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

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 (CE). 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 CE 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.

Characteristics and pH-Responsiveness of SDBS–Stabilized Crude Oil/Water Nanoemulsions

“…IFT is also directly related to the emulsifier adsorption at the interface between the emulsion droplet and the surrounding bulk of liquid. With further increase in the population of the emulsifier molecules at the interface, the interfacial density of the emulsifier will increase (higher packing density of the emulsifier molecules at the interface), resulting in a lower IFT [ 50 , 51 , 52 , 53 ]. Higher packing of the emulsifier molecules at the interface increases the repulsion between emulsion droplets, promoting an increased emulsion stability.…”

Polyamide Nanofiltration Membranes from Emulsion-Mediated Interfacial Polymerization

“…Adding a small concentration of Span 80 resulted in a substantial improvement of divalent cation rejection (Figure C), which is again likely attributable to the mechanism of SARIP. It requires a lower concentration of Span 80 than Tween 80 to induce similar enhancement in divalent cation rejection, which is likely because Span 80 has a higher surface excess concentration than Tween 80 (Figure A) and can thus form a denser interfacial surfactant network than Tween 80 at the same bulk concentration . However, as Span 80 molecules were integrated into the PA network by an increasing extent with heightened Span 80 concentration, the rejection of divalent cations systematically decreased.…”

Tapping the Role of Microbial Biosurfactants in Pesticide Remediation: An Eco-Friendly Approach for Environmental Sustainability

“…Lipopeptides are the type of natural product produced by non-ribosomal peptide synthases (NRPS) ( De Giani et al, 2021 ), which are huge multifunctional enzyme clusters ( Williams and Trindade, 2017 ; Lamilla et al, 2021 ). Surfactin is considered one of the most potent biosurfactants ( Meena et al, 2021 ) composed of cyclic lipopeptides with seven amino acid ringed structures linked to a fatty acid chain through lactone linkage ( Figure 3 ; Onaizi, 2018 ; Sarwar et al, 2018 ). Table 1 summarizes the type of biosurfactant as well as the microbes that produce them and their roles in pesticide remediation.…”