Measurement of adhesive properties by nanoindentation

Adhesion properties of surfaces, should it be a desired property or not, can be an indicator of surface preparation (cleanliness, wettability, polymerization state, etc.). Surface adhesion is of particular interest when developing adhesive joints, sealing or depositing protective or decorative layers. Adhesion of a surface coating on a substrate is commonly measured by scratch tests, while adhesive properties of the top surface are often measured by “Tack” testing. Nanoindentation method is however a perfect candidate to measure adhesive properties of a surface at the same time as determining the mechanical properties of thin films. In this application report, nanoindentation as a tool for measurement of surface adhesion of soft and sticky films and materials will be presented. Recently we have seen a large interest in measurement of adhesive properties of many materials, including mainly packaging and various electronic components. One of the dominant applications in this field are optically clear adhesives (OCA). The OCAs have become very important in production of mobile phones since the introduction of smartphones with large touchscreens. To determine the adhesive properties together with the mechanical properties of this adhesive film, very few methods are currently available. Nanoindentation is considered as one of the candidates for the simultaneous measurement of adhesive properties and of mechanical properties. Both these properties can depend on temperature, ultraviolet radiation and time and it is therefore important to test the different types of the OCA films.
This application report presents the nanoindentation method for simultaneous measurements of adhesive forces and mechanical properties on various materials. A short introduction to the theory of adhesion is followed by showing typical adhesion measurements on soft materials and OCA films.