Self-assembly of a surfactin nanolayer at solid–liquid and air–liquid interfaces

Abstract

Surfactin, a sustainable and environmentally friendly surface active agent, is used as a model to study the adsorption of biosurfactants at hydrophobic and hydrophilic solid-liquid interfaces as well as the air-liquid interface. Surfactin adsorption was monitored as a function of time and concentration using surface plasmon resonance (SPR) technique in the case of the solid-liquid interfaces or the drop shape analysis (DSA) technique in the case of the air-liquid interface. The results obtained in this study showed that surfactin adsorption at the "hard" hydrophobic (functionalized with octadecanethiol) solid-liquid and the "soft" air-liquid interface were 1.12 ± 0.01 mg m(-2) (area per molecule of 157 ± 2 Å(2)) and 1.11 ± 0.05 mg m(-2) (area per molecule of 159 ± 7 Å(2)), respectively, demonstrating the negligible effect of the interface "hardness" on surfactin adsorption. The adsorption of surfactin at the hydrophilic (functionalized with β-mercaptoethanol) solid-liquid interface was about threefold lower than its adsorption at the hydrophobic-liquid interfaces, revealing the importance of hydrophobic interaction in surfactin adsorption process. The affinity constant of surfactin for the investigated interfaces follows the following order: air > octadecanethiol > β-mercaptoethanol. Biosurfactants, such as surfactin, are expected to replace the conventional fossil-based surfactants in several applications, and therefore the current study is a contribution towards the fundamental understanding of biosurfactant behavior, on a molecular level, at hydrophobic and hydrophilic solid-liquid interfaces in addition to the air-liquid interface. Such understanding might aid further optimization of the utilization of surfactin in a number of industrial applications such as enhanced oil recovery, bioremediation, and detergency.

Benchmarking the Self‐Assembly of Surfactin Biosurfactant at the Liquid–Air Interface to those of Synthetic Surfactants

“…the solution [22][23][24]. When ionic surfactants co-exist with a relatively higher concentration of the counter-ion(s), as it is the case in this study, the value of n approaches unity [10,19,25]. The simplicity of Eq.…”

Effect of Diethylene Glycol on the Inkjet Printability of Reactive Dye Solution for Cotton Fabrics

“…Surface tension depends on the solute concentration at the interface. 48,49 From the above results, we could infer that the R-218 concentration increased at the interface with prolonged surface age, but the other two dye molecules were hardly distributed at the interface. This might relate to the position of the hydrophilic groups on a dye molecule.…”

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

“…Looking again at Figure 3 reveals the continuous decrease in the IFT between diesel and the nanoemulsions. This is an interesting observation since it is commonly known that the decrease in the interfacial/surface tension usually levels off when the surfactant concentration exceeds its critical micelle concentration (CMC) [ 48 , 49 ]. Since the CMC of SDBS is below 0.1 wt% [ 49 , 50 ], it would be intuitively expected that increasing SDBS concentration in the studied range (0.1–4 wt%) should not result in a significant change in the IFT of the diesel/emulsion interface, which is not the case.…”