Repurposing aromaticity for organic electronics: Making,breaking, and stacking π‐circuits

This article summarizes a series of lectures I presented in Taiwan as a visiting lecturer sponsored by the Ministry of Science and Technology.     

On the mechanism of proton conductivity in H3OSbTeO6

Pyrochlore-type H₃OSbTeO₆ is a remarkable proton conductor exhibiting an outstanding electrical conductivity even at ambient temperature. It consists of a three-dimensional interconnected (Sb,Te)O₆ framework, built from randomly distributed corner-shared SbO₆ and TeO₆ octahedra, forming large cages in which the H₃O⁺ ions are located. The dynamics of the caged species has been investigated by temperature-dependent neutron diffraction, quasielastic neutron scattering, and NMR experiments. Three types of motion may be discerned, namely, stochastic rotations of the H₃O group around its 3-fold axis, jumps between four equivalent positions within the cage, and long-range inter-cage translational diffusion. The onset of ionic conductivity is clearly reflected by structural changes. Details of the complex diffusion mechanism are given.     

Kinetic study on catalytic cracking of Brazilian high-boiling-point petroleum fractions

This work proposed a technique to estimate the kinetic parameters of cracking reaction. High-boiling-point petroleum fractions (>623.15?K) were analyzed. The experiments were performed using a thermal analysis system with a differential scanning calorimetry module at different linear heating rates (15, 20, 25, and 30?K?min^?1) in the temperature range from 303.15 to 823.15?K. The Arrhenius, Kissinger, and Flynn?COzawa?CWall methods were used to determine the kinetic parameters. The compensation effect and the dependence on the activation energy of the conversion degree were evaluated. The catalyst used was a typical FCC regenerated catalyst containing 48.3?mass% of alumina, and particle size of 67???m. The effect of catalyst loading was studied using 3, 5, and 10?mass%. Analysis of the DSC curves showed a major transitional stage between 693.15 and 723.15?K, identified as an endothermic region of high temperature oxidation (HTO). Empirical kinetic models were produced and data were obtained from the kinetic analysis of the HTO region. Under non-isothermal heating conditions higher activation energies were found as the API gravity of the high-boiling-point petroleum fraction decreased. On the other hand, the results showed consistent effects for the dependence of the activation energy on the extent of cracking conversion under non-isothermal conditions, showing a decrease with the extent of conversion. The catalytic loading effect is remarkable, and provides an alternative route for the cracking with lower activation energy with increasing catalyst weight. The kinetic parameters formulated will be used in the mathematical modeling of the reactive molecular distillation process for upgrading high-boiling-point petroleum fractions.     

1-Million droplet array with wide-field fluorescence imaging for digital PCR

Digital droplet reactors are useful as chemical and biological containers to discretize reagents into picolitre or nanolitre volumes for analysis of single cells, organisms, or molecules. However, most DNA based assays require processing of samples on the order of tens of microlitres and contain as few as one to as many as millions of fragments to be detected. Presented in this work is a droplet microfluidic platform and fluorescence imaging setup designed to better meet the needs of the high-throughput and high-dynamic-range by integrating multiple high-throughput droplet processing schemes on the chip. The design is capable of generating over 1-million, monodisperse, 50 picolitre droplets in 2-7 minutes that then self-assemble into high density 3-dimensional sphere packing configurations in a large viewing chamber for visualization and analysis. This device then undergoes on-chip polymerase chain reaction (PCR) amplification and fluorescence detection to digitally quantify the sample's nucleic acid contents. Wide-field fluorescence images are captured using a low cost 21-megapixel digital camera and macro-lens with an 8-12 cm(2) field-of-view at 1× to 0.85× magnification, respectively. We demonstrate both end-point and real-time imaging ability to perform on-chip quantitative digital PCR analysis of the entire droplet array. Compared to previous work, this highly integrated design yields a 100-fold increase in the number of on-chip digitized reactors with simultaneous fluorescence imaging for digital PCR based assays.     

Magnetic phase transition in a nanostructured antiferromagnet CoO embedded in porous glass

The onset of long-range magnetic order in a nanostructured antiferromagnet CoO embedded in porous glass is revealed by neutron diffraction. The Néel temperature and the volume-averaged magnetic moment/ion are found to be smaller than those in a bulk sample.     

Crystalline and magnetic structures of La1−x BixMnO3+δ manganites

The crystalline and magnetic structures and magnetic properties of La_1?x Bi_xMnO_3+δ (0.4 ≤ x ≤ 0.6, 0 ≤ δ ≤ 0.06) manganites have been studied. The solid solutions having the stoichiometric oxygen content are shown to be orbitally ordered A-type antiferromagnets. An increase in the oxygen content above the stoichiometric value is found to cause Mn⁴⁺ ions in the perovskite lattice, to remove the cooperative Jahn-Teller distortions, and to form a long-range ferromagnetic order. This order becomes broken as the concentration of the tetravalent manganese ions increases further. The tendency toward breaking the ferromagnetic order increases with the bismuth content. The magnetic properties are interpreted in terms of superexchange interactions on the assumption of local lattice distortions induced by anisotropy of the 6s ²(Bi³⁺)-2p ⁶(O^2?) chemical bonds.     

Crystal structure and cation distribution in the solid solution series 2(ZnX)-CuInX2 (X=S, Se, Te)

The solid solution series (2ZnX)_x (CuInX₂)_1−x (X=S, Se, Te) were studied by the combination of laboratory and synchrotron X-ray and by neutron powder diffraction. Within the homologous series the tetragonal distortion ¼-u increases in the sequence S→Se→Te whereas the tetragonal deformation η=c/2a decreases. Besides that, with increasing 2ZnX content in CuInX₂ the anion position parameter u increases as expected. The cation site occupancy in the chalcopyrite type phase of single phase tetragonal samples was obtained by Rietveld analysis of the neutron diffraction data. A non-statistic Zn distribution could be deduced for all three systems. The high temperature in situ diffraction experiments with synchrotron radiation on CuInX₂ powder samples revealed the Cu-In anti-site occupation as the driving force of the temperature dependent phase transition from the chalcopyrite to the zinc-blende type structure.     

Superconducting and normal state properties of dilute alloys of LaSn3 containing Ce impurities

The dependence of the superconducting transition temperature T_c on Ce impurity concentration and the specific heat jump at T_c as a function of T_c are reported for the system ($\text{La}$Ce)Sn₃. The experimental results are analyzed using a theory due to Kaiser concerning the effect on superconductivity of nonmagnetic localized resonant impurity states This analysis yields values for the intraatomic Coulomb repulsion parameter U_eff and the Ce local density of states at the Fermi level N_? (E_F). The results of low temperature normal state heat capacity and magnetic susceptibility measurements which give independent estimates of N_? (E_F) are also reported. A large pressure dependence of the T_c of ($\text{La}$Ce)Sn₃ alloys was observed for pressures up to 20 kbar. This behavior is similar to that previously observed in several other superconducting matrix-Ce impurity systems in which the Ce solute 4f electron shell undergoes a continuous-pressure induced demagnetization.     

Synthesis and alignment of discrete polydiacetylene-peptide nanostructures

Oligopeptides bearing internal diacetylene units are shown to self-assemble in water into one-dimensional nanostructures and aligned macroscopic hydrogels. The diacetylene units can be photopolymerized into polydiacetylenes that run coincident to the nanostructure and noodle long axes, and the resulting nanostructures show evidence for ambipolar charge transport. This self-assembly, alignment and polymerization technique provides a rapid way to produce globally aligned collections of conjugated polymer chains.