Specific ion effects on the micellization of aqueous mixed cationic/anionic surfactant systems with various counterions

Adsorption and Aggregation Behavior in Aqueous Solution of Tetrasiloxane-based Carboxylate Surfactants via "Thiol-ene" Photochemical Reaction

Anionic silicone surfactants have long been a neglected field. In this paper three anionic silicone surfactants were synthesized first time from dichloromethylvinylsilane through hydrolysis-condensation, "thiol-ene" photo- chemical and then salting reaction. The critical aggregate concentration (CAC), surface tension, minimum surface area per surfactant molecule and surface pressure at CAC were studied by both surface tension and electrical conductivity. The results showed that they had significant surface activity at the gas/liquid interface and were capable to reduce the surface tension of water to approximately 20 mN m-1 . The results of transmission electron microscopy showed that the three silicone surfactants self-assembled into spherical aggregates of uniform size in aqueous solution above the CAC. The dynamic light scattering results demonstrated that the size of the aggregates was determined to be in the range from 60 to 300 nm at 0.05 mol L-1 and the order of the size of the aggregates is (Me3 SiO)3 SiCO2 Li<(Me3 SiO)3 SiCO2 Na<(Me3 SiO)3 SiCO2 K.

Effect of Divalent and Monovalent Salts on Interfacial Dilational Rheology of Sodium Dodecylbenzene Sulfonate Solutions

This study presents the equilibrium surface tension (ST), critical micelle concentration (CMC) and the dilational viscoelasticity of sodium dodecylbenzene sulfonate (SDBS)-adsorbed layers in the presence of NaCl, KCl, LiCl, CaCl2 and MgCl2 at 0.001–0.1 M salt concentration. The ST and surface dilational viscoelasticity were determined using bubble-shape analysis technique. To capture the complete profile of dilational viscoelastic properties of SDBS-adsorbed layers, experiments were conducted within a wide range of SDBS concentrations at a fixed oscillating frequency of 0.01 Hz. Salts were found to lower the ST and induce micellar formation at all concentrations. However, the addition of salts increased dilational viscoelastic modulus only at a certain range of SDBS concentration (below 0.01–0.02 mM SDBS). Above this concentration range, salts decreased dilational viscoelasticity due to the domination of the induced molecular exchange dampening the ST gradient. The dilational viscoelasticity of the salts of interest were in the order CaCl2 > MgCl2 > KCl > NaCl > LiCl. The charge density of ions was found as the corresponding factor for the higher impact of divalent ions compared to monovalent ions, while the impact of monovalent ions was assigned to the degree of matching in water affinities, and thereby the tendency for ion-pairing between SDBS head groups and monovalent ions.

Development of CO2-Sensitive Viscoelastic Fracturing Fluid for Low Permeability Reservoirs: A Review

There are economic and technical challenges to overcome when increasing resource recovery from low permeability reservoirs. For such reservoirs, the hydraulic fracturing plan with the development of clean and less expensive fracturing fluid plays a vital aspect in meeting the energy supply chain. Numerous recent published studies have indicated that research on worm-like micelles (WLMs) based on viscoelastic surfactant (VES) fluid has progressed substantially. This study looks at the development of CO2-sensitive viscoelastic fracturing fluid (CO2-SVFF), its applications, benefits, limitations, and drawbacks of conventional fracturing fluids. The switchable viscoelasticity of CO2-SVFF system signifies how reusing of this fluid is attained. Compared to conventional surfactants, the CO2-SVFF system can be switched to high viscosity (to fracture formation and transporting proppants) and low viscosity (easy removal after causing fracture). The effect of pH, conductivity, temperature, and rheological behaviors of CO2-SVFFs are also highlighted. Further, the aid of Gemini surfactants and nanoparticles (NPs) with low concentrations in CO2-SVFF can improve viscoelasticity and extended stability to withstand high shear rates and temperatures during the fracturing process. These studies provide insight into future knowledge that might lead to a more environmentally friendly and successful CO2-SVFFs in low-permeability reservoirs. Despite the increased application of CO2-SVFFs, there are still several challenges (i.e., formation with high-temperature range, pressure, and salinity).

