General adsorption isotherm for polyoxyethylene alkyl ethers CnEOm adsorbed at the water/air surface

An empirical adsorption isotherm model is presented based on fundamental thermodynamic equations of adsorption for the homologous series of the nonionic surfactants polyoxyethylene alkyl ethers (CnEOm) at the aqueous solution surface to determine the surface tension and surface pressure isotherms, surface equation of state, and molar characteristics for the adsorbed surfactant molecules. The new model describes the surface properties of CnEOm much better than the original Langmuir adsorption model used as thermodynamic basis. The analysis of the results shows that the increase of the alkyl chain length n (hydrophobic part) leads to an increase in the adsorption activity, while the increase of hydrophilic head group given by the number of EO units m, leads to a better solubility in water, and hence, to a smaller adsorbed amount. The results also show that the ethylene oxide group mainly influences the molar sur-face area.(c) 2023 Elsevier B.V. All rights reserved.

Automated summary

An empirical adsorption isotherm model based on fundamental thermodynamic equations of adsorption is presented for the nonionic surfactants CnEOm. The model describes the surface properties of CnEOm better than the original Langmuir adsorption model. The results show that the increase of the alkyl chain length n leads to higher adsorption activity, while the increase of hydrophilic head group given by the number of EO units m leads to better solubility in water and smaller adsorbed amount.