Micellar structure and transformations in sodium alkylbenzenesulfonate (NaLAS) aqueous solutions: effects of concentration, temperature, and salt

Rafique, Aysha S.; Khodaparast, Sepideh; Poulos, Andreas S.; Sharratt, William N.; Robles, Eric S. J.; Cabral, João T.

doi:10.1039/d0sm00982b

Cited by 39 publications

(26 citation statements)

References 64 publications

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“…It is used in emulsifiers, detergents, and wetting agents. The phase behavior of NaLAS in water has been characterized with respect to the different phases that form at different temperatures and concentrations. − For example, Richards et al and Stewart et al studied the phase behavior of NaLAS in water. Both studies showed that at low NaLAS concentrations, a single micellar (L 1 ) phase was present.…”

Section: Introductionmentioning

confidence: 99%

Aqueous Phase Behavior of a NaLAS–Polycarboxylate Polymer System

et al. 2021

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Linear alkylbenzene sulfonate (NaLAS) surfactant is often combined with polycarboxylate polymers in detergent formulations. However, the behavior of these aqueous surfactant–polymer systems in the absence of an added electrolyte is unreported. This work investigates the behavior of such systems using polarized light microscopy, small-angle X-ray scattering (SAXS), centrifugation, and 2H NMR techniques. A phase diagram at 50 °C is reported for 0–50 wt % NaLAS concentrations and 0–10 wt % polycarboxylate concentrations. The NaLAS–water system is micellar at concentrations <35 wt %, and a 2-phase micellar–lamellar system is seen at higher NaLAS levels, consistent with that reported by previous studies. As polymers are added at low surfactant concentrations (∼10 to 20 wt % NaLAS), a second optically isotropic phase is formed; this is thought to be a polymer-rich phase. Further addition of polycarboxylate leads to the formation of a lamellar phase. At high surfactant concentrations (>20 wt % NaLAS), the addition of a polymer induces a second lamellar phase. These observed behaviors are thought to arise as a result of depletion flocculation and salting-out effects. The observed lamellar phases adopt colloidal multilamellar vesicle (MLV) structures, and the average MLV radii were estimated using 2H NMR by probing the diffusion and anisotropy of D2O within the bilayers of the vesicles. The NMR results show that as the polymer concentration was increased from 0 to 10 wt %, an increase in the average multilamellar vesicle size from ∼200 to ∼500 nm was observed. This increase in the calculated average MLV radius likely results from depletion flocculation-induced MLV fusion.

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Section: Introductionmentioning

confidence: 99%

Aqueous Phase Behavior of a NaLAS–Polycarboxylate Polymer System

et al. 2021

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“…As for NaDBS, it is known to be composed of sulfonates with different chain lengths [ 34 ]. Thus, its exact composition was determined via high-performance liquid chromatography coupled with mass spectrometry (HPLC-MS; for technical details, see below).…”

Section: Methodsmentioning

confidence: 99%

“…In particular, a marked decrease in the surface tension as well as CMC with increasing salt concentration is observed at the presence of electrolytes at a fixed temperature [ 5 , 9 , 12 , 13 , 14 , 15 , 30 , 31 , 32 , 33 , 34 , 35 ]. For NaDBS as well as other sulfonates, this stems from (1) the reduction of repulsive forces acting between negatively charged head-groups as a result of cation–sulfonate interactions, and from (2) the decreased hydration of surfactant molecules owing to strong cation hydration, which in turn promotes hydrophobic interactions [ 14 , 15 , 31 , 34 , 35 , 36 ]. The interplay of these two effects leads to the well-known order of ‘salting-out’, observed first for proteins by Hofmeister [ 15 , 37 ].…”

Section: Introductionmentioning

confidence: 99%

Binding of Ca2+ Ions to Alkylbenzene Sulfonates: Micelle Formation, Second Critical Concentration and Precipitation

et al. 2023

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Anionic surfactants, such as sodium linear alkylbenzene sulfonates (NaLAS), are utilized in various fields, including industry, household, and agriculture. The efficiency of their use in aqueous environments is significantly affected by the presence of cations, Ca2+ and Mg2+ in particular, as they can decrease the concentration of the surfactant due to precipitation. To understand cation–sulfonate interactions better, we study both NaLAS colloidal solutions in the presence of CaCl2 and precipitates forming at higher salt concentrations. Upon addition of CaCl2, we find the surface tension and critical micelle concentration of NaLAS to decrease significantly, in line with earlier findings for alkylbenzylsulfonates in the presence of divalent cations. Strikingly, an increase in the surface tension is discernible above 0.6 g L–1 NaLAS, accompanied by the decrease of apparent micelle sizes, which in turn gives rise to transparent systems. Thus, there appears to be a second critical concentration indicating another micellar equilibrium. Furthermore, the maximum salt tolerance of the surfactant is 0.1 g L–1 Ca2+, above which rapid precipitation occurs yielding sparingly soluble CaLAS2∙2H2O.

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“…These techniques are nowadays rather robust and well developed; however, they lack sensitivity at a molecular scale to characterize the aggregates themselves. To perform this determination, one has to revert to more involved methods like X-rays and neutron scattering , or nuclear magnetic resonance (NMR) spectroscopy . Optical methods have also been proposed such as fluorescence, ,, Raman spectroscopy, resonant Rayleigh scattering, , or a nonresonant one as in dynamic light scattering or quasi elastic light scattering , as well as resonant hyper-Rayleigh scattering (HRS) and third harmonic scattering .…”

Section: Introductionmentioning

confidence: 99%

Multistep Micellization of Standard Surfactants Evidenced by Second Harmonic Scattering

et al. 2021

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Processes involving in solution a reduced number of molecules are difficult to identify and characterize. Here, we show that micellization of standard surfactants, namely sodium dodecyl sulfate and trimethyl tetradecyl ammonium bromide, two nonefficient compounds for quadratic nonlinear optics, can be investigated by second harmonic scattering (SHS). In particular, the formation of aggregates at concentrations smaller than the critical micellar concentration is evidenced through a nonmonotonic behavior of the SHS intensity as a function of the surfactant concentration. A simple model based on chemical equilibria between monomers and micelles is proposed to account for the experimental observations. Signature of long-range molecular orientation correlation is revealed by polarization resolved experiments and is discussed regarding micellization and charge-induced effects.

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Micellar structure and transformations in sodium alkylbenzenesulfonate (NaLAS) aqueous solutions: effects of concentration, temperature, and salt

Abstract: We investigate the shape, dimensions, and transformation pathways of micelles of linear sodium alkylbenzenesulfonate (NaLAS), a common anionic surfactant, in aqueous solution. Employing Small Angle Neutron Scattering (SANS) and surface...

Cited by 39 publications

References 64 publications

Aqueous Phase Behavior of a NaLAS–Polycarboxylate Polymer System

Aqueous Phase Behavior of a NaLAS–Polycarboxylate Polymer System

Binding of Ca2+ Ions to Alkylbenzene Sulfonates: Micelle Formation, Second Critical Concentration and Precipitation

Multistep Micellization of Standard Surfactants Evidenced by Second Harmonic Scattering

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