Density dependence of the structural properties and translational diffusion of carbonyl sulphide diluted in monoatomic solvents. A molecular dynamics investigation

We report a study of the intermolecular structure and translational diffusion of Carbonyl Sulphide (OCS) dissolved in Ne and Kr, using Molecular Dynamics (MD) simulation. The mixtures have been investigated at different thermodynamic points corresponding to the pressures between 5 and 300 bar and at temperature of 293 K. The computations were carried out with effective site-site Lennard-Jones (LJ) potential model. We found that the proposed model predicts a non-linear T-shaped dimer structure of Ne-OCS and Kr-OCS in accordance with experiment. The study of the local structure of the solute-solvents was based upon the calculated relevant pair distribution functions. The self-diffusion coefficients of both components in the mixtures were calculated and compared. The results show a non-linear dependence in the density range under study. In the case of Kr as solvent and at the whole density range under study, the diffusion coefficient of Kr appears to be larger than that of OCS. This unusual result on the solute-solvent diffusivities (m_OCS < m_Kr, D_OCS < D_Kr) has been further discussed in terms of the microscopic dynamics of the species.     

Molecular force field investigation for Sulfur Hexafluoride: A computer simulation study

Force fields for Sulfur Hexafluoride (SF₆) from the literature, were investigated by means of their ability to reproduce experimental data in a wide range of thermodynamic conditions, including liquid, gas, vapor–liquid coexistence curve as well as supercritical states. Experimental data include numerous PVT state points, corresponding structural properties in terms of radial distribution functions, diffusion coefficient and shear viscosity. The existing force fields were extensively examined in the framework of molecular dynamics simulations and it is found that they do not accurately reproduce the macroscopic properties of the fluid, especially at high densities. To overcome this problem with the aim to obtain improved potential parameters that better reproduce experimental data, a multi-variable optimization of the force field parameters procedure has been systematically applied based on the “Simplex” method. Finally, it is found that for some common functional forms of these force fields, the new optimized parameters predict better the experimental properties of SF₆ under investigation compared to the original ones.     

Liquid chromatography techniques for characterizing poly(Vinyl Alcohol)

Poly(vinyl alcohol) (PVOH) samples may contain several heterogeneities requiring the development of chromatographic techniques for characterization. Size exclusion separations have been carried out using a number of aqueous eluents, incorporating electrolyte, or electrolyte/organic modifier, or surfactant. The most favourable molecular size separation was obtained using 0.25% w/v sodium lauryl sulfate as eluent. Reasonable values for molecular weights of PVOH samples have been determined. Compositional distributions in copolymer systems can be assessed using high-performance liquid chromatography employing a reversed-phase separation mechanism. For poly(vinyl alcohol), gradient elution with water/tetrahydrofuran (THF) with a wide pore polystyrene-based packing produced separations dependent on degree of hydrolysis and sequence length distribution. The elution results were verified with a column packed with non-porous beads. Partially hydrolysed PVOH samples appeared to have a broad distribution of composition.     

Artificial amino acids in nickel(II) and nickel(II)/lanthanide(III) chemistry

The synthesis and magnetic properties of five new homo- and heterometallic nickel(II) complexes containing artificial amino acids are reported: [Ni(4)(aib)(3)(aibH)(3)(NO(3))](NO(3))(4)·3.05MeOH (1·3.05MeOH), [Ni(6)La(aib)(12)](NO(3))(3)·5.5H(2)O (2·5.5H(2)O), [Ni(6)Pr(aib)(12)](NO(3))(3)·5.5H(2)O (3·5.5H(2)O), [Ni(5)(OH)(2)(l-aba)(4)(OAc)(4)]·0.4EtOH·0.3H(2)O 6(4·0.4EtOH·0.3H(2)O), and [Ni(6)La(l-aba)(12)][La(2)(NO(3))(9)] (5; aibH = 2-aminoisobutyric acid; l-abaH = l-2-aminobutyric acid). Complexes 1 and 4 describe trigonal-pyramidal and square-based pyramidal metallic clusters, respectively, while complexes 2, 3, and 5 can be considered to be metallocryptand-encapsulated lanthanides. Complexes 4 and 5 are chiral and crystallize in the space groups I222 and P2(1)3, respectively. Direct-current magnetic susceptibility studies in the 2-300 K range for all complexes reveal the presence of dominant antiferromagnetic exchange interactions, leading to small or diamagnetic ground states.     

