Binglei Song

Solution behavior and solid phase transitions of quaternary ammonium surfactants with head groups decorated by hydroxyl groups.

Hydrogen bonds are strong intermolecular interactions, which are very important in molecular aggregation and new phase formation. Three long-chain quaternary ammonium surfactants, N,N-diethyl-N-(2-hydroxyethyl)-N-octadecylammonium bromide with one hydroxyl group, N-ethyl-N,N-bis (2-hydroxyethyl)-N-octadecylammonium bromide with two hydroxyl groups and N,N,N-tris (2-hydroxyethyl)-N-octadecylammonium bromide with three hydroxyl groups, abbreviated as SHQ, DHQ, and THQ, respectively, were synthesized in this work. Their solution behavior and solid phase transitions were investigated by surface tension, differential scanning calorimetry (DSC), X-ray diffraction (XRD), polarizing optical microscopy (POM), and Infrared (IR) spectroscopy. The hydrogen bonds introduced by the substituted hydroxyl groups promoted surfactant adsorption at the air/water interface and aggregation in solution. In the crystal state, an increased number of hydroxyl groups caused a larger tilt angle of the long axis of surfactant molecules with the layer normal. Above certain temperatures, SHQ and DHQ formed highly ordered smectic T and smectic A phases while THQ only formed less ordered smectic A phase. The weakened electrostatic attractions between opposite ions and the thicker polar sublayers of mesophases caused by the enhanced number of hydrogen bonds are responsible for the mesophase formation and transition of these surfactants.

Photoresponsive Foams Generated by a Rigid Surfactant Derived from Dehydroabietic Acid

Innovation in the structure of surfactants is crucial to the construction of a surfactant-based system with intriguing properties. With dehydroabietic acid as a starting material, a nearly totally rigid azobenzene surfactant (R-azo-Na) was synthesized. The trans-R-azo-Na formed stable foams with half-lives of 636, 656, 976, and 872 min for 0.3, 1, 2, and 4 mmol·L-1 aqueous solutions, respectively. Under UV light irradiation, a fast collapse of the foams was observed, showing an in situ response. The excellent foam stability of trans-R-azo-Na leads to the extremely high photoresponsive efficiency. As revealed by dynamic surface tension and pulsed-field gradient NMR methods, an obvious energy barrier existed in the adsorption/desorption process of trans-R-azo-Na on the air/water interface. The foams formed by trans-R-azo-Na are thus stable against coarsening processes. The results reveal the unique photoresponsive behavior of a surfactant with a rigid hydrophobic skeleton and provide new insights into the structure causing aggregation of surfactants.

Improving performances of double-chain single-head surfactants for SP flooding by combining with conventional anionic surfactants

ABSTRACT The binary surfactant mixtures of 1,3-dialkyl (diC8-diC12) glyceryl ether ethoxylates with didodecylmethylhydroxylpropyl sulfobetaine (diC12HSB) are good formulations for surfactant–polymer flooding of Daqing crude oil, China, but suffer from low aqueous solubility. By combining with α-olefin sulfonates (AOS) at small molar fractions, the aqueous solubility of the formulations can be significantly improved due to the formation of charged mixed micelles. The ternary formulations can reduce Daqing crude oil/connate water interfacial tension to ultralow at a wide range of total surfactant concentration (0.625 ∼ 10 mM), have good resistance to adsorption by sandstone, and can keep sandstone surface water-wet. GRAPHICAL ABSTRACT

Synthesis of a new sulfobetaine surfactant with double long alkyl chains and its performances in surfactant-polymer flooding

ABSTRACT A new zwitterionic surfactant with double long alkyl chains, 3-((3-((1,3-bis (decyloxyl) propane-2-yl) oxy) -2-hydroxypropyl) dimethylamonio) -2-hydroxypropane-1-sulfonate (diC10GE-HSB), was synthesized, and its performances in Surfactant-Polymer (SP) flooding were studied. As a hydrophobic surfactant diC10GE-HSB solely cannot reduce Daqing crude oil/connate water IFT to ultralow, but ultralow IFT can be achieved by using binary mixtures of diC10GE-HSB with various conventional hydrophilic surfactants such as α–olefin sulfonates, dodecyl polyoxyethylene (10) ether, and cetyl dimethyl hydroxypropyl sulfobetaine, over a wide total concentration range (0.625 ∼ 10 mM) at reservoir temperature. This new sulfobetaine surfactant is therefore a good candidate for SP flooding free of alkali. GRAPHICAL ABSTRACT

Viscoelastic properties of supramolecular gemini-like surfactant solutions in the absence of inorganic salts

Exploration of novel wormlike micelle systems is important for both the theory and applications of surfactant self-assembly. A new anionic surfactant, sodium 2-phenoxyhexadecanoate (sodium Ph-C16), was synthesized in this work. This surfactant can self-assemble in solution to form wormlike micelles with the help of a bolaform salt, ethane-1,2-bis(trimethyl ammonium bromide) (N-2-N bromide), by removing inorganic salts. The resultant aqueous system was investigated using rheological measurements, freeze-fractured-TEM and 2D NOESY 1H NMR experiments. A supramolecular gemini-like structure constructed from electrostatic interactions was a prerequisite for the wormlike micelle formation. The zero shear viscosity (η0) of the system had a very strong dependence on the surfactant concentration with a scaling exponent of 16.8 in the semi-dilute region, which is attributed to the extremely strong electrostatic attraction between the surface-active anions and bolaform cations. These results are beneficial for understanding anionic wormlike micelles in the absence of inorganic salts.

