Effect of EO group on the interfacial dilational rheology of fatty acid methyl ester solutions

Abstract

The interfacial dilational rheological properties of oxyethylated fatty acid methyl ester solutions, C18=E3, C18=E5 and C18=E10, have been investigated by means of drop shape analysis method. The influences of oxyethylene (EO) numbers on interfacial dilational properties have been expounded. The experimental results show that the number of EO units plays a key role in controlling the interfacial film. C18=En is nonionic surfactant with long alkyl chain, meaning slower diffusion of the molecules to the interface. The EO units tend to lie flat at the interface as the number of EO unit increases and enter into the water sub-phase under compression, which causes the new relaxation process and results in an increase in the interfacial dilational modulus and the viscosity nature of film for C18=E5. The appearance of a more elastic film for the C18=E10 because the interfacial molecules can’t retain the compact structure due to the steric hindrance, which would weaken stronger intermolecular interaction and results in a decrease of dilational modulus.