Adsorption of Sophorolipid Biosurfactants on Their Own and Mixed with Sodium Dodecyl Benzene Sulfonate, at the Air/Water Interface

Abstract

The adsorption of the lactonic (LS) and acidic (AS) forms of sophorolipid and their mixtures with the anionic surfactant sodium dodecyl benzene sulfonate (LAS) has been measured at the air/water interface by neutron reflectivity, NR. The AS and LS sophorolipids adsorb with Langmuir-like adsorption isotherms. The more hydrophobic LS is more surface active than the AS, with a lower critical micellar concentration, CMC, and stronger surface adsorption, with an area/molecule ∼70 Å(2) compared with 85 Å(2) for the AS. The acidic sophorolipid shows a maximum in its adsorption at the CMC which appears to be associated with a mixture of different isomeric forms. The binary LS/AS and LS/LAS mixtures show a strong surface partitioning in favor of the more surface active and hydrophobic LS component but are nevertheless consistent with ideal mixing at the interface. In contrast, the surface composition of the AS/LAS mixture is much closer to the solution composition, but the surface mixing is nonideal and can be accounted for by regular solution theory, RST. In the AS/LS/LAS ternary mixtures, the surface adsorption is dominated by the sophorolipid, and especially the LS component, in a way that is not consistent with the observations for the binary mixtures. The extreme partitioning in favor of the sophorolipid for the LAS/LS/AS (1:2) mixtures is attributed to a reduction in the packing constraints at the surface due to the AS component. Measurements of the surface structure reveal a compact monolayer for LS and a narrow solvent region for LS, LS/AS, and LS/LAS mixtures, consistent with the more hydrophobic nature of the LS component. The results highlight the importance of the relative packing constraints on the adsorption of multicomponent mixtures, and the impact of the lactonic form of the sophorolipid on the adsorption of the sophorolipid/LAS mixtures.

Structure of Bolaamphiphile Sophorolipid Micelles Characterized with SAXS, SANS, and MD Simulations

“…In this case, areas reported lie between 102 to 141 Å 2 for the most ionized micelles, comparable to that reported by Chen et al 92 for SL at the air−water interface (104 Å 2 ).…”

Production of Sophorolipids from Non-edible Jatropha Oil by Stamerella bombicola NBRC 10243 and Evaluation of their Interfacial Properties

“…Compared to A-SL, L-SL had a lower γ CMC , and the CMC of L-SL was more than 10-fold lower than that of A-SL; this agrees broadly with previous data 37 . Moreover, the CMC and γ CMC of A-SL-Na were lower than that of sodium dodecyl sulfate SDS 38 .…”

Chemical characterization and surface properties of a new bioemulsifier produced by Pedobacter sp. strain MCC-Z

“…Many prokaryotic and eukaryotic microorganisms synthesize a wide range of surface active compounds (SACs) which exhibit surface activities at interfaces, including the ability to lower surface and interfacial tension of liquids and to form micelles and microemulsions between different phases [1][2][3]. They exist in a wide variety of structurally different amphiphilic molecules containing both hydrophilic and hydrophobic units.…”