Synthesis and surface activity of mono- and diphosphate ester mixture with different alkyl chain length

A series of alkyl phosphate esters were synthesized and each of them was a mixture of monophosphate and diphosphate esters in a high or low mono/dimole ratio. The structure of hexadecyl phosphate ester with a low mono/dimole ratio was confirmed by FTIR, 1H NMR, and31P NMR. The surface tensions of these alkyl phosphate esters were analyzed using a surface tensionmeter. The results showed that the critical micelle concentration (CMC) and critical surface tension (γCMC) of phosphate esters with a high mono/di ratio decreased with the increase of alkyl chain length. However, for the phosphate esters with a low mono/di ratio, the CMC, and γCMC decreased initially and increased afterwards with the increase of alkyl chain length. Meanwhile, the butanol and octanol phosphate esters with a high mono/di ratio had higher CMC and γCMC than their low mono/di ones, while the dodecyl and hexadecyl phosphate esters presented an opposite result. The results indicated that the mono- and diphosphate esters in the mixture may have a synergistic effect on the arrangement of molecules.