High-strain tensile deformation of a sphere-forming triblock copolymer/mineral oil blend

Abstract

Films of a blend of styrene–isoprene triblock copolymer and mineral oil have been simple-cast and roll-cast from a toluene solution. Their microstructure has been analyzed by transmission electron microscopy and small-angle X-ray scattering. The blend formed polystyrene spheres arranged on a body-centered cubic lattice in a matrix composed of polyisoprene and mineral oil, and the samples display large grain sizes and very long-range order. The roll-cast sample exhibits approximately uniaxial symmetry around the rolling direction, which corresponds to the [111] crystallographic direction of the lattice. The glassy spheres act as physical crosslinks of known crosslinking functionality in the soft rubbery matrix. The high-strain deformation mechanism of this oriented cubic material has been studied by a simultaneous tensile–SAXS experiment, where the sample was stretched up to 300% along the [111] direction. By monitoring the position of the (222) and (110) reflections, the deformation of the lattice is shown to be affine with the macroscopic deformation of the sample, and the Poisson's ratio is approximately 0.46. The first zero of the sphere form factor in the SAXS patterns remains also essentially unchanged up to 300% deformation indicating that the reinforcing glassy PS domains retain their spherical shape throughout the deformation. Deformation of the microstructure is totally reversible upon unloading. A model of {hk0} faults is proposed to describe the microstructural changes induced by high-strain deformation. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1625–1636, 1998