Experimental Observations of Graphene at Phospholipid Monolayers.

Interactions between particles and phospholipids at fluid-fluid interfaces play an important role in biological systems, nanotechnology, and consumer products. Two-dimensional (2D) particles are atomically thick particles whose interaction with phospholipid films is little understood and challenging to study experimentally. In this work we have quantified the diffusivity of graphene, a well-studied 2D particle, at a phospholipid monolayer using experimental methods. Particle diffusivities are used to identify how the graphene arranges in the phospholipid film. Diffusion coefficients of graphene particles were calculated from tracking their displacements at an air-water interface covered with Dipalmitoylphosphatidylcholine (DPPC) phospholipids. DPPC surface area concentration was varied, and diffusivities of the particles were compared with model predictions to deduce whether the particles were embedded within the phospholipid film or interacted primarily with one side of the film. Discrepancies between experimentally obtained diffusivities and theoretically predicted diffusivities suggest that the graphene particles fabricated in this work interact primarily with DPPC hydrocarbon tails rather than displacing DPPC molecules to embed within the film.