Microstructure and morphology of amine-cured epoxy coatings before and after outdoor exposures - an AFM study / Xiaohong Gu in JOURNAL OF COATINGS TECHNOLOGY AND RESEARCH, Vol. 2, N° 7 (07/2005)  

[article]  inJOURNAL OF COATINGS TECHNOLOGY AND RESEARCH > Vol. 2, N° 7 (07/2005) . - p. 547-556 Titre : Microstructure and morphology of amine-cured epoxy coatings before and after outdoor exposures - an AFM study Type de document : texte imprimé Auteurs : Xiaohong Gu, Auteur ; Y. C. Jean, Auteur ; Derek L. Ho, Auteur ; Jonathan W. Martin, Auteur ; Eric Byrd, Auteur ; Li-Piin Sung, Auteur ; Aziz Rezig, Auteur ; Joan Jasmin, Auteur ; Bouchra Kidah, Auteur ; David Martin, Auteur ; Mounina Oudina, Auteur ; Tinh Nguyen, Auteur Année de publication : 2005 Article en page(s) : p. 547-556 Note générale : Bibliogr. Langues : Américain (ame) Tags : Dégradation  photooxydante  photochimique  Propriété  chimique  Etude  expérimentale  Diffusion  neutron  centrale  Microscopie  force  atomique  Résistance  intempérie  Méthode  analyse  Durabilité  Epoxyde  résine  Structure  surface  Temps  exposition  Relation  mise  en  oeuvre  propriété  Amine  Durcissement(matière  plastique)  Vieillissement  produit  Matériau  revêtement  Morphologie  Microstructure Index. décimale : 667.9 Revêtements et enduits Résumé : Atomic force microscopy (AFM) has been used to study the morphology and microstructure of an amine-cured epoxy before and after outdoor exposure. Measurements were made from samples prepared in an essentially CO2-free, H2O-free glove box and from samples prepared in ambient conditions. For those prepared in a CO2-free glove box, AFM imaging was conducted on (1) an unexposed air/coating surface, (2) an unexposed coating bulk, (3) an unexposed coating/substrate interface, and (4) a field exposed air/coating surface. For samples prepared in ambient conditions, only the unexposed air/coating surface was investigated. The same regions of the exposed samples were scanned periodically by the AFM to monitor changes in the surface morphology of the coating as UV exposure progressed. Small angle neutron scattering and Fourier transfonn infrared spectroscopy (FTIR) studies were performed to verify the microstructure and to follow chemical changes during outdoor exposure, respectively. The results have shown that amine blushing, which occurs only under ambient conditions, had a significant effect on the surface morphology and microstructure of the epoxy. The surface morphology of the samples prepared under CO2-free, dry conditions was generally smooth and homogeneous. However, the interface and the bulk samples clearly revealed a two-phase structure consisting of bright nodular domains and dark interstitial regions, indicating an inhomogeneous microstructure. Such heterogeneous structure of the bulk was in good agreement with results obtained by small angle neutron scattering of unexposed samples and by AFM phase imaging of the degraded sample surface. The relationship between submicrometer physical changes and molecular chemical degradation is discussed. DOI : 10.1007/s11998-005-0014-x En ligne : https://link.springer.com/content/pdf/10.1007%2Fs11998-005-0014-x.pdf Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=3802 [article]

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Probing photodegradation beneath the surface : a depth profiling study of UV-degraded polymeric coatings with microchemical imaging and nanoindentation / Xiaohong Gu in JOURNAL OF COATINGS TECHNOLOGY AND RESEARCH, Vol. 4, N° 4 (12/2007)  

