The effect of molecular properties on mechanical behaviour of PMMA—III. Environmental stress crazing in methanol

The correlation between the stress-relaxation curves of methanol-equilibrated poly(methyl methacrylate) (PMMA) and environmental fracture behaviour indicates the role of molecular entanglements in determining if the fracture process of PMMA in methanol occurs via stress-cracking (Regime II) or stress-crazing (Regime I and Transition Regime). The fracture data for high molecular weight (MW) PMMA (Regime I) and medium MW PMMA (Transition Regime) were analyzed by linear, elastic fracture-mechanics (LEFM) and Williams-Marshall (WM) theory. High MW PMMA absorbed more energy and had a wider crack-opening-displacement (COD) than medium MW PMMA, due to a thicker primordial craze thickness. Craze matter in the high MW sample gave a slower crazing stress decay and a better stretching capability with time than that of medium MW sample. The craze-initiation and the craze-growth obeyed a flow-controlled mechanism and relaxation-controlled mechanism, respectively.     

The effect of terminal chain modifications on the mesomorphic properties of 4,4′-disubstituted diphenyldiacetylenes

The typical sidewalls produced in the fabrication of protrusion electrodes are proposed to create a low voltage (4.5 V_rms) and high transmittance (93%) blue-phase liquid crystal display (BP-LCD). The tilted electrodes produce a strong horizontal electrical field that reduces the operating voltage considerably. The common problem of the ‘dead zones’ is solved by reflecting the light onto the electrodes. In order to estimate the phase retardation of the reflected light, a ray tracing simulation program for anisotropic mediums has been developed. The proposed device is more competitive than vertical field switching based BP-LCD and also, has the advantages of protruded in-plane-switching structures. These facts make this technology a potential candidate for the next generation of BP-LCDs.     

The effect of β-cyclodextrin on the properties of cetyltrimethylammonium bromide micelles

The effect of ß-cyclodextrin (ß-CD) on cetyltrimethylammonium bromide (CTAB) micellar properties was studied by the determination of the diffusion coefficient, D. When the CTAB micelles have a spherical structure, D firstly increased and then remained unchanged, while the micellar aggregation number, N, decreased with the addition of ß-CD. When the CTAB concentration was less than the first critical micellar concentration, CTAB molecules could be included into ß-CD cavities with the molar ratio of CTAB to ß-CD being about 1:1. However, when the CTAB concentration was higher than the first critical micellar concentration, mixed spherical micelles were formed with the molar ratio of CTAB to ß-CD being 9:1.     

DFT study of the conductance of molecular wire:The effect of coupling geometry and intermolecular interaction on the transport properties

The density functional theory (DFT) combining with the non-equilibrium Green functions (NEGF) method is applied to the study of the electronic transport properties for a Di-thiol-benzene (DTB) molecule coupled to two Au(111) surfaces. The dependence of the transport properties on the bias, the coupling geometry of the molecule-electrode interface, and the intermolecular interaction are examined in detail. The results show that the existence of the hydrogen atom at the end of the DTB molecule would significantly decrease the transmission coefficients, and then the differential conductance (dI/dV). By changing the position of the DTB molecule located between two electrodes a maximum value of calculated current is observed. It is also found that the intermolecular interaction will strongly influence the transport properties of the system studied.     

The effect of the precursor structure on the catalytic properties of the nickel—chromium catalysts of hydrogenation reactions

The influence of the Ni²⁺/Cr³⁺ ratio in the precursor compound on the formation of the catalyst structure and its transformation upon the thermal treatment and reductive activation in hydrogen was studied. The precursors with the cation ratio Ni²⁺/Cr³⁺ = (2.3–3)/1 represent a homogeneous system of the stichtite-type structure. The treatment of the precursors at T ～400 °C in an inert atmosphere forms a nanosized phase of the NiO-type structure with the lattice parameter a = 4.186±0.005 Å. At 600 °C the lattice parameter of this phase decreases to the tabulated value (a = 4.177±0.005 Å). The phase of nickel chromite of the cubic spinel structure with the lattice parameter a = 8.320±0.005 Å is also observed. Hydrogen activation of the catalyst preheated at 300 °C in an inert gas leads to the formation of Ni⁰ crystallites with a size of ～5.5 nm and a specific surface area of ～7.0 m² g^?1. This catalyst exhibits high activity and selectivity in benzene hydrogenation and preferential CO hydrogenation in the presence of CO₂. The catalysts with the ratio Ni²⁺/Cr³⁺ = 1/(2?3) containing nickel and chromium hydroxocarbonates as precursors are less active in the hydrogenation of benzene to cyclohexane.     

