title: Mechanistic Origin of the Ultrastrong Adhesion between Graphene and a-SiO2: Beyond van der Waals.
abstract: The origin of the ultrastrong adhesion between graphene and a-SiO2 has remained a mystery. This adhesion is believed to be predominantly van der Waals (vdW) in nature. By rigorously analyzing recently reported blistering and nanoindentation experiments, we show that the ultrastrong adhesion between graphene and a-SiO2 cannot be attributed to vdW forces alone. Our analyses show that the fracture toughness of the graphene/a-SiO2 interface, when the interfacial adhesion is modeled with vdW forces alone, is anomalously weak compared to the measured values. The anomaly is related to an ultrasmall fracture process zone (FPZ): owing to the lack of a third dimension in graphene, the FPZ for the graphene/a-SiO2 interface is extremely small, and the combination of predominantly tensile vdW forces, distributed over such a small area, is bound to result in a correspondingly small interfacial fracture toughness. Through multiscale modeling, combining the results of finite element analysis and molecular dynamics simulations, we show that the adhesion between graphene and a-SiO2 involves two different kinds of interactions: one, a weak, long-range interaction arising from vdW adhesion and, second, discrete, short-range interactions originating from graphene clinging to the undercoordinated Si (≡Si·) and the nonbridging O (≡Si-O·) defects on a-SiO2. A strong resistance to relative opening and sliding provided by the latter mechanism is identified as the operative mechanism responsible for the ultrastrong adhesion between graphene and a-SiO2.
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: Sandeep
authors.initials: S
authors.lastname: Kumar
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: David
authors.initials: D
authors.lastname: Parks
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: Ken
authors.initials: K
authors.lastname: Kamrin
keywords: a-SiO2; graphene; mechanochemistry; ultrastrong adhesion; vdW