抄録
Flow-induced orientation changes of 0.5 wt% xanthan gum solution in planar channels have been studied using flow-induced birefringence (FIB) method. Two kinds of 4:1:4 abrupt contraction and a successive abrupt expansion channels with different middle slit length of 1 mm and 10 mm were tested in the experiments. The FIB system was adapted to a microscope. We have obtained remarkable differences in the development of birefringence between these cases. In the case with slit length of 10 mm, the birefringence measured on the centerline of the channel was rapidly decreased just after the expansion, then showed temporal increase. After these regions, the polymer gradually aligned parallel to the flow direction. In contrast, the temporal increase in birefringence and alignment to the transverse direction in molecular orientation was not observed in the case with slit length of 1 mm. Flow-induced orientational change of polymers in planar channels with expansions were considerably affected with slit length in the contracted section.