The effect of structure and phase transformation on the mechanical properties of Re₂N and the stability of Mn₂N

First‐principles calculations were carried out on recently synthesized Re₂ and Re₃ as well as hypothetical Tc and Mn nitrides. It is found that structure and covalent bonds play an important role in determining mechanical properties. Under a large strain along (0001)〈101 0〉direction, Re₂N undergoes a phase transformation with a slight increase in ideal shear strength. On the other hand, it is transformed into a phase with weaker mechanical properties, if the strain is along Re₂〈1 21 0〉 direction. Mn₂N can be synthesized under moderate conditions due to its more negative formation energy. Re₂N, Re₃N, and Mn₂N show structure‐related mechanical property under larger strains to ReB₂ but exhibit much lower ideal strengths, which is attributed to the larger ionicity of cation–anion bond. Three‐dimensional framework of strong covalent bonds is thus highly recommended to design superhard materials. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011     

Note on the effect of activity coefficients on the NMR association constants for the 2,4-dinitrotoluene—diphenylamine system. The Qureshi—Varshney—Kamoonpuri equation. Possible role of hydrogen bonding.

The NMR studies of the charge transfer complex between 2,4-dinitrotoluene and diphenylamine in CCl₄ are reinvestigated. The proposed Qureshi-Varshney-Kamoonpuri equation shows that activity coefficients have a profound effect on the NMR association constants. The possibility of hydrogen bonding in the system has also been considered.     

Intermolecular interaction in solution—IV. The influence of solvent on the association of proton donors and acceptors

Infrared spectroscopic studies of indole, diphenylamine and tertiary butanol with proton acceptors, diethylacetamide and ethyl acetate show that the solvent used has a strong directive influence on the association. From a consideration of band frequencies and frequency shifts due to association the solvents were arranged according to the effects produced, while a linear correlation was not observed between the spectroscopic measurements on dilterent donor-acceptor systems and the solvents present.     

The role of μ-hydroxo-ligands in the catalytic properties of binuclear copper—tertiary amine complexes

The influence of the structure of copper/tert. amine-complexes on their catalytic activity in oxidative coupling reactions has been investigated. Only binuclear complexes with bridging hydroxo ligands proved to be catalytically active compounds. This has been revealed using a model complex of copper chloride and N,N,N′,N′-tetramethylethane-1,2-diamine, for which spectroscopic and structural data are presented.We studied the same phenomenon by using soluble copper complexes with two non-crosslinked linear copolymers of styrene, acting as polymeric amine ligands: at-Poly-styrene-co-4-vinylpyridine and at-Poly-styrene-co-N- vinylimidazole. A similar effect of the OH⁻ ions on the catalytic activity has been observed using these polymeric homogeneous catalysts.     

The effect of molecular distortions on spin–orbit coupling in simple hydrocarbons

Recent work [D.N.S. Parker et al., Chem. Phys. Lett. 469 (2009) 43–49] has found intersystem crossing (ISC) on an ultrafast timescale in electronically excited benzene, a surprise as hydrocarbons generally have small spin–orbit coupling. In this paper, the effect of molecular distortions on spin–orbit coupling (SOC) is calculated for cyclobutadiene and benzene. At equilibrium the SOC in both molecules is negligible, and therefore terms arising from molecular distortions must play a significant role in any fast ISC. We show that out-of-plane C–H bends, which leads to the hybridisation of σ and π orbitals, are responsible for the most significant effect. The S₁/S₀ conical intersection is an important feature for understanding the photochemistry of these molecules. We examine the SOC along the vector from the Franck–Condon point to the lowest energy point on the crossing seam and discuss the potential importance of the SOC to the ultrafast dynamics.     

