Understanding and Engineering Molecular Interactions and Electronic Transport at 2D Materials Interfaces

2D materials are defined as solids with strong in-plane chemical bonds but weak out-of-plane, van der Waals (vdW) interactions. In order to realize potential applications of 2D materials in the areas of optoelectronics, surface modification, and complex materials, there are many engineering challenges associated with understanding and engineering molecular interactions at 2D materials interfaces, which requires understanding and engineering multiscale physical phenomena. With this in mind, the goal of this thesis has been to combine continuum modeling, molecular dynamics (MD) simulations, chemical synthesis, and device fabrication to understand and engineer molecular interactions at 2D materials interfaces at different length scales. The three main topics considered include: (i) wetting behavior of graphene (micrometer scale), (ii) solution processing of graphene and graphene oxide (nanometer scale), and (iii) electronic modification in graphene and molybdenum disulfide (atomic scale). The first part of my thesis investigates the wetting behavior of graphene-coated surfaces. Based on the classical theory of van der Waals interactions, monolayer graphene acts like a “nonlinear translucent” barrier, transmitting about 30% of the original water-substrate interactions through it. The contact angle on a graphene-coated substrate is determined by both liquid-graphene and liquid-substrate interactions. This, in turn, results in different degrees of “wetting transparency”. By combining theoretical analysis, MD simulations, and contact angle measurements, I show that monolayer graphene becomes more “transparent” to wetting on hydrophilic substrates and more “opaque” to wetting on hydrophobic substrates. The second part of my thesis develops a fundamental understanding and engineering strategies to disperse graphene and graphene oxide in a liquid phase. The mechanism of stabilization of liquid-phase exfoliated graphene sheets in polar solvents is investigated using potential of mean force (PMF) calculations and MD simulations. Along with a kinetic theory of colloid aggregation, the graphene sheets are predicted to aggregate based on thermodynamic arguments. Because of the dif-