Steady-Shear Rheology of Block Copolymer Melts and Concentrated Solutions:  Disordering Stress in Body-Centered-Cubic Systems

Abstract

We use steady-shear rheology to study the shear-disordering phenomenon in block copolymers in the body-centered-cubic (bcc) mesophase. Polystyrene-polyisoprene and polystyrene-poly-(ethylene-alt-propylene) diblock, triblock, and starblock systems of varying molecular weight and composition were studied in the melt and as concentrated solutions in a selective solvent. The bcc lattice exhibits a low-frequency modulus G bcc 0 which scales with the cube of the lattice spacing and additionally depends only on the proximity to the order-disorder transition (ODT). Steady shear destroys the bcc lattice at a critical shear stress, which is found to be directly proportional to the lattice modulus: τc ) 0.038G bcc 0 for all block copolymer melts and highly concentrated solutions investigated. The critical stress is thus uniquely determined by the lattice spacing and the proximity to the ODT. The rheological behavior conforms in a remarkably quantitative manner to the shear-melting processes observed in other soft crystalline systems, such as colloidal crystals.

Morphology and elasticity of polystyrene-block-polyisoprene diblock copolymers in the melt

“…This result is in agreement with the works of Sebastian et al (2002a); Sebastian et al (2002b). The slow ordering results from the high temperature the experiment was performed at, which is just slightly below the order-disorder transition temperature T ODT .…”

“…Their study revealed that the steady-state viscosity strongly decreases above a critical shear stress. Furthermore the critical stress is a function of the lattice spacing and the temperature in relation to T ODT (Sebastian et al (2002a).) The phase behavior of various PS-b-PI diblock copolymers was 3 investigated by Förster et al (1994) using transmission electron microscopy (TEM), scattering techniques and rheological experiments.…”

Pattern formation mechanisms in sphere-forming diblock copolymer thin films

“…The copolymer was synthesized through sequential living anionic polymerization of styrene and isoprene followed by selective saturation of the isoprene block [23]. Because the two polymer species are immiscible, the minority polystyrene forms spherical microdomains within the majority poly(ethylene-alt-propylene).…”

Analysis of stability and viscoelastic properties of melts of polystyrene-block-polyisoprene diblock copolymers in oscillatory shear and creep-recovery experiments

“…Furthermore, it was shown that orientation phenomena take place in large amplitude oscillatory shear flow [4]. The works of Sebastian et al [5,6] reveal that the lattice structure of an ordered polystyrene-block-polyisoprene diblock copolymer melt can be broken up in steady shear. This shear-induced disordering is reflected in the rheological quantities.…”