Synthesis and mesomorphism behaviour of chalcones and pyrazoles type compounds as photo-luminescent materials

The following organic and organic–inorganic hybrid compounds were prepared as photo-luminescent materials following efficient and practical synthetic methods: 1,3-bis[4-(n-alkoxy)phenyl]-2-propen-1-one (where, n-alkoxy: O(CH₂)_nH, n = 6,7,8,9 or 10); 3,5-bis[4-(n-alkoxy)phenyl]-1H-pyrazole (where, n-alkoxy: O(CH₂)_nH, n = 6,7,8,9 or 10) (in case of n = 7, a mixture of 3,5-bis(4-heptyloxyphenyl)-1H-pyrazole and 3,5-bis(4-heptyloxyphenyl)-4H-pyrazole was detected) and bis(3,5-bis [4-(n-alkoxy) phenyl]-1H-pyrazole) silver(I) nitrate (where, n-alkoxy: O(CH₂)_nH, n = 6,7,8,9 or 10). The prepared compounds have been characterised and their structures were elucidated depending upon (FTIR, UV-Vis, ¹HNMR, ¹³CNMR, 2D ¹H-¹H-COSY, 2D ¹H-¹³C-HSQC and mass spectra) in addition to molar conductivity measurements for silver(I) complexes. The mesomorphism behaviour of the prepared compounds was studied using polarised light optical microscopy and confirmed with differential scanning calorimetry and X-ray powder diffraction techniques. The studies showed that among all of these compounds only the pyrazole derivatives are liquid crystal materials. The luminescent properties of all the prepared compounds were also investigated which confirmed that all of these compounds are photo-luminescent in the crystalline solid state and in the mesophase.     

A Sequential Debonding Fracture Model for Hydrogen-Bonded Hydrogels

Hydrogen bonds are known to play an important role in prescribing the mechanical performance of certain hydrogels such as polyether-based polyurethanes. The quantitative contribution of hydrogen bonds to the toughness of polymer networks, however, has not been elucidated to date. Here, a new physical model is developed to predict the threshold fracture energies of hydrogels physically crosslinked via hydrogen bonds. The model is based on consecutive and sequential dissociation of hydrogen-bonded crosslinks during crack propagation. It is proposed that the scission of hydrogen bonds during crack propagation allows polymer strands in the deformation zone to partially relax and release stored elastic energy. The summation of these partial chain relaxations leads to amplified threshold fracture energies which are 10–45 times larger than those predicted by the classical Lake–Thomas theory. Experiments were performed on a hydrophilic polyurethane hydrogel where urea additions were used to control the density of hydrogen bonds. The measured fracture energies were in good agreement with the calculated values. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1287–1293     

Combustion Behaviour of Nitrocellulose and its Complexes with Copper Oxide. Hot stage microscopic studies

Complexes of nitrocellulose (NC – low and high nitrogen content) with copper oxide (CuO) have been synthesized and studied for morphological behaviour on heating from room temperature to 500°C with the help of hot stage microscopy (HSM). During decomposition, NC:CuO complexes show contraction of fibrous boundaries followed by mass movement of matrix, with the evolution of brown yellow colour gas at higher temperatures as compared to NC alone. This revised version was published online in July 2006 with corrections to the Cover Date.     

Intractable high‐Tg thermoplastics processed with epoxy resin: Interfacial adhesion and mechanical properties of the cured blends

The intractable, high‐temperature‐resistant thermoplastics (TPs) polyphenylenether (PPE) and polyetherimide (PEI) were processed by dissolution into epoxy–amine precursors and a subsequent reaction of the precursors. Because the TP concentration was higher than the critical concentration, the phase separation produced a dispersion of crosslinked thermoset (TS) particles into a TP matrix. The morphology of the blends was examined with transmission electron microscopy and dynamic mechanical thermal spectroscopy, which showed completion of the phase separation. The interfacial adhesion at the TP‐matrix/TS‐particle interface was estimated on TP/TS bilayers to be 10 J/m² in PEI blends, whereas it was 70 J/m² in PPE blends, where there is strong evidence for in situ grafting between PPE phenolic chain ends and glycidyl functions of the reactive TS. Yielding in the compressive mode occurred at an intermediate yield stress between the components' values, and the anelastic deformation was separated from the plastic deformation. Fractures in the tensile mode occurred through debonding at the matrix/particle interfaces and coalescence of these defects, which led to microcrack formation and brittle failure. Mode I fracture toughness was, therefore, higher for PPE blends than for PEI blends, a result of the higher interfacial adhesion. However, a decrease from pure TP was observed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 363–373, 2001     

Main-chain biodegradable liquid crystal based on cholesteryl end-capped polycarbonate copolymers

