Structure of and diffusion in O/W/O double emulsions by CLSM and NMR–comparison with W/O/W

O/W/O double emulsions are studied by means of 1H nuclear magnetic resonance (NMR) and confocal laser scanning microscopy (CLSM) with respect to their structural and diffusion properties. Due to the structure of double emulsions, common droplet sizing techniques such as laser scattering methods show limited applicability, especially with respect to the inner droplet size distribution and dynamic effects on the molecular level. However, geometrical and structural information can be extracted from pulsed field gradient stimulated echo (PFG-STE) NMR measurements, as the molecules in the different phases experience hindered and restricted diffusion due to the interfaces. Additionally, the permeability of the interfaces and the diffusion across the intermediate (hetero) phase can be observed either by PFG-STE NMR or by exploiting the possibilities of paramagnetic relaxation enhancement. The NMR results are confirmed by CLSM with respect to both the droplet size distribution and the exchange of molecules in this publication especially for the O/W/O type of double emulsions.