Adsorption of Biomimetic Amphiphilic Heteropolymers onto Graphene and Its Derivatives

The adsorption of a polymer chain from a bulk solution onto a solid surface is the fundamental mechanism behind many industrial and biological applications. Here, we used molecular dynamics simulations to investigate the driving factors in the adsorption of a poly(methyl methacrylate)-based biomimetic random heteropolymer (RHP) containing polar (ethylene glycol, or PEG), nonpolar (ethylhexyl), and charged groups (sulfopropyl acid) onto graphene and its derivatives (graphene oxide and carbon nanotube). We applied a combination of unbiased and biased simulations with machine learning to investigate the adsorption mechanism. The long PEG side chains drive the nearby short monomers to be adsorbed. After a short period of side-chain adsorption, due to the glassy nature of the backbone, the adsorption terminates and will only proceed by adding plasticizers, changing the backbone to be more flexible, or raising the temperature over the glass transition temperature. Meanwhile, thermodynamically, the adsorption is favorable due to the amphiphilicity of PEG. The surface hydrophilicity and curvature influence the adsorption as well. This work provides atomistic details of the interaction between an amphiphilic RHP and a hard surface, which can serve as the basis to understand the adsorption of such RHPs on more complex interfaces such as protein surfaces.