Film formation of heterogeneous latex systems—a comparative study by mechanical testing, electron microscopy, interferometry and solid state NMR

The influence of latex morphology, composition and drying conditions on film formation and film properties is investigated for heterogeneous poly(acrylate) latex model systems. For blends of small latex particles water evaporation is the rate limiting process of film formation and the critical hard phase content reaches theoretical predictions. Upon increasing the size of the particles, their deformation becomes rate limiting which results in lower critical hard phase content, which significantly depends on film thickness. Film forming properties of blends are compared with that of heterogeneous lattices possessing different morphology. According to conventional measurements of the minimum film forming temperature, core-shell lattices with a glassy (high Tg) shell are non-film forming. A more thorough investigation reveals significant differences depending on latex composition and even film formation. It is demonstrated that this film formation is rate limited by particle deformation. Electron microscopy, turbidity measurements, electromechanical testing and interferometrical thickness determination are used to investigate film densification and particle deformation. Solid state NMR spin diffusion measurements are applied to characterize morphological changes during film formation and interdiffusion.