Water pores in alkyl ketene dimer (AKD) dispersions studied by NMR diffusometry and optical microscopy

Water borne alkyl ketene dimer (AKD) dispersions have been investigated by means of optical microscopy and NMR diffusometry (NMR-D). In two different formulations, different amounts of entrapped water in pores with different sizes are obtained, which can be compared to a water-in-oil-in-water (w/o/w) dispersion. It is shown that the amount of entrapped water inside the AKD particles can conveniently be measured with the NMR-D technique. The pore size is however not obtained correctly from the NMR-D experiment. Due to the small size of the water pores, the pore size is underestimated when measured with NMR-D. This effect is investigated in more detail by Brownian dynamic simulations from which a correction factor is obtained that allows a more correct value of the pore size from NMR-D measurements. When the pore size is too small to be observed by optical microscopy, typically below 0.5 μm, NMR diffusometry combined with Brownian dynamic simulations are shown to be a rapid and reliable tool for quantifying the porosity in these types of systems.