Dilational rheological properites of oxyethylated fatty acid methyl esters at kerosene-water interface

Abstract

Dilational rheological properties of oxyethylated fatty acid methyl esters (FMEEs) with different structure (C12E5、C14E5、C16E5 and C18=E5) at kerosene-water interface have been investigated as a function of time, frequency and bulk concentration by the oscillating drop method. The experimental results show that the dilational modulus increases with an increase in the alkyl chain length for FMEEs with saturated alkyl chains (C12E5、C14E5 and C16E5) due to the enhanced hydrophobic interaction among the molecules at interface and the slowed diffusion-exchange process. At the same time, the phase angles are relative low, which embodies characteristics of nonionic surfactants containing EO chain. As for C18=E5, the introduction of a double bone causes a decrease in the dilational modulus and a slight increase in the phase angle, as evidenced by an increase in the value of the slope of curve, because the flexible unsaturated alkyl chain enhances the diffusion-exchange process. Moreover, the modulus vs interfacial pressure curve passes through a maximum during higher interfacial pressure range for C18=E5, which indicates that the interfacial rearrangement process affects the nature of adsorption layer.