Temperature and crystallinity profiles in polyolefines isothermal and non-isothermal solidification processes

Temperature and crystallinity profiles developed during the isothermal and dynamic solidification of polypropylene (PP) and high density polyethylene (HDPE), which were measured using different experimental techniques, are analyzed. Appropriate models are developed and used to correlate those experimental results. Profiles obtained by simulation showed to be very similar to those obtained experimentally. This means that those models can predict the degree of crystallinity developed during solidification stages, and values for properties directly related to it, that are relevant technical specifications for the PP and HPDE possible applications. This technique could also make possible the optimization of processing parameters.     

Cross section coherence energy and interaction time in heavy ion dissipative collisions

A recent formulation of the cross section autocorrelation function, specially developed to take into account the angular momentum effects, is compared to the experimental results concerning the²⁸Si +⁴⁸Ti and²⁸Si +⁶⁴Ni reactions. The possibility of determining the mean lifetime of the dinucleus excited states populated in dissipative collisions is also discussed.     

Reactivity of (ferrocenylmethyl)phosphine toward palladium and platinum chlorides. X-ray structure of [Pd(PH2CH2Fc)Cl(mu-PHCH2Fc)]4 (Fc = ferrocenyl), a unique complex containing a Pd4P4 cycle

The reaction of 2 equiv of the air-stable primary phosphine (ferrocenylmethyl)phosphine (PH2CH2Fc, 1) with [Pd(cod)Cl2] (Fc = ferrocenyl; cod = 1,5-cyclooctadiene) at 298 K gave the phosphanido-bridged Pd(II) tetramer [Pd(PH2CH2Fc)Cl(mu-PHCH2Fc)]4 (2), which shows an unprecedented arrangement of four Pd atoms embedded in an eight-membered Pd4P4 ring. An X-ray diffraction study showed that 2 crystallizes in the triclinic space group P with a = 17.607(7) A, b = 17.944(7) A, c = 18.792(7) A, alpha = 107.120(12) degrees, beta = 96.344(13) degrees, gamma = 117.087(15) degrees . Each molecule contains four palladium atoms in a distorted square-planar coordination formed by one chlorine and three phosphorus atoms. Two of the latter belong to bridging primary phosphanides and the remaining one is contributed by a terminal PH2CH2Fc ligand. The coordination environments of neighboring metal centers adopt an almost perpendicular mutual orientation. The reaction of 2 equiv of 1 with [Pt(cod)Cl2] at 323 K yielded the analogous Pt(II) tetramer of formula [Pt(PH2CH2Fc)Cl(mu-PHCH2Fc)]4 (3), which was fully characterized by multinuclear and dynamic NMR, IR, and elemental analyses. Single-crystal X-ray diffraction on 3 confirmed the tetranuclear arrangement in the solid state, but orientational disorder of the molecule precludes a more detailed discussion of the structure. Low-temperature NMR experiments in CD2Cl2 showed the presence of two slowly interconnecting conformers. Reaction of 1 and [M(cod)Cl2] (M = Pd or Pt) at lower temperatures (273 K for Pd, 295 K for Pt) in dichloromethane allowed the detection in solution of the mononuclear species cis-[M(PH2CH2Fc)2Cl2] (M = Pd, 4; M = Pt, 5) which, upon heating, transformed into the tetramers 2 and 3, respectively. Solid samples of 4 and 5 could be isolated after workup at low temperature and were characterized by conventional spectroscopic methods.     

Mode of Action and Design Rules for Additives That Modulate Crystal Nucleation

Molecular dynamics simulations reveal that the key factors that determine the ability of an additive to modulate crystal nucleation are the strength of its interaction with the solute, its disruptive ability (which may be based on steric, entropic, or energetic effects), and interfacial properties, along with its ability to serve as a template for nucleation (see snapshot of an emerging nucleus with a single‐particle additive: black spheres).

     

Interactions suppress quasiparticle tunneling at Hall bar constrictions

Tunneling of fractionally charged quasiparticles across a two-dimensional electron system on a fractional quantum Hall plateau is expected to be strongly enhanced at low temperatures. This theoretical prediction is at odds with recent experimental studies of samples with weakly pinched quantum-point-contact constrictions in which the opposite behavior is observed. We argue here that this unexpected finding is a consequence of electron-electron interactions near the point contact.     

Tuning the optical properties of Prussian blue-like complexes

The rational design of the organic ligand allows to finely tune the degree of delocalization of mixed-valence Prussian blue-like molecules.