Dynamics and rheology of miscible polymer blends

The dynamics of miscible polymer blends has been a subject of interest for decades. Competing models attempt to explain well-known anomalies, such as the failure of time-temperature superposition, asymmetric glass transition broadening, and strange composition dependence of component diffusion coefficients. In order to distinguish between different theories for component dynamics in miscible blends, the terminal relaxation time was measured for each component of poly(isoprene)/polyvinyl ethylene) (PI/PVE) blends over a wide range of temperatures and compositions. Additionally, the tracer diffusion coefficients of PI in a matrix of PVE and PVE in a matrix of PI were measured. This data indicates that the dynamics of the PI/PVE blend system are well described by the self-concentration approach of Lodge and McLeish (2000). The predictions of this model are in near quantitative agreement for PI, and capture the general trends in the composition and temperature dependence of the dynamics of PVE.; The measured values of PI and PVE terminal dynamics are in good agreement with literature data for segmental dynamics. This agreement between segmental and terminal dynamics is not general for miscible polymer blends. Diffusion and rheology measurements on a polyethylene oxide) (PEO) tracer in a poly(methyl methacrylate) matrix indicate that the terminal dynamics of the PEO tracer are many orders of magnitude slower than what is anticipated from segmental dynamics.; Existing molecular models were adopted to produce a method capable of predicting the composition dependence of miscible blend viscosity. The general approach is to use self-concentration to predict component friction, reptation and a new tube dilation model to determine the terminal relaxation time for each blend component, and double reptation to calculate viscosity. This model anticipates all of the different categories of qualitative behavior in the literature, and shows encouraging agreement with experimental data from model miscible blends.