Fracture in Silica/Butadiene Rubber: A Molecular Dynamics View of Design-Property Relationships.

Despite intense investigation, the mechanisms governing the mechanical reinforcement of polymers by dispersed nanoparticles have only been partially clarified. This is especially true for the ultimate properties of the nanocomposites, which depend on their resistance to fracture at large deformations. In this work, we adopt molecular dynamics simulations to investigate the mechanical properties of silica/polybutadiene rubber, using a quasi-atomistic model that allows a meaningful description of bond breaking and fracture over relatively large length scales.

Towards realistic simulations of polymer networks: tuning vulcanisation and mechanical properties.

Simulations of coarse-grained network models have long been used to test theoretical predictions about rubber elasticity, while atomistic models are still largely unexplored. Here we devise a novel algorithm for the vulcanisation of united-atom poly(cis-1,4-butadiene), characterize the topology of the resulting networks and test their mechanical properties. We observe clear changes in the network structure when using slower vulcanisation, contrary to the traditional view that cross-linking simply freezes the melt configuration.

A Coarse-Grained Force Field for Silica-Polybutadiene Interfaces and Nanocomposites.

We present a coarse-grained force field for modelling silica-polybutadiene interfaces and nanocomposites. The polymer, poly(cis-1,4-butadiene), is treated with a previously published united-atom model. Silica is treated as a rigid body, using one Si-centered superatom for each SiO 2 unit.

Ballistic nanofriction.

Sliding parts in nanosystems such as nanoelectromechanical systems and nanomotors increasingly involve large speeds, and rotations as well as translations of the moving surfaces; yet, the physics of high-speed nanoscale friction is so far unexplored. Here, by simulating the motion of drifting and of kicked Au clusters on graphite--a workhorse system of experimental relevance--we demonstrate and characterize a new 'ballistic' friction regime at high speed, separate from drift at low speed. The temperature dependence of the cluster slip distance and time, measuring friction, is opposite in these two regimes, consistent with theory.

Adhesive contact of rough surfaces: comparison between numerical calculations and analytical theories.

The authors have employed a numerical procedure to analyse the adhesive contact between a soft elastic layer and a rough rigid substrate. The solution to the problem, which belongs to the class of the free boundary problems, is obtained by calculating Green's function which links the pressure distribution to the normal displacements at the interface. The problem is then formulated in the form of a Fredholm integral equation of the first kind with a logarithmic kernel.