What is the problem/issue being addressed?
Two-dimensional (2D) materials are a relatively new class of thin materials consisting of a single layer of covalently bonded atoms. The unprecedented characteristics of 2D materials have already led to the observation of new physics and lend themselves to a wide range of technology-focused applications. Both in the fabrication process and in applications, liquids frequently interact with 2D materials. Due to the small length scales associated with these scenarios, the van der Waals (vdW) interaction between different subjects (such as between the thin solid and the substrate and between the thin liquid and the substrate) plays a crucial role in determining the final state of the system. The key scientific problem this project is focusing on is how thin solids and thin liquids are deformed at small scales in the presence of vdW interactions. In particular, motivated by recent experiments, we addressed two sub-problems: (1) the statics and dynamics of droplets on thin liquids that behave as a lubricating layer on solid substrates; (2) the equilibrium of thin sheets on adhesive substrates with liquids trapped at the interface.
Why is it important for society?
The analysis of these problems not only provides new insights into the controlling mechanisms in different systems but also suggests new methods through which the presence of thin liquids/droplets can be controlled and exploited in relevant applications that are important for society.
For example, a relevant application for problem 1 is liquid-infused surfaces (LISs) formed by coating surface with a thin layer of oil lubricant. This liquid coating has found a variety of applications including the creation of surfaces that are anti-biofouling, anti-icing and facilitate water harvesting. In many of these applications, the deformation of the lubricant surface caused by a droplet is particularly important while our analysis of problem 1 can provide direct controlling parameters on how large this deformation can be as well as how fast the completion of this deformation takes. A relevant application for problem 2 is the coupling between strain and electronic properties in graphene bubbles, which has been found to produce pseudomagnetic fields (PMFs) of magnitudes on the order of 100 Tesla. Such gigantic PMFs might be used for the design of valley filtering and valley splitting devices. Our analysis of problem 2 can be directly used to predict the shape and size of the bubble by balancing the elastic forces due to the thin sheets and van der Waals forces. Such predictions are useful for the deterministic design of graphene bubbles for relevant valley filtering and valley splitting devices.
What are the overall objectives?
The research objective of this project is to develop theoretical frameworks within which problem1 and 2 can be addressed. Particularly central to our objective is to elucidate the statics and dynamics of the competition between elasticity of 2D materials and substrates, liquid viscosity and capillarity, and interfacial vdW interactions. The training objective of this project is to allow the fellow to gain extensive scientific competence in the area of thin film mechanics by the implementation of this project.
Conclusions of the action
This project aims to understand the deformation of thin solids and thin liquids at small scales where van der Waals forces are particularly important. Based on recent experiments on LISs and graphene bubbles, this project focuses on two specific problems: the statics and dynamics of droplets on LISs and the competition between elasticity and vdW interactions in graphene bubbles.
