Molecular Dynamics Study of Comb Polymer Melts under Start-up Shear

The stress and structural behaviors of non-entangled comb polymer melts under start-up shear flow were studied by molecular dynamics simulations, and compared with those of linear polymer. It is found that the stress-strain response of the unentangled comb polymer with short branched chain is almost the same as that of the linear polymer under different shear strengths, and only the numerical difference exists. Under weak shear strength, the stress reaches the platform value after short temporary increase, and there is no stress overshoot behavior. Under strong shear strength, the stress first increases rapidly and then decreases to the plateau value. In this process, there is an overshoot peak. In addition, we further studied the structural properties of comb polymers under start-up shear. Under weak shear strength, the main chain of comb polymer has only slight deformation and orientation and the branched-chain is not basically stretched. Under strong shear strength, the main chain of comb polymer is strongly stretched, but the branch chain still has no obvious change. The results show that compared with the main chain of comb polymer, the branched chain is slightly stretched under start-up shear, which indicates that the influence of branched chain on the rheological behavior of non-entangled comb polymer is weak, so that the properties of comb polymer under start-up shear are similar to those of linear polymer. The simulation results in this paper will help to understand the macroscopic mechanical properties and microstructural changes of comb polymer systems, which are of great significance for designing new polymer materials with desired properties. [GRAPHICS] .