Amorphous internal friction

The dissipation factor (the ratio of the energy dissipated to the energy stored per cycle) is affected by the frequency, temperature, crystallinity, and void content of the fabricated stmcture. At certain temperatures and frequencies, the crystalline and amorphous regions become resonant. Because of the molecular vibrations, appHed electrical energy is lost by internal friction within the polymer which results in an increase in the dissipation factor. The dissipation factor peaks for these resins correspond to well-defined transitions, but the magnitude of the variation is minor as compared to other polymers. The low temperature transition at —97° C causes the only meaningful dissipation factor peak. The dissipation factor has a maximum of 10 —10 Hz at RT at high crystallinity (93%) the peak at 10 —10 Hz is absent. 

The yield depends on the pressure according to crsh/y = crshyo I gP 50.3 + 0.204P MPa such a relationship has been found for many amorphous, glassy polymers g, i.e. the coefficient of internal friction, usually shows values between 0.1 and 0.25, depending on the polymer, whereas for semi-crystalline polymers this coefficient is smaller... 

Internal friction measurements have also been carried out on amorphous poly acetaldehyde and showed a main amorphous transition at -18° C. Poly-n-butyraldehyde had a transition at room temperature (Figure 1). 

Amorphous viscoelastic polymers are good damping materials, having high internal friction High damping or internal... 

B. S. Berry and W. C. Pritchet, Thermally-Activated Internal Friction Peaks in Amorphous Films of Nb Ge and Nb Si, in "Rapidly Quenched Metals III", Vol. 2, B. Cantor, ed.. The Metals Society, London (1978). 

O. Yoshinari, M. Koiwa, A. Inoue and T. Masumoto, Hydrogen Related Internal Friction Peaks in Amorphous and Crystallized Pd-Cu-Si Alloys, Acta Metall. 31 2063 (1983). 

The lubricity theory explains the resistance of a polymer to deformation. Stiffness and rigidity are explained as the resistance of intermolecular friction. The plasticizer acts as a lubricant to facilitate movement of macromolecules over each other, thus giving the resin an internal lubricity. The gel theory is applied to predominantly amorphous polymers. It proposes that their rigidity and resistance to flex are due to an internal three-dimensional honeycomb structure or gel. The spatial dimensions of the cell in a brittle resin are small because their centers of attraction are closely spaced and deformation cannot be accommodated by internal movement in the cell-locked mass. Thus, the elasticity limit is low. Conversely, a thermoplastic or thermosetting polymer with widely separated points of attachment between its raacroraolecules is flexible without plasticization. 

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