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Chain branching detection by Cole–Cole modeling of rheological properties changes during PET mechanical recycling

The detection of branched chains in thermally degraded thermoplastic polymers is far from simple, especially at a low conversion ratio, mainly because of the low sensitivity of commonly used laboratory analytical techniques. The objective of this article is to present an approach able to demonstrate the formation of such macromolecular structures during thermal degradation of molten PET at low oxygen partial pressures (typically for pressures lower than 9% of atmospheric pressure). Such ageing conditions are met during PET mechanical recycling by extrusion, and can be simply reproduced by sequential nitrogen/air tests in a rheometer cavity. The approach consists of a careful analysis of the complex shear modulus changes in a Cole–Cole diagram. Values obtained for Cole–Cole model parameter K′ indicate clearly an accumulation of branched chains in the melt with the time of residence in the reactor.     

Epsilon–delta surgery over $${\mathbb{Z}}$$

The purpose of this paper is to prove a controlled surgery exact sequence, including a stability theorem, as used in the construction of exotic homology manifolds. The approach is to show that this result is a formal consequence of the Chapman–Ferry Alpha-approximation theorem.     

Co-grafting of porphyrins and fullerenes on ZnO nanorods: Towards supramolecular donor-acceptor assembly

This work presents the synthesis and physico-chemical characterization of a novel artificial photosynthetic design, using anisotropic semiconducting nanorods as scaffolds to assemble organic donor-acceptor complexes on their surface. These hierarchical hybrid D-A assemblies were obtained by the co-grafting of porphyrins and fullerenes on the ZnO nanorods. Polarity of the solvent and porphyrin to fullerene ratios were investigated to be markedly influencing the donor-acceptor interaction under the co-grafted conditions on ZnO nanorods. Fourier transform infrared spectroscopy, cyclic voltammetry, electronic absorption and fluorescence spectroscopic techniques were used to characterize the formation and investigate the optoelectronic properties of porphyrin-fullerene complexes on the surface of ZnO. To the best of our knowledge, this is the first example of highly interacting porphyrin-fullerene complexes on ZnO nanorods, which may allow generating efficient nanosystems for artificial photosynthesis and harvesting of solar energy.     

Direct imaging of electron states in open quantum dots

We use scanning gate microscopy to probe the ballistic motion of electrons within an open GaAs/AlGaAs quantum dot. Conductance maps are recorded by scanning a biased tip over the open quantum dot while a magnetic field is applied. We show that, for specific magnetic fields, the measured conductance images resemble the classical transmitted and backscattered trajectories and their quantum mechanical analogue. In addition, we prove experimentally, with this direct measurement technique, the existence of pointer states. The demonstrated direct imaging technique is essential for the fundamental understanding of wave function scarring and quantum decoherence theory.     

Experimental investigation of nanoparticle dispersion by beads milling with centrifugal bead separation

A new type of beads mill for dispersing nanoparticles into liquids has been developed. The bead mill utilizes centrifugation to separate beads from nanoparticle suspensions and allows for the use of small sized beads (i.e. 15-30 microm in diameter). The performance of the beads mill in dispersing a suspension of titanium dioxide nanoparticle with 15 nm primary particles was evaluated experimentally. Dynamic light scattering was used to measure titania particle size distributions over time during the milling process, and bead sizes in the 15-100 microm range were used. It was found that larger beads (50-100 microm) were not capable of fully dispersing nanoparticles, and particles reagglomerated after long milling times. Smaller beads (15-30 microm) were capable of dispersing nanoparticles, and a sharp peak around 15 nm in the titania size distribution was visible when smaller beads were used. Because nanoparticle collisions with smaller beads have lower impact energy, it was found by X-ray diffraction and transmission electron microscopy that changes in nanoparticle crystallinity and morphology are minimized when smaller beads are used. Furthermore, inductively-coupled plasma spectroscopy was used to determine the level of bead contamination in the nanoparticle suspension during milling, and it was found that smaller beads are less likely to fragment and contaminate nanoparticle suspensions. The new type of beads mill is capable of effectively dispersing nanoparticle suspensions and will be extremely useful in future nanoparticle research.