R. van der Linde

Forces operative during film formation from latex dispersions

Abstract In this paper, the different forces operative on the latex particles during film formation are examined and estimates are given of the contribution of the forces to the deformation of these particles. The forces examined are gravitational forces, Van der Waals forces, electrostatic repulsion forces due to the overlap of diffuse double layers, capillary forces due to the receding water/air interface, and capillary forces due to liquid bridges between the latex particles. The magnitude of these forces is compared to the force needed to obtain sufficient deformation, i.e. the closure of the voids between the particles. Calculations show that both capillary forces are from the same order of magnitude, 1–3 10 −7 N. The Van der Waals contribution is smaller by a factor of 20 than the contribution due to the capillary forces. However, for deformation the Van der Waals forces may be of considerable importance since the Van der Waals forces diverge for very small distances. A sound incorporation of the Van der Waals forces can be achieved by using the JKR equations. Under the assumption of constant potential, the electrostatic repulsion forces are approximately a factor of 1000 smaller than the capillary forces. The gravitational forces, 1×10 −16 N, are negligible. The force needed for successful deformation amounts to 10 −7 N, assuming that the Hertz theory is applicable in the description of polymer particle deformation. Furthermore, an equation for the capillary force due to the receding water/air interface is derived which is applicable for a wider range of degrees of deformation than is the Mason-equation. Three descriptions of the particles response to deformation are examined: (i) the Hertz theory for purely elastic spheres, (ii) the JKR-theory for purely elastic spheres in the presence of Van der Waals forces, and (iii) the Yang-theory for linear visco-elastic spheres. These descriptions are combined with both capillary forces resulting in criterions determining successful deformation.

Surface studies of partially fluorinated polymethacrylates: a combined XPS and LEIS analysis

Thin films of copolymers of 1,1-dihydroperfluoroheptyl methacrylate (FHMA) and methyl methacrylate (MMA) were investigated with respect to both their molecular and macroscopic surface properties. Introduction of FHMA entities in copolymer decreases the surface energy to a large extent. Angle resolved X-ray photoelectron spectroscopy (XPS) measurements show an increased average fluorine concentration in a surface layer thickness of a few nanometers, when compared to the fluorine concentration in the bulk. Static LEIS experiments, which selectively probe the outermost atomic layer, show an even stronger enrichment of fluorine atoms.

Oxidative drying of alkyd paints catalysed by a dinuclear manganese complex (MnMeTACN)

SummariesThe application of a dinuclear manganese complex (MnMeTACN) as a catalyst in the oxidative drying of alkyd coatings is described. Experimental results on the film properties (drying time and film hardness) for various solvent- and water-borne alkyd coatings demonstrate that MnMeTACN is a potential alternative for commercially-available Co- and Mn-based catalysts. MnMeTACN appears to be suitable for both water-borne and solvent-borne alkyd systems. Confocal Raman microscopy is used to study the depth profile of the drying of alkyd coatings catalysed by different catalysts, and it has been found that slow surface drying is somewhat compensated by relatively fast deep layer drying.RésuméL’application d’un complexe dinucléaire de manganèse (MnMeTACN) comme catalyseur dans le séchage oxydatif des revêtements alkyds est décrite. Les résultats expérimentaux, en ce qui concerne les propriétés du feuil (temps de séchage et dureté du feuil) pour divers revêtements alkyds à l’eau et à solvant, démontrent que le MnMeTACN représente potentiellement une solution alternative aux catalyseurs à base de Co- et de Mn- qui sont disponibles dans le commerce. Il parait que le MnMeTACN est convenable pour les systèmes alkyds et à l’eau et à solvant. La microscopie Raman confocale est utilisée pour étudier le profil de profondeur du séchage de revêtements alkyds catalysés par divers catalyseurs et il a été trouvé que la lenteur du séchage à la surface est plutôt compensée par la relative rapidité du séchage aux couches profondes.ZusammenfassungWir beschreiben, wie ein dinuklarer Mangankomplex als Katalysator zum oxidativen Trocknen einer Alkydfarbe aufgetragen wird. Die Filmeigenschaften (Trockenzeit und Härte) für verschiedene lösungsmittel- und wasserlösliche Alkydfarben werden experimentell ermittelt und ergeben, daß MnMeTACN als eine potentielle Alternative für die kommerziell verwendeten Co- und Mn-Katalysatoren anzusehen ist. MnMeTACN scheint sowohl für lösungsmittel- und wasserlösliche Alkydsysteme geeignet zu sein. Das Tiefenprofil der durch verschiedene Katalysatoren katalysierten Alkydtrocknung wurde durch confokale Ramanmikroskopie studiert und zeigte, daß die langsame Trocknung an der Oberfläche etwas durch die relativ schnellere Tiefentrocknung ausgeglichen wird.

Use of poly(2-vinylpyridine)-b-poly(ɛ-caprolactone) copolymers as pigment stabilizers in powder coatings

Four poly(2-vinylpyridine)-b-poly(ɛ-caprolactone) copolymers, differing in buoy block length and anchor/buoy block length ratio, have been used as TiO2 pigment dispersants in a polyester powder coating resin. When the TiO2 surface was fully covered with the block copolymers, the colloidal stability of the TiO2 dispersions at typical curing temperatures was significantly improved because of the formation of a steric layer around the pigment particles. As a result, powder coatings with excellent flow, high gloss, and low haze values were obtained. Because of the high affinity of the dispersants for the TiO2 surface, pretreatment of the pigments with the block copolymers was not necessary. At full pigment surface coverage, the chain length of the stabilizing polymer had little effect on the performance of the dispersants used.