Crystallinity changes in plastically deformed isotactic polypropylene evaluated by x‐ray diffraction and differential scanning calorimetry methods

The crystallinity of isotactic polypropylene (iPP), when deformed with plastic plane‐strain compression, was studied with wide‐angle X‐ray scattering (WAXS) and differential scanning calorimetry (DSC) techniques. A comparison of the obtained crystallinity data with annealed iPP samples was performed. The material used in this study was commercial iPP (weight‐average molecular weight = 117.400 g/mol; number‐average molecular weight = 17.300 g/mol). A significant decrease in the crystallinity was observed with increasing deformation pressure when the X‐ray method was employed, whereas only a small decrease was registered when the DSC method of crystallinity determination was used. However, the annealed iPP samples demonstrated a slight crystallinity increase when evaluated by both techniques. The reason for the difference between WAXS and DSC crystallinity results is discussed. This study of iPP specimens subjected to large deformation led us to the conclusion that the WAXS method provides accurate crystallinity values for the deformed material, whereas the values obtained by the DSC method do not reproduce the real crystallinity of the deformed material. This is due to the inherent heating process of the method, which causes a relaxation process and a significant change in the crystallinity of the deformed material, providing values nearer to its intrinsic equilibrium state. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 896–903, 2002     

Brillouin scattering in liquid mixtures: CCl4/CHCl3

The Brillouin light scattering spectra of mixtures of liquid CCl₄ and CHCl₃ have been obtained. The resulting relaxation rates and the relaxing energy reservoir were studied as a function of the mole fraction over the entire concentration range. The energy exchange between the pertinent degrees of freedom are discussed in terms of the relaxation rates of homomolecular and heteromolecular collisions. We came to the conclusion that the resonance energy transfer between vibrational levels play a significant role in determining the vibration—translation energy migration observed by Brillouin scattering'     

On the polymerisation of the epoxidised biodiesel: The importance of the epoxy rings position,the process and the products

Polyesters were prepared using epoxidised methyl esters of oleic acid (EP_OAME) and epoxidised biodiesel (mixture of methyl esters) from sunflower oil (EP_SOME) and linseed oil (EP_LOME) with cis-1,2-cyclohexanedicarboxylic anhydride and triethylamine. The kinetic of partial processes involved in the polymerisation were elucidated and related to epoxy rings position in the fatty acid chain. The activation energies (E_a) for the epoxy ring opening by the catalyst are 298, 216 and 136 kJ/mol for EP_OAME, EP_SOME and EP_LOME respectively. The reactions of the epoxy rings in the positions C9–C10, C12–C13 and C15–C16 with anhydride require average activation energies of 116, 32 and 22 kJ/mol, respectively. The compensation effect between activation energy and pre-exponential factor is observed. The polymerisation enthalpy, molecular weight, glass transition temperature and electrical properties were determined. The polyesters studied show promising properties for use in various technological applications.     

Analysis of the Kω spectrum

We present results of a spin-parity analysis of the Kω system from threshold to 1.52 MeV based on 12 500 events of the type K^?p→K^?π⁺π^?π^op at 7.3 GeV/c. We also present evidence for a possible resonant state decaying into Kω at a mass 1710 ± 15 MeV and width 110 ± 50 MeV.     

Network formation studied by temperature scanning Brillouin scattering and differential scanning calorimetry techniques. I. The cure of 1,4-butanediol diglycidyl ether with cis-1,2-cyclohexanedicarboxylic anhydride initiated by triethylamine

The network formation process of the triethylamine-initiated reaction of 1,4-butanediol diglycidyl ether with cis-1,2-cyclohexanedicarboxylic anhydride has been investigated by conventional differential scanning calorimetry and temperature scanning Brillouin light scattering as a new experimental method for the estimation of the reaction's conversion factor. The time-temperature evolution of the observed quantities (reaction enthalpy in the calorimetric measurements and hypersound velocity in the light scattering) reflects in both sets of experimental data, but results in different kinetic parameters obtained by the assumption of an Arrhenius behavior. These differences are ascribed to the relation of the observed properties with respect to the evolution of the reaction. The enthalpy production of the system observed in the calorimetric experiment is shown to be connected directly to the chemical reaction, whereas the change in the hypersound velocity measured by the light scattering method is sensitive to the solidification of the system. © 1995 John Wiley & Sons, Inc.     

Pressure and temperature dependence of the hydrogen bonding in supercritical ethanol: a computer simulation study

As a step toward deeper insight on the "hydrogen bonding" in supercritical ethanol (scEtOH), we carried out NVT molecular dynamics simulations of the fluid over a wide range of temperatures and pressures. The fluid was studied at SC conditions for which thermodynamic and spectroscopic (NMR, infrared, Raman, dielectric) data are available. The various site-site pair distribution functions (pdf's) were calculated, and their temperature and pressure dependence was obtained. It was found that over the thermodynamic conditions investigated here, scEtOH remains highly structured. Moreover, the characteristic behavior of the first peaks in H-H, O-O, and H-O pdf's reveals that hydrogen bonds still exist in scEtOH. The analysis focuses also on the reorientational dynamics of the bond unit vectors O-H, C-O, and of the permanent dipole moment of the molecules as well as the total dipole moment of the sample. The corresponding Legendre time correlation functions were discussed in connection to the "hydrogen bonding" in the fluid and in the context of experimental results. Specifically, the behavior of the O-H dynamics exhibits the well-known associative nature of the molecules in the system. A further analysis of the hydrogen bonds was carried out, and the degree of aggregation (average number of H-bonds per molecule) was obtained and compared with results from NMR chemical shift studies. Also the estimated monomer and free O-H groups in the fluid were compared with results from IR and Raman vibrational spectroscopy. The percentage analysis fi of the liquid and scEtOH molecules, with i = 0, 1, 2, 3, ... hydrogen bonds per molecule, has been obtained. The results show the existence of small, linear-chain oligomers formed mainly by two molecules, whereas the number of the three body oligomers, and specifically that of four body oligomers in the sample, is relatively small.     

Crystalline properties and morphological changes in plastically deformed isotatic polypropylene evaluated by X-ray diffraction and transmission electron microscopy

The isotatic polypropylene (i-PP) plastically deformed by uniaxial plane strain compression was investigated using X-ray diffraction and transmission electron microscopy. The apparent crystallinity was evaluated by means of X-ray diffraction with a profile matching using a FULLPROF code. Two crystalline phases, α and β, were identified in the non-deformed polymer as well as with an amorphous halo. The deformation with 3, 10 and 100 MPa, induces an increase of the amorphous halo. The microstructural orientation of the i-PP, before and after deformation was evaluated using the “Quantikov” image analysis of transmission electron microscopy (TEM) data. The non-deformed material presents spherulitic structure, without any preferential orientation. The high resolution, in the nanometer scale, shows two preferential orientation axes. The deformation at 3, 10 and 100 MPa, affects the spherulitic, as well as, the lamellae structure, introducing fiber orientation, a break up of the lamellae in to small blocks and consequently amorphization of the system.     

Numerical simulation of biological base pairs considering geometric and energetic criteria

The aim of this work is the numerical simulation of the formation of hydrogen-bonded base pairs between adenine, thymine, guanine and cytosine. We use a Monte Carlo diffusion simulation with geometric (molecular distances and orientation) and energetic (acceptance proportional to the Boltzmann factor) criteria. Our results show that the occurrence of the different types of base pairs is strongly influenced by base geometry. Such results can help to understand some mechanisms, which occur at processes related to mutation.     

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.