OPTICAL AND MECHANICAL-PROPERTIES OF A STAR DIBLOCK COPOLYMER MELT IN OSCILLATORY SHEAR-FLOW

Mechanical rheometry and birefringence measurements are used to study the low-frequency dynamics of a homogeneous, star diblock copolymer melt as it is cooled through its microphase separation temperature (MST). Anomalous low-frequency behavior in both mechanical and optical properties are observed at temperatures close to the MST. We conclude that a general condition must be satisfied before unusual low-frequency behavior is observed, namely that the time scale of flow must be less than the relaxation time of structural features perturbed by flow. Furthermore, because of the similarities between the low-frequency dynamics of the present star diblock copolymer and those of linear diblock and triblock copolymers, we also conclude that block copolymer architecture does not play a critical role in determining the low-frequency behavior of these materials.