ISSN:
0887-6266
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Polyethylene films were stressed in uniaxial tension at room temperature while the infrared (FTIR) or Raman spectra were simultaneously measured. The purpose of these experiments was to gain an understanding of the molecular origins of the stress-induced vibrational frequency shifts Δν and determine the mechanisms of molecular deformation and fracture of PE molecules with stress σ. The PE samples consisted of ultradrawn, high-density, ultrahigh-molecular-weight, solid-state-extruded films and the stress was applied parallel to the nearly perfectly oriented orthorhombic crystal c-axis direction. The experimental frequency shifting coefficients α = (∂ν/∂σ)σ→0 were compared with calculated α values determined from a vibrational analysis of an isolated PE chain using conformational energy minimization methods in which both harmonic and anharmonic (Morse) potential energy functions were used for the C—C stretching modes in the valence force field. The following α values were obtained and are compared with theory (anharmonic case in parentheses, in cm-1/GPa): C—C symmetric stretch, α(1127) = -5.9 (-5.3); CC asymmetric stretch, α(1059) = -11.2 to -5.7 (-5.8); CH2 rock, α(730/720) = -2.0 to -3.0 (-2.2); CH2 scissors, α(1472/1462) = -1.0 to -1.2 (-1.1); CH2 twist, α(1295) ≃ 0(0.8); CH2 wag, α(1370) undetermined owing to weak bands (-4.6); CH2 stretch α(3000) ≈ 0. The largest negative frequency shifts were observed for the C—C stretching modes, in agreement with the calculations using the Morse potential. The harmonic potential for C—C stretching resulted in small positive α values for both the CC stretching and CH2 wagging modes, while the other modes were unaffected by this choice of potential. The relative contribution of C—C bond stretching and CĈC valence angle bending to the c-axis strain was about 1:1, in agreement with experiment. The Young's tensile modulus of a PE chain was calculated as Ec = 267 GPa.
Additional Material:
19 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/polb.1986.090240508
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