Effect of Shear Flow on the Polymeric Gels Formed by Macroscopic Phase Separation

Abstract

Summary: Shear-induced phase behavior of poly(ethylene oxide-b-(DL-lactic acid-co-glycolic acid)-b-ethylene oxide) (PEO-PLGA-PEO) triblock copolymers in water is investigated using rheology and small-angle neutron scattering equipped with an in situ Couette shear cell. For gels formed by the macroscopic phase separation, the steady shear experiment reveals that the flow-induced anisotropy on a nanometer length scale at a critical shear rate and the phase separation on a larger length scale are successively induced with a further increase in the shear rate. In particular, the hard gels show a memory effect inscribed by a pre-high shear in contrast to the soft gels.