[article]  inJOURNAL OF COATINGS TECHNOLOGY AND RESEARCH > Vol. 4, N° 4 (12/2007) . - p. 389-399 Titre : Probing photodegradation beneath the surface : a depth profiling study of UV-degraded polymeric coatings with microchemical imaging and nanoindentation Type de document : texte imprimé Auteurs : Xiaohong Gu, Auteur ; Jonathan W. Martin, Auteur ; Tinh Nguyen, Auteur ; David Martin, Auteur ; Joan Jasmin, Auteur ; Peter L. Drzal, Auteur ; Chris A. Michaels, Auteur Année de publication : 2008 Article en page(s) : p. 389-399 Note générale : Bibliogr. Langues : Américain (ame) Catégories : Epoxydes Fourier, Spectroscopie infrarouge à transformée de Nanoindentation Photodétérioration Polyuréthanes Revêtements -- Effets du climat:Peinture -- Effets du climat Revêtements -- Propriétés mécaniques:Peinture -- Propriétés mécaniques Index. décimale : 667.9 Revêtements et enduits Résumé : Photodegradation of polymer coatings generally involves photooxidation, resulting in the formation of oxidized products, chain scission, and crosslinking. On severe exposure to ultraviolet (UV) light in the presence of air, chemical degradation transforms into substantial changes in the physical and mechanical properties, leading to failures of the coatings. Systematic research by NIST on service life prediction of polymeric coatings indicates that the degradation of polymer coatings starts from the sub-micrometer degradation-susceptible regions at the surface and then grows in width and depth. Additionally, due to the oxygen diffusion effect and the attenuation of the UV light passing through the polymer, the degradation can be spatially heterogeneous. In this study, the changes with depth of the mechanical and chemical properties of a UV-exposed epoxy/polyurethane system were measured by nanoindentation and Fourier transform infrared spectroscopy (FTIR) microscopy using cross-sectioned specimens. Multilayers of epoxy/polyurethane samples were prepared by a draw-down technique. After curing, samples were exposed to the outdoors in Gaithersburg, MD, for four months. Cross-sectioned slices of the exposed and unexposed samples, approximately 500 nm thick as-prepared by microtoming, were used for micro-FTIR imaging. Samples for nanoindentation were prepared by embedding the epoxy/polyurethane multilayers (both exposed and unexposed) in a molding compound, followed by microtoming and polishing the embedded films in the thickness direction. Micro-FTIR images clearly show that, for the outdoor exposed samples, substantial amounts of oxidation products are distributed in the 60 µm deep region from the surface to the epoxy bulk, decreasing in the center of epoxy region and increasing again toward the epoxy/urethane interface. Nanoindentation results also show that the modulus significantly increases in the first 60 µm region after UV degradation, and then decreases gradually with depth until a value slightly higher than the modulus of the undegraded epoxy is reached. The modulus rises again in the region near the epoxy/urethane interface. These similarities in the depth profiles of the properties indicate the linkage between the chemical degradation and the mechanical degradation. The study clearly shows that the spatial distribution of chemical species and mechanical properties is heterogeneous in the thickness direction for polymer coatings after UV degradation. It also demonstrates that cross-sectional analysis using nanoindentation and micro-FTIR imaging techniques is a useful method to characterize the mechanical and chemical depth profiles of polymer coating degradation. DOI : 10.1007/s11998-007-9052-x En ligne : https://link.springer.com/content/pdf/10.1007%2Fs11998-007-9052-x.pdf Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=3627 [article]

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Relationship between chemical degradation and thickness loss of an amine-cured epoxy coating exposed to different UV environments / Aziz Rezig in JOURNAL OF COATINGS TECHNOLOGY AND RESEARCH, Vol. 3, N° 3 (07/2006)  

