Molecular dynamics simulation investigation into the effects of polymerization degree on the tribological properties of NBR

This study employs molecular dynamics (MD) simulations to systematically investigate the effects of the degree of polymerization (DP 10, 20, and 35) on the mechanical and tribological properties of nitrile butadiene rubber (NBR) against a copper (Cu) probe. Mechanical property analysis reveals that increasing the DP from 10 to 35 enhances the Young’s modulus and shear modulus by 11.9 % and 16 %, respectively, establishing a more rigid structural foundation. Tribological simulations demonstrate that increasing DP significantly optimizes performance, yielding a 44.3 % reduction in the coefficient of friction (COF) and a 36.9 % relative decrease in the wear rate. Microscopic analysis of atomic concentration, velocity distribution, and radial distribution functions (RDF) indicates that higher DP promotes a denser network of physical entanglements, which effectively mitigates adhesive shearing and restricts molecular migration at the friction interface. Energy evolution profiles further confirm that high-DP matrices suppress potential energy surges and local heat accumulation, thereby enhancing thermal stability and structural integrity. These findings demonstrate that increasing DP significantly strengthens the internal physical entanglements and intermolecular interactions within the NBR matrix, providing a theoretical basis and molecular design strategy for developing high-performance, wear-resistant materials for water-lubricated bearings.