Abstract
Styrene-rich butadiene–styrene (BS) diblock copolymers dispersed in dibutyl phthalate (DBP) formed micelles with B cores and S cilia. As the concentration was increased, these micelles arranged themselves on a macrolattice, and the system began to show plasticity and also thixotropy. When the temperature was raised, the system underwent a transition from plastic to viscoelastic behavior. This rheological transition was found to be associated with disordering of the macrolattice. The mechanism was interpreted as follows. With increasing temperature, the S and B blocks intermix more extensively in the interphase, making the interphase more diffuse. The mobility of the B–S junctions in the diffuse interphase increases, and hence, the stability of the macrolattice is reduced. This interpretation is supported by the following two findings: no transition occurred when the micelle cores were crosslinked in order to prevent intermixing of the B and S blocks and to anchor the junctions tightly on the cores; no plastic behavior was observed for DBP solutions of tapered block copolymers (tBS) with the characteristics comparable to those of the BS/DBP micellar solutions. In such a tBS solution, micelles with a diffuse BS interphase were formed, and the macrolattice became unstable. Thixotropy of the system having a macrolattice was apparently caused by breakage of the macrolattice but not necessarily that of the micelles. In fact, the macrolattice system of BS micelles with crosslinked B cores exhibited thixotropy, while random suspensions of the micelles were neither plastic nor thixotropic.
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Watanabe, H., Kotaka, T. Rheology of Styrene–Butadiene Diblock Copolymers in Selective Solvent: Mechanisms of Thixotropy and Thermally Induced Rheological Transition. Polym J 15, 337–347 (1983). https://doi.org/10.1295/polymj.15.337
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DOI: https://doi.org/10.1295/polymj.15.337
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