Browsing by Author "Gargallo, L."

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    CONFORMATIONAL CHARACTERISTICS OF POLY(VINYLPYRROLIDONE) - SOLVENT-DEPENDENCE OF THE CHAIN DIMENSIONS
    (HUTHIG & WEPF VERLAG, 1993) Tarazona, M.P.; Saiz, E.; Gargallo, L.; Radic, D.
    Conformational energies as function of rotational angles over two consecutive skeletal bonds for both meso and racemic diads of poly(N-vinyl-2-pyrrolidone) have been computed. The results of these calculations were used to formulate a statistical model that was then employed to calculate the unperturbed dimensions of this polymer. The conformational energies are sensitive to the Coulombic interactions, which are governed by the dielectric constant of the solvent, and to the size of the solvent molecules. Consequently, the calculated values of the polymeric chain dimensions are strongly dependent on the nature of the solvent, as it was experimentally found before.
  • Thumbnail Image
    Item
    Contributions of Dipolar Relaxation Processes and Ionic Transport to the Response of Liquids to Electrical Perturbation Fields
    (AMER CHEMICAL SOC, 2011) Sanchis, M. J.; Ortiz Serna, P.; Carsi, M.; Diaz Calleja, R.; Riande, E.; Gargallo, L.; Radic, D.
    The objective of this work was to study the influence of small variations in the chemical structure on the molecular dynamics of liquids using as models bis(cyclohexylmethyl) 2-methyl- and dicyclohexyl 2-methylsuccinate. The dielectric behavior of the low molecular weight liquids was studied over a wide range of frequencies and temperatures. The results show that the temperature dependence of the dielectric strengths, relaxation times, and shape parameters of the secondary and glass liquid relaxations are very sensitive to the slight differences in the structures of the liquids. Significant changes take place in the dielectric strength of the beta relaxation in the glass liquid transition. Moreover, the temperature dependence of the beta relaxation exhibits Arrhenius behavior in the glassy state and departs from this behavior in the liquid state. Special attention is paid to the temperature dependence of low-frequency relaxations produced by the motion of a macrodipole arising from charges located near the liquid-electrode boundaries.
  • Thumbnail Image
    Item
    Dipolar and Ionic Relaxations of Polymers Containing Polar Conformationally Versatile Side Chains
    (AMER CHEMICAL SOC, 2010) Sanchis, M. J.; Carsi, M.; Ortiz Serna, P.; Dominguez Espinosa, G.; Diaz Calleja, R.; Riande, C.; Alegria, L.; Gargallo, L.; Radic, D.
    This work reports a comparative study of the response of poly(2,3-dimethoxybenzyl methacrylate), poly(2,5-dimethoxybenzyl methacrylate). and poly(3,4-dimethoxybenzyl methacrylate) to electrical perturbation fields over wide frequency and temperature windows with the arm of investigating the influence of the location of the dimethoxy substituents in the phenyl moieties on the relaxation behavior of the polymers The dielectric loss isotherms above T-g exhibit a blurred relaxation resulting from the over lapping of secondary relaxations with the glass rubber or alpha relaxation. At high temperatures and low frequencies, the a relaxation is hidden by the ionic conductive contribution to the dielectric loss As usual, the real component of the complex dielectric permittivity in the frequency domain increases with deer easing frequency until a plateau is reached corresponding to the glass rubber (alpha) relaxation However, at high temperatures, the real permittivity starts to increase;Warn with decreasing Frequency until a second plateau is reached, a process that presumably reflects a distributed Maxwell-Wagner-Sillars relaxation or alpha' absorption The a and alpha' processes appear respectively as asymmetric and symmetric relaxations in the loss electrical modulus isotherms in the frequency domain. To facilitate the deconvolution of the overlapping absorptions, the time retardation spectra of the polymers were computed from the complex dielectric permittivity in frequency domain using linear programming regularization parameter techniques The spectra exhibit three secondary absorptions named. in increasing order of time gamma', gamma, and beta followed by the a relaxation At long times and well separated from the a absorption the alpha' relaxation appears The replacement of the hydrogen of the phenyl group in position 2 by the oxymethyl moiety enhances the dielectric activity of the poly(dimes hoxybenzyl methacrylate)s The temperature dependence of the relaxation times associated with the different relaxations is studied, and the molecular origin of the secondary relaxations is qualitatively discussed
  • No Thumbnail Available
    Item
    Relaxations in Poly(di-n-alkyl and di-isoalkyl itaconates)
    (AMER CHEMICAL SOC, 1995) Calleja, R.D.; Gargallo, L.; Radic, D.
    A systematic study about the viscoelastic and dielectric relaxations was performed for a family of poli(di-n-alkyl and diisoalkyl itaconates): poly(dimethyl itaconate) (PDMI), poly(diethyl itaconate) (PDEI), poly(di-n-propyl itaconate) (PDPI), poly(di-n-butyl itaconate) (PDBI), poly(diisopropyl itaconate) (PDIPI), and poly(diisobutyl itaconate) (PDIBI). Three dielectric relaxation processes, labeled as alpha, beta, and gamma were observed in all cases. Nevertheless, in some polymers a poor resolution of the peaks is observed and only small indications of the phenomena can be seen. In the case of PDPI and PDBI measurements at very low temperatures were performed and dielectric absorption processes are found at those temperatures. Behavior similar to that observed for dielectric relaxations is found for the mechanical one. The temperature at which the a relaxation, associated with the glass transition temperature, is present diminishes as the length of the n-alkyl side group increases. This behavior is similar to that reported for poly(n-alkyl methacrylates). a relaxation is only detected at some frequencies, and it is more easily detected in terms of E'' or epsilon'' than in terms of tan delta. This relaxation is less pronounced than in the case of poly(n-alkyl methacrylates). An important difference between these polymers and poly(n-alkyl methacrylates) is the existence of a new relaxation process labeled as gamma relaxation between -40 and -120 degrees C. This relaxation is very sensitive to the dryness of the sample or to the presence of molecules of low molecular weight in the matrix.
  • No Thumbnail Available
    Item
    Thermal stability of aromatic poly(monoitaconates)
    (GORDON BREACH SCI PUBL LTD, 1996) Radic, D.; Tagle, L.H.; Opazo, A.; Gargallo, L.
    Thermogravimetric analysis of poly(mono-benzyl itaconate), (PMBzI) poly(mono-ethylphenyl itaconate) (PMEPI) and poly(mono-n-propyl itaconate) (PMPPI), were performed by dynamic thermogravimetry. The thermal stability of these polymers depends on the side chain structure. The kinetic analysis of the degradation data shows that the thermal decomposition of these polymers follows a 0.5 kinetic order in all the cases.