A. E. Akinay (1), W. Brostow (1), R. Maksimov (2)

(1) LAPOM, Department of Materials Science, University of North Texas, Denton, TX 76203-5310
(2) Institute of Polymer Mechanics of the University of Latvia, 23 Aizkraukles iela, 1006 Riga, Latvia

ABSTRACT

The material studied is a longitudinal polymer liquid crystal (PLC). The creep behavior of the PLC is examined in the region of nonlinear viscoelasticity. The creep compliance D curves at nine different stress σ levels, from 10 to 50 J • cm^-3 at a constant temperature are determined and shifted along the log time axis for  σ_ref = 10 J • cm^-3 to produce the D versus t/a_σ master curve. A fairly general formula for stress shift factor a_σ based on free volume v^f and the chain relaxation capability (CRC) derived by one of the authors is applied. The formula predicts values that agree with the experimental ones within the limits of the experimental accuracy. Thus, experiments at several stress levels can serve for prediction of long-term behavior from short-term tests. The same value of the Doolittle constant B is obtained separately from temperature shift and stress shift experiments for the PLC.