Salt induced polystyrene latex flocs investigated by neutron scattering.

Studies with a model system consisting of polystyrene latex particles showed that the protein from seeds of Moringa trees adsorbs to the surface and causes flocculation as unusually dense aggregates. In this study, electrolytes sodium chloride (NaCl), ferric chloride (FeCl3) and aluminium sulfate (Al2(SO4)3) have been used to aggregate model polystyrene particles. The study augments previous work using neutron scattering on the flocculation of polystyrene latex with protein from seeds of Moringa trees that had indicated higher floc dimension, df, values as the concentration of particles increased. The measurements were made using ultra small-angle neutron scattering. Generally the fractal dimension, and thus the floc density, increased with particle concentration and salt concentration. Flocculation was apparent at much lower concentrations of FeCl3 and Al2(SO4)3 than of NaCl. The values of df were found not to simply scale with ionic strength for the three electrolytes studied with FeCl3 being the most effective flocculating agent.

Magnetic Surfactants and Polymers with Gadolinium Counterions for Protein Separations.

New magnetic surfactants, (cationic hexadecyltrimethlyammonium bromotrichlorogadolinate (CTAG), decyltrimethylammonium bromotrichlorogadolinate (DTAG), and a magnetic polymer (poly(3-acrylamidopropyl)trimethylammonium tetrachlorogadolinate (APTAG)) have been synthesized by the simple mixing of the corresponding surfactants and polymer with gadolinium metal ions. A magnetic anionic surfactant, gadolinium tri(1,4-bis(2-ethylhexoxy)-1,4-dioxobutane-2-sulfonate) (Gd(AOT)3), was synthesized via metathesis. Both routes enable facile preparation of magnetically responsive magnetic polymers and surfactants without the need to rely on nanocomposites or organic frameworks with polyradicals. Electrical conductivity, surface tensiometry, SQUID magnetometry, and small-angle neutron scattering (SANS) demonstrate surface activity and self-aggregation behavior of the magnetic surfactants similar to their magnetically inert parent analogues but with added magnetic properties. The binding of the magnetic surfactants to proteins enables efficient separations under low-strength (0.33 T) magnetic fields in a new, nanoparticle-free approach to magnetophoretic protein separations and extractions. Importantly, the toxicity of the magnetic surfactants and polymers is, in some cases, lower than that of their halide analogues.

Interactions between quaternary ammonium surfactants and polyethylenimine at high pH in film forming systems.

HYPOTHESIS: Film formation and film structure in films formed on solutions of cationic surfactants with polyethylenimine is influenced by the surfactant structure, including both the tail length and the nature of the headgroup, which alter the micelle properties. EXPERIMENTS: A series of cationic surfactants were synthesized and conductivity measurements were used to compare the critical micelle concentrations for these surfactants and their behaviour with and without polyethylenimine at high pH. Small angle neutron scattering measurements were used to characterise the size and shape of the micelles in the presence and absence of the polymer. Film formation between polyethylenimine and the various surfactants was trialled, and the interfacial film structures measured using neutron reflectivity. FINDINGS: Film formation is shown to depend on surfactant tail length, with thicker films forming for surfactants with longer hydrophobic tails. The surfactant headgroup structure affects counterion binding to the micelles, and in the case of the aromatic headgroups, the headgroup affects the extent of micellar growth when polymer is added. Films with the greatest mesostructural ordering were grown using hexadecylpyridinium bromide surfactants.

CO2-responsive microemulsions based on reactive ionic liquids.

We demonstrate that the nanodomains within a ternary system consisting of oil, surfactant, and a new reactive ionic liquid can be tuned reversibly upon exposure to and removal of CO2 under mild conditions of temperature and pressure. The equilibrium microstructures of these domains have been characterized by small-angle neutron scattering and demonstrate that control over emulsion morphology (and therefore physicochemical properties such as viscosity) and the breaking of emulsions can be achieved without the need for irreversible changes in system composition or significant energy input.

Spatially Resolved Concentration and Segmental Flow Alignment in a Shear-Banding Solution of Polymer-Like Micelles.

We measure the spatially resolved microstructure and concentration in the plane of flow for a viscoelastic solution of polymer-like micelles comprised of mass fraction 6.0% (volume fraction 6.6%) solution of 2:1 molar ratio cetylpyridinium chloride/sodium salicylate in 0.5 mol/L NaCl/D2O through the shear banding transition. Spatially resolved flow small-angle neutron scattering measurements in the velocity-velocity gradient (1-2) plane of flow establish the local microstructure, and scanning narrow-aperture flow ultrasmall-angle neutron scattering (SNAFUSANS) measurements indicate no flow-induced concentration gradients within measurement accuracy. These results show shear banding in this solution is not associated with an isotropic-nematic transition and are fundamentally important for validating models of shear-banding complex fluids. Improvements in the SNAFUSANS method are also documented.

Self-assembled films formed at the air-water interface from CTAB/SDS mixtures with water-soluble polymers.

We have investigated the spontaneous self-assembly of solid, mesostructured films that form at the air-solution interface on solutions containing a neutral water-soluble polymer and catanionic surfactant mixtures of hexadecyl-trimethylammonium bromide (CTAB) and sodium dodecylsulphate (SDS). The formation processes and structures were probed using neutron reflectivity, X-ray reflectivity, off-specular time-resolved scattering, and grazing incidence diffraction. The mesostructures of films prepared with polyethylene oxide, polyethylenimine, and polyacrylamide at various cationic/anionic surfactant molar ratios are compared. The results suggest that polymers having a weak interaction with the surfactants cause a depletion aggregation process that results in a lamellar phase, whereas polymers having a stronger interaction with the surfactants produce more complex mesostructures in the films.