Block Copolymer Rheology

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.

Steady-shear viscosity of a styrene-isoprene diblock forming polystyrene spheres
Steady-shear viscosity of a styrene-isoprene diblock forming polystyrene spheres, with TODT = 197°C. Note the factor-of-104 drop in viscosity at the critical stress, where the microdomain lattice disorders (Sebastian et al., Macromolecules, 35, 2700 (2002)).

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).