Elastic recovery of immiscible blends - Part 2: Transient flow histories

Immiscible polymer blends are known to display an unusual elastic recovery after stress release. Recoil after steady-state shearing is well understood and obeys specific scaling relations. Releasing the stress before the stea dy-state morphology has been reached results in a more complex elastic reco very, including very large final values. This behaviour is investigated sys tematically. Model blends are used, consisting of nearly inelastic componen ts; hence the measured recoil can be attributed totally to contributions fr om the interface. The instantaneous structure at the onset of the recoil ca n vary greatly in transient experiments, ranging from slightly deformed dro plets to highly elongated filaments. The effects of this initial structure on the ultimate recoil and time scale of the recovery are studied. The morp hological changes during recovery are considered as well. It is demonstrate d that they can be computed from the normal stresses during stress relaxati on with comparable initial morphologies. This indicates that the same morph ological changes occur during stress relaxation and constrained recoil. A s caling relation for the recoil curves has been derived from the Doi-Ohta th eory, which is confirmed by the experiments.