A Shape‐Induced Orientation Phase within 3D Nanocrystal Solids

When nanocrystals self assemble into ordered superstructures they form functional solids that may inherit the electronical properties of the single nanocrystals. To what extent these properties are enhanced depends on the positional and orientational order of the nanocrystals within the superstructure. Here, the formation of micrometer‐sized free‐standing supercrystals of faceted 20 nm Bi nanocrystals is investigated. The self‐assembly process, induced by nonsolvent into solvent diffusion, is probed in situ by synchrotron X‐ray scattering. The diffusion‐gradient is identified as the critical parameter for controlling the supercrystal‐structure as well as the alignment of the supercrystals with respect to the substrate. Monte Carlo simulations confirm the positional order of the nanocrystals within these superstructures and reveal a unique orientation phase: the nanocrystal shape, determined by the atomic Bi crystal structure, induces a total of 6 global orientations based on facet‐to‐facet alignment. This parallel alignment of facets is a prerequisite for optimized electronic and optical properties within designed nanocrystal solids.     

Ligand Shell Engineering to Achieve Optimal Photoalignment of Semiconductor Quantum Rods for Liquid Crystal Displays

The photoalignment process to align semiconductor quantum rods (QRs) in the liquid crystal monomer (LCM) matrix is a flexible technology; however, the optical quality of the resulting enhancement films drops at high concentrations of the QRs. The compatibility between the ligand shell on the QRs and the LCM plays an important role in avoiding this issue. Herein, several kinds of ligand shells on the rod‐in‐rod CdSe/CdS QRs are designed, without affecting the optical properties of QRs, and their compatibility with LCM molecules is studied. Promesogenic dendritic ligands in combination with relatively short alkylphosphonic acids are found to provide the highest optical quality, without QR aggregation, and so the high brightness of the resulting enhancement films, even at higher concentrations of QRs in LCM, which is perfectly suitable for the application in liquid crystal displays.     

Charge‐Separation Dynamics in Inorganic–Organic Ternary Blends for Efficient Infrared Photodiodes

Knowledge about the working mechanism of the PbS:P3HT:PCBM [P3HT=poly(3‐hexylthiophene), PCBM=[6,6]‐phenyl‐C₆₁ ‐butyric acid methyl ester] hybrid blend used for efficient near‐infrared photodiodes is obtained from time‐resolved photoluminescence (PL) studies. To understand the role of each component in the heterojunction, the PL dynamics of the ternary (PbS:P3HT:PCBM) blend and the binary (PbS:P3HT, PbS:PCBM and P3HT:PCBM) blends are compared with the PL of the pristine PbS nanocrystals (NCs) and P3HT. In the ternary blend the efficiency of the charge transfer is significantly enhanced compared to the one of PbS:P3HT and PbS:PCBM blends, indicating that both hole and electron transfer from excited NCs to the polymer and fullerene occur. The hole transfer towards the P3HT determines the equilibration of their population in the NCs after the electron transfer towards PCBM, allowing their re‐excitation and new charge transfer process.     

Hybridization of poly(rI) with poly(rC) adsorbed to the carbon nanotube surface

Hybridization of homopolynucleotide poly(rC) adsorbed to the carbon nanotube surface with poly(rI) free in solution has been studied by absorption spectroscopy and molecular dynamics method. It was found that hybridization on the nanotube surface has a slow kinetics, the behavior of which differs essentially from fast hybridization of free polymers. The duplex obtained is characterized with the reduced thermostability and a lower hyperchromic coefficient than it was observed when the duplex was formed in the absence of the nanotube. These features point to the imperfectness in the structure of the duplex hybridized on the nanotube surface. Computer simulation showed that the strong interaction of nitrogen bases with the nanotube surface weakens significantly hybridization of two complementary oligomers, as the surface prevents the necessary conformational mobility of the polymer to be hybridized.     

