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      Dynamic surface tension and adsorption mechanism of surfactin biosurfactant at the air-water interface.

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          Abstract

          The dynamic adsorption of the anionic biosurfactant, surfactin, at the air-water interface has been investigated in this work and compared to those of two synthetic surfactants: the anionic sodium dodecylbenzenesulfonate (SDBS) and the nonionic octaethylene glycol monotetradecyl ether (C14E8). The results revealed that surfactin adsorption at the air-water interface is purely controlled by diffusion mechanism at the initial stage of the adsorption process (i.e., [Formula: see text]), but shifts towards a mixed diffusion-barrier mechanism when surface tension approaches equilibrium (i.e., [Formula: see text]) due to the development of an energy barrier for adsorption. Such energy barrier has been found to be a function of the surfactin bulk concentration (increases with increasing surfactin concentration) and it is estimated to be in the range of 1.8-9.5 kJ/mol. Interestingly, such a trend (pure diffusion-controlled mechanism at [Formula: see text] and mixed diffusion-barrier mechanism at [Formula: see text]) has been also observed for the nonionic C14E8 surfactant. Unlike the pure diffusion-controlled mechanism of the initial surfactin adsorption, which was the case in the presence and the absence of the sodium ion (Na+), SDBS showed a mixed diffusion-barrier controlled at both short and long time, with an energy barrier of 3.0-9.0 and 3.8-18.0 kJ/mol, respectively. Such finding highlights the nonionic-like adsorption mechanism of surfactin despite its negative charge.

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          Author and article information

          Journal
          Eur Biophys J
          European biophysics journal : EBJ
          Springer Science and Business Media LLC
          1432-1017
          0175-7571
          Sep 2018
          : 47
          : 6
          Affiliations
          [1 ] Department of Chemical Engineering, King Fahd University of Petroleum and Minerals, Dhahran, 31216, Saudi Arabia. onaizi@kfupm.edu.sa.
          Article
          10.1007/s00249-018-1289-z
          10.1007/s00249-018-1289-z
          29497770
          131586b4-a484-4072-84f0-057093c7992a
          History

          Adsorption mechanism,Biosurfactant,Diffusion-controlled,Dynamic surface tension,Mixed diffusion-barrier controlled,Surfactin

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