Local density augmentation and dynamic properties of hydrogen-and non-hydrogen-bonded supercritical fluids: a molecular dynamics study

The local density inhomogeneities in neat supercritical fluids were investigated via canonical molecular dynamics simulations. The selected systems under investigation were the polar and hydrogen-bonded fluid methanol as well as the quadrupolar non-hydrogen-bonded carbon dioxide one. Effective local densities, local density augmentation, and enhancement factors were calculated at state points along an isotherm close to the critical temperature of each system (T(r)=1.03). The results obtained reveal strong influence of the polarity and hydrogen bonding upon the intensity of the local density augmentation. It is found that this effect is sufficiently larger in the case of the polar and associated methanol in comparison to those predicted for carbon dioxide. For both fluids the local density augmentation values are maximized in the bulk density region near 0.7rho(c), a result that is in agreement with experiment. In addition, the local density dynamics of each fluid were investigated in terms of the appropriate time correlation functions. The behavior of these functions reveals that the bulk density dependence of the local density reorganization times is very sensitive to the specific intermolecular interactions and to the size of the local region. Also, the estimated local density reorganization time as a function of bulk density of each fluid was further analyzed and successfully related to two different time-scale relaxation mechanisms. Finally, the results obtained indicate a possible relationship between the single-molecule reorientational dynamics and the local density reorganization ones.     

Thermal stability of boron subphthalocyanines as a function of the axial and peripheral substitution

In this work, we have carried out the synthesis and thermogravimetric study of 10 different axially and peripherally substituted boron subphthalocyanines, in order to compare their thermal stabilities under non-oxidizing conditions. We demonstrate that, in general, these compounds enjoy a relatively high thermal stability, a property that is fundamental for future potential applications. The loss of the axial group is usually the first thermal degradation process to occur, and the temperature at which it takes place increases as a function of the nature of this substituent in the order: Br < OH ? OPh ∼ Cl. Peripheral substituents also have an influence on the thermal properties of subphthalocyanines, though their role is somewhat less notable.     

Stress–strain behaviour of poly(ethylene terephthalate) (PET) during large plastic deformation by plane strain compression: the relation between stress–strain curve and thermal history, temperature and strain rate

This study presents an experimental investigation of the large plastic deformation of poly(ethylene terephthalate) (PET) submitted to plane strain compression. PET samples, obtained by injection moulding, annealed and non-annealed, were deformed using a specific compression device developed for this purpose. The obtained stress–strain curves at different temperatures and strain rates are useful for engineering applications and show a significant temperature dependence and a minor dependence on the strain rate. A softening temperature as a minimum temperature necessary to initiate deformation when a minimum, almost zero, stress is applied is introduced. This temperature, at the zero stress and strain limit, we denominate “Stress–Strain independent softening Temperature (T _SOF)”. The T _SOF values, 104 and 113°C for non-annealed and annealed PET, respectively, have been obtained using three different strain rates, indicating that the property is sensitive to the thermal history of the material.     

Interaction of (hydroxypropyl) cellulose with anionic surfactants in dilute regime

(Hydroxypropyl)cellulose (HPC) dilute aqueous solutions in the presence of sodium cholate (CS), sodium deoxycholate (DC), and sodium dodecylsulphate (SDS) were investigated. The hydrophobicity parameter (I ₁/I ₃) from fluorescence has shown a critical aggregation concentration (CAC) lower than the critical micellar concentration (CMC). One or two breakpoints were observed in the curve conductivity vs surfactant concentration. The thermodynamic parameters of aggregation (, and ) and the degree of counterion dissociation were calculated. Evidences for the secondary aggregation of CS/water system were found. The relative viscosity increases for HPC/bile salt solutions only at high surfactant concentrations, whereas for HPC/SDS, it passes through a maximum. The cloud points of both HPC/bile salt solutions at higher surfactant concentrations reach a temperature plateau value around 324 K, while for HPC/SDS, it exceeds 373 K at low SDS concentrations. Dynamic light scattering has demonstrated that the surfactants bind to HPC already at concentrations lower than CAC.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.