Crazing of nanocomposites with polymer-tethered nanoparticles

Abstract

The crazing behavior of polymer nanocomposites formed by blending polymer grafted nanoparticles with an entangled polymer melt is studied by molecular dynamics simulations. We focus on the three key differences in the crazing behavior of a composite relative to the pure homopolymer matrix, namely, a lower yield stress, a smaller extension ratio, and a grafted chain length dependent failure stress. The yield behavior is found to be mostly controlled by the local nanoparticle-grafted polymer interfacial energy, with the grafted polymer-polymer matrix interfacial structure being of little to no relevance. Increasing the attraction between nanoparticle core and the grafted polymer inhibits void nucleation and leads to a higher yield stress. In the craze growth regime, the presence of "grafted chain" sections of ≈100 monomers alters the mechanical response of composite samples, giving rise to smaller extension ratios and higher drawing stresses than for the homopolymer matrix. The dominant failure mechanism of composite samples depends strongly on the length of the grafted chains, with disentanglement being the dominant mechanism for short chains, while bond breaking is the failure mode for chain lengths >10Ne, where Ne is the entanglement length.

Perspective: Outstanding theoretical questions in polymer-nanoparticle hybrids

“…Similarly, Meng et al have looked at the crazing of glassy PNCs with polymer-grafted NPs. 281 These workers have also looked at the distribution of mechanical stresses in the material. While these are informative, there is currently no understanding of the role of NP dispersion on the mechanical properties that result.…”

Uncovering the rupture mechanism of carbon nanotube filled cis-1,4-polybutadiene via molecular dynamics simulation

“…The other one is the tri-axial deformation to induce the failure, namely the simulation box is extended in one direction, while the other two dimensions are held xed, which results in a positive effective stress in all directions. 40,41 In this case, there is no rigid walls. Periodic boundary conditions are applied in three directions.…”

“…We adopted the latter approach to induce the occurrence of the voids. 40,41 The uniaxial tensile tests are performed by stretching the simulation box along one direction at a constant strain velocity (10 10 S À1 adopted by the previously published works [42][43][44] ) while keeping the box length unchanged in other two directions. Meanwhile, the average stress-strain curve is obtained by independently deforming each system along x, y and z directions, respectively.…”

Mechanical properties of polymer grafted nanoparticle composites

“…And as P/N increases, w decreases. 29 Further, if the brushmatrix interactions are repulsive, 30 interaction decreases and leads to a lower yield strength than pure matrix. For attractive filler-matrix interactions, computation predicts that the yield strength will be the same as the matrix.…”