US-Ireland R&D Partnership: Mechanics of the Formation and Function of 2D Material Pleats

A central challenge in fulfilling the tremendous potential of nanoscale materials is that they are hard to control, manipulate, and mass-produce into useful structures and devices. This is in part due to the small size, their tendency to stick to one another, and their susceptibility to thermal vibrations. Thus, it is important to understand the nanoscale forces behind these effects, including adhesion and friction.

The key to developing this knowledge lies in understanding and taking advantage of the beneficial aspects of these forces. One such case is the phenomenon of self-assembly, where nanoscale materials organize themselves into ordered structures. This award supports research which aims to understand how forces conspire in a particularly striking case of such behavior: the spontaneous formation of long, folded pleats of atomically thin, two-dimensional materials that can be seen with a simple magnifying glass.

Experiments and simulations will be used to understand what controls and drives this process, conducted by an interdisciplinary team of collaborators who will combine their unique and ideal expertise to tackle the problem. The goal is to uncover the mechanical principles governing the formation of these pleats. The work has broad scientific and technological impact, as it focuses on the fundamental mechanics of these materials but with a view toward controlling their assembly and construction into useful structures and devices.

The award will also support educational outreach by training undergraduate, graduate, and postdoctoral researchers. This will include mentored international personnel exchanges between the collaborators’ laboratories; engaging K-12 students and the public in outreach events; and developing an online short course for researchers about the nanoscale mechanics of these materials.

Two-dimensional material pleats are long, folded structures that have been recently discovered. Their formation is triggered by puncturing a substrate-supported two-dimensional materials like graphene with a nanoindenter tip. This is followed by subsequent growth of a folded ribbon of the two-dimensional material, up to 10’s of micrometers.

However, little is known about the fundamental mechanics of these remarkable structures. While a continuum-level model has been developed that gives some qualitative insight into pleat formation, there is no atomistic-level understanding of the mechanisms that govern the phenomenon. This project addresses this gap by performing an atomistically-informed investigation of the mechanics of pleat formation and their mechanical properties once formed.

Doing this requires an effort that integrates material synthesis, nanomechanical characterization, and atomistic and coarse-grained simulations. An interdisciplinary team of collaborators from the US, the Republic of Ireland, and Northern Ireland, UK will use their unique combination of expertise to tackle this problem. The primary goal is to uncover the fundamental mechanical principles governing pleat nucleation, growth, and interaction with the environment.

A long-term, broad impact of this work will be to establish design principles for fabricating useful devices from the wide and growing array of two-dimensional and thin materials.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.