Dynamic Viscoelastic Behavior of the Solutions of Styrene-Butadiene Block Copolymers

Abstract

The behavior of block copolymer solutions may be highly different from that of homopolymer solutions, because of the microdomain structures formed in the systems.
The behavior of decalin solutions of a PS-PB-PS and a PS-PB block copolymers were similar to that of homopolymer solutions corresponding to the homogeneity of the systems. However, in the decane solutions, the PS-blocks aggregated to form precipitated domains, then a quasi-network structure was formed in the former while a micelle structure in the latter. Corresponding to such structures, the former showed a behavior similar to crosslinked rubbers and the latter a plateau region in G″ in the lower frequency range.
For SB/SBS blend systems dissolved in n-tetradecane, the difference between the micelle and quasi-network systems became more prominant when the nonlinearity of the systems was compared. While the quasi-network system showed the rubberlike linear viscoelasticity, the micelle system showed nonlinear behavior, in which odd harmonics appeared in shear stress, the fundamental harmonics had a plateau region, and the nonlinearity of the system decreased as the frequency increased.
These characteristic behavior of the micelle system can be understood as a Bingham-type viscoelastic behavior. The difference between the micelle and the quasi-network systems seems to be caused by the restriction from the microdomain structures that the shear flow occurs in the former by slipping aggregated PS domains with each other, while it does not in the latter without breaking the PS domains.