A new insight to the role of bubble properties on inertial effect in particle–bubble interaction

In this study the impact of bubble surface characterization (mobility or immobility), its diameter and velocity is investigated on inertial forces in particle–bubble collision efficiency (E_C). Three models including Sutherland (E_C-SU), Schulze (E_C-SC), and generalized Sutherland Equation (E_C-GSE) were taken into account with regard to their differences from the inertial point of view in the particle size range of 1–100?µm. Bubble diameters of 0.08, 0.12, and 0.15?cm and bubble velocities of 10, 20 and 30?cm/s were selected to study the flotation of chalcopyrite. Weber and Paddock collision model (E_C-W&P) was taken for evaluation of the effect of bubble surface mobility on E_C. It was found that when the bubble diameter is 0.12?cm, reducing bubble velocity from 30 to 20?cm/s, the inertia force can be ignored for wider range of particle size. Corresponding particle size in cross-sectional point between GSE and Schulze collision models was introduced for better evaluation of the positive and negative particle inertial effects. The best agreement between them was taken for bubble diameter of 0.12?cm and velocity of 20?cm/s. It was concluded that the influence of bubble velocity is more effective than bubble diameter regarding its role on particle inertial forces in particle–bubble interaction.     

Polymerizations initiated by boron fluoride etherate—III. The role of the electrodic processes in polymerizations under electric field

The electrodic processes occurring when a d.c. electric field is applied to the polymerization of vinyl-aromatic monomers initiated by boron trifluoride etherate in 1,2-dichloroethane solution have been investigated. Retardation of the polymerization rate by the field, sometimes overcoming the well known field acceleration, has been attributed to electrochemical reactions at the cathode. Linear and cyclic voltammetries on the various reactants show that the field acceleration is due to anodic oxidation of the monomer, that boron trifluoride etherate is easily reducible and that the electrolysis of water and of its complexes with BF₃ is hardly relevant. Electrolyses of solutions of the etherate at its reduction potential, as well as the use of the electrolysed solutions to initiate anethole polymerization, confirm the cathodic formation of inhibiting species, among which chloride ion has been identified. An ECE reduction mechanism of boron trifluoride etherate consistent with the experimental results is proposed. The non-electrolytic component of the field acceleration observed by other authors and by us in polymerizations carried out in cells with external electrodes is discussed.     

Electron beam crosslinked gels—Preparation,characterization and their effect on the mechanical,dynamic mechanical and rheological properties of rubbers

Electron beam (EB) crosslinked natural rubber (NR) gels were prepared by curing NR latex with EB irradiation over a range of doses from 2.5 to 20 kGy using butyl acrylate as sensitizer. The NR gels were systematically characterized by solvent swelling, dynamic light scattering, mechanical and dynamic mechanical properties. These gels were introduced in virgin NR and styrene butadiene rubber (SBR) matrices at 2, 4, 8 and 16 phr concentration. Addition of the gels improved the mechanical and dynamic mechanical properties of NR and SBR considerably. For example, 16 phr of 20 kGy EB-irradiated gel-filled NR showed a tensile strength of 3.53 MPa compared to 1.85 MPa of virgin NR. Introduction of gels in NR shifted the glass transition temperature to a higher temperature. A similar effect was observed in the case of NR gel-filled SBR systems. Morphology of the gel-filled systems was studied with atomic force microscopy. The NR gels also improved the processability of the virgin rubbers greatly. Both the shear viscosity and the die swell values of EB-irradiated gel-filled NR and SBR were lower than their virgin counterparts as investigated by capillary rheometer.     

