Single-Layer Graphenes Functionalized with Polyurea: Architectural Control and Biomolecule Reactivity

Abstract

The nondestructive, covalent reactivity of single-layer graphene oxide (SLGO) and hydrazine-reduced graphene oxide (rGO) in relation to its 3-dimensional geometry has been previously considered for various chemical reactions. However, the capability of the modified system to undergo additional chemistry is now demonstrated through an in-situ polycondensation reaction resulting in various linear or hyperbranched condensed polymers [e.g., polyureas, polyurethanes, and poly(urea–urethane)-bonded graphenes]. The use of aliphatic diisocyanates as the anchor molecule initially forms star-like clusters of SLGO and rGO, and on in-situ polycondensation reaction with aliphatic diamines, the underlying graphene architecture is further modified into scroll-like domains with extensive intersheet bridging. The use of aromatic isocyanates as bridging molecules keeps the graphene structure flat and is maintained throughout the polycondensation reaction with aromatic diamines. Critical point drying of the graphene–polymer composites shows that changes to the architecture of the composite occur in the solution phase and not through surface tension effects on drying. According to TGA analysis, the aliphatic systems have higher grafted polymer weight proportions of polyurea than the aromatic counterparts and the rGO systems are found to be greater than the SLGO composites. In all experiments, the external surface of the graphene–polyurea macrostructure is demonstrated to be reactive toward biomolecules such as ferritin and is therefore useful toward a solution chemistry development of morphology-controlled graphene-based bio-nano applications.