Diluent and blending

The use of diluents ( plasticizers ) to reduce the relaxation times of polymers is a well established method for altering their physical properties. Often the desired result of incorporating some small molecule liquid is a reduction in the viscosity of the polymer melt, which facilitates processing. The reduction is caused by two effects - the dilution of the chain entanglements and the decrease of the local friction. The latter is the case, at least if the friction coefficient of the diluent is less than that of the polymer, which is the expectation if the former has a lower glass transition temperature. 

The detailed consequences of mixing on polymer dynamics are not fully understood [57]. Segmental relaxation times of the diluent and the polymer are expected to be closer in magnitude when mixed, than when in their respective pure states. Free-volume concepts would suggest that a polymer mixed with a 

A number of recent studies have shown deviations from this simple behavior when the components have nearly equal T s. For mixtures of polymers with diluent [35,58-61], as well as for polymer blends [62-64], measured relaxation times are not always found to be intermediate between those of the pure components. Specifically, addition of a higher component often increases the relaxation rate. 

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