Dynamic covalent surfactants were designed to prepare pH switchable emulsions. A dynamic covalent bond between nonamphiphilic building blocks (polyethylenimine (PEI) and benzaldehyde (B)) was introduced to form the dynamic covalent surfactant PEI-B. The dynamic nature of covalent bond in PEI-B was confirmed by 1H NMR and fluorescence probe analysis. Stable emulsions were successfully prepared with interfacial active PEI-B at pH 7.8 with various water/paraffin oil ratios under sonication. When lowering the pH to 3.5, a complete phase separation was observed as a result of breaking dynamic covalent bond in the interfacial active PEI-B. After tuning the pH back to 7.8, stable emulsion was obtained again due to the reformation of the dynamic covalent bond and hence interfacial active PEI-B. The emulsification and demulsification were dependent on the formation and breaking of dynamic covalent bond in PEI-B. Such pH-triggered emulsification and demulsification can be switched at least three times. Application of dynamic covalent surfactants will open up a novel route for preparing responsive emulsions.

•W/O emulsions were prepared with electrolytes adjusting the PIT.•NaCl can decrease the PIT of the system below 20 °C.•The W/O emulsions cannot be easily diluted because of the high viscosity of the oil.•The destabilization processes of the emulsions were sedimentation and coalescence.The phase inversion temperature (PIT) is an inherent property of many water/nonionic surfactant/oil systems. It tends to form O/W emulsions when the PIT is high and vice versa. In the present paper, formation of W/O emulsions was studied in aqueous/polyoxyethylene 4 lauryl ether/paraffinic oil systems by simply homogenizing. Polyoxyethylene 4 lauryl ether is a common hydrophilic surfactant and is normally used to produce O/W emulsions. Inorganic electrolyte species and their concentrations were appropriately chosen to reduce the PIT for the formation of W/O emulsions. Furthermore, the effects of surfactant concentration and oil/water phase volume ratio on the PIT were investigated by measuring the conductivity variation. Stability of W/O emulsions was studied as a function of inorganic electrolyte concentration and storage time by bottle test, microscope observation, and viscosity measurement, which shows that the sedimentation and coalescence lead to the destabilization of W/O emulsions.Emulsion type map and the destabilization process of a water-in-oil emulsion sample prepared with electrolyte addition at constant temperature.

Single-crystalline Fe3O4 nanosheets were obtained for the first time by simply adjusting the pH of a magnetite particle dispersion, using a hydrophilic terpolymer as stabilizer. We experimentally observed the magnetite nanoparticles spontaneous, template-free organization into nanosheets. This transformation occurs in an acidic environment at the zeta potential minimum by the abrupt, oriented self-assembly of polymer-stabilized magnetite particles at room temperature. The driving forces of the oriented self-assembly process includes the interplay of anisotropic dipolar forces, electrostatic interactions and isotropic van der Waals forces.

Magnetic polystyrene nanospheres with high magnetite content and abundant surface carboxyl groups were prepared by emulsifier-free emulsion polymerization in the presence of aqueous magnetic fluid coated with oleic acid and 10-undecenoic acid as primary and secondary surfactants respectively. The effects of initiator concentration, initiator type (water-soluble or oil-soluble), monomer concentration and ferrofluid content on the particle characteristics such as the size, morphology, magnetic properties and the number of carboxyl groups were investigated. When water-soluble potassium peroxodisulfate (KPS) was used as the initiator, magnetite nanoparticles were uniformly encapsulated in polystyrene particles, while in the oil soluble benzoyl peroxide (BPO) system, magnetite particles were located on one side of magnetic polystyrene nanospheres. The results showed that two mechanisms for the nucleation and growth of nanospheres were involved according to the kind of initiator used in the polymerization. The magnetic nanospheres were superparamagnetic with the highest saturation magnetization of 29.78 emu/g and the corresponding magnetite content of 41.67%. The maximum amount of surface carboxyls was 0.5594 mmol/g. BSA (bovine serum albumin) was used to test the immobilization capacity of proteins onto the magnetic spheres. The immobilization capacity was about 196.2 mg BSA/g. These carboxylated magnetic polystyrene nanospheres have extensive potential biomedical applications.

A high-temperature solution phase hydrolysis has been developed for the synthesis of amine-functionalized Fe3O4 nanostructures. The concentrations of the reagents and the reaction time have great influence on the morphologies of the products. Increasing the amounts of poly (propylene glycol) bis (2-aminopropyl ether) transformed the product morphology from hollow nanostructures to magnetite nanoparticles. Single-crystal solid spherical aggregates, hollow spheres, loose nanoclusters and polyhedral-like magnetite particles can be selectively synthesized by varying the synthesis parameters, including the reaction time or the weight ratio of iron precursors to polyetheramine. The morphological transformation could be attributed to the cooperation of oriented aggregation and Ostwald ripening mechanisms. By using poly (propylene glycol) bis (2-aminopropyl ether) as the capping agent, the amine-functionalized nanoparticles show high water dispersibility and thermo-responsive. In addition, the Pickering emulsion stabilized by amine-functionalized nanoparticles was fabricated. One of the most promising applications of the as-prepared single-crystal hollow structures is as support materials for biological testing, catalysis and targeted drug delivery.

The cloud points (CP) of aqueous solutions of two ethylene oxide–propylene oxide–ethylene oxide tri-block copolymers (EO)10(PO)16(EO)10 and (EO)1(PO)17(EO)1 were measured in the presence of additives, such as salts, alkalis, acids, polymer and ionic surfactant. The results obtained in this study indicated that salts decrease the CP of the two tri-block copolymers in the order of NaCl>CaCl2>MgCl2 and Na3PO4>Na2SO4>NaCl. Alkalis caused a sharp drop of CP of the two tri-block copolymers. Acids increased the CP. Water soluble polymer such as polyvinylpyrrolidone (PVP), hydrolysis polyacrylamide (HPAM) and cation-polyacryamide (cation-PAM) decreased the CP. Ionic surfactants such as sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) increased the CP. The extent of lowering depends on the structure and concentration of additives and the number of ethylene oxide group of tri-block copolymers.