Transient stresses and morphology of immiscible polymer blends under varying shear flow

Transient morphological and rheological properties of immiscible model polymer blends composed of poly-isobutylene (PIB) and poly-dimethylsiloxane (PDMS) are investigated under traditional thixotropic loop test and a modified one, in which an additional opposite process of the former test has been performed. It is shown that evident thixotropic behaviors appear only under certain shear strength and time scale where the breakups of droplets take place and the morphological evolution lag behind the shear rate change. In addition, a detailed analysis is given on morphological evolution under modified loop test, through combining the viscoelastic measurements and models calculation. Particularly, the evolution of droplets size under varying shear is estimated with Palierne model, suggesting that dominant breakup mechanism is determined not only by the strength of the flow field, but also by its evolution with time.