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Wang J.,Shandong Provincial Key Laboratory of Test Technology for Material Chemical Safety | Wang J.,Shandong Supervision and Inspection Institute for Product Quality | Zhang J.,Shandong University | Wang W.,Shandong Provincial Key Laboratory of Test Technology for Material Chemical Safety | And 5 more authors.
Journal of Dispersion Science and Technology

The occurrence of double phase inversion of emulsions stabilized by positively charged layered double hydroxide (LDH) particles and single-chain anionic surfactant sodium dodecyl benzene sulfonate (SDBS) has been investigated. That is, the original oil-in-water (ow(1)) emulsions inverted to water-in-oil (w/o) type and finally reconverted to o/w(2) emulsions. Laser-induced fluorescent confocal micrographs and emulsion droplet size measurements together confirmed that the initial o/w(1) and intermediate w/o emulsions are stabilized by LDH particles, whereas the final o/w(2) emulsions are stabilized mainly by excess SDBS surfactants. The adsorption behavior of SDBS on LDH particles was further studied by combining x-ray diffraction, zeta potential measurements, and contact angle measurements to reveal the inversion mechanism. © 2013 Copyright Taylor and Francis Group, LLC. Source

Zhang J.,Shandong University | Li L.,Shandong University | Wang J.,Shandong Provincial Key Laboratory of Test Technology for Material Chemical Safety | Sun H.,Shandong University | And 2 more authors.

The effects of salt on emulsions containing sorbitan oleate (Span 80) and Laponite particles were investigated. Surprisingly, a novel double phase inversion was induced by simply changing the salt concentration. At fixed concentration of Laponite particles in the aqueous phase and surfactant in paraffin oil, emulsions are oil in water (o/w) when the concentration of NaCl is lower than 5 mM. Emulsions of water in oil (w/o) are obtained when the NaCl concentration is between 5 and 20 mM. Then the emulsions invert to o/w when the salt concentration is higher than 50 mM. In this process, different emulsifiers dominate the composition of the interfacial layer, and the emulsion type is correspondingly controlled. When the salt concentration is low in the aqueous dispersion of Laponite, the particles are discrete and can move to the interface freely. Therefore, the emulsions are stabilized by particles and surfactant, and the type is o/w as particles are in domination. At intermediate salt concentrations, the aqueous dispersions of Laponite are gel-like, the viscosity is high, and the transition of the particles from the aqueous phase to the interface is inhibited. The emulsions are stabilized mainly by lipophilic surfactant, and w/o emulsions are obtained. For high salt concentration, flocculation occurs and the viscosity of the dispersion is reduced; thus, the adsorption of particles is promoted and the type of emulsions inverts to o/w. Laser-induced fluorescent confocal micrographs and cryo transmission electron microscopy clearly confirm the adsorption of Laponite particles on the surface of o/w emulsion droplets, whereas the accumulation of particles at the w/o emulsion droplet surfaces was not observed. This mechanism is also supported by the results of rheology and interfacial tension measurements. © 2012 American Chemical Society. Source

Liu G.-P.,Shandong University | Liu G.-P.,University of Jinan | Wang J.,Shandong University | Wang J.,Shandong Provincial Key Laboratory of Test Technology for Material Chemical Safety | And 3 more authors.
Gaodeng Xuexiao Huaxue Xuebao/Chemical Journal of Chinese Universities

Three aqueous dispersions of MgAl double hydroxide particles with different forms were prepared by a coprecipitation method. And then Pickering emulsions were prepared from them. The properties of the aqueous particle dispersions and the emulsions were studied. X-ray diffraction (XRD) and transmission electron microscope (TEM) characterizations indicate that the low crystallized particles dispersed in water in the manner of irregular shaped and loose structured particles with rough surfaces, while the well crystallized particles were the compact structured hexagonal platelets with smooth surfaces. Zeta potential measurements show that NaCl reduced the zeta potential of the three particles, resulting in particle flocculation in water. But the well crystallized particle dispersion flocculated in a higher salt concentration. The three double hydroxide particle/NaCl dispersions were used to prepare emulsions containing equal volumes of oil and water, respectively. The stability of the three emulsion systems was further compared. The results show that the stability of all emulsions was improved to some extent by the addition of NaCl. The emulsifying ability of the well crystallized particles appeared to be better than that of the low crystallized particles. For the low crystallized double hydroxides, the larger particles were better emulsion stabilizers than the smaller ones. Source

Zhang J.,Shandong University | Li L.,Shandong University | Wang J.,Shandong Provincial Key Laboratory of Test Technology for Material Chemical Safety | Xu J.,Shandong University | Sun D.,Shandong University

Emulsions stabilized by clay particles and sorbitan monooleate (Span 80) were investigated, and an abnormal phase inversion was observed by increasing the concentration of clay particles in the aqueous phase. At a fixed concentration of Span 80 in the oil phase, the emulsions were oil-in-water (o/w) when the concentration of clay particles in the aqueous phase was low. Surprisingly, the emulsion inverted to water-in-oil (w/o) when the concentration of the hydrophilic clay particles was increased. On the basis of the results of rheological measurements and laser-induced fluorescent confocal microscopy observation, we suggest that this phase inversion is induced by the gel structures formed at high concentration of clay particles. The effects of clay concentration on the stability and the droplet size of these emulsions were also investigated. © 2013 American Chemical Society. Source

Gao C.,Nanjing University | Gao C.,Shandong Provincial Key Laboratory of Test Technology for Material Chemical Safety | Ai M.,Nanjing University | Li X.,Nanjing University | Xu Z.,Nanjing University
Journal of Polymer Science, Part A: Polymer Chemistry

This work reports a simple and effective method to prepare polyaniline (PANI) nanotubes with rectangular or circular cross section and hollow microspheres by using basic amino acids L-lysine or L-arginine as dopants and pH buffer agents, respectively. The research reveals that the pH value of the reaction solution at the beginning stage is a crucial factor to form PANI microstructures. The L-lysine and L-arginine have isoelectric point 9.74 and 10.76, which can maintain reaction solution at high pH value at the beginning reaction and assist aniline to couple in ortho-position forming phenazine unit in the oligomer chain. The oligomer produces rectangular nanorods or microspheres by interaction. These oligomer microstructures act as templates for further polymerization to form PANI rectangular nanotubes and hollow microspheres. Decreasing the concentration of the basic amino acid or using acidic amino acid, the round nanotubes are formed. This method provides a simple route to prepare PANI microstructures with different morphologies without any foreign template or surfactant, and raises a new view on the polymerization process. © 2011 Wiley Periodicals, Inc. Source

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