Film Formation of a Non-ionic Ethylene-Vinyl Acetate Latex Dispersion in Cement Pore Solution

摘要

Environmental scanning electron microscopy (ESEM) and complementary methods were employed to study the time dependent film formation of a non-ionic latex dispersion in water when pH 12.8 and cement pore solution. A commercial liquid ethylene-vinyl acetate latex dispersion stabilized with PVOH possessing a minimum film forming temperature (MFFT) of 3°C and a T_g of 19°C was employed in the study. Prior to ESEM imaging the latex dispersion was stored at room temperature and then transferred into the ESEM instrument for imaging. Subsequently, micrographs monitoring its film forming behaviour are obtained. The analysis revealed that upon removal of water, film formation occurs as a result of particle packing, particle deformation and finally particle coalescence. In synthetic cement pore solution film formation occurs faster than in water and is complete within one day. This acceleration can be ascribed to the presence of PVOH on the surface of the latex particles. In water at neutral pH, PVOH forms a shell around the latex particle and hinders the interdiffusion of the macromolecules while in cement pore solution, PVOH precipitates due to high pH and high concentration of cations. This way the latex particles can coalesce faster into a polymer film.