MORPHOLOGY TRANSITION FROM CYLINDRICAL TO LAMELLAR MICRODOMAINS OF BLOCK COPOLYMERS

Thermally induced morphology transition from cylindrical to lamellar microdomains was found for a poly(styrene-block-butadiene-block-styrene) (SBS) triblock copolymer having a 0.56 weight fraction of polystyrene blocks by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Polybutadiene (PB) cylinders with hexagonal close packing were formed in a polystyrene (PS) matrix when the SBS was cast from a methyl ethyl ketone solution. It was found that the PB cylinders were transformed into lamellae on annealing at 150 -degrees-C. This is a transition from thermodynamically quasi-stable to stable morphologies. On the basis of SAXS and TEM, the transition turned out to occur via coalescence of cylinders without their translational movements. It is proposed that an undulation of the interface induced by the instability of the interface might play an important role for the coalescence of the cylinders. It was also found by TEM that the coherency of lamellar microdomains thus formed became higher with further annealing; i.e., the persistence length of the undulating lamellae became longer.