This study presents a comprehensive investigation of the aggregation behavior of a malonamide extractant molecule (N,N′-dimethyl,N,N′-dioctylhexylethoxymalonamide (DMDOHEMA)) in three different solvents, including two piperidinium- and (trifluoromethylsulfonyl)imide-based ionic liquids (1-ethyl-1-butylpiperidinium bis(trifluoromethylsulfonyl)imide ([EBPip+][NTf2–]) and 1-ethyl-1-octylpiperidinium bis(trifluoromethylsulfonyl)imide ([EOPip+][NTf2–])) and n-dodecane. By combining polarizable molecular dynamics simulations and small-angle X-ray scattering experiments, we extensively investigated the arrangement of supramolecular assemblies of the extractant molecules. Our results showed that the insertion of the alkyl chains of the extractant molecules into the apolar domain of [EOPip+][NTf2–] has a significant impact on the aggregation behavior of the extractant molecules, leading to the formation of smaller aggregates having a higher dispersion compared to other solvents. These findings provide new insights into the physicochemical properties of this type of system and are crucial in designing more effective solvents for rare earth metal extraction.