Browsing by Author "Gonzalez Nilo, F"

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    Dynamic mechanical and dielectric relaxational behavior of poly(cyclohexylalkyl methacrylate)s
    (AMER CHEMICAL SOC, 2001) Calleja, RD; Garcia Bernabe, A; Sanchez Martinez, E; Hormazabal, A; Gargallo, L; Gonzalez Nilo, F; Radic, D
    The dynamic mechanical and dielectric behavior of three poly(cyclohexylalkyl methaerylate)s with different spacer groups has been studied. The study was performed by determining the components of the complex relaxation modulus E* and the complex dielectric permittivity epsilon*. Results are discussed in terms of the effect of the side chain structure and the insertion of flexible spacer groups. Molecular dynamic calculations for the repeating unit of the polymers under study are analyzed. Close to room temperature the interconversion between axial and equatorial conformations is not observed whitin the total time of 5 ns. The analysis was then performed from 1000 to 1500 K, and the results were extrapolated to lower temperatures. By this way the fraction of axial and equatorial conformations was calculated. The free energy change against the number of carbon atoms in the side chain is in excellent agreement with the experimental data. This means that the gamma relaxation associated with the chair-to-chair conformational change in the cyclohexyl group is also influenced by the length of the spacer group. The molecular dynamics approach allows to observe the relative incidence of the two conformations of the cyclohexyl group which can be related to the motions responsible for the gamma relaxation.
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    N-1-alkylitaconamic acids-co-styrene copolymers. Surface characterization
    (ELSEVIER SCI LTD, 2003) Miranda, B; Gargallo, L; Urzua, M; Leiva, A; Gonzalez Nilo, F; Radic, D
    A serie of six N-1-alkylitaconamic acids-co-styrene copolymers with alkyl groups varying in side chain length from 3 to 12 was used in this study. The surface behaviour of the copolymers has been studied as function of the side chain length. Contact angle data for two of these copolymer surfaces were obtained in water and several liquids. From this information the surface energy was determined. Differences in the wettability of N-1-alkylitaconamic acid-co-styrene are found. The results are discussed in terms of hydrophobic and polar effect of the copolymers. Results on spread monolayers characteristics of these copolymers on water surfaces are also reported. Surface pressure-area (pi-A) isotherms on a pure water subphase exhibit a transition region depending on the length of the alkyl side chain of the itaconamic acid moiety. It was also analyzed the phase transition in the monolayer at the air/water interface by brewster angle microscopy (BAM). Molecular mechanics approach was used to obtain predictions about the local interaction energies between segments. It was possible to conclude that the local interaction energies of propyl and decyl derivatives are quite similar while the hexyl derivative has higher interaction energy. The analysis of the coulombic energies together with the dispersion van der Waals energies (VDW) would be indicative, in first approximation, that carbonyl groups are more exposed in the case of propyl than in the other copolymers studied. (C) 2003 Elsevier Science Ltd. All rights reserved.
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    Surface characterization and study of Langmuir films of poly(4-vinylpyridine) quaternized with n-alkylbromide
    (JOHN WILEY & SONS LTD, 2001) Gargallo, L; Miranda, B; Rios, H; Gonzalez Nilo, F; Radic, D
    The surface behaviour of poly(4-vinylpyridine)s (P4VP) quaternized with four different alkyl chains (pentyl, hexyl, octyl and decy bromide) were studied. Surface pressure-area isotherms (pi -A) at the air-water interface were determined. Depending on the length of the side-chains, the pi -A isotherms show a plateau region. An extensive plateau is observed for n >6. The plateau pressures are similar for n = 8 and n = 10. The monolayers are stable and exhibit hysteresis phenomena. Brewster angle microscopy (BAM) is used to monitor the monolayer topography of the polymer on water subphase. To obtain information about the surface energy (SE) and the degree of hydrophobicity of these systems, we have estimated the critical surface tension, gamma (c), and the dispersion force and polar contributions to SE, gamma (D) and gamma (P), respectively, by measurements of the contact angle (CA) of water and bromobenzene on the polymer surface. The results obtained are depend on the length of the alkyl lateral chain of the functionalized polymers. (C) 2001 Society of Chemical Industry.