Anionic–Nonionic Mixed Surfactant Systems: Micellar Interaction and Thermodynamic Behavior

Synergistic behavior of SLS-OPE-10 binary mixtures at their CMC

The micellation behaviour of mixtures of sodium lauryl sulphate (SLS) and octylphenol ethoxylate-10 (OPE-10) was investigated using tensiometry and dye solubilisation. The interaction parameters for the system were determined using Rubingh’s model for non-ideality and the adsorption parameters were calculated. The surfactant mixture was found to behave synergistically in terms of CMC reduction and dye solubilisation. Furthermore, the mixture appears to mimic the adsorption and micellation properties of OPE-10 more closely than SLS, regardless of composition. With this knowledge, and considering that OPE-10 is typically more expensive than SLS, the formulator can now use only a fraction of the required amount of OPE-10 for a given application (instead of using 100% OPE-10), resulting in high performance yet economical products. It was also found that the said mixture exhibits azeotropic behaviour at a certain fixed composition.

Effect of Electrolytes on Solution and Interfacial Behaviors of Double Chain Cationic-Nonionic Surfactant Mixtures for Hydrophobic Surface Wetting and Oil/Water Emulsion Stability Applications

The solution behaviors of the binary mixture of double chain cationic surfactant didodecyldimethylammonium bromide (DDAB) with nonionic surfactants of varied head groups, EO-9 and EO-40, in the presence and absence of electrolytes were studied and found nonideal behavior. The different physicochemical properties such as Gibb's surface excess (Γ), minimum area per molecule (A_min), and interaction parameters at bulk (β^M) and interface (β^σ) were calculated. In the presence of nonionic surfactants, lowering of CMC, CVC, and surface tension at these two concentrations of DDAB were observed. The β^M and β^σ values indicate strong interaction between DDAB and EO-40 mixed system. Further, addition of electrolytes to the mixed systems show increased interaction and change of physicochemical properties because of the combination of electrical and salting out effects.

Ionic liquid-biosurfactant blends as effective dispersants for oil spills: Effect of carbon chain length and degree of saturation

The well-known toxicity of conventional chemical oil spill dispersants demands the development of alternative and environmentally friendly dispersant formulations. Therefore, in the present study we have developed a pair of less toxic and green dispersants by combining lactonic sophorolipid (LS) biosurfactant individually with choline myristate and choline oleate ionic liquid surfactants. The aggregation behavior of resulted surfactant blends and their dispersion effectiveness was investigated using the baffled flask test. The introduction of long hydrophobic alkyl chain with unsaturation (attached to choline cation) provided synergistic interactions between the binary surfactant mixtures. The maximum dispersion effectiveness was found to be 78.23% for 80:20 (w/w) lactonic sophorolipid-choline myristate blends, and 81.15% for 70:30 (w/w) lactonic sophorolipid-choline oleate blends at the dispersant-to-oil ratio of 1:25 (v/v). The high dispersion effectiveness of lactonic sophorolipid-choline oleate between two developed blends is attributed to the stronger synergistic interactions between surfactants and slower desorption rate of blend from oil-water interface. The distribution of dispersed oil droplets at several DOR were evaluated and it was observed that oil droplets become smaller with increasing DOR. In addition, the acute toxicity analysis of developed formulations against zebra fish (Danio rerio) confirmed their non-toxic behavior with LC₅₀ values higher than 400 ppm after 96 h. Overall, the proposed new blends/formulations could effectively substitute the toxic and unsafe chemical dispersants.

Chemical computational approaches for optimization of effective surfactants in enhanced oil recovery

The surfactant flooding becomes an attractive method among several Enhanced Oil Recovery (EOR) processes to improve the recovery of residual oil left behind in the reservoir after secondary oil recovery process. The designing of a new effective surfactant is a comparatively complex and often time consuming process as well as cost-effective due to its dependency on the crude oil and reservoir properties. An alternative chemical computational approach is focused in this article to optimize the performance of effective surfactant system for EOR. The molecular dynamics (MD), dissipative particle dynamics (DPD) and density functional theory (DFT) simulations are mostly used chemical computational approaches to study the behaviour in multiple phase systems like surfactant/oil/brine. This article highlighted a review on the impact of surfactant head group structure on oil/water interfacial property like interfacial tensions, interface formation energy, interfacial thickness by MD simulation. The effect of entropy in micelle formation has also discussed through MD simulation. The polarity, dipole moment, charge distribution and molecular structure optimization have been illustrated by DFT. A relatively new coarse-grained method, DPD is also emphasized the phase behaviour of surfactant/oil/brine as well as polymer-surfactant complex system.

Thermodynamics of Micellization, Interfacial Behavior and Wettability Alteration of Aqueous Solution of Nonionic Surfactants

The present work deals with the physiochemical properties of polyoxyethylene sorbitan fatty acid esters (polysorbates), which are commonly known under the trade name Tween. Thermodynamics of micellization and adsorption at air-water interface for these nonionic surfactants solutions have been studied over a broad range of temperature. As the temperature of the surfactant solutions increases, the surface tension decreases whereas the critical micelle concentration (CMC) of each surfactant solution initially decreases and then increases. The free Gibb free energies of the micelle formation Δ G m o $\Delta {\rm{G}}_{\rm{m}}^{\rm{o}}$ , and the surfactant adsorption Δ G ads o $\Delta {\rm{G}}_{{\rm{ads}}}^{\rm{o}}$ , are calculated for the CMC of each surfactant at different temperatures. The surface or expanding pressure (Πcmc), minimum area per molecule (Amin), maximum surface excess (Γmax) are also calculated. The interfacial tension (IFT) between the aqueous surfactant solutions and the crude oil are measured at different concentrations of the surfactants using a spinning drop tensiometer. The contact angles are determined on an oil wet quartz surface to investigate the wettability alteration in the presence of Tween surfactants with varying salinity. FTIR analysis of quartz at dry and oil wet state, crude oil and COBRS (crude oil-brine-rock-surfactant) combinations are performed to identify the associated functional groups and their mutual interactions.

Ionic liquids as modulators of physicochemical properties and nanostructures of sodium dodecyl sulfate in aqueous solutions and potential application in pesticide microemulsions

The change of morphology of ILs/SDS aggregates with increased concentration of ILs.