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Results from a molecular dynamics simulation of a melt of unentangled polymers are presented. The translational motion, the large-scale and the local reorientation processes of the chains, as well as their relations with the so-called “normal” and “segmental” dielectric relaxation modes are thoroughly investigated in wide temperature and pressure ranges. The thermodynamic states are well fitted by the phenomenological Tait equation of state. A global time-temperature-pressure superposition principle of both the translational and the rotational dynamics is evidenced. The scaling is more robust than the usual Rouse model. The latter provides insight but accurate comparison with the simulation calls for modifications to account for both the local chain stiffness and the nonexponential relaxation. The study addresses the issue whether the temperature or the density is a dominant control parameter of the dynamics or the two quantities give rise to comparable effects. By examining the ratio |α[sub τ]|/α[sub P] between the isochronic and isobaric expansivities, one finds that the temperature is dominant when the dynamics is fast. If the relaxation slows down, the fluctuations of the free volume increase their role and become comparable to those of the thermal energy. Detectable cross-correlation between the “normal-mode” and the “segmental” dielectric relaxations is found and contrasted with the usual assumption of independent modes. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Investigates the dynamics of monoepoxy, diepoxy an triepoxy glass-formers from below the above glass transition temperature behavior of relaxation times, strengths and conductivity. Main and secondary relaxations defining a splitting temperature; Strengths behavior reflecting the distribution of the overall energy between the relaxation processes.

We describe the performance of an analog phase follower used together with an active pendulum with interferometric sensing. The pendulum length is increased electronically by moving the suspension point horizontally by means of a piezoelectric transducer. This is driven by a feedback signal proportional to the relative displacement of the pendulum mass with respect to the suspension point. This displacement creates a phase shift Ψ in the optical path of the interferometer which in turn gives an output proportional to sin Ψ and not to Ψ, as this is required as the feedback signal. The device described here performs in an analog way the transformation sin Ψ [larger_closed_square] Ψ. At 0.5 Hz the dynamic range is ±500 rad corresponding to ±25-μm elongation of the pendulum mass. [ABSTRACT FROM AUTHOR]