Effect of metal catalyst facets on polyethylene adsorption

Catalytic methods are one of the major solutions for tackling the global problem of plastic waste production. The products' molecular weight distribution depends on the location along the chain where the C-C scission happens and, thereby, on the conformation of the PE chain on the catalyst surface. However, catalyst surfaces are not entirely flat, but exist in different morphologies.

The effects of catalyst morphology on polymer melt adsorption are not well understood. Here, we study Pt surfaces of different terminations and polymers of varying chain sizes to probe the impact of terrace width on polyethylene (PE) conformations on the catalyst surface. We parametrize an atomistic force field using Density Functional Theory (DFT) calculations and perform Replica-Exchange Molecular Dynamics (RE-MD) simulations on the PE-catalyst systems.

We find that the surface morphology alters the conformations of PE. Stepped surfaces favor shorter adsorbed segments but more such segments adsorb per chain. They also induce more ordering in the adsorbed segments than the flat surface, which has implications for the use of mean-field models for polymer adsorption on surfaces and their subsequent reaction. Even small length alkanes show a distribution in conformations on these stepped surfaces, unlike their behavior on flat surfaces. We discuss the ramifications of these findings for adsorption on nanoparticles of varying sizes and facets.