Insights into the structure and dynamics of complex W/O-emulsions by combining NMR, rheology and electron microscopy

It could be shown that 1H NMR diffusion measurements can be used to study the dynamic exchange processes of water molecules in commercial W/O emulsions. In addition, it could be demonstrated that two different types of water droplets are present in the emulsions studied with a volume fraction of φ=0.67. Present besides isolated droplets with restricted diffusion behavior of water are also close-packed droplets in which the diffusion of water is hindered. is of the behavior of the two diffusion coefficients in the emulsions shows that the contribution of hindered diffusion increases relative to that of restricted diffusion with increasing energy input during production. Highly homogenized emulsions accordingly contain almost exclusively water that shows hindered diffusion. ts exist that are so closely packed that the interface and surrounding oil phase is no longer fully impenetrable for the water molecules. Therefore there is a certain probability that water can diffuse from one droplet through the interface into another droplet as described in the literature for high internal phase emulsions (φ=0.96) [J. Phys. Chem. 98 (1994) 393; J. Colloid Interface Sci. 182 (1996) 539; Langmuir 15 (1999) 988]. sults could be confirmed on model emulsions in which the volume fraction was varied from φ=0.5 to 0.86. Dynamic oscillatory measurements show a critical volume fraction φc=0.77 above which there is a sharp increase in the network point density. In TEM studies the transition from a particle solution below φc to a close-packed network above φc is observable. At values below the critical volume fraction both types of water droplets can be detected. In contrast, at values above φc the external oil phase of the emulsion is no longer fully impermeable to water molecules from the internal phase and the water molecules show hindered diffusion behavior.