AN EVALUATION OF THE DOI-OHTA THEORY FOR AN IMMISCIBLE POLYMER BLEND

The theory developed by Doi and Ohta was evaluated for its ability to predict the rheology of an immiscible polymer blend. The theory descri bes the additional stresses arising as a consequence of interfacial te nsion in two phase systems in which the constituents consist of Newton ian fluids and have equal viscosities. The blend considered in this pa per consisted of an immiscible mixture of poly(ethylene terephthalate) (PET) and nylon 6,6 at a composition ratio of 25/75 w/w PET/nylon 6,6 . The rheological properties of this blend were found to be stable for the time frame required for the rheological experiments used in this work (e.g., < 5 min). The Doi-Ohta theory was found to be capable of q ualitatively predicting the extra stresses arising as a result of the interfacial tension as observed in the steady state viscosity and stea dy state first normal stress difference. The transient shear stress an d first normal stress difference at the start up of steady shear flow were qualitatively predicted by the Doi-Ohta theory while the recovery of the initial overshoot observed experimentally was not. The oversho ot observed experimentally during step-up experiments and the undersho ot observed during step-down experiments were not predicted by the the ory in which it was predicted that the stresses change monotonically w ith a stepwise change of the shear rate to the final steady state valu e. While the shear thinning behavior observed for this blend was not p redicted by the theory, the scaling relation for the transient stresse s predicted by the theory was found to hold for the blend using stepwi se changes of shear rate at a constant step ratio. (C) 1996 Society of Rheology.