Rheologica Acta, Vol.54, No.3, 185-205, 2015
Onset of entanglement and reptation in melts of linear homopolymers: consistent rheological simulations of experiments from oligomers to high polymers
The shear rheological behavior is investigated in this work for a series of poly(ethyl acrylate) samples, whose molar mass ranges from oligomers to high polymers. The focus was on studying the onset of entanglement effects over selected reptation models in order to ascertain their ability to reproduce the complex shear modulus of the polymers and to provide consistent values of the microscopic parameters driving the structural relaxation of the polymer system. Among ordinary reptation topological models, we found that the Doi-Edward model, implemented with contour length fluctuation and constraint release mechanism for the tube relaxation, better reproduced the rheological response of the materials. Most importantly, we were able to simulate material functions to obtain consistent microscopic information on the materials, such as Rouse time and entanglement molar mass, over the whole range of investigated molar masses, therefore overcoming the discrepancy usually found, mostly in the mass region of partial entanglement. Finally, descriptions of the polymer entanglement features, in agreement with the experimental and microscopic model findings, are provided in the framework of the packing-length phenomenological model and by means of analytical calculations of the polymer viscosity according to the Milner-McLeish-Likhtman model.