Characterization of cross‐linking depth for thin polymeric films using atomic force microscopy

Thin polymeric films made with various elastomers, like polyisoprene, and elastomer composites were prepared for characterization of cross‐linking depth in this study. Various cross‐linking methods have been applied to get mechanically stronger, more thermally stable and chemically resistant polymer coatings. However, there is no existing approach that could effectively characterize the degree or depth of cross‐linking for thin polymer films. The objective of this work is to use atomic force microscopy to characterize cross‐linking depth in a precise way. Hyperthermal hydrogen bombardment‐induced cross‐linking was employed as a cross‐linking method and the depth of cross‐linking was estimated via local change of the elastic modulus along the sample cross‐section with precise force measurement and high spatial resolution. It is found that the cross‐linking depth is closely related to the chemical composition of thin films. Understanding the depth of cross‐linking is vital for a broad range of applications. It is believed that the developed technique is also applicable for studying other cross‐linkable materials. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41493.     

INES – An Interface Between Experiments and Simulation to Support the Development of Robust Process Designs

The development of chemical processes is based on both experiments and process simulations. Data evaluation and reconciliation, model development and validation, and design of experiments are essential steps in this procedure. The different tools and approaches available are usually not supported in an integrated way in the process developer's workflow. Therefore, a framework for process design was created and integrated in a tool box which supports process design comprehensively. It contains methods for data selection and reconciliation, sensitivity analysis, model validation and model adjustment.     

Quantum dots for human mesenchymal stem cells labeling. A size-dependent autophagy activation

Lately certain cytotoxicity of quantum dots (QDs) and some deleterious effects of labeling procedure on stem cells differentiation abilities were shown. In the present study we compared cytotoxicity and intracellular processing of two different-sized protein-conjugated QDs after labeling of the human mesenchymal stem cells (hMSC). An asymmetrical intracellular uptake of red (605 nm) and green (525 nm) quantum dots was observed. We describe for the first time a size-dependent activation of autophagy, caused by nanoparticles.     

Overcoming low Ge ionization and erosion rate variation for quantitative ultralow energy secondary ion mass spectrometry depth profiles of Si(1-x)Ge(x)/Ge quantum well structures

We specify the O(2)(+) probe conditions and subsequent data analysis required to obtain high depth resolution secondary ion mass spectrometry profiles from multiple Ge/Si(1-x)Ge(x) quantum well structures (0.6 ≤ x ≤ 1). Using an O(2)(+) beam at normal incidence and with energies >500 eV, we show that the measured Ge signal is not monotonic with concentration, the net result being an unrepresentative and unquantifiable depth profile. This behavior is attributed to a reduced Ge ionization rate as x approaches 1. At lower beam energies the signal behaves monotonically with Ge fraction, indicating that the Ge atoms are now ionizing more readily for the whole range of x, enabling quantitative profiles to be obtained. To establish the depth scale a point-by-point approach based on previously determined erosion rates as a function of x is shown to produce quantum well thicknesses in excellent agreement with those obtained using transmission electron microscopy. The findings presented here demonstrate that to obtain reliable quantitative depth profiles from Ge containing samples requires O(2)(+) ions below 500 eV and correct account to be taken of the erosion rate variation that exists between layers of different matrix composition.     

Polypyrenes as High‐Performance Cathode Materials for Aluminum Batteries

The pressing need for low‐cost and large‐scale stationary storage of electricity has led to a new wave of research on novel batteries made entirely of components that have high natural abundances and are easy to manufacture. One example of such an anode–electrolyte–cathode architecture comprises metallic aluminum, AlCl₃:[EMIm]Cl (1‐ethyl‐3‐methylimidazolium chloride) ionic liquid and graphite. Various forms of synthetic and natural graphite cathodes have been tested in recent years in this context. Here, a new type of compelling cathode based on inexpensive pyrene polymers is demonstrated. During charging, the condensed aromatic rings of these polymers are oxidized, which is accompanied by the uptake of aluminum tetrachloride anions (AlCl₄^?) from the chloroaluminate ionic liquid. Discharge is the fast inverse process of reduction and the release of AlCl₄^?. The electrochemical properties of the polypyrenes can be fine‐tuned by the appropriate chemical derivatization. This process is showcased here by poly(nitropyrene‐co‐pyrene), which has a storage capacity of 100 mAh g^?1, higher than the neat polypyrene (70 mAh g^?1) or crystalline pyrene (20 mAh g^?1), at a high discharge voltage (≈1.7 V), energy efficiency (≈86%), and cyclic stability (at least 1000 cycles).