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.