Phase behaviour and structural properties of two members of biphenylyl benzoate chiral mesogenic series

ABSTRACT

Phase behaviour and structural properties of two members of biphenylyl benzoate chiral mesogenic series (2F3R and 3F3R) have been investigated. While both the compounds exhibit SmC* phase over a wide temperature range, 2F3R forms orthogonal SmA* from tilted SmC* on heating but 3F3R melts directly to the isotropic phase. The SmA* phase of 2F3R is found to have de vries characteristics with small effective layer contraction. Both the samples on cooling form hexagonal SmF* phase below SmC* phase. On further cooling soft crystal like hexagonal SmJ* phase is formed in 2F3R, undergoing a change in the tilt direction, but in 3F3R, SmG* phase is formed without any change in the tilt direction. A coexistence phase of (SmC*+SmF*) is also observed in a certain temperature range. Slight differences in the dipole moment and molecular conformation of the two molecules give rise to a subtle change in the intermolecular interaction and play an important role in the appearance of different phases in the two compounds. Cell parameters of SmF*, SmG*, SmJ* phases have also been determined. Layer spacings, tilt angles, average intermolecular spacings and correlation lengths have been measured. How some of these properties compare with other members of the series has been discussed.     

Effect of chemical structure of polycarbonates on entanglement spacing

The master curves of a series of aliphatic polycarbonates(APCs) with different lengths of methylene segments in the repeat unit were obtained by dynamic rheological measurements.The plateau modulus and entanglement molecular weight were determined and cross-checked by different methods.Though having distinct difference in chemical structure of repeat units,both APCs and bisphenol-A polycarbonates have the similar entanglement weight and entanglement spacing.On the other side,the plateau modulus decreases with increasing the length of the side group of aliphatic polycarbonates with different side-chain lengths in the literature.The packing length model can explain the relationship between chain structure and entanglements.     

Isotope Effects in Liquid Metals

Abstract

The areas treated in this article are:

(i) The Haeffner effect; where the light isotope moves towards the anode in all cases so far investigated.

(ii) Self diffusion and mutual diffusion.

(iii) Shear viscosity of pure isotopes of Li⁶ and Li⁷.

In the course of the discussion, the Haeffner effect is shown to be directly related to electrical resistively at the level of the lowest order Born approximation.

Models used for treating isotopic mass effects are then considered; limitations and usefulness being assessed by comparison with experimental data on liquid metals. The marked contrast with low temperature isotope effects is finally commented on.     

Static heterogeneity in metallic glasses and its correlation to physical properties

Glasses exhibit intriguing physical and mechanical properties resulting from their structure. We have investigated metal-glass dynamics using inelastic X-ray scattering and ultrasonic techniques for several Pd-, Pt-, and Zr-based glasses with varying fragility. In some cases we have observed a faster phase velocity at short wavelengths than long wavelengths, or positive dispersion. Here we apply elastic wave scattering theory to suggest that the behavior of acoustic phonons can be understood by considering the presence of intrinsic nanoscale elastic inhomogeneity with a certain correlation length, i.e., “static heterogeneity”. Furthermore, we suggest that such an elastic inhomogeneity could be the origin of many of the interesting physical and mechanical properties of metallic glasses.     

Raman spectroscopic study of the uranyl titanate mineral euxenite (Y,Ca,U,Ce,Th) (Nb,Ta,Ti)2O6

Raman spectra of the uranyl titanate mineral euxenite were analysed and related to the mineral structure. A comparison is made with the Raman spectra of uranyl oxyhydroxide hydrates. The observed bands are attributed to the Ti O and (UO₂)²⁺ stretching and bending vibrations, as well as lattice vibrations of rare‐earth ions. The Raman bands of euxenite are in harmony with those of the uranyl oxyhydroxides. The mineral euxenite is metamict as is evidenced by the intensity of the U O stretching and bending modes, which are of lower intensity than expected, and with bands that are significantly broader. Copyright © 2010 John Wiley & Sons, Ltd.     

Conformational Characteristics of Polyimide Initiator for the Synthesis of Poly(Methylmethacrylate) Grafted Block-Copolymers

Molecular properties of a highly functionalized new polyimide multicenter macroinitiator were studied using viscometry, static and dynamic light scattering, and analytical ultracentrifugation in dilute N,N-dimethylformamide solutions. Exponents of the Mark–Kuhn–Houwink equations were obtained for translational friction and intrinsic viscosity. The studied polyimide is a flexible chain polymer, Kuhn segment length being 2–3 nm.     

Topological Properties of Fibonacci Networks

The Fibonacci numbers are the numbers defined by the linear recurrence equation,in which each subsequent number is the sum of the previous two.In this paper,we propose Fibonacci networks using Fibonacci numbers.The analytical expressions involving degree distribution,average path length and mean first passage time are obtained.This kind of networks exhibits the small-world characteristic and follows the exponential distribution.Our proposed models would provide the valuable insights into the deterministically delayed growing networks.     

Probability routing strategy for scale-free networks

This study proposes a probability routing strategy for improving traffic capability on scale-free networks. Compared with the shortest path routing strategy depending on central nodes largely and the efficient routing strategy avoiding hub routers as much as possible, the probability routing strategy makes use of hub routers more efficiently, transferring approximate average amount of packs of the whole network. Simulation results indicate that the probability routing strategy has the highest network capacity among the three routing strategies. This strategy provides network capacity that can be more than 30 times higher than that of the shortest path routing strategy and over 50% higher than that of the efficient routing strategy. In addition, the average routing path length of our proposed strategy is over 10% shorter than that of the efficient routing strategy and only about 10% longer than that of the shortest path routing strategy.     

Influence of intermolecular interactions on molecular geometry and physical quantities in electrolyte systems

In this paper, using Fourier transform infrared (FTIR) spectroscopy, ion conductivity measurements and first-principle density functional theory (DFT) calculations, we study intermolecular interactions between three molecules (methyl tetrahydrophthalic anhydride (MeTHPA), succinonitrile (SN) plastic crystal, and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt) constituting the lithium-ion battery electrolyte. The C–O stretching band position in MeTHPA shifts to a lower frequency in the order of MeTHPA–SN < MeTHPA < MeTHPA–LiTFSI/SN < MeTHPA–LiTFSI; the average C–O bond length in MeTHPA increases in the same order, which reveals the linear correlation between the vibration frequency shift and bond length change. Furthermore, the lithium ionic conductivities of MeTHPA–LiTFSI/SN and MeTHPA–LiTFSI are consistent with this linear relationship, which confirms that the bond length, vibration frequency and lithium-ion transport are strongly influenced by molecular-level interactions. Our results provide fundamental insights valuable for the understanding of the effect of intermolecular interactions on molecular geometry and physical quantities in different electrolytes, and could be utilized to guide the design of high-performance electrolyte materials.     

Insight into the activity of efficient acid–base bifunctional catalysts for the coupling reaction of CO2

The fixation of carbon dioxide with epoxide catalysed by a series of carboxylic acidic functionalised ionic liquids (ILs) catalysts is investigated by density functional theory method. Except for the catalysts reported by the experiment, the catalytic activity of a new designed catalyst (4c see Scheme 1) is also explored. These ILs are categorised into four groups according to the different cation structures and number of functional groups. The effects of different chain length, anion, and cation structure on the catalytic activity are explored. The elongation of alkyl chain length in cation will increase the product yield, while increasing the chain bulk has almost negligible effect on the enhancement of catalytic activity. Utilisation of imidazole group as the cation is better than pyridine group. And the cation with two functional groups will have a better catalytic activity than that with one functional group.