[article]  inJOURNAL OF COATINGS TECHNOLOGY AND RESEARCH > Vol. 3, N° 3 (07/2006) . - p. 173-184 Titre : Relationship between chemical degradation and thickness loss of an amine-cured epoxy coating exposed to different UV environments Type de document : texte imprimé Auteurs : Aziz Rezig, Auteur ; Tinh Nguyen, Auteur ; David Martin, Auteur ; Li-Piin Sung, Auteur ; Xiaohong Gu, Auteur ; Joan Jasmin, Auteur ; Jonathan W. Martin, Auteur Année de publication : 2006 Article en page(s) : p. 173-184 Note générale : Bibliogr. Langues : Américain (ame) Catégories : Durée de vie (Ingénierie) Epaisseur -- Mesure Epoxydes Microscopie à force atomique Photodétérioration Réflexion totale atténuée Revêtements -- Effets du rayonnement ultraviolet Thermodurcissables Index. décimale : 667.9 Revêtements et enduits Résumé : The relationship between chemical degradation and thickness loss of an unpigmented, nonUV-stabilized, crosslinked amine-cured epoxy coating exposed to three UV conditions was investigated. Spin-coated samples having a thickness of approximately 7 µm on an Si substrate were prepared from a stochiometric mixture of a bisphenol A epoxy resin and a tetra-functional amine curing agent. Samples were exposed outdoors and to two accelerated laboratory UV environments. Chemical degradation and thickness loss were measured by transmission Fourier transform infrared spectroscopy (FTIRS) and laser scanning confocal microscopy (LSCM), respectively. In addition, surface roughness and morphological changes were measured by atomic force microscopy (AFM) and LSCM. Substantial chemical degradation, thickness loss, and morpholocal changes occurred in the exposed films, and the rate of chemical degradation was greater than that due to the thickness loss. This additional chemical loss was attributed to an inhomogeneous degradation process in which nanoscale localized depressions initiate at certain sites on the surface, which then enlarge and deepen with exposure time. The results of this study provide a better understanding of the degradation mechanism and should lead to the development of scientific-based models for predicting the service life of crosslinked amine-cured epoxy coatings. DOI : 10.1007/BF02774507 En ligne : https://link.springer.com/content/pdf/10.1007%2FBF02774507.pdf Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=3690 [article]

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Use of laser scanning confocal microscopy for characterizing changes in film thickness and local surface morphology of UV-exposed polymer coatings / Li-Piin Sung in JOURNAL OF COATINGS TECHNOLOGY AND RESEARCH, Vol. 1, N° 4 (10/2004)  

[article]  inJOURNAL OF COATINGS TECHNOLOGY AND RESEARCH > Vol. 1, N° 4 (10/2004) . - p. 267-276 Titre : Use of laser scanning confocal microscopy for characterizing changes in film thickness and local surface morphology of UV-exposed polymer coatings Type de document : texte imprimé Auteurs : Li-Piin Sung, Auteur ; Joan Jasmin, Auteur ; Xiaohong Gu, Auteur ; Tinh Nguyen, Auteur ; Jonathan W. Martin, Auteur Année de publication : 2004 Article en page(s) : p. 267-276 Note générale : Bibliogr. Langues : Américain (ame) Tags : Propriété  surface  Epaisseur  film  Etude  expérimentale  Durabilité  Méthode  non  destructive  Microscope  laser  Microscopie  confocale  étude  Morphologie  Rugosité  Temps  exposition  Dégradation  photochimique  Vieillissement  accéléré  Mélamine  résine  Uréthanne  copolymère  Acrylique  dérivé  Matériau  revêtement Index. décimale : 667.9 Revêtements et enduits Résumé : Laser scanning confocal microscopy (LSCM) has been used to characterize the changes in film thickness and local surface morphology of polymer coatings during the UV degradation process. With the noninvasive feature of LSCM, one can obtain thickness information directly and nondestructively at various exposure times without destroying the specimens or deriving the thickness values from IR measurement by assuming uniform film ablation. Two acrylic polymer coatings were chosen for the study, and the physical and chemical changes of the two systems at various exposure times were measured and analyzed. Those measurable physical changes caused by UV exposure include film ablation, formation of pits and other surface defects, and increases in surface roughness. It was found in both coatings that changes in measured film thickness by LSCM were not correlated linearly to the predicted thickness loss using the changes in the CH band obtained by the Fourier Transform Infrared (FTIR) spectroscopy measurements in the later degradation stages. This result suggested it was not a uniform film ablation process during the UV degradation. At later stages, where surface deformation became severe, surface roughness and profile information using LSCM were also proven to be useful for analyzing the surface degradation process. DOI : 10.1007/s11998-004-0029-8 En ligne : https://link.springer.com/content/pdf/10.1007%2Fs11998-004-0029-8.pdf Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=3858 [article]

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