Zonglin Chu

Wormlike micelles and solution properties of a C22-tailed amidosulfobetaine surfactant.

Wormlike micelles have been observed and explained in a wide variety of different types of surfactants except sulfobetaine ones. Here, we first report branched worms formed by a C22-tailed amidosulfobetaine surfactant-3-(N-erucamidopropyl-N,N-dimethyl ammonium) propane sulfonate (EDAS). Increasing EDAS concentration in the semidilute region increases the viscosity by several orders of magnitude and forms viscoelastic micellar solution of entangled and branched worms. The intermicellar branching is proved by rheological methods and Cryo-TEM observation. Besides, the rheological experiments indicate that EDAS worms show some advantages such as low overlapping concentration, insensitive to inorganic salt, stable over the whole pH range.

Thermally induced structural transitions from fluids to hydrogels with pH-switchable anionic wormlike micelles.

A novel pH-switchable anionic wormlike micellar system has been developed by simply changing pH value of natural erucic acid solutions without needing specialized organic synthesis or addition of hydrotropes. Through rheology, optical transmittance, and cryo-TEM observation, it was found that at 60 °C, the 100 mM erucic acid solutions transform from low viscous emulsion-like fluids to viscoelastic hydrogels when the pH is increased from 8.03 to 12.35, and when the pH is cycled between 9.02 and 12.35, the viscosity of the solutions varies correspondingly between 2 and 200,000 mPas, five orders of magnitude in viscosity range. Such a reversible switch can be easily cycled more than four times without any deterioration. In addition, when the pH is fixed between 9.0 and 12.35, the solutions shift to highly elastic solid-like gels with decreasing temperature. These pH-switchable and temperature-sensitive rheological properties are attributed to the presence of carboxylic groups in the erucic acid molecules. With increasing pH, erucic acid is converted into an anionic surfactant, sodium erucate, which self-assembles into aggregates evolving from spherical micelles to wormlike micelles; when temperature is decreased, these disordered micellar structures become highly ordered under the effect of crystallization of hydrophobic erucate chains, forming opaque solid-like hydrogels.

Amidosulfobetaine surfactant gels with shear banding transitions

Wormlike micellar gels formed by concentrated 3-(N-erucamidopropyl-N,N-dimethyl ammonium) propanesulfonate (EDAS) solutions show both gel-like behavior and shear banding transitions. Such surfactant gels are strong viscoelastic fluids with ultra-long but finite relaxation time, instead of bulk gels with infinite zero-shear viscosity and relaxation time. We demonstrate for the first time the relationship between the yield stress and shear banding transition of the surfactant gels.

“Green” anionic wormlike micelles induced by choline

In such application fields as oilwell stimulation, tertiary oil recovery and drug release, environmental-friendly wormlike micelles are largely preferred. The present work reports a “green” wormlike micellar system formed by a bio-based anionic surfactant, sodium erucate (NaOEr), and a biodegradable hydrotrope, choline. The micellar solutions were examined by means of rheology and cryo-TEM observation. Besides possessing lower toxicity, choline exhibits a stronger ability to induce micelle growth than tetramethylammonium, which is commonly used to promote the formation of anionic worms, and the choline–NaOEr system is more thermosensitive with increasing counterion concentration. These notable advantages enable the choline–NaOEr wormlike micellar system to find potential applications in biomedical areas and clean fracturing fluids.

Aging mechanism of unsaturated long-chain amidosulfobetaine worm fluids at high temperature

Both fundamental and technological research interests have highlighted in recent years a remarkable growing focus on surfactant wormlike micelles. Nevertheless, long-term thermal stability, as well as the corresponding aging mechanism of viscoelastic worm fluids was rarely examined. We report for the first time the high-temperature aging effect on wormlike micellar solutions formed by an unsaturated C22-tailed amidosulfobetaine surfactant in the absence and presence of a reducer, by means of rheological methods, cryo-TEM observations, IR and 1H NMR measurements. It was found that the aging effect mainly resulted from the degradation of the carbon–carbon double bond in the surfactant tail rather than its amido head group; and the addition of a small amount of reducing agent could effectively improve thermal stability of the worm fluids.

Oligomeric alkylpyridinium surfactants prepared via ATRP

Abstract A series of oligomeric alkylpyridinium surfactants were prepared directly in aqueous media by atom transfer radical polymerization (ATRP) of a surfmer, 4- vinyl-N-dodecylpyridinium bromide, and their surface activities were examined in comparison with the surfmer. The resulting oligomers have narrow molecular weight distributions, with polydispersity indices in the range of 1.17-1.23. By using 2-morpholinoethyl 2-bromo-2-methylpropanoate as ATRP initiator, the molecular weight of oligomeric surfactants was characterized by 1H NMR and the results were close to those obtained from GPC analysis. It was found that critical micelle concentration (CMC) of the oligomeric alkylpyridinium surfactants shifted to lower concentrations with increasing degree of polymerization (DPn), and their γ-cmc values were smaller by about 4 to 8 mN/m than that of the corresponding surfmer. Among the series of surfactants, the oligomer with highest DPn showed the greatest efficiency in lowering the surface tension in aqueous solution.