Main-chain biodegradable liquid crystal (LC) based on cholesteryl end-capped polycarbonate copolymers was investigated. The novel LC was synthesised through ring-opening copolymerisation of trimethylene carbonate with ε-caprolactone (CL) initiated by cholesterol, without adding any catalyst. The chemical structure of the resulting polymers was confirmed by ¹H NMR. The liquid crystalline properties were validated by X-ray diffraction, differential scanning calorimetry and polarising optical microscopy. The results showed that the synthesised polycarbonate copolymers Chol-(TMCL)x + y exhibited liquid crystallinity in particular temperature ranges because of the incorporation of the cholesterol moieties. Furthermore, the effect of CL content on the mesomorphism properties of Chol-(TMCL)_x+y was also investigated; the higher the CL content, the lower the mesomorphism properties. It might be attributed to the hindered orientation of LC caused by the crystallinity of the poly(ε-caprolactone) (PCL) segments in the polymer chain.     

Unusual electro-optical behaviour of the nematic polyacrylate

ABSTRACT

High sensitivity of liquid crystals to the electric field makes them highly demanded and widely used in different applications. Despite the large number of the electro-optical research on the low-molar-mass liquid crystals electro-optics of the liquid crystalline (LC) polymers is much less studied. Herein, the comparative electro-optical behaviour of two nematic comb-shaped polyacrylates with phenylbenzoate mesogenic side groups was studied in detail. These two polyacrylates have completely the same structure of polymer backbone and spacer length but different in the direction of the ester group in the phenylbenzoate fragments. It was found that this difference predetermines their completely opposite electro-optical properties.

The influence of the electric field of different strength and frequency on the orientation of the mesogenic groups of these polymers is studied. It is shown that application of the electric field at temperatures above the glass transition temperature (~25°C) induces reorientation of the mesogenic groups along or perpendicular to the electric field direction depending in its turn on the ester group direction. For one of the polyacrylates an unusual textural transition is found; during cooling of the polymer sample under applied field at definite temperature a sharp change in the mesogen’s orientation from homeotropic to planar one is found. This electro-optical phenomenon is observed for the first time and probably associated with sharp change in sign of anisotropy of dielectric permittivity from positive (at high temperatures) to negative one (at lower temperatures). Kinetics of the electro-optical switching at different temperatures, influence of the molar masses of the polymer and frequency of the applied AC field on electro-optical behaviour of the polymers are studied. The possibility of the fixation of the electroinduced homeotropic alignment of the mesogenic groups by photopolymerisation of the diacrylate dissolved in the polymer is demonstrated.     

Annealing of melt-crystallized nylon 6

Effect of annealing on thermal behaviour and crystalline structure of meltcrystallized nylon 6 has been investigated.The annealing process is found to be characterized by an incubation period followed by a more or less doubling of the SAXS long spacing and of the crystallinity.The extrapolated heat of melting of the crystalline phase of nylon 6 in the-modification is 188 Jg^–1 and its extrapolated equilibrium melting temperature is 260 °C.Presented in part at 28th IUPAC Symposium on Macromolecules, Strasbourg, July, 1981.     

Positive solutions for Lotka–Volterra competition system with large cross-diffusion in a spatially heterogeneous environment

In this paper, we study the stationary problem for the Lotka–Volterra competition system with cross-diffusion in a spatially heterogeneous environment. Although some sufficient conditions for the existence of positive solutions are obtained by using global bifurcation theory, the information for their structure is far from complete. In order to get better understanding of the competition system with cross-diffusion, we focus on the asymptotic behaviour of positive solutions and derive two shadow systems as the cross-diffusion coefficient tends to infinity, moreover, the structure of positive solutions of the limiting system is analysed. The result of asymptotic behaviour also reveals different phenomena from that studied in Wang and Li (2013).     

Exact and explicit solutions of Euler-Painlevé equations through generalized Cole-Hopf transformations

More general Euler-Painlevé equations are exactly linearized using generalized Cole-Hopf transform and are shown to admit exact solutions in terms of Kummer functions. The asymptotic behaviours of Euler-Painlevé equations are also derived.     

Emergence of density dynamics by surface interpolation in elementary cellular automata

A classic problem in elementary cellular automata (ECAs) is the specification of numerical tools to represent and study their dynamical behaviour. Mean field theory and basins of attraction have been commonly used; however, although the first case gives the long term estimation of density, frequently it does not show an adequate approximation for the step-by-step temporal behaviour; mainly for non-trivial behaviour. In the second case, basins of attraction display a complete representation of the evolution of an ECA, but they are limited up to configurations of 32 cells; and for the same ECA, one can obtain tens of basins to analyse. This paper is devoted to represent the dynamics of density in ECAs for hundreds of cells using only two surfaces calculated by the nearest-neighbour interpolation. A diversity of surfaces emerges in this analysis. Consequently, we propose a surface and histogram based classification for periodic, chaotic and complex ECA.