A combined experiment and molecular dynamics simulation study of hydrogen bonds and free volume in nitrile-butadiene rubber/hindered phenol damping mixtures

By combining experiment and molecular simulation, in this work we have systematically elucidated the fundamental mechanism of the significantly improved damping property of nitrile-butadiene rubber (NBR) contributed by the introduction of hindered phenol (AO-80) small molecules. At the molecular level, through FTIR, ¹H-NMR and temperature-dependent FTIR, it is observed that hydrogen bonds (H-bonds) interaction exists between AO-80 small molecules and NBR polymer chains, leading to the formation of a H-bonds network structure. Meanwhile, positron annihilation lifetime spectrometer (PALS) and molecular dynamics simulation were also employed to characterize the fractional free volume for different NBR/AO-80 mixtures and it reached the minimum at the blending mass ratio of 100/60, which also possesses the largest number of H-bonds and the greatest binding energy through quantitative comparison. All of these microscopic analyses just rationalize the maximum dynamic loss factor. Therefore, it was indicated that there was an optimum ratio of rubber to hindered phenol molecules for achieving the maximum damping property. These fundamental studies are expected to provide some useful information to design and fabricate the high-performance polymeric damping materials.