Wormlike micelles properties and oil displacement efficiency of a salt-tolerant C22-tailed amidosulfobetaine surfactant

Wormlike micelles formed by amidosulfobetaine surfactants present advantage in increasing viscosity, salt-tolerance, thermal-stability and shear-resistance. In the past few years, much attention has been paid on rheology behaviours of amidosulfobetaine surfactants that normally bear C18 or shorter tails. Properties and oil displacement performances of the wormlike micelles formed by counterparts bearing the long carbon chain have not been well documented. In this paper, the various properties of C22-tailed amidosulfobetaine surfactant EHSB under high salinity (TDS = 40g/L) are investigated systematically, including solubility, rheology and interfacial activity. Moreover, its oil displacement performance is studied for the first time. These properties are first compared with those of C16-tailed counterpart HDPS. Results show that the Krafft temperature( TK) of EHSB decreases from above 100°C to 53°C with the increase of TDS to 40 g/L. Increasing concentration of EHSB in the semidilute region induces micelle growth from rod-like micelles to wormlike micelles, and then the worms become entangled or branched to form viscoelastic micelle solution, which will increase the viscosity by several orders of magnitude. The interfacial tension with oil can be reduced to ultra-low level by EHSB solution with concentration below 4.5 mM. Possessing dual functions of mobility control and reducing interfacial tension, wormlike micelles formed by EHSB present a good displacement effect as a flooding system, which is more than 10% higher than HPAM with the same viscosity. Compared with the shorter tailed surfactant, the ultra-long tailed surfactant is more efficient in enhancing viscosity and reducing interfacial tension, so as to enhance more oil recovery. Our work provides a helpful insight for comprehending surfactant-based viscoelastic fluid and provides a new viscoelastic surfactant flooding agent which is quite efficient in chemical flooding of offshore oilfield.

Hysteresis of conductivity in a micellar surfactant solution near the Krafft point

The specific conductivity of aqueous cetyltrimethylammonium bromide solutions has been investigated below and above the critical micelle concentration, in order to elucidate slow structural changes. Around the Krafft temperature (?25?C) the monomer solubility reaches the critical micelle concentration, and a significant increase in charge transport is recorded. When a temperature decreases, the micellar surfactant solution passes through the Krafft temperature, and a hysteresis phenomenon is observed with the appearance of crystals in a solution. We have scrutinized the conditions leading to this hysteresis and quantified some of the relevant parameters. We also outline a simple procedure that allows the ?erasure? of such structural memory effects, which are potentially detrimental to the formation of adsorbed self-assembled monolayers from solution.

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.