Aggregation properties of N,N,N',N'-tetraoctyl-3-oxapentanediamide (TODGA) in n-dodecane

N,N,N',N'-Tetraoctyl-3-oxapentanediamide (TODGA) in n-dodecane was studied to characterize the aggregation properties of the extractant and the formation of a third-phase when nitric acid is extracted. Tensiometry and small-angle x-ray and neutron scattering (SAXS and SANS) revealed the presence of small aggregates dispersed in the diluent. The aggregates are spherical reverse micelles consisting of a polar core containing water and the extracted ions and surrounded by approximately four extractant molecules. When the initial nitric acid content is increased, the aggregates remain spherical, their size increases as more water and ions are extracted and inter-particle attraction increases. The sticky hard-sphere model proposed by Baxter was used successfully to describe the small reverse micelles of the organic TODGA phases and quantify their interactions. These attractive interactions were found responsible for the formation of the third-phase.