Corresponding Author

El-Bayaa, A.

Document Type

Original Article

Subject Areas

Mathematics, Statistics, Computer Science, Physics and Astronomy


Surface tension; Humic acids; pH; Entropy; olive


In this study, surface tension measurements were used to study the surface-active properties of olive humic acid (HAO) and commercial humic acid (HA2). The study was performed under different conditions of concentration, temperature, pH and time. The measurements showed that the amphiphilic character of the humic acids solutes at the air/water interface lowers the surface tension () of the solution with an increasing concentrations and temperatures. The critical micelle concentration (CMC) values of both humic acids decreased with an increase in the temperature. Positive values of ∆So and ∆Ho suggested that, their adsorption at air/water interface, is endothermic and entropy driven. The surface tension–pH curve featured a minimum for both humic solutions, declining from higher and lower pH values.

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