Tensile testing of ultra-thin films on water surface

Abstract

The surface of water provides an excellent environment for gliding movement, in nature and modern technology, from surface living animals such as the water strider to Langmuir-Blodgett films. The high surface tension of water keeps the contacting objects afloat, and its low viscosity enables almost frictionless sliding on the surface. Here we utilize the water surface as a nearly ideal underlying support for free-standing ultra-thin films and develop a novel tensile testing method for the precise measurement of mechanical properties of the films. We use our method, namely, the pseudo free-standing tensile test, to overcome the limitations of existing tensile tests of thin films such as difficulties in the fabrication and handling of free-standing specimens without damages, or the accurate extraction of mechanical properties from the tensile tests of supports thin films. In our method, all specimen preparation and testing procedures are performed on the water surface resulting in easy handling and almost frictionless sliding without specimen damages or substrate effects. We further utilize van der Waals adhesion between polymer coated metal grips and specimen’s grip-sections for the damage-free grip-ping of an ultra-thin film specimen. Our approach can potentially be used to explore the mechanical properties of emerging 2D materials such as graphene, ultra-thin Si, metal oxides, and organic-inorganic hybrids, as well as biomembranes essentially in contact with a liquid surface.