Determination of Critical Micelle Concentration from the Diffusion-Driven Dilution of Micellar Aqueous Mixtures

Micellization is a phenomenon of central importance in surfactant solutions. Here, we demonstrate that the diffusion-based spreading of the free boundary between a micellar aqueous solution and pure water yields a one-dimensional spatial profile of surfactant concentration that can be used to identify the critical micelle concentration, here denoted as C*. This can be achieved because dilution of micelles into water leads to their dissociation at a well-defined position along the concentration profile and an abrupt increase in the diffusion coefficient. Rayleigh interferometry was successfully employed to determine C* values for three well-known surfactants in water at 25 °C: Triton X-100 (TX-100), sodium dodecyl sulfate (SDS), and poly(oxyethylene)(4)Lauryl Ether (Brij-30). The dependence of C* on salt concentration was also characterized for TX-100 in the presence of Na₂SO₄, NaCl, and NaSCN. Accurate values of C* can be directly identified by visual inspection of the corresponding concentration-gradient profiles. To apply the method of least squares to experimental concentration profiles, a mathematical expression was derived from Fick's law and the pseudophase separation model of micellization with the inclusion of appropriate modifications. While Rayleigh interferometry was employed in our experiments, this approach can be extended to any experimental technique that yields one-dimensional profiles of surfactant concentration. Moreover, diffusion-driven surfactant disaggregation is precise, noninvasive, requires single-sample preparation, and applies to both nonionic and ionic surfactants. Thus, this work provides the foundation of diffusion-driven dilution methods, thereby representing a valuable addition to existing techniques for the determination of C*.

Self-assembly of sodium dodecylsulfate and dodecyltrimethylammonium bromide mixed surfactants with dyes in aqueous mixtures

The micellar property of mixed surfactant systems, cationic (dodecyltrimethylammonium bromide, DTAB) and anionic (sodium dodecylsulfate, SDS) surfactants with variable molar ratios in aqueous system has been reported by using surface tension and conductivity measurements at T = 293.15, 298.15 and 303.15 K. DTAB concentrations are varied from 1.0 × 10^-4 to 3 × 10^-4 mol l^-1 in 1.0 × 10^-2 mol l^-1 SDS solution while the SDS concentration is varied from 1.0 × 10^-3 to 1.5 × 10^-2 mol l^-1 in approximately 5.0 × 10^-3 mol l^-1 DTAB, so that such concentrations of DTAB-SDS (DTAB-rich) and SDS-DTAB (SDS-rich) solutions were chosen 3 : 1 ratio. The critical micellar concentration, as well as surface and thermodynamic properties for DTAB-rich and SDS-rich solutions, were evaluated by the surface tension (γ) and conductivity (κ) methods. The pseudo phase separation model was coupled with the dissociated Margules model for synergism. The Krafft temperature behaviour and optical analysis of mixed surfactants are studied using conductivity and UV-Vis spectroscopy, respectively. The dispersibility and stability of DTAB-rich and SDS-rich solutions with and without dyes (2.5 × 10^-5 mol l^-1 of methyl orange and methylene blue) are carried out by using UV-Vis spectroscopy and dynamic light scattering.

Synthesis, Properties, and Aggregation Behavior of Tetrasiloxane-Based Anionic Surfactants

Three silicone surfactants, 3-tris(trimethylsiloxy)silylpropyl sulfonate with different alkaline counterions (lithium, sodium, and potassium), were synthesized for the first time. Their chemical structures were confirmed by FT-IR spectra, ¹H NMR, and ESI-MS, and their behaviors in aqueous solutions were investigated by surface tensiometry, electrical conductivity, dynamic light scattering, and different transmission electron microscopy techniques. These anionic silicone surfactants exhibited remarkable surface activity and could reduce the surface tension of water to as low as 19.8 mN/m at the critical aggregate concentration (CAC). The adsorption and aggregation behaviors of these surfactants were assessed by determining the adsorption efficiency, minimum average area per surfactant molecule, and thermodynamic parameters. The cryo-TEM results verified that these molecules could form vesicles in water above the CAC. Moreover, the lowest surface tension, the smallest CAC value, and the largest aggregate size have been reached with potassium counterions. Thus, the different behavior of these surfactants in water can be explained by the different sizes of the hydrated ions.