Three-dimensional microscale flow of polymer coatings on glass during indentation
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Research Letter
Three-dimensional microscale flow of polymer coatings on glass during indentation L. R. Bartell, School of Applied and Engineering Physics, Cornell University, Ithaca, New York, 14853, USA* N. Y. C. Lin, Department of Physics, Cornell University, Ithaca, New York, 14853, USA J. L. Lyon, M. L. Sorensen, D. A. Clark, M. J. Lockhart, J. R. Matthews, G. S. Glaesemann, and M. E. DeRosa, Corning Research and Development Corporation, Corning, New York, 14831, USA I. Cohen, Department of Physics, Cornell University, Ithaca, New York, 14853, USA *Address all correspondence to Lena R. Bartell at [email protected] (Received 11 August 2017; accepted 28 September 2017)
Abstract We present an indentation-scope that interfaces with confocal microscopy, enabling direct observation of the three-dimensional (3D) microstructural response of coatings on substrates. Using this method, we compared microns-thick polymer coatings on glass with and without silica nanoparticle filler. Bulk force data confirmed the >30% modulus difference, while microstructural data further revealed slip at the glasscoating interface. Filled coatings slipped more and about two times faster, as reflected in 3D displacement and von Mises strain fields. Overall, these data indicate that silica-doping of coatings can dramatically alter adhesion. Moreover, this method compliments existing theoretical and modeling approaches for studying indentation in layered systems.
Introduction Protective coatings are widely used and studied across science, technology, and engineering. For example, coatings enhance the chemical stability of organic materials and semiconducting photoelectrodes[1,2], protect metals from corrosion[3], and inhibit mechanical damage in glasses[4]. Organic polymeric coatings are commonly employed due to their high processability and photo-curability. For many years, these polymeric materials have been further enhanced by the addition of a second material phase. In particular, many recent studies focus on small, rigid inorganic additives, such as glass or ceramic nanoparticles. Such nanoparticle additives are useful because they increase the coating toughness without substantially decreasing the modulus, increasing the viscosity, or changing the glass transition temperature[5–8]. Indentation testing is a common and versatile technique for understanding material behavior, including in coated systems. For example, indentation tests are used to measure coating hardness[9], coating–substrate adhesion[10], fracture properties of the coating and substrate[4,11], and coating and substrate moduli[12–14]. Such data are also utilized to compare various models of the substrate and coating material behavior[15–19]. Traditional methods include extracting bulk force-displacement data during indentation with Vickers or ball-type tips[14], with the possible addition of video recording during indentation[10,20] and surface analysis after tip retraction[12]. Instrumented nanoindentation, with the possible addition of concurrent two-dimensional microscopy,
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