Interface Activity and Thermodynamic Properties of Cardanol Polyoxyethylene Ether Carboxylates

Abstract A series of saturated cardanol polyoxyethylene ether carboxylates was synthesized using renewable saturated cardanol originating from Cashew Nut Shell Liquid as raw material. The structures were characterized by hydrogen nuclear magnetic resonance spectroscopy. The studies of their surface activity and interface activity were carried out to analyze the influence of the chemical structures of the series of cardanol surfactants on the adsorption and micellization. Results showed that saturated cardanol polyoxyethylene ether carboxylates had a good surface activity and interface activity, and the interface activities of the Gemini cardanol surfactants were better than those of the corresponding monomer cardanol surfactants. The critical micelle concentrations (CMC) of all investigated cardanol surfactants, obtained from surface tension measurements, were low in the order of 10 −5 mol/L. The CMCs decreased and the oil-water interface tension for the same cardanol surfactants increased with the increase of the oxyethylene number. The process of micellization became easier with increasing the oxyethylene number. The Δ G θ m values of the Gemini cardanol surfactants were more negative than those of the corresponding monomer cardanol surfactants. The micellization for all cardanol surfactants was a spontaneous process and exhibited enthalpy-entropy compensation. The micellization of all the cardanol surfactants was entropy-driven.