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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 11258-11263 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The second-order memory function (SOMF) for the dicyclohexylmetyl-2metyl succinate is obtained by using simple numerical manipulation of the experimental dielectric data. According to the prescription given in a previous paper [J. Chem. Phys. 109, 9057 (1998)], the frequency behavior of the real and imaginary parts of the SOMF is discussed in terms of the Havriliak-Negami equation of the dielectric function, and together with the three-variable model describing the evolution of the torque-autocorrelation function. Furthermore, in this paper we present the temperature dependence of the parameters, which characterize the SOMF behavior for two ester substances. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 9057-9061 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper the use of the second-order memory function to represent experimental results of dielectric relaxation data of amorphous and glass forming materials is presented, and particularly, its interpretation in terms of the frequency dependence of the complex shear modulus, shear viscosity, and diffusion coefficient is pointed out. The method used for its evaluation is applied to consider the experimental results for three ester substances, and their particular features are discussed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 1906-1913 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The curves describing the temperature dependence of the dielectric loss for poly(4-acryloxyphenyl)–(4-chlorophenyl)–methanone exhibit a well developed subglass absorption followed in order of increasing temperature by an ostensible glass–rubber relaxation or α process. Free charge conductivity processes and blocking electrode phenomena become dominant in the α relaxation at frequencies below 10 Hz. An electric model is proposed to interpret the dielectric results covering the glassy state and the glass–rubber transition. The model is basically a parallel configuration involving a condenser (CΓα), a resistance (R), and a Havriliak–Negami-type impedance (ZHN*) coupled in series with an impedance (Ze*) representing the electrode phenomena. The circuit allows one to split the dipolar processes from both free charges and blocking electrode conductivity contributions to the real ε' and loss ε‘ parts of the complex dielectric permittivity at temperatures above the glass transition temperature of the polymer. At low frequencies the model predicts that ε' and ε‘ scale with frequency as ε'∼ω−(1+α¯) and ε‘∼ω−α¯, the exponent α¯ not being restricted to the conventional value of 0.5 commonly found in the literature. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 1047-1053 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The considerable dielectric activity exhibited by acrylate polymers containing chlorocyclohexyl side groups is investigated by using both global and partial thermally stimulated depolarization current (TSDC) techniques. The critical interpretation of the spectra obtained by TSDC experiments on poly(2-chlorocyclohexyl acrylate) (P2CCA), together with previous results related to the dynamics of 2-chlorocyclohexyl acetate, model compound of the side group of P2CCA, seem to suggest that conformational transitions about O–Cy and CH–C*O* bonds, rather than chair to reverse chair transition in the cyclohexyl group, may be involved in the absorption exhibited by these polymers in the glassy state. Attempts are also made to link the relaxation spectra obtained by TSDC techniques with the ac dielectric spectra. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 3685-3691 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dielectric activity of poly(monocyclohexylmethylene itaconate) (PMCI) and poly(dicyclohexylmethylene itaconate) (PDCI) in the glassy region and in the glass–rubber transition is studied by thermostimulated discharge current (TSDC) techniques. The spectra obtained by global TSDC experiments show a prominent α-glass–rubber relaxation peak with maxima located at 97 and 55 °C for PMCI and PDCI, respectively, following in decreasing order of temperature for a well developed β absorption and a comparatively low intensity relaxation. Better resolution of the relaxation behavior of these polymers in the glassy region is obtained by calculating the components of the complex dielectric permittivity ε* at extremely low frequencies from partial TSDC experiments. The ac spectra thus obtained suggest that the β absorption is composed by two relaxations, each of them presumably associated with the motions of a side group. The differences observed in these spectra with those reported for the β mechanical relaxation reported for these polymers in the literature are interpreted in terms of the restrictions that the side groups produce in the conformational space of phase of the backbone. These restrictions also explain the small changes in enthalpy in the glass–rubber transition which preclude the possibility of obtaining the glass–rubber transition temperature of these polymers by differential scanning calorimetric techniques. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5761-5761 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Since the discovery of the high-Tc superconductors, there is a great interest in the magnetic properties of copper oxides due to the possibility of a magnetic origin of the pairing mechanism. With this perspective, we decide to reinvestigate the structure and the magnetic properties of Bi2CuO4, a compound we use successfully as precursor of the Bi-Sr-Ca-Cu high-Tc superconductors. A neutron powder diffraction experiment allowed us to resolve the ambiguity in the structure, and revealed the existence of a magnetic phase transition to a 3D antiferromagnetic ordered state below 50 K. The nuclear structure can be described as formed by stacks of CuO4 units in the c-axis direction, linked in the stacks and with units in other stacks by BiO2 chains, so each stack is connected with four stacks. The space group was confirmed to be P4/ncc. The magnetic space group is P4/n'cc. There is a ferromagnetic ordering of the magnetic moments on Cu atoms along the stacks, and an antiferromagnetic ordering between the stacks. We present an interpretation of the magnetic properties of this compound, at the light of our previous results, and a discussion of a calorimetric experiment.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 4436-4442 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dielectric activity of poly {5-[(acryloxy)methyl]-5-methyl-1,3-dioxacyclohexane} (PAMMD), poly{5-[(acryloxy)methyl]-5-ethyl-1,3-dioxacyclohexane} (PAMED) and poly{5-[(acryloxy) methyl]-2-phenyl-5-ethyl-1,3-dioxacyclohexane} (PAEDP) is studied by thermostimulated discharge current (TSDC) techniques. The global TSDC curves corresponding to PAMMD, PAMED, and PAEDP exhibit subglass absorptions centered in the vicinity of −105, −100, and −120 °C, respectively. The dielectric activity of PAEDP in the glassy region is negligible in comparison with that of both PAMMD and PAEDP which have nearly similar relaxation strengths. Prominent peaks associated with the glass–rubber transition are located at 41, 38, and 57 °C for PAMMD, PAMED, and PAEDP, respectively. The real and loss components of the complex dielectric permittivity in the frequency domain (10−10–10−2 Hz) were calculated at several temperatures from elementary peaks obtained by partial TSDC curves in the glassy region. The differences observed in the spectra are discussed in terms of previous molecular dynamics studies carried out in model compounds of the flexible side groups of these polymers. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 261-266 
    ISSN: 0887-6266
    Keywords: poly(monoitaconates) ; mechanical relaxation ; empirical model ; master curves ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dynamic mechanical relaxation measurements were carried out on two poly(monoalkylitaconates). Three relaxation peaks between -120 and 140°C were present. A prominent subglass relaxation (β) near -60°C was studied by means of the Fuoss-Kirkwood formalism. A slight viscoelastic activity (β′) was observed at room temperature, and then a high temperature peak (α), probably related to the glass transition, was found. A biparabolic model, double Cole constant phase element was used to model the experimental data in this zone. © 1996 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 2749-2756 
    ISSN: 0887-6266
    Keywords: poly(monoethylphenyl itaconate) ; mechanical relaxation ; dielectric absorption ; dielectric loss modulus ; deconvolution method ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dynamic mechanical and dielectric relaxational behavior of poly(monoethylphenyl itaconate) at different frequencies and temperatures was studied. Three relaxation zones are found. The dynamic mechanical response is dominated by a relaxation peak at room temperature, labeled β relaxation. Two prominent shoulders labelled as γ and α relaxations are observed. Because of the overlapping of the α and γ with the β relaxation, a deconvolution method to improve the understanding of these phenomena is proposed. In spite of the complexity of the experimental spectra, the proposed deconvolution method seems to be a convenient approach to interpret the relaxational behavior of this polymer. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2749-2756, 1997
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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