Rheology and phase separation in a model upper critical solution temperature polymer blend

Abstract

The viscoelastic properties of a model binary polymer blend exhibiting an upper critical solution temperature phase diagram were investigated by utilizing small amplitude oscillatory and steady shear measurements. A mixture of unentangled monodisperse polystyrene and poly(phenyl methyl siloxane), exhibiting Newtonian shear viscosity, was used, and its phase diagram was established by turbidity and dynamic light scattering measurements. In the miscible region, the concentration dependence of the viscosity was adequately described by a mixing rule accounting for the surface fractions instead of volume fractions. Near the phase separation temperature and far from the glass transition, critical concentration fluctuations dominated the linear viscoelastic response and were responsible for the observed thermorheological complexity. An appropriate quantitative account of these fluctuations resulted in the accurate rheological determination of both the binodal and spinodal temperatures, extending thus the applicability of the relevant procedure earlier applied to lower critical solution temperature blends involving higher molecular weight entangled polymers. In the phase separated regime, the normal stress of the dispersed phase undergoing spinodal decomposition followed a recent scaling proposed for molecular mixtures with large viscosity difference.

Rheological Investigation of Shear Induced‐Mixing and Shear Induced‐Demixing for Polystyrene/Poly(vinyl methyl ether) Blend

“…Assuming that the interaction parameter is given by w ¼ A þ B/T, the above equations predict a linear dependence of [G 00 (o) 2 /G 0 (o)T] 2/3 versus 1/ T, leading to an intercept with the 1/T-axis yielding the spinodal temperature, T s . This procedure has been successfully applied to LCST and UCST polymer blends by Vlassopoulos et al [33,39] This approach was also worked effectively in our rheological studies for the PaMSAN/ PMMA blend (LCST-type phase diagram). [22] Typical experimental results of [G 00 (o) 2 /G 0 (o)T] 2/3 versus 1/T for the PS/PVME ¼ 40/60 blend at different constant shear rates are shown in Figure 11.…”

Dynamics of partially miscible polylactide-poly(ε-caprolactone) blends in the presence of cold crystallization

“…The rheological response in the pre-transitional area of binary blend systems has been employed before in many reports in order to determine their phase boundary Chopra et al 1998;Kapnistos et al 1996b;Vlassopoulos et al 1997;Zhang et al 2001). The enhanced concentration fluctuations near the transition have been shown to be the origin of the complex rheological response in the vicinity of the critical region, giving rise to enhanced viscoelastic moduli at long times (Bousmina et al 2002;Kapnistos et al 1996b;Zhang et al 2008).…”

Interrelations between Rheology and Phase Behaviour in Partially Miscible Blends: The Case of Polydimethylsiloxane/Polyethylmethylsiloxane (PDMS/PEMS)

“…The images shown in Figure 2 reveal the onset of phase separation, manifested by a nucleation and growth type mechanism, once the temperature becomes lower Figure 4) and extrapolating the inverse intensity data to zero (corresponding to the temperature where the structure factor becomes infinite, i.e., the critical point according to mean field theory; see also Vlassopoulos et al, 1997). As expected, the spinodal temperatures lie below the binodal temperatures (see Figure 3).…”

“…More information on this technique can be found elsewhere (Berne and Pecora, 1976;Vlassopoulos et al, 1997). The measurements started from a high temperature in the homogeneous region.…”