Molecular Mechanism on the Fracture Property of Slide-Ring Crosslinked Elastomer

Abstract

The slide-ring (SR) crosslinked elastomer (SRCE) has attracted much attention due to the excellent fracture toughness, but molecular mechanism is unclear. Therefore, a coarse-grained model of SRCE with different crosslink densities and coverages of SR is constructed in this work. By performing a triaxial deformation, the maximum fracture energy of SRCE obtained at the moderate crosslink density of SR is about 72 times higher than that without crosslink bonds. However, it decreases by about 3.5 times with increasing coverage of SR from 5% to 20%. To understand it, asphericity factor of chains, percentage of SR at the end region of chains and the average sliding distance of SR are first analyzed which rise at the low strain with increasing crosslink density or coverage of SR. This indicates the high sliding rate of SR from the inner region to end region of chains. However, the strain at the maximum asphericity factor or percentage of SR at the end region of chains or average sliding distance of SR is reduced. This is because the number of broken bonds rises while the strain at the beginning of bond breakage is reduced. Meanwhile, the percentage of broken backbone bonds is lower than that of broken crosslink bonds because one backbone bead bears less stress than one crosslink bead. Moreover, the position of bond breakage changes from the end region to inner region of chains with increasing crosslink density or coverage of SR which can be further proved by the ratio of local stress by one end bead to that by one inner bead. Subsequently, the evolution process of voids is quantified by calculating the number, volume fraction and surface of voids. Voids are nucleated in the polymer region with a low local elastic modulus at the low strain while they appear in the positions of broken bonds at the large strain. The high crosslink density and low coverage of SR can reduce the growth and coalescence rate of voids. In summary, this work presents a deep and clear insight into the molecular mechanism on fracture property of SRCE.