Rheology On A Triblock Copolymer: Mechanical Hole Burning Spectroscopy

Mechanical hole burning spectroscopy was developed for probing the dynamic heterogeneity of polymeric materials. In this technique, a mechanical oscillatory perturbation is applied to the sample to excite the dynamic heterogeneities and this is followed by a small linear strain. Comparison between linear response after perturbation and that without any perturbation can result in vertical and horizontal modifications in the response that are referred to as ``holes.'' The holes are thought to be a signature of the dynamic heterogeneity of polymers. To quantitatively characterize the dynamic heterogeneity, a block copolymer was used and the study was performed in the vicinity of its order-disorder transition temperature. The results indicate that the mechanical holes can be successfully burned in the heterogeneous phase (T$<$TODT), while in the homogeneous or disordered phase, no apparent holes were observed. More importantly, the hole intensity decreases sharply in the vicinity of the ODT, which provides a correlation between hole intensity and the length scale of the heterogeneity.