Role of alkyl chain branching on aggregation behavior of two symmetrical diglycolamides: small angle neutron scattering studies

Abstract

The two long alkyl chain derivatives of diglycolamide (DGA), viz. N,N,N',N'-tetraoctyl diglycolamide (TODGA) and N,N,N',N'-tetra(2-ethylhexyl)-diglycolamide (T2EHDGA) have been found promising for actinide partitioning from high-level waste. The solvent extraction studies have suggested the participation of three to four DGA molecules in the extracted complex of trivalent actinides and lanthanides. However, coordination of 3-4 tridentate DGA ligands with trivalent f-elements seems to be unusual due to restricted coordination sites in these metal ions. Nonetheless, the extraction data have been explained in view of the formation of aggregates of these ligands in the organic phase. Small Angle Neutron Scattering (SANS) measurements were carried out to investigate the aggregation behavior of DGA ligands in deuterated n-dodecane. The aggregation of DGA molecules was facilitated by the presence of acid. However, the presence of nitrate ions in the aqueous phase had no significant effect on the aggregation of DGA. Similarly, the presence of metal ions such as Sr(II) or Eu(III) marginally affected the aggregation tendency of DGA molecules. TODGA displayed higher aggregation tendency than that of T2EHDGA. The extraction data of trivalent f-elements were in conformity with the aggregation tendency of the two DGA ligands.