Home » Examining Interfacial Adhesion of Biomedical Coatings
The examination of coating adhesion and coating failure analysis are critical methods used to determine a coating’s life expectancy and performance. Adhesion failure involves separation of the coating from the substrate and can be caused by mechanical or thermal stress, corrosion, or chemical degradation.1 The separation of coating materials may be found in many different formats: cracking, delamination, spallation, chipping or plastic deformation. It is common to see multiple types of failure features occurring in one single application. The examination of coating adhesion and coating failure analysis require reliable and practical methods used for quantifying coating-to-substrate adhesion strength and to characterize failure mechanisms. Adhesion strength data and adhesion failure mechanisms are important information for preventing or stalling adhesion failures. Understanding these areas improves overall coating quality and performance.
According to Mittal, “adhesion strength” can be considered from two different perspectives: “fundamental adhesion” and “practical adhesion”.2 Fundamental adhesion involves intrinsic properties between two ideal smooth surfaces; it is the summation of all intermolecular or interatomic attractions at the interface due to chemical or physical interactions. Fundamental adhesion can be expressed as: W12 = g1 + g2 - g12, where g1 and g2 stand for the surface free energy of two specific surfaces, 1 and 2, and g12 stands for surface free energy of interfacial surface between surfaces 1 and 2.3 Fundamental adhesion is the thermodynamic work to break the chemical bonds or the specific energy needed to separate two surfaces and depends on the intermolecular interactions between the two contacting surfaces. Fundamental adhesion is the predominant factor that determines coating adhesion strength. This factor can be measured through surface free energy analysis via contact angle measurement by selecting suitable probe liquids and theories.4 From fundamental adhesion, coatings can be qualified as “good” or “poor” for their intended applications, and coating adhesion to the substrate may be improved by modifying surface free energy components. However, knowing fundamental adhesion provides no information on real work required to break the coating from the substrate.
November is our Emerging Technologies issue. Check out articles on photosensitive haptic coatings for athletic footwear, autonomous spray robots, new developments in industrial and marine protective coatings, a new approach to sustainable pretreatments for industrial coatings, and more.