2 central fragment. In the crystal, trimers of triiodide anions are connected through secondary intermolecular I...I interactions into almost linear I9 3− polyanions. The non-centrosymmetric OMTTF radical cations are linked by S...S interactions into centrosymmetric dimers, while the centrosymmetric OMTTF cations remain as discrete units. The (OMTTF^\bullet+) radical cations and the triiodide anions are linked by weak C—H...I and C—H...S interactions into a three-dimensional network. This work reports the fourth crystalline modification of the C14H16S4^\bullet+·I3 − salt. The three previous modifications were obtained from a mixture of acetonitrile and toluene [Konarev et al. (2005). Synth. Met. 151, 231–238].

Crystalline modification of a rare earth nucleating agent for isotactic polypropylene based on its self-assembly

In this paper, the crystalline modification of a rare earth nucleating agent (WBG) for isotactic polypropylene (PP) based on its supramolecular self-assembly was investigated by differential scanning calorimetry, wide-angle X-ray diffraction and polarized optical microscopy. In addition, the relationship between the self-assembly structure of the nucleating agent and the crystalline structure, as well as the possible reason for the self-assembly behaviour, was further studied. The structure evolution of WBG showed that the self-assembly structure changed from a needle-like structure to a dendritic structure with increase in the content of WBG. When the content of WBG exceeded a critical value (0.4 wt%), it self-assembled into a strip structure. This revealed that the structure evolution of WBG contributed to the K β and the crystallization morphology of PP with different content of WBG. In addition, further studies implied that the behaviour of self-assembly was a liquid–solid transformation of WBG, followed by a liquid–liquid phase separation of molten isotactic PP and WBG. The formation of the self-assembly structure was based on the free molecules by hydrogen bond dissociation while being heated, followed by aggregation into another structure by hydrogen bond association while being cooled. Furthermore, self-assembly behaviour depends largely on the interaction between WBG themselves.