Polymer blends, component dynamics relaxation

Simulation Study of Relaxation Processes in the Dynamical Fast Component of Miscible Polymer Blends. 

J. Zawada, C. Ylitalo, G. Fuller, R. Colby, and T. Long, Component relaxation dynamics in a miscible polymer blend Polyethylene oxide)/poly(methyl methacrylate), Macromolecules, 25,2896 (1992). 

Another example from polymer blends can be taken from the dynamics of the faster poly(ethyl methacrylate) (PEMA, Tg = lA C) component in blends with poly(4-vinylphenol) (PVPh, Tg = 171 C) (Zhang et al 2002). Neat PEMA has a resolved JG relaxation, which is continued to be observed in the blend and practically unchanged with blending. Since Tg of the PEMA component in the blend is shifted to higher temperature by the slower poly(4-vinylphenol) component, therefore ogXaf Tgf) - ogxpf Tgf)) of the PEMA component increase at constant Xa(Tg). 

The hterature about dielectric relaxation is rich. For instance, there are several recent reviews available for that field (Simon and Schonhals 2003 Runt 1997 Floudas et al. 2011 Colmenero and Arbe 2007). For instance, by application of dielectric spectroscopy to polymeric blends, the phase behavior of a system can be probed or the degree of miscibihty of the blend components in the different phases can be discussed and estimated. This concerns also the question of the dynamic heterogeneity in miscible blend systems or confinement effects in dynamically asymmetric polymer blends (Colmenero and Arbe 2007). 

Besides the dynamic heterogeneity discussed above, binary miscible polymer blends can be considered as dynamically asymmetric if the two components have a large difference in the glass transition temperatures. Usually the dynamic asymmetry is defined by A = where x " is the relaxation time of the... 

Equations for Tg based on the free-volume concept have been proposed for miscible polymer blends and they are similar to the Kelly-Bueche equation given above for polymer-diluent systems. Likewise, this description in terms of a single Tg over-simplifies the dynamics of the components in the blend and neglects some important elements. An important element for interpreting the relaxation behavior of blends is fluctuations in concentration or composition [102]. Models have been... 

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