Pathway and kinetics of cylinder-to-sphere order-order transition in blockcopolymers

The pathway and kinetics for the cylinder-to-sphere order-order transition in a mixture of a matched diblock and triblock copolymer of styrene and eth ylene-butene-1 is reported. The microstructure transformation was monitored by viscoelastic measurements, and the structural assignments of the interm ediate states were performed by electron microscopy. The kinetics of transf ormation from macroscopically unaligned wormlike cylindrical microdomains t o spherical microdomains arranged on a bcc lattice were extremely slow. The wormlike cylinder-to-sphere transition slowed with decreasing quench depth from the order-disorder transition. Additionally, these order-order kineti cs were in quantitative agreement with those for the development of spheric al microdomains from an initial disordered state. Further, during the initi al induction time following a temperature jump from a wormlike cylindrical order to a spherical state, the sample exhibited liquidlike viscoelastic ch aracteristics and structurally showed the absence of long-range order. In c ontrast, shear-aligned cylinders rapidly transformed to spheres, adopting a viscoelastic pathway distinct from that of the unaligned samples. The cyli nder-to-sphere transition is thermotropically reversible, with the viscoela sticity-based kinetics of the sphere-to-cylinder transition being slower th an the cylinder-to-sphere transition.