J. Adhesion Sci. Technol., Vol. 20, No. 10, pp. 1079–1089 (2006)  VSP 2006. Also available online - www.vsppub.com A methodology for detecting interfacial debonding in clay/epoxy nanocomposites JAE-HYUN KIM, GALE A. HOLMES ∗ and CHAD R. SNYDER National Institute of Standards and Technology, Polymers Division, Characterization and Methods Development Group, 100 Bureau Drive Stop 8541, Gaithersburg, MD 20899-8541, USA Received in final form 30 April 2006 Abstract—A novel methodology is presented for detecting the onset of debonding in clay-based nanocomposites. The procedure is based on constant illumination of the test specimen as it is subjected to tensile deformation by sequential strain-steps. After each strain-step, an image of the specimen is taken along its gauge length using a digital camera and the image is stored in a computer for later analysis using image analysis software. Test results from a nanocomposite containing a weak interface between the clay and the matrix indicate that interface debonding begins to occur above 1% strain, as evidenced by a reduction in the transmitted light through the specimen with increasing strain. Based on related research, the darkening of the specimen was interpreted as clay/matrix debonding. In contrast to the approximately 11% failure strain of the base epoxy resin, the nanocomposite specimen with the weak interface failed at 3.6% strain. Keywords: Nanocomposite; failure analysis; montmorillonite; debonding. 1. INTRODUCTION The potential application of clay-based nanocomposites in structural applications has led to a broadening of the research focus on these materials to include discussions about their strain-to-failure relative to the unmodified polymer. Early researchers envisioned using nanotechnology to achieve significant increases in base material performance without significant sacrifices to key engineering properties that are critical to their success in such applications. As an example, the tensile strength, tensile modulus and strain-to-failure of clay nanocomposites prepared from polyurethane [1, 2] and elastomeric epoxy [3] resins have been shown to increase relative to neat matrices. Interestingly, since the clay is treated with an alkyl ammonium salt to facilitate exfoliation, these property improvements are achieved ∗ To whom correspondence should be addressed. Tel.: (1-301) 975-5280. Fax: (1-301) 975-3928. E-mail: gale.holmes@nist.gov