Material profile influences in bulk‐heterojunctions

The morphology in mixed bulk‐heterojunction films are compared using three different quantitative measurement techniques. We compare the vertical composition changes using high‐angle annular dark‐field scanning transmission electron microscopy with electron tomography and neutron and x‐ray reflectometry. The three measurement techniques yield qualitatively comparable vertical concentration measurements. The presence of a metal cathode during thermal annealing is observed to alter the fullerene concentration throughout the thickness of the film for all measurements. However, the absolute vertical concentration of fullerene is quantitatively different for the three measurements. The origin of the quantitative measurement differences is discussed. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1291–1300     

Experimental investigation of electrohydrodynamic instabilities in micro channels

The European Physical Journal Special Topics - An electric field is applied to destabilize the interface between two Newtonian and immiscible liquids flowing in a rectangular micro channel. The...     

Atomic and electronic structure of mixed and partial dislocations in GaN

Here we present a detailed study of mixed dislocations in GaN, in which the complexities of the atomic arrangement in the cores have been imaged directly for the first time using an aberration corrected scanning transmission electron microscope. In addition to being present as a full-core structure, the mixed dislocation is observed to dissociate into partial dislocations separated by a stacking fault only a few unit cells in length. The generation of this stacking fault appears to be impurity driven and its presence is consistent with theoretical predictions for dislocation dissociation in materials with hexagonal crystal symmetry.     

Role of the n+1 amino acid residue on the deamidation of asparagine in pentapeptides

Deamidation plays an important role in biochemical phenomena such as aging. The role of the n + 1 residue on the deamidation of asparagine (asparagine being the nth residue) in three pentapeptide chains (GGNGG, GGNMG and GGNIG) has been analysed with hybrid computational tools. Potentials of mean force at 300 K were calculated from the MD/replica exchange simulations using weighted histogram analysis (WHAM) in explicit water. The snapshots were clustered taking into account the requirements of the plausible deamidation mechanisms, as such the tautomerisation of the asparagine side chain as initial step has been confirmed, based on the proximity of water to the deamidation site. The ultimate goal being to gain an insight on the peptide backbone N-H acidity, quantum mechanical calculations have been carried out. For this purpose, the distribution of Φ/Ψ, Φ₂/Ψ and end-to-end distances deduced from the WHAM diagrams have been considered and a total of 110 structures have been sampled. These neutral pentapeptides as well as their corresponding anions have been optimised (B3LYP/6-31++G(d,p)) in implicit water in order to gain an insight on the peptide backbone N-H acidity. In this study, we have shown that the open conformations of the neutrals and the anions, which display a β sheet like structure are well populated and their pK_as rank in the same order as the deamidating half-lives, that is the peptides that deaminate fastest can more readily access conformations that are more acidic.     

Effect of the direction of the electric field on the interfacial instability between a passive fluid and a viscoelastic polymer

In this paper, we study the linear stability of the interface between an Upper Convective Maxwell fluid and a hydrodynamically passive fluid subject to an electric field applied either parallel or normal to the flat interface between the two fluids. The fluids are leaky-dielectric and we apply surface-coupled model. We solve the model equations analytically and study the dispersion and neutral curves for various parameters representing the applied potential, the fluid’s elasticity, the physical and the electrical properties of the fluids, and the heights of the fluids in the presence of both normal and parallel electric fields. It is found that the critical wavenumber is independent of the Weissenberg number. However, increasing the Weissenberg number increases the maximum growth rate for both the normal and the parallel fields. The critical wavenumber increases with the dimensionless applied voltage for the normal field. Lastly for the normal field, for some values of the dimensionless parameters, the growth rate reached very large values representing some type of singularity as has been observed in the literature. However, for the same values of the parameters no singularity is observed for the parallel field.     

Ultra stable ordered mesoporous phenol/formaldehyde polymers as a heterogeneous support for vanadium oxide

Ordered mesoporous phenol/formaldehyde polymers are presented as an ultra stable heterogeneous support for vanadium oxide.     

Exact Solution of a Generalized ANNNI Model on a Cayley Tree

We consider the Ising model on a rooted Cayley tree of order two with nearest neighbor interactions and competing next nearest neighbor interactions restricted to spins belonging to the same branch of the tree. This model was studied by Vannimenus who found a new modulated phase, in addition to the paramagnetic, ferromagnetic, antiferromagnetic phases and a (+ + - -) periodic phase. Vannimenus’s results are based on an analysis of the recurrence equations (relating the partition function of an n ? generation tree to the partition function of its subsystems containing (n ?1) generations) and most results are obtained numerically. In this paper we analytically study the recurrence equations and obtain some exact results: critical temperatures and curves, number of phases, partition function.     

The stability of L3 sponge phase in acidic solutions

In the synthesis of the disordered lyotropic liquid crystalline L3 sponge phase prepared with the cosurfactants cetylpyridinium chloride and hexanol, aqueous NaCl solution is used as the solvent. When this sponge phase is used as the template for L3 silica-phase processing, we replace NaCl with HCl to facilitate the acid catalysis of tetramethoxysilane in forming a templated silica gel, assuming that changing the solvent from NaCl(aq) to HCl(aq) of equivalent ionic strength does not affect the stability range of the L3 phase. In this work, we confirm that changing the pH of the solvent from neutral to acidic (with HCl) has negligible effect on the L3 phase region. Equivalent ionic strength is provided by either NaCl(aq) or HCl(aq) solvent; therefore, a similar phase behavior is observed regardless of which aqueous solvent is used.