Engineering oriented hierarchical lamellar structures in SBS/PS blends via a pressure-induced flow field

Abstract

Inorganic materials with a hierarchical lamellar architecture based on bio-inspired design principles found in seashell nacre and bone are expected to have high performance. Recently, great progress has been achieved in the fabrication of thin films, while incorporation of these supramolecular designs into synthetic polymer materials in the bulk still faces a great challenge. We demonstrate how a hierarchical layered micro- and nano-structure can be generated in the bulk from a variety of polymer blends such as polystyrene/poly(styrene–butadiene–styrene) (PS/SBS) as a model compound reported herein via a pressure-induced flow field technique. In this blend system, minority spherical rubbery SBS in these PS/SBS blends was biaxially deformed into lamellae having nanometer scale thickness within a rigid glassy PS phase as indicated by transmission electron microscopy and small angle X-ray scattering experimental results. Benefiting from such a hierarchical lamellar structure, the resulting strength, stiffness and toughness along the lamellar normal direction were simultaneously enhanced, while the modulus remained constant. The enhanced strength of the blend system resulted from the orientation of the macromolecules at and near the phase-separated boundaries of the lamellar domains within the PS matrix, as indicated by infrared spectroscopy results. The mechanism of this remarkably increased toughness was due to the fact that the crazes generated during impact experiments were efficiently terminated by the SBS lamellar domain. Such a biomimetic design for rubber-toughened glassy materials could also be easily transferred into other materials consisting of either blends of two immiscible polymers or semi-crystalline polymers through this efficient pressure-induced flow field technique.