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.

Graphical Abstract

Keywords:

• Alkyl chain length
• dilational modulus
• interface
• phase angle
• oxyethylated fatty acid methyl ester

Additional information

Funding

The National Natural Science Foundation of China 51604079 and 21703269.