Phase diagram and phase structure of the sodium di-n-pentyl phosphate-water system.1H pulsed-gradient NMR self-diffusion,31P NMR and x-ray diffraction studies

Sodium di-n-pentylphos phate (DPP) has been synthesized, and the phase diagram of the DPP-water system consisting of five regions (I, II, III, IV, and V) has been determined. The phase structure has been investigated by¹H pulsed-gradient NMR self-diffusion,³¹P NMR and x-ray low angle diffraction methods. The results are summarized as follows. In region I, there exist two critical micelle concentrations (CMC), indicating that this region is in a monomer-micelle equilibrium and that variation in the aggregated state occurs at the second CMC. Region II is a two phase area in which regions I and IV coexist. In region III, hydrated crystals and an aqueous solution of DPP coexist. Region IV is a homogenous, transparent and fluid phase and the results of³¹P NMR spectra and x-ray diffraction patterns reveal the formation of a highly organized structure, similar to a lamellar-like structure. Region V is a homogenous, transparent and fluid phase and the self-diffusion coefficient value and³¹P NMR spectra show that its phase structure is very similar to that for the concentrated sample in region I.