Time lapse tool 2.2 crack
With microns or sub-micron resolutions, environmental scanning electron microscopy (ESEM), ellipsometry, atomic force microscopy (AFM) were used to detect particles’ packing process, during which particles gathered with their Brownian motions restricted 9, 20, 21, 22. Nuclear magnetic resonance profiling (NMR) 11, Raman microspectroscopy 18 and infrared microscopy 19 can non-destructively measure the distribution of water concentration inside the latex, but lack the resolution to see particles. Gravimetric analysis and videography, which record global water loss and film appearance respectively, are most common methods 7, 17. Also, experimental approaches were exploited to analyze the drying inhomogeneity. More recent studies show that interactions between particles, water-soluble molecules and interfacial tensions all influence the spatial distribution of latex particles 9, 15, 16. Theoretical models on the drying inhomogeneity were established to simulate the time-evolution of non-uniform distribution of simple hard spheres 5, 8, 10, 13.
Time lapse tool 2.2 crack skin#
In the horizontal direction, the “coffee ring” effect 4 packs particles and macromolecules near the circumferential edge, causing short open time for film leveling 5, 6, 7 in the vertical direction, the “snow plow effect” 8, 9 packs particles and macromolecules near the top surface, causing skin layer formation 10, 11 with the loss of water, interfacial tensions (or capillary forces) between particles build up the internal compressive stresses that tend to shrink the volume of the latex film, and the restriction by the substrate which counteracts the shrinkage leads to the formation of cracks when the polymer’s glass-transition temperature ( T g) is higher than the room temperature (for which particles lack deformation) 12, 13, 14. During its drying process, the latex can suffer from “drying inhomogeneity”, in which the spatial distribution of latex particles is non-uniform and changes with drying time, usually resulting in the formation of defects 3. Waterborne latex systems are widely used in coating and adhesive products, as well as inks, cosmetics, pharmaceuticals, vehicle coatings, paper coatings, carpet backing, etc. In some applications, such as architectural coatings and roofing, the thicknesses of the dried films range from tens of microns to as much as several millimeters. By drying a pool of latex with a specific thickness (typically from tens to hundreds of microns), a polymer film can be formed to cover a material surface for protective, aesthetic and adhesive purposes.
Latex is normally produced by emulsion polymerization 1, with a global demand of more than 10 million metric tons (around 30 billion US dollars) per year 2. Particle sizes in latexes range from tens to hundreds of nanometers. Latex, or polymer colloids, is a colloidal system of polymer particles suspended in aqueous medium. This method can be employed for fundamental studies of colloids and for evaluations of industrial latex products. The OCT-Gravimetry-Video method serves as a general and robust approach to investigate the drying process of waterborne latex system. Furthermore, we find that the particle size affects packing and cracking phenomena remarkably. The drying curve, measured by gravimetry, shows the drying rate and the water content of the latex at each drying stage. Video recordings show the formation of cracks and the propagation of the drying boundary in the horizontal direction. OCT structural and speckle images of the latex’s internal structure show the packing process of particles, the detachment of latex and the formation of apparent shear bands in cross-sectional views. To study drying inhomogeneity of latex, we developed a system integrating optical coherence tomography (OCT) with gravimetric and video analysis (OCT-Gravimetry-Video method) to non-destructively monitor the drying process of non-film-forming latexes consisting of hard polystyrene spheres over time. Drying of a latex is inhomogeneous, during which the spatial distribution of particles is non-uniform and changes with time, usually resulting in a compromise of the integrity of a dried film.
Latex, an aqueous dispersion of sub-micron polymer particles, is widely used as polymer binder in waterborne coatings and adhesives.