Production and properties of polyacenaphthylene—VI. Influence of polymerization conditions on chain structure

Low molecular weight polyacenaphthylenes produced by azo initiators through thermal or free-radical means are slightly yellow. The colouring is more intense the higher the polymerization temperature. It can be shown through spectroscopic investigations that the colouring is caused by conjugated double bonds in the polymer backbone chain and/or by the location of double bonds next to the ester end-groups. Chain branching influences the chain form and the hydrodynamic volume of the molecule; it can be used to explain the behaviour of the polymers in gel permeation chromatography.     

Polyacrylonitrile molecular weight effect on the structural and magnetic properties of metal–carbon nanomaterial

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Radiation-chemical decomposition of heavy metal azides—III. The role of two-valence impurity cations in radiation-stimulated processes in silver azide

Ion and electron transfer in the irradiation field as well as silver azide radiolysis doped with Cu²⁺, Pb²⁺, Cd²⁺ cations topography and kinetics have been studied. A certain part of impurity cations appeared to enter the crystal lattice to form solid solutions, they being chemisorbed partially on the surface to form complexes with low mobility. Ion transfer parameters change greatly due to interstitial silver ions concentration decrease, cation vacancy concentration increase and because of doped cations participating in the transfer in doped systems. Impurity cations being electron traps and recommendation centers influence the radiation conductivity value. In addition, Cu²⁺ ions lose their mobility caused by their transition into the atomic state.In fact, during silver azide radiation-chemical decomposition bivalent impurity cations become radiolytic metal particle formation centers. This has been inferred from the fact that the radiolytic metal contains as much as 30% of dopants at the initial stages, which has experimentally been proved. This results in kinetic curve change and general radiolysis acceleration at the initial stage with decomposition proceeding under nonstationary conditions. The impurity cation effect seemed insignificant for larger degrees of radiolysis with decomposition proceeding under stationary conditions.The scheme of silver azide radiolysis with no radiolytic particle metal participating in the growth process during thermo-activated stages has been proposed, accounting for the results obtained.     

The effect of continuous CO<Subscript>2</Subscript> laser radiation on the thermal and molecular—Topological properties of polytetrafluoroethylene

The impact of high-intensity laser radiation on a polymer in vacuum is accompanied by the release of gaseous products of degradation and, in some cases, of clusters of the partially destroyed polymer. Polytetrafluoroethylene (PTFE) exhibits an abnormal behavior in this process: being exposed to continuous CO₂ laser radiation, it degrades at a high rate and its clusters have a fibrous form. Depending on the irradiation conditions, the fibrous fraction forms two types of product, “cotton wool” and “felt”. Polytetrafluoroethylene and its laser-modified “cotton wool“ product have a semicrystalline topological structure. The preliminary γ-irradiation of PTFE enhances the laser ablation process.     

The effect of olefinic terminal chains on the mesomorphic properties of 4,4′-disubstituted diphenyldiacetylenes

New diphenyldiacetylenes of the type with A, B = H and/or F; m = 0, 1; n = 1–4; and X = C _n H_2n+1, F, CF₃ or CN were synthesized and their mesomorphic properties determined by hot stage polarizing microscopy and DSC. When m = 0, all of these compounds showed only a nematic phase except when X = CF₃ when both nematic and smectic A phases were seen. Both clearing and melting temperatures were higher than those reported for substitution with the corresponding alkyl chains but the much larger increase in clearing temperatures produced considerably wider nematic phases. Eutectic mixtures of a few of these olefins yielded nematic materials also having much wider temperature ranges and higher clearing temperatures than the eutectic mixtures of the alkyl compounds, while retaining their high birefringence and low viscosities. Such materials are of interest for beam-steering devices. Four of the diacetylenes with m = 1 (A, B = H) were also prepared (X = C₆H₁₃, F, n= 2, 3). When X was C₆H₁₃ (n=2), the nematic range was smaller in the 2- than in the 1-olefin but wider than in the alkyl series. When X=F, either no nematic phase or a monotropic one was observed, whereas the 1-olefins gave a much wider nematic phase. Both transition temperatures were lower than those for the corresponding 1-olefin and alkyl analogues. The compound with X=C₆H₁₃ and n=2 had a melting temperature below room temperature.