Structural and dynamical properties of thermoplastic polyurethane/fullerene nanocomposites: a molecular dynamics simulations study

In this work, the structural and dynamical properties of thermoplastic polyurethane (TPU)/fullerene (C60) nanocomposites are investigated using atomistic molecular dynamics simulations, focusing on the glass transition, thermal expansion, polymer mobility, polymer-C60 interactions, and diffusion behavior of C60. The results show a slight increase in the glass transition temperature (Tg) with increasing C60 weight fraction (wt%), attributed to hindered polymer dynamics, and a remarkable reduction in the coefficient of thermal expansion above Tg. Results of the mean squared displacement and the time decay of bond-reorientation autocorrelation indicate that the mobility of TPU hard segments is more restricted than that of soft segments, owing to the electrostatic attractions and the pi-pi stacking between isocyanate groups and C60 molecules. Analysis of TPU-C60 interaction energy reveals that the electrostatic interactions are weakened with an increase in the C60 wt%, while the van der Waals contributions become more significant due to the TPU-C60 interfacial characteristics. Further analysis shows that the translational and rotational diffusion of C60 are both increasingly suppressed with the increase of C60 wt%, indicating a violation of Stokes-Einstein (SE) and Stokes-Einstein-Debye (SED) relations, presumably due to the polymer chain-mediated hydrodynamic interactions arising from chain bridges between neighboring C60 particles. This is highlighted by a stronger decoupling of translational-rotational diffusion and a lower ratio of translational-rotational diffusion coefficient (DT/DR) with increasing C60 wt%. This work elucidates an atomistic understanding of the structure and properties of polymer/C60 nanocomposites. The structural and dynamical properties of TPU/C60 nanocomposites have been investigated using atomistic molecular dynamics simulations, focusing on the glass transition, polymer mobility, polymer-C60 interactions, and C60 diffusion behavior.

Automated summary

The structural and dynamical properties of TPU/C60 nanocomposites were investigated using atomistic molecular dynamics simulations. Results showed that an increase in C60 weight fraction slightly increased the glass transition temperature, hindered polymer dynamics, and significantly reduced the coefficient of thermal expansion above Tg. The mobility of TPU hard segments was more restricted compared to soft segments due to electrostatic attractions and pi-pi stacking. Analysis of TPU-C60 interaction energy revealed weakened electrostatic interactions and increased van der Waals contributions as C60 weight fraction increased. The translational and rotational diffusion of C60 were both suppressed with increasing C60 weight fraction, indicating a violation of Stokes-Einstein relationships.