The rheological behavior of concentrated cationic wormlike micellar surfactant solutions (cetyltrimethylammonium bromide) near the isotropic-nematic (I-N) transition is studied as a function of composition and temperature to determine the relationship between shear banding, fluid microstructure and underlying equilibrium phase behavior. The combination of conventional rheometry, velocimetry, and spatially-resolved flow-small angle neutron scattering allows detailed exploration of the differences between shear banding and non-shear banding solutions. The shear rheology of isotropic WLM solutions are shown to be well-described by the Giesekus constitutive model, which provides a quantitative discrimination between banding and non-banding wormlike micellar fluids through the drag anisotropy coupling parameter. This anisotropy parameter is shown to correlate with the order parameter describing the relative distance to the equilibrium I-N transition. Combining this information with measurements of the critical shear rates for shear banding allows the construction of a non-equilibrium state diagram for the shear banding fluid in terms of the Weissenberg number and the compositional order parameter.

In the 2010 Deepwater Horizon rig explosion and subsequent oil spill, five million barrels of oil were released into the Gulf over the course of several months. Part of the resulting emergency response was the unprecedented use of nearly two million gallons of surfactant dispersant at both the sea surface and well head, giving rise to previously untested conditions of high temperature gradients, high pressures, and flow conditions. To better understand the complex interfacial transport mechanisms that this dispersant poses, we develop a model surfactant-oil-aqueous system of Tween 80 (a primary component in the Corexit dispersant used in the Gulf), squalane, and both simulated seawater as well as deionized water. We measure surfactant adsorption dynamics to the oil-aqueous interface for a range of surfactant concentrations. Using techniques developed in our laboratory, we investigate the impact of convection, step changes in bulk concentration, and interfacial mechanics. We observe dynamic interfacial behavior that is consistent with a reorganization of surfactant at the interface. We demonstrate irreversible adsorption behavior of Tween 80 near a critical interfacial tension value, as well as measure the dilatational elasticity of equilibrium and irreversibly adsorbed layers of surfactant on the oil-aqueous interface. We report high values of the surface dilatational elasticity and surface dilatational viscosity, and discuss these results in terms of their impact regarding oil spill response measures.

The influence of particle adsorption on liquid/liquid interfacial tension is not well understood, and much previous research has suggested conflicting behaviors. In this paper we investigate the surface activity and adsorption kinetics of charge stabilized and pH-responsive polymer stabilized colloids at oil/water interfaces using two tensiometry techniques: (i) pendant drop and (ii) microtensiometer. We found, using both techniques, that charge stabilized particles had little or no influence on the (dynamic) interfacial tension, although dense silica particles affected the "apparent" measured tension in the pendent drop, due to gravity driven elongation of the droplet profile. Nevertheless, this apparent change additionally allowed the study of adsorption kinetics, which was related qualitatively between particle systems by estimated diffusion coefficients. Significant and real interfacial tension responses were measured using ∼53 nm core-shell latex particles with a pH-responsive polymer stabilizer of poly(methyl methacrylate)-b-poly(2-(dimethylamino)ethyl methacrylate) (pMMA-b-pDMAEMA) diblock copolymer. At pH 2, where the polymer is strongly charged, behavior was similar to that of the bare charge-stabilized particles, showing little change in the interfacial tension. At pH 10, where the polymer is discharged and poorly soluble in water, a significant decrease in the measured interfacial tension commensurate with strong adsorption at the oil-water interface was seen, which was similar in magnitude to the surface activity of the free polymer. These results were both confirmed through droplet profile and microtensiometry experiments. Dilational elasticity measurements were also performed by oscillation of the droplet; again, changes in interfacial tension with droplet oscillation were only seen with the responsive particles at pH 10. Frequency sweeps were performed to ascertain the dilational elasticity modulus, with measured values being significantly higher than previously reported for nanoparticle and surfactant systems, and similar in magnitude to protein stabilized droplets.

Reverse osmosis and nanofiltration are highly adopted, growing technologies that are used to remove salts and other small molecules in water treatment. Both of these technologies primarily use cross-linked polyamide membranes to achieve the desired separation. Many novel nanoporous materials are being developed as alternatives or complements to polyamides, including graphene, graphene oxide, block copolymers, liquid crystals, aquaporins, and other biologically inspired molecular channels. This article evaluates each of these technologies by (i) reviewing the current progress in each area, (ii) identifying key needs for immediate research, and (iii) evaluating considerations for commercial development. The economic benefits of these technologies in reverse osmosis applications are further reviewed to help frame the expected commercial value proposition.

Pendant bubble and drop devices are invaluable tools in understanding surfactant behavior at fluid-fluid interfaces. The simple instrumentation and analysis are used widely to determine adsorption isotherms, transport parameters, and interfacial rheology. However, much of the analysis performed is developed for planar interfaces. The application of a planar analysis to drops and bubbles (curved interfaces) can lead to erroneous and unphysical results. We revisit this analysis for a well-studied surfactant system at air-water interfaces over a wide range of curvatures as applied to both expansion/contraction experiments and interfacial elasticity measurements. The impact of curvature and transport on measured properties is quantified and compared to other scaling relationships in the literature. The results provide tools to design interfacial experiments for accurate determination of isotherm, transport and elastic properties.