Terminal component dynamics in poly(ethylene oxide)/poly(methyl methacrylate) blends.

摘要

Miscible polymer blends exhibit thermal and dynamic phenomena that are currently not very well understood: failure of time-temperature superposition, widening of the calorimetric glass transition temperature, dynamic heterogeneities and a decoupling of segmental and terminal dynamics. Obtaining insight into the underlying processes that may cause these phenomena hinges on the availability of component data.; During this work, novel methods of obtaining terminal component dynamics are developed using a commercial rheometer and requiring no special chemistry. These methods rely on blends where a small fraction of high-M chains (tracers) of either component are blended with a matrix of low-M components of varying composition. The presence of the tracers gives rise to distinct features in rheological material functions, which reveal the tracer component's contribution to the blend dynamics.; The data obtained via these methods agree with data obtained via forced Rayleigh scattering well. Poly(methyl methacrylate) (PMMA) dynamics are found to be profoundly affected by the presence of poly(ethylene oxide) (PEO). A tracer of PMMA in PEO assumes the friction of the host matrix. PEO is not so affected by the presence of PMMA. It exhibits significantly lower friction than the matrix dictates at a PMMA volume fraction of &phgr;PMMA>0.5. This phenomenon occurs concurrently with the failure of time-temperature superposition (TTS) for PEO tracer blends.; The contribution of hydrogen bonds to PEO/PMMA blend dynamics is found to be small.; A framework is developed for determining whether a blend is entangled, and if so, what the tube diameter is. The results of this protocol are supported by a map of the dynamic landscape. Using the protocol, it is found that matrix molecular weight has little effect on the component dynamics. It is found that tracer molecular weight has little effect on per-monomer tracer dynamics as well.; A tribological model is presented, which enjoys great success in predicting PMMA dynamics and PEO dynamics before the onset of PEO-mobility/matrix viscosity decoupling. Once this phenomenon occurs, the model fails to predict PEO dynamics well.; SANS data show that PMMA does not swell in the blend. No conclusive remark could be stated regarding PEO.