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.

Ion pair interactions were explored to design a fatty acid solvent of switchable miscibility with water. Fatty acids of medium length chains are immiscible with water but become miscible with water when ion pairs are formed with amines. The ion pairs become phase separated after bubbling CO2 into the solution due to the dissociation of the fatty acid-amine complexes. Ion pairs of caprylic acid (C8) and low toxic poly(oxypropylene) diamine (Jeffamine D-230) were characterized by FT-IR and 1H NMR. Log Kow values and surface activity were used to understand the switchable solvent mechanism in removing and recovering oily contaminants. More importantly, the ion pairs show a negligible adsorption on solid surfaces. Furthermore, both C8 and D-230 were recycled during the washing process. Thus the fatty acid as switchable solvent could be applied for oily contaminant removal from oily solid wastes.Download high-res image (157KB)Download full-size image

The petrous bone is a strategic area within the skull base. The cochlea and the carotid artery canal are extremely close to each other within that area. Pulsatile tinnitus requires intact hearing and usually source of sound. It can be arterial or venous in origin, or originating in-between. The aim of this study was to use the MDCT in measurement of the thickness of the bony plate between the internal carotid artery and cochlea within the skull base in patients with pulsatile tinnitus showing no other detectable etiology on MDCT basis as well as for detection of any bony dehiscence involving this bony plate.ResultsThis study was conducted on 8 adult patients. The dehiscences ranged between 0.7 and 1.7 mm (average 1.04 mm). Two male patients showed bilateral dehiscences together with excessive pneumatization of both petrous apices. Six female patients showed only unilateral dehiscences. In the controls, the internal carotid artery to cochlea (ICA/Ch) distance ranged from 0.59 mm to 3.1 mm and was 1.618 mm in average. The dehiscences were more common in female. However when they occur in males, they tend to be bilateral and seems to be predisposed by excessive pneumatization of both petrous apices.

Effects of gravity on liquid crystal phase transitions (LCPT) in polydisperse aqueous suspensions of Mg 2Al layered double hydroxide (LDHs) were studied under normal gravity condition. Samples with different suspension concentration (SC) were tested for 15 days and the relevant changes in samples were observed through crossed polarizers. Our results showed: (a) the samples were still isotropic (I) when SC < 23 wt%; (b) when 23 wt% < SC < 30 wt%, a shear-induced birefringence appeared after preparation, and finally coexistence of four phases was reached, including an opaque isotropic top phase, a birefringent middle phase, a faint birefringence phase and a sediment layer of larger platelets resulting from the high polydispersity; (c) when SC > 30 wt%, the suspensions were in a gel state, and the gel network slowed down the LCPT. The above different behavior of phase transitions is apparently due to the concentration gradient and fractionation caused by gravity. This study provides guidance on how to select samples of LDHs suspensions for LCPT used in the upcoming experiment in the space program SJ-10 satellite.

•Long chain oil nanoemulsion was formed by W/O microemulsion dilution method.•Nanoemulsions with different charge, even positive charge, were formed W/O microemulsion dilution method.•Thermodynamically stable W/O microemulsion, can be diluted to nanoemulsion on demand, is an alternative to nanoemulsion.•Easy-to-prepare systems in this work show important application, especially in water-based drilling fluids.The preparation of nanoemulsions using long chain oil (C20 to C33) with remarkably small droplet size by microemulsion dilution method is generally difficult. In this work, a simple, W/O microemulsion dilution method was used to prepare O/W nanoemulsions with long chain oil in water/Span 80 − Tween 80/paraffin system. With the increase of dilution temperature from 40 to 80 °C, the emulsion droplet diameter decreased from 1.2 μm to 61 nm. The increase in the amount of dilution water led to the increase of the droplet diameter of nanoemulsions. Meanwhile, nanoemulsions with different charge, even positive charge, were also formed by adding various concentration of Jeffamine (D230) or cetyltrimethylammonium bromide (CTAB) in the W/O microemulsions. More importantly, paraffin nanoemulsions, formed in situ when W/O microemulsion was added to water-based drilling fluids, have effective lubrication and permeability plugging ability. Hence, formation of nanoemulsion by microemulsion dilution method demonstrated here is of great importance for practical applications.

•First, we introduce a novel method of breaking emulsions by using CO2 switchable solvent N,N-dimethylcyclohexylamine (DMCHA).•Second, nowadays, studies on preparation of CO2-responsive emulsions were mainly focused on using switchable surfactants.•Here, we used a conventional surfactant sodium dodecyl benzene sulfonate (SDBS) to prepare CO2-responsive emulsions.•Finally, DMCHA could be separated from the lower water phase upon removal of CO2 and recycled.Figure optionsProposed emulsification and phase separation process.We prepared a CO2 responsive emulsion by using switchable hydrophobic tertiary amine, N,N-dimethylcyclohexylamine (DMCHA). DMCHA exhibits little miscibility with water in the absence of CO2, but shows a complete miscibility with water in the presence of CO2. DMCHA converts to water-soluble bicarbonate salts upon treatment with CO2, which could induce the ionic strength increase of aqueous phase. Together with paraffin oil, DMCHA was used to prepare CO2 responsive O/W emulsions with a conventional surfactant, sodium dodecyl benzene sulfonate (SDBS), as the emulsifier. Emulsions containing DMCHA in paraffin oil were more stable than those without DMCHA, as a result of electrostatic interactions between a small fraction of protonated DMCHA and SDBS, confirmed by surface tension and 1H NMR measurements. However, when exposed to CO2 most of the paraffin oil and water separate from the emulsion with formation of a middle phase microemulsion. More significantly, DMCHA could be separated from the lower water phase upon removal of CO2 and recycled.Schematic illustration of the phase separation process.

In this work, we show the formation of concentrated green O/W nanoemulsion (dispersed phase mass fraction was up to 0.5) by diluting W/O microemulsion in the water/Tween 80/biodiesel system. The mechanism of the formation of nanoemulsions was examined and illustrated by small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM). At high temperature, nanosized droplets formed spontaneously due to the surfactant migration and inversion upon dilution of W/O microemulsions, but these droplets were highly unstable. When