Despite the widespread application of block copolymers, their rheology in the two-phase state, characterized by large viscosities and elasticities, has only recently yielded to understanding. We investigated the flow behavior of sphere-forming block copolymers. In the ordered state, at low shear stresses, the microdomains are ordered, giving the molten rubber a large viscosity. However, as shown in the figure below, at a critical shear stress the viscosity drops precipitously as the microdomains are "shear-disordered". We showed that this stress is uniquely related to the spacing between ordered microdomains, allowing us to control the value of this stress through molecular design or the addition of a selective solvent.
Supported by the National Science Foundation, Materials Research Science and Engineering Center (MRSEC) Program, through the Princeton Center for Complex Materials
Group Members Involved, and Their Project Titles:
Daniel Vega PDRA – “Phase Behavior and Rheology of Block Copolymer Gels”
John Sebastian PhD *01 – “Rheology of Spherical-Phase Block Copolymer Melts and Solutions”
J. LaMonte Adams PhD *96 – “Rheology and Phase Behavior of Styrene-Diene Block Copolymers”
Relevant Group Publications:
J.M. Sebastian, W.W. Graessley, and R.A. Register, “Steady-Shear Rheology of Block Copolymer Melts and Concentrated Solutions: Defect-Mediated Flow at Low Stresses in Body-Centered-Cubic Systems”, J. Rheol., 46, 863-879 (2002).
J.M. Sebastian, C.J. Lai, W.W. Graessley, and R.A. Register, “Steady-Shear Rheology of Block Copolymer Melts and Concentrated Solutions: Disordering Stress in Body-Centered-Cubic Systems”, Macromolecules, 35, 2707-2713 (2002).
J.M. Sebastian, C.J. Lai, W.W. Graessley, and R.A. Register, “Steady-Shear Rheology of Block Copolymer Melts: Zero-Shear Viscosity and Shear-Disordering in Body-Centered-Cubic Systems”, Macromolecules, 35, 2700-2706 (2002).
D.A. Vega, J.M. Sebastian, Y.-L. Loo, and R.A. Register, “Phase Behavior and Viscoelastic Properties of Entangled Block Copolymer Gels”, J. Polym. Sci. B: Polym. Phys., 39, 2183-2197 (2001).
J.L. Adams, D.J. Quiram, W.W. Graessley, R.A. Register, and G.R. Marchand, “Ordering Dynamics of Compositionally Asymmetric Styrene-Isoprene Block Copolymers”, Macromolecules, 29, 2929-2938 (1996).
J.L. Adams, W.W. Graessley, and R.A. Register, “Rheology and the Microphase Separation Transition in Styrene-Isoprene Block Copolymers”, Macromolecules, 27, 6026-6032 (1994).