Effect of the shear flow on the phase behaviour of polystyrene/poly(vinyl methyl ether) blend

The effects of simple shear flow on the phase behaviour of polystyrene/poly (vinyl methyl ether) (PS/PVME) blend, which shows a lower critical temperat ure (LCST)-type phase diagram, have been studied by cloud point measurement s, by using a special shear apparatus. The shear-induced demixing and mixin g have been observed for all of the compositions at low and high shear rate , respectively. However, at higher shear rate, the cloud points were indepe ndent of the shear rate and almost constant. In addition, the shear effect was found to be composition dependent and the largest change took place nea r the critical composition. The effects of rotation speed and sample thickn ess were also studied for the sample of PS/PVME = 30/70. The values of the cloud point were strongly affected by the rotation speed and the minimum of the cloud point systematically shifted to higher shear rate values with in creasing rotation speed under the constant sample thickness. The sample thi ckness was also found to have a pronounced effect on the cloud point under constant rotation speed, where the immiscibility region in the cloud point- shear rate diagram seemed broader with increasing sample thickness. However , the samples of PSI PVME = 30/70 completely phase separated at 17 degrees C above the quiescent cloud point at high shear rate, regardless of the app lied rotation speed and sample thickness. (C) 1998 Elsevier Science Ltd. Al l rights reserved.