Ionic liquid crystals with novel thermal properties formed by the gemini surfactants containing four hydroxyl groups

Modification of the molecular structures of surfactants is a feasible way to construct ionic liquid crystals (ILCs) with novel properties. Five quaternary ammonium gemini surfactants with different spacers, whose head groups were substituted by four hydroxyethyl groups, abbreviated as 12(2OH)-s-12-(2OH) (s = 3, 4, 5, 6, 8), were prepared. The mesomorphic behaviors of these gemini surfactants were investigated by polarized optical microscopy (POM), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and temperature-dependent FT-IR spectroscopy. These surfactants form smectic A (SmA) phases, the region of which is dependent on the spacer length. The presence of suitable spacer length and multiple hydroxyl groups is helpful in stabilizing the mesophases. Noticeably, because of synergistic effect of the spacer and the hydroxyl groups, the phase enthalpy change of SmA to crystal transitions can be slowly released below the phase transition temperature. This interesting discovery, which has never been reported in ILC systems formed by small molecular weight surfactants, could pave the way for special applications of ILCs in the area of sustained-release materials of heat and could widen the application of ionic liquid crystals.

Highly stable foams generated in mixed systems of ethanediyl-1,2-bis(dodecyldimethylammonium bromide) and alcohols

Stable foams were generated using a cationic gemini surfactant, ethanediyl-1,2-bis(dodecyldimethylammonium bromide) (12-2-12) together with a linear alcohol, hexanol (C6OH) or heptanol (C7OH), in aqueous solution. The foam stability was determined using the half-life of foam height falling (t1/2) as the index. The results showed that C7OH was more efficient than C6OH together with 12-2-12 to stabilize the foams. To generate the most stable foams, the optimum addition for both C6OH and C7OH was determined. The adsorption of the mixtures at the air/water interface was studied using surface tension measurements. The intermolecular interactions and the composition of the mixed monolayer were estimated by Rubingh–Rosen theory and the surface excess was derived from the Gibbs equation. The total surface excess that included both 12-2-12 and alcohols, was shown to significantly increase following the addition of alcohols suggesting the active molecules were more densely packed at the interface. The interfacial dilational rheology of the films was examined using the oscillating drop technique. The results showed that a highly stable foam always corresponded to a highly elastic adsorption film. The present study suggests a new formula for the generation of highly stable foams using a gemini surfactant with a short spacer together with a linear alcohol.

Surface dilatational properties of Gemini surfactants containing multiple hydroxyl groups

Surfactant adsorption films at the air/water interface, which usually exert a significant influence over system behaviour, are closely related to the surfactant molecular structure. In this research, a series of Gemini surfactants containing four hydroxyl groups at the head groups, namely: alkanediyl-α,ω-bis[di(2-hydroxylethyl) dodecylammonium bromide], abbreviated to 12(2OH)-s-12(2OH), where s = 3, 6, 8 and 10, respectively, were investigated by using interfacial dilatational rheological measurements. The effects of oscillating frequency, bulk concentration and spacer length on the dilatational behaviour of 12(2OH)-s-12(2OH) were investigated. The variation of dilatational modulus of 12(2OH)-8-12(2OH) with concentrations showed two peaks which were attributed to different configurations adopted by the spacer, revealing the effects of dynamic configuration of the spacer on surfactant interfacial adsorption. The fit to the results, with that data available, using the Lucassen/van den Tempel (LVT) model showed that the presence of hydroxyl groups near the head groups of Gemini surfactants enhanced the interfacial elasticity of the adsorption films.

Novel Oil‐in‐Water Emulsions Stabilised by Ionic Surfactant and Similarly Charged Nanoparticles at Very Low Concentrations

Novel oil-in-water (O/W) emulsions are prepared which are stabilised by a cationic surfactant in combination with similarly charged alumina nanoparticles at concentrations as low as 10-5  m and 10-4  wt %, respectively. The surfactant molecules adsorb at the oil-water interface to reduce the interfacial tension and endow droplets with charge ensuring electrical repulsion between them, whereas the charged particles are dispersed in the aqueous films between droplets retaining thick lamellae, reducing water drainage and hindering flocculation and coalescence of droplets. This stabilization mechanism is universal as it occurs with different oils (alkanes, aromatic hydrocarbons and triglycerides) and in mixtures of anionic surfactant and negatively charged nanoparticles. Further, such emulsions can be switched between stable and unstable by addition of an equimolar amount of oppositely charged surfactant which forms ion pairs with the original surfactant destroying the repulsion between droplets.