Interfacial rheological behavior of N-acyl amino acid surfactants derived from vegetable oils

Abstract

Surfactants based on natural building blocks instead of traditional petroleum chemicals have attracted increasing attention in recent years. N-acyl amino acid surfactants derived from vegetable oils and amino acids are popular because of their excellent interfacial properties, biodegradability and low toxicity. Due to the variety of vegetable oils, it is significant to understand the effect of the composition and fatty acids structure of the vegetable oils on the interfacial properties of the synthesized amino acid surfactants. In the study presented herein, two N-acyl amino acid surfactants (Cas-Gly-Na and Cot-Gly-Na) were synthesized using glycine and different vegetable oils, i.e. castor oil and cottonseed oil. The interfacial dilational rheological behavior of the resulting surfactants were investigated. The long hydrophobic tails of Cot-Gly-Na enhanced the intermolecular van der Waals interactions, while the hydroxyl group present on the ricinoleate acyl moiety of Cas-Gly-Na inhibited the interactions between the hydrophobic tails. Thus, Cot-Gly-Na exhibited a higher interfacial activity and could generate stronger adsorption films. Moreover, the hydroxyl group on the hydrophobic tails of Cas-Gly-Na may have caused a molecular reorientation during adsorption at the interface. The obtained results demonstrated that the fatty acyls of amino acid surfactants introduced from different vegetable oils exhibited a significant influence on the interfacial properties.