Nanocharacterization of Surface and Interface of Different Epoxy Networks
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DD10.9.1
Nanocharacterization of Surface and Interface of Different Epoxy Networks X. Gu1, D. Raghavan1, D.L. Ho2, L. Sung3, M.R. VanLandingham3 and T. Nguyen3 1 Chemistry Department, Howard University, Washington D.C. 20059 2 National Institute of Standards and Technology Center for Neutron Research, 100 Bureau Drive, stop 8562, Gaithersburg, MD 20899. 3 Building and Fire Research Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, stop 8621, Gaithersburg, MD 20899. ABSTRACT The effect of network changes on the surface and interface properties of amine-cured epoxy has been investigated. Samples of different crosslinked epoxies are prepared by mixing stoichiometrically pure diglycidyl ether of bisphenol A (n=0.03) with different ratios of 1,3bis(aminomethyl)cyclohexane (terafunctional amine) and cyclohexylmethylamine (difunctional amine). All samples are cured in CO2-free air. Both the film surface in contact with air and that in contact with the silicon substrate (the interface) are analyzed using atomic force microscopy (AFM) and nanoindentation. Small angle neutron scattering (SANS), attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, and contact angle measurements, are used to assist in the interpretation of AFM results. Substantial morphological and mechanical differences are observed between the surface and the interface for different crosslinked epoxies. The findings have strong implications on the wettablity, adhesion, and durability of amine-cured epoxies.
INTRODUCTION Crosslinking is an important process in the film formation of coatings and the network structure of the coating is usually related to its application [1]. Changes in network structure invariably cause changes in the chemical, physical, and mechanical properties of a coating. Such changes can occur at surfaces and interfaces. Because surface and interface properties control the wettability, adhesion, and durability of coatings, the study of network effects on these properties is important for improving coating performance. However, little work has been reported on this subject. In this research, the effects of crosslink density on the chemical, mechanical and morphological properties of both surfaces and interfaces of epoxy coatings are investigated. The properties are characterized using AFM, nanoindentation, SANS, ATR-FTIR spectroscopy and contact angle measurements.
EXPERIEMNTAL* Materials and specimen preparation Highly pure diglycidyl ether of bisphenol A with weight per epoxy equivalent of 172 g/eq. was used. The curing agents used were mixtures of 1,3-bis(aminomethyl)-cyclohexane (BAC) and cyclohexylmethylamine (CMA). Samples of four different crosslinked epoxies were
DD10.9.2
prepared with stoichiometric blends of DGEBA with appropriate amine mixtures. The corresponding mole ratios of BAC to CMA for epoxy samples of E1000, E7525, E5050, and E2575 are listed in Table 1. For dynamic mechanical analysis, freestanding films of approximately 150 µm in thickness were made by molding
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