The effect of phase-separated morphology on the rheological properties of polystyrene/poly(vinyl methyl ether) blend

The effect of phase-separated morphology on the rheological properties of polystyrene/poly(vinyl methyl ether) (PS/PVME) blend was investigated by optical microscopy (OM), light scattering (LS) method, and rheology. The blend had a lower critical solution temperature (LCST) of 112 degrees C obtained by turbidity experiment using LS at a heating rate of 1 degrees C/h. Three different blend compositions (critical 30/70 PS/PVME by weight) and two off-critical (50/50 and 19/90)) were prepared. The rheological properties of each composition were monitored with phase-separation time after a temperature jump from a homogeneous state to the preset phase-separation temperature. For the 30/70 and 50/50 blends, it was found that with phase-separation time, the storage and loss moduli (G' and G") increased at shorter times due to the formation of co-continuous structures resulting from spinodal decomposition. Under small oscillatory shearing, shear moduli gradually decreased with time at longer phase-separation times due to the alignment of co-continuous structures toward the flow direction, as verified by scanning electron microscopy. However, for the 10/90 PS/PVME blend, the rheological properties did not change with phase-separation times. (C) 1999 John Wiley & Sons, Inc.X1123sciescopu