HIGH-STRAIN TENSILE DEFORMATION OF A SPHERE-FORMING TRIBLOCK COPOLYMER MINERAL-OIL BLEND

Films of a blend of styrene-isoprene triblock copolymer and mineral oi l have been simple-cast and roll-cast from a toluene solution. Their m icrostructure has been analyzed by transmission electron microscopy an d small-angle X-ray scattering. The blend formed polystyrene spheres a rranged on a body-centered cubic lattice in a matrix composed of polyi soprene and mineral oil, and the samples display large grain sizes and very long-range order. The roll-cast sample exhibits approximately un iaxial symmetry around the rolling direction, which corresponds to the [111] crystallographic direction of the lattice. The glassy spheres a ct as physical crosslinks of known crosslinking functionality in the s oft rubbery matrix. The high-strain deformation mechanism of this orie nted cubic material has been studied by a simultaneous tensile-SAXS ex periment, where the sample was stretched up to 300% along the [111] di rection. By monitoring the position of the (222) and (1(1) over bar0$) reflections, the deformation of the lattice is shown to be affine wit h the macroscopic deformation of the sample, and the Poisson's ratio i s approximately 0.46. The first zero of the sphere form factor in the SAXS patterns remains also essentially unchanged up to 300% deformatio n indicating that the reinforcing glassy PS domains retain their spher ical shape throughout the deformation. Deformation of the microstructu re is totally reversible upon unloading. A model of {hk0} faults is pr oposed to describe the microstructural changes induced by high-strain deformation. (C) 1998 John Wiley & Sons, Inc.