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 m and 10 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.

Novel oil-in-water (O/W) emulsions are prepared which are stabilised by ac ationic surfactant in combination with similarly charged alumina nanoparticles at concentrations as low as 10 À5 m and 10 À4 wt %, respectively.T he surfactant molecules adsorb at the oil-water interface to reduce the interfacial tension and endowd roplets with charge ensuring electrical repulsion between them, whereas the charged particles are dispersed in the aqueous films between droplets retaining thickl amellae,r educing 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,s uch emulsions can be switched between stable and unstable by addition of an equimolar amount of oppositely charged surfactant whichf orms ion pairs with the original surfactant destroying the repulsion between droplets.

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 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.

It is of great significance to explore novel applications of renewable resources. In this study, a rosin-based anionic surfactant (abbreviated R-11-2-Na), which contains a large hydrophobic group of 30 carbon atoms, was synthesized. R-11-2-Na forms wormlike micelles in the presence of the equimolar organic salt choline chloride, endowing solutions with strong viscoelasticity. The wormlike micellar solutions were investigated using rheology, small-angle X-ray scattering, and freezefracture transmission electron microscopy (FF-TEM) methods at 25 °C. Due to the strong van der Waals interactions caused by the large hydrophobic group contained in R-11-2-Na, the zero-shear viscosity (η 0 ) of solutions showed extremely strong dependence on the concentration with an exponent of 23.4. The cross-sectional diameter of the wormlike micelles in the present system was significantly larger than that of the wormlike micelles formed by surfactants containing conventional alkyl tails. This finding may be attributed to the steric hindrance brought by the bulky and rigid dehydroabietic acid unit in the hydrophobic part. The wormlike micelles also showed high tolerance to the organic salt concentration. The present study reveals the notable qualities of rosin-based derivatives in forming complex fluids and facilitates new utilizations of forest resources.

Alkyl carboxyl betaines are good surfactants for reducing crude oil/connate water interfacial tension (IFT) in the absence of alkali and are therefore potential surfactants for surfactant–polymer (SP) flooding. However, they suffer from high adsorption retention and hydrophobizing sandstones by forming a monolayer at the sandstone/water interface with head-on configuration, which brings a risk of making the sandstone surfaces oily wet. In this paper, a poly alkylammonium bromide, N 1,N 1′-(propane-1,3- diyl) bis­(N 1,N 1,N 3,N 3,N 3-penta­methyl­propane-1,3-diaminium) bromide, abbreviated as tetra-N(3)-Br, was synthesized and its properties in inhibiting the hydrophobization of sandstones via adsorption of alkyl carboxyl betaines were examined. The results indicate that alkyl carboxyl betaines with either single or double long alkyl chains can hydrophobize significantly the negatively charged solid surfaces even in neutral aqueous media by forming a monolayer at solid/water interface with head-on configuration. The tetra-N(3)-Br, which has a high positive charge density, can adsorb strongly at negatively charged solid/water interface with the adsorption depending only on its equilibrium concentration regardless of the presence of alkyl carboxyl betaines. The negative charges on the solid surfaces are neutralized, the adsorption of alkyl carboxyl betaines is significantly inhibited, and the effective concentration of the tetra-N(3)-Br is as low as 10–6 mol/L. On the other hand the presence of tetra-N(3)-Br in aqueous solution does not affect the IFT behavior of alkyl carboxyl betaines in a wide concentration range up to 0.1 mM. Tetra-N(3)-Br is thus an excellent agent in inhibiting hydrophobization of sandstones via adsorption of alkyl carboxyl betaines in SP flooding.

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A new type of sulfobetaine with double alkyl polyoxyethylene (n) ether chains, dicoconut oil alcohol polyoxethylene (n) ether methylhydroxylpropyl sulfobetaine (diC12–14EnHSB) was synthesized using a commercial nonionic surfactant, coconut oil alcohol polyoxethylene (n) ether, as raw material and its properties as a surfactant for enhanced oil recovery (EOR) in the absence of alkali was studied. The purified product is a mixture of homologues with mainly C12/C12, C12/C14 and C14/C14 alkyl chains and widely distributed EO chains (n = 2.2 on average) with an average molar mass of 742.6 g/mol. The diC12–14E2.2HSB has an improved aqueous solubility at 25 °C compared with didodecylmethylhydroxylpropyl sulfobetaine (diC12HSB), a homologue without an EO chain, and is highly surface active as reflected by its low CMC (4.6 × 10−6 mol/L), high saturated adsorption (6.8 × 10−10 mol/cm2) and small cross sectional area (0.24 nm2/molec.) at the air/water interface. With a hydrophile–lipophile balance well matched with Daqing crude oil/connate water system, the sulfobetaine can reduce Daqing crude oil/connate water interfacial tension to ultra‐low values at 45 °C in the absence of alkali, and displays a low saturated adsorption at the sandstone/water interface (0.0024 mmol/g), reduced by 69 and 92 % respectively in comparison with that of the corresponding carboxyl betaine, diC12–14E2.2B and its homologue without an EO chain, didodecylmethylcarboxyl betaine (diC12B). With these excellent properties diC12–14E2.2HSB gives a high tertiary recovery, 18.4 % original oil in place, when mixed with other hydrophobic and hydrophilic sulfobetaines in surfactant‐polymer (SP) flooding free of alkali. The insertion of EO chains in combination with the replacement of carboxyl betaine by sulfobetaine is therefore very efficient for improving the properties of the double chain hydrophobic carboxyl betaines as surfactants for SP flooding free of alkali.

Novel oil-in-water (O/W) Pickering emulsions (PEs) were prepared using mesoporous nanosilica in combination with a pH-insensitive cationic surfactant as a stabilizer and show an interesting sensitivity to acids and bases. Adding a suitable amount of NaOH (n NaOH /n cationic surfactant ≥ 1) led to prompt demulsification within 10 s. Upon further adding HCl solutions (n HCl / n NaOH = 1), stable PEs re-formed after homogenization. These emulsions remained stable for over 30 days after 60 cycles, switching from stable to unstable and back to stable states, and showed a high salt tolerance. A mechanism for the switching of the Pickering emulsion (PE) to unstable and back to stable states was derived and involved anionic and neutral forms of hydroxyl groups at the mesopores of the mesoporous silica nanoparticles (MSNPs). This work reveals a switchable PE system involving a pH-insensitive surfactant, in which the species of oils and cationic surfactants can be arbitrarily selected, a feature that greatly expands the applicability of PEs.