Dynamics and Structure of Monolayer Polymer Crystallites on Graphene

Abstract

Graphene-based nanostructured systems and van der Waals heterostructures comprise a material class of growing technological and scientific importance. Joining materials with vastly different properties, polymer/graphene heterosystems promise diverse applications in surface and nanotechnology, including photovoltaics or nanotribology. Fundamentally, molecular adsorbates are prototypical systems to study confinement-induced phase transitions exhibiting intricate dynamics, which require a comprehensive understanding of the dynamical and static properties on molecular time and length scales. Here, we investigate the dynamics and the structure of a single polyethylene chain on free-standing graphene by means of molecular dynamics simulations. In equilibrium, the adsorbed polymer is orientationally linked to the graphene as two-dimensional folded-chain crystallite or at elevated temperatures as a floating solid. The associated superstructure can be reversibly melted on a picosecond time scale upon quasi-instantaneous substrate heating, involving ultrafast heterogeneous melting via a transient floating phase. Our findings elucidate time-resolved molecular-scale ordering and disordering phenomena in individual polymers interacting with solids, yielding complementary information to collective friction and viscosity, and linking to recent experimental observables from ultrafast electron diffraction. We anticipate that the approach will help in resolving nonequilibrium phenomena of hybrid polymeric systems over a broad range of time and length scales.

Direct Evidence of Graphene‐Induced Molecular Reorientation in Polymer Films

“…Reorientation is not observed for the oxygen-free polymer, meaning polymer chains may migrate when introduced to graphene to induce favorable electrostatic interactions between the chains and the graphene surface. [63][64] Our oxygen-containing polymer also shows better graphene coverage post-transfer across all solvent cases compared to the oxygen-free polymer. These results suggest that polymer composition dominates interactions at the graphene-polymer interface.…”

Interface and Interphase in Polymer Nanocomposites with Bare and Core-Shell Gold Nanoparticles

“…Enhancement of "trans" population would be expected to affect the crystallinity of PE chains as well as the mechanical properties of the hybrid system. Such a behavior has been observed for PE adsorbed on planar carbon-based surfaces, such as graphite or graphene, where the structure of PE commensurate to the underlying crystal structure of the substrate [3,96,125,126]. Here the enhancement of "trans" population is rather weak.…”

Glass transition temperature of a polymer thin film: Statistical and fitting uncertainties

“…This could be improved using a hierarchical modelling approach that uses quantum simulations to parameterise the PE-graphene force field parameters, similar to the development of an interface potential for polystyrene on gold [11]. In addition, a graphene surface will enhance crystallisation of PE, as observed for an adsorbed PE chain [36]. Crystallisation is not observed in the current simulations due to the very high cooling rates but would be an important consideration in slower cooling and in experimental measurements.…”