Mechanical properties of the double gyroid phase in oriented thermoplasticelastomers

We investigate the mechanical properties of triblock copolymers with orient ed double gyroid (DG) morphology in poly(styrene-b-isoprene-b-styrene) (SIS ) triblock copolymers by deforming textured samples along both the [111] di rection and transverse to this direction. The modulus anisotropy for the tw o directions of this cubic material is approximately a factor of 5. Deforma tion along [111] causes the sample to form a distinct neck and draw, while the deformation in the transverse direction proceeds without neck formation . In addition, the mechanical hysteresis of the [111] stretch is 50% higher than that transverse to the [111] direction. Upon unloading and annealing above the polystyrene Tg, the DG structure recovers fully, both macroscopic ally and microscopically. The mechanical properties of the DG are compared to those of the classical block copolymer morphologies to gain insight into the deformation mechanism. (C) 2000 Kluwer Academic Publishers.