Yh. Kim et al., Phase structure development in poly(styrene-co-acrylonitrile)/poly(methyl methacrylate) blend under elongational flow, POLYMER, 41(12), 2000, pp. 4747-4749
Elongational how behaviour of a poly(styrene-co-acrylonitrile) (SAN)/poly(m
ethyl methacrylate) (PMMA) blend of a near critical composition (similar to
40/60) was examined below and above its lower critical solution temperatur
e T-s(= 195 degrees C) via elongational flow opto-rheometry (EFOR) which en
abled us to simultaneously monitor transient tensile stress sigma(epsilon o
ver dot (0); t) and birefringence Delta n (epsilon over dot (0); t) as a fu
nction of time t. Thus the stress optical rule (SOR) was tested on the blen
d below and above T-s. The morphology change with time t was examined by ex
situ transmission electron microscopy (TEM) and the resulting TEM pictures
were subjected to a fast Fourier transform (FFT) analysis. In the miscible
region at 150 degrees C, the stress optical coefficient of the blend C-Ble
nd [= Delta n(epsilon over dot (0); t)/sigma(epsilon over dot (0); t)] was
found to be constant (congruent to -1.2 x 10(-9) Pa-1) independent either o
f the strain rate Co the Hencky strain epsilon(= epsilon over dot t) or sig
ma(epsilon over dot (0); t). At 215 degrees C above T-s, however, the sign
of C-blend changed from negative to positive in the early stage of elongati
on and the value itself increased as the blend was stretched to a larger ex
tent. Under such a condition the SOR was clearly violated, for which a larg
e contribution of form birefringence was responsible due to the highly orie
nted and elongated domain structure, as revealed by TEM-FFT analysis, of th
e SAN phase with a large optical anisotropy. (C) 2000 Elsevier Science Ltd.
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