A comparative study on the surface activity and micellar behaviour of some N-acylamino acid based surfactants

Abstract

N-Hexadecanoyl derivatives of amino acids viz alanine, sarcosine, glycine, aspartic acid, glutamic acid and dioctanoyl derivative of lysine and their sodium salts have been synthesised and characterised spectrophotometrically and by elemental analysis. Activation energy for thermal decomposition of these surfactants has been obtained using thermogravimetric analysis. Studies on surface activity and micellization of these N-acylamino acid based surfactants using surface tension and dye-solubilization techniques reveal specific relationship between their structural characteristics and solution behaviour. The observed trend of CMC for these amphiphiles are explained in terms of varying hydrophobicity with changes in their molecular architecture. Dioctanoyllysinate displays high CMC value by virtue of two short C_g-chains compared to the single and more hydrophobic C₁₆-chain of the other surfactants. Hexadecanoylaspartate and glutamate, with their hydrophilicity enhanced by the presence of two carboxylate head groups, also display relatively higher CMCs. Solubilizing properties for these surfactants follow an order similar to that observed for their CMCs. Areas per molecule calculated indicate the influence of molecular structure on the packing of these surfactants at the air-water interface.