Direct observation of freeze-thaw instability of latex coatings via high pressure freezing and cryogenic SEM / Cheng-Le Zhao in JOURNAL OF COATINGS TECHNOLOGY AND RESEARCH, Vol. 3, N° 2 (04/2006)  

[article]  inJOURNAL OF COATINGS TECHNOLOGY AND RESEARCH > Vol. 3, N° 2 (04/2006) . - p. 109-115 Titre : Direct observation of freeze-thaw instability of latex coatings via high pressure freezing and cryogenic SEM Type de document : texte imprimé Auteurs : Cheng-Le Zhao, Auteur ; L. E. Scriven, Auteur ; H. Ted Davis, Auteur ; Haiyan Ge, Auteur ; Alan Smith, Auteur ; Shane J. Stafslien, Auteur Année de publication : 2006 Article en page(s) : p. 109-115 Note générale : Bibliogr. Langues : Américain (ame) Catégories : Colloides Composés organiques volatils Copolymères greffés Floculation Latex Microscopie électronique à balayage Morphologie (matériaux) Oxyde d'éthylène L'oxyde d'éthylène, ou 1,2-époxyéthane, oxyde de diméthylène, oxacyclopropane, ou encore oxirane est un composé organique, le plus simple de la classe des époxydes. Il est important pour l'industrie chimique, entre autres dans la production d'éthylène glycol, ainsi que dans les industries pharmaceutique et agroalimentaire. Polyacryliques Polyméthacrylate de butyle Revêtements en bâtiment:Peinture en bâtiment Revêtements en phase aqueuse:Peinture en phase aqueuse Stabilité thermique Index. décimale : 667.9 Revêtements et enduits Résumé : Despite its industrial importance, the subject of freeze-thaw (F/T) stability of latex coatings has not been studied extensively. There is also a lack of fundamental understanding about the process and the mechanisms through which a coating becomes destabilized. High pressure (2100 bar) freezing fixes the state of water-suspended particles of polymer binder and inorganic pigments without the growth of ice crystals during freezing that produce artifacts in direct imaging scanning electron microscopy (SEM) of fracture surfaces of frozen coatings. We show that by incorporating copolymerizable functional monomers, it is possible to achieve F/T stability in polymer latexes and in low-VOC paints, as judged by the microstructures revealed by the cryogenic SEM technique. Particle coalescence as well as pigment segregation in F/T unstable systems are visualized. In order to achieve F/T stability in paints, latex particles must not flocculate and should provide protection to inorganic pigment and extender particles. Because of the unique capabilities of the cryogenic SEM, we are able to separate the effects of freezing and thawing, and study the influence of the rate of freezing and thawing on F/T stability. Destabilization can be caused by either freezing or thawing. A slow freezing process is more detrimental to F/T stability than a fast freezing process; the latter actually preserves suspension stability during freezing. DOI : 10.1007/s11998-006-0013-6 En ligne : https://link.springer.com/content/pdf/10.1007%2Fs11998-006-0013-6.pdf Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=3701 [article]

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Role of van der Waals force in latex film formation / Xiaobo Gong in JOURNAL OF COATINGS TECHNOLOGY AND RESEARCH, Vol. 5, N° 3 (09/2008)  

[article]  inJOURNAL OF COATINGS TECHNOLOGY AND RESEARCH > Vol. 5, N° 3 (09/2008) . - p. 271-283 Titre : Role of van der Waals force in latex film formation Type de document : texte imprimé Auteurs : Xiaobo Gong, Auteur ; H. Ted Davis, Auteur ; L. E. Scriven, Auteur Année de publication : 2008 Article en page(s) : p. 271-283 Note générale : Bibliogr. Langues : Américain (ame) Catégories : Coalescence (Sciences physiques) Colloides Emulsions Formation de film Latex Microscopie électronique à balayage Revêtements -- Propriétés physiques Séchage Van der Waals, Forces de Index. décimale : 667.9 Revêtements et enduits Résumé : Capillary pressure force and direct surface tension force are known to be sufficient though probably not necessary to drive the compaction stage of latex film formation. There is abundant evidence that van der Waals force can draw particles together progressively more around the perimeters of interparticle contacts, but their role in compaction remains unanswered. With the powerful technique of high-resolution cryogenic scanning electron microscopy (cryo-SEM), together with fast-freezing and freeze-drying followed by controlled annealing at temperatures below and around the nominal glass transition temperature, we have documented the role of van der Waals force in film formation in the water-free condition, i.e., with capillary pressure and surface tension forces absent. Results of imaging the freeze-dried and annealed coatings are fully consistent with the hypothesis that van der Waals force alone can compact a latex coating. The rate at which particles flatten and thus the coating compacts by annealing increases, as expected, with temperature and time. The results of rewetting tests of coatings annealed at various temperatures demonstrate that compacted coating is not necessarily coalesced, and that even full compaction of solid particles can be elastic, hence reversible, rather than viscoelastic or viscoplastic. Some of the results suggest that soluble ionic surfactant and oligomeric and grafted polymeric stabilizers at particle surfaces, collapse to undetectable dimensions during freeze-drying, yet reswell to detectable size during rewetting, if they have not dissolved into polymer particles during. DOI : 10.1007/s11998-008-9095-7 En ligne : https://link.springer.com/content/pdf/10.1007%2Fs11998-008-9095-7.pdf Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=2972 [article]

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