Rheological Modeling ofthe Mutual Diffusion and the Interphase Development for an AsymmetricalBilayer Based on PMMA and PVDF Model Compatible Polymers.

The mutual diffusion process and interphase developmenttaking place at an asymmetrical polymer–polymer interface betweentwo compatible model polymers, poly(methyl methacrylate) (PMMA) withvarying molecular weights and poly(vinylidene fluoride) (PVDF) inthe molten state, were investigated by small-amplitude oscillatoryshear measurements. The rheology method, Lodge–McLeish model,and test of the time–temperature superpositon (tTS) principlewere employed to probe the thermorheological complexity of this polymercouple. The monomeric friction coefficient of each species in theblend has been examined to vary with composition and temperature andto be close in the present experimental conditions, and the failureof the tTS principle was demonstrated to be subtle. These were attributedto the presence of strong enthalpic interaction between PMMA and PVDFchains that couples the component dynamics. Hence, a quantitativerheological model modified from a primitive Qiu–Bousmina’smodel that connected the mobility in the mixed state to the propertiesof the matrix was proposed to determine the mutual diffusion coefficient(Dm). The modified model takes into accountthe rheological behavior of the interphase for the first time. Inturn, viscoelastic properties and thicknesss of the interphase havebeen able to be quantified on the basis of the modified model. Effectsof the annealing factors like welding time, angular frequency, temperature,and the structural properties as well molecular weight and Flory–Hugginsparameter (χ) on the kinetics of diffusion and the interphasethickness and its viscoelastic properties were investigated. On onehand, Dmwas observed to decrease withfrequency until leveling off at the terimnal zone, to depend on temperatureobeying the Arrhenius law, and to be nearly independent of PMMA molarmass, corroborating the prediction of the fast-mode theory. On theother hand, the generated interphase which reached dozens of micrometerswas revealed to own a rheological property approaching its equivalentblend. Scanning electron microscopy coupled with energy dispersiveX-ray analysis (SEM-EDX) and transmission electron microscopy(TEM)were also carried out and confronted to the rheological results. Comparisonsbetween mathematical modeling of concentration profile based on the Dmobtained from rheology and the experimentalones of SEM-EDX and TEM were conducted. Thus, a better correlationbetween theory and experimental results in terms of mutual diffusionand the interphase properties was nicely attained. The obtained dataare in good agreement with literatures using other spectroscopicalmethods. [ABSTRACT FROM AUTHOR]