Solution Self-Assembly of the Sophorolipid Biosurfactant and Its Mixture with Anionic Surfactant Sodium Dodecyl Benzene Sulfonate

Abstract

The self-assembly in aqueous solution of the acidic (AS) and lactonic (LS) forms of the sophorolipid biosurfactant, their mixtures, and their mixtures with anionic surfactant sodium dodecyl benzene sulfonate, LAS, has been studied using predominantly small-angle neutron scattering, SANS, at relatively low surfactant concentrations of <30 mM. The more hydrophobic lactonic sophorolipid forms small unilamellar vesicles at low surfactant concentrations, in the concentration range of 0.2 to 3 mM, and transforms via a larger unilamellar vesicle structure at 7 mM to a disordered dilute phase of tubules at higher concentrations, 10 to 30 mM. In marked contrast, the acidic sophorolipid is predominantly in the form of small globular micelles in the concentration range of 0.5 to 30 mM, with a lower concentration of larger, more planar aggregates (lamellar or vesicular) in coexistence. In mixtures of AS and LS, over the same concentration range, the micellar structure associated with the AS sophorolipid dominates the mixed-phase behavior. In mixtures of anionic surfactant LAS with the AS sophorolipid, the globular micellar structure dominates over the entire composition and concentration range studied. In contrast, mixtures of LAS with the LS sophorolipid exhibit a rich evolution in phase behavior with solution composition and concentration. At low surfactant concentrations, the small unilamellar vesicle structure present for LS-rich solution compositions evolves into a globular micelle structure as the solution becomes richer in LAS. At higher surfactant concentrations, the disordered lamellar structure present for LS-rich compositions transforms to small vesicle/lamellar coexistence, to lamellar/micellar coexistence, to micellar/lamellar coexistence, and ultimately to a pure micellar phase as the solution becomes richer in LAS. The AS sophorolipid surfactant exhibits self-assembly properties similar to those of most other weakly ionic or nonionic surfactants that have relatively large headgroups. However, the more hydrophobic nature of the lactonic sophorolipid results in a more complex and unusual evolution in phase behavior with concentration and with concentration and composition when mixed with anionic surfactant LAS.

Surface charge of acidic sophorolipid micelles: effect of base and time

“…On the basis of SANS spectra analysis, Penfold at al. 16 have admitted several hypotheses on the shape of the assemblies for various sophorolipids mixtures but lack of microscopy data could not confirm their assumptions. largely justifies the intense low-q scattering signal in SANS spectra, are regularly observed but at the moment it is unclear how to isolate and stabilize them.…”

“…The tests that we have done using both α= 0.83 (not presented here) and α variable show that the most important discrepancies concern the absolute values of Rc and L/Rc, respectively over-and under-estimated ( chain has been proposed both by us 15 and Penfold. 16 These considerations suggest that keeping α= 0.83 does not provide a consistent value for the actual chain size.…”

“…Supramolecular assembling is known since 2004 but more detailed pieces of information have been achieved since 2010. 14,15,16,17 In our early work, 14 we have mainly shown how SL-COOH based micelles can be exploited as porogenic agents for the synthesis of silica thin films and there we did briefly show how pH strongly affects the long-range interactions among SL-COOH micelles. The pH-responsive behaviour has been addressed in a specific work 15 in which we put in evidence three distinct regimes during which the self-assembly of SL-COOH is different.…”

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.…”

One-Step Introduction of Broad-Band Mesoporosity in Silica Particles Using a Stimuli-Responsive Bioderived Glycolipid

“…In fact, we know from previous works 17,18,25 that SL can form micrometersized networks under basic pH conditions so it becomes possible that silica is directly stabilized by such structures, which constitute the actual template. A similar hypothesis was emitted in the formation of large mesopores in sophorolipid-templated silica thin films under basic conditions.…”