Influence of the Chemical Structure on the Mechanical Relaxation of Dendrimers

The rheological properties of macromolecules represent one of the fundamental features of polymer systems which expand the possibilities of using and developing new materials based on them. In this work, we studied the shear-stress relaxation of the second generation PAMAM and PPI dendrimer melts by atomistic molecular dynamics simulation. The time dependences of relaxation modulus G(t) and the frequency dependences of the storage G '(omega) and loss G ''(omega) moduli were obtained. The results were compared with the similar dependences for the polycarbosilane (PCS) dendrimer of the same generation. The chemical structure of the dendrimer segments has been found to strongly influence their mechanical relaxation. In particular, it has been shown that hydrogen bonding in PAMAM dendrimers leads to an entanglement of macromolecules and the region is observed where G '(omega) > G ''(omega). This slows down the mechanical relaxation and rotational diffusion of macromolecules. We believe that our comprehensive research contributes to the systematization of knowledge about the rheological properties of dendrimers.

Automated summary

In this study, the shear-stress relaxation of second generation PAMAM and PPI dendrimer melts was investigated through atomistic molecular dynamics simulation. The time dependences of relaxation modulus G(t) and the frequency dependences of storage G'(omega) and loss G''(omega) moduli were obtained and compared with a similar dendrimer of the same generation. The results showed that the chemical structure of the dendrimer segments strongly influenced their mechanical relaxation, with hydrogen bonding in PAMAM dendrimers leading to entanglement of macromolecules and slowing down of mechanical relaxation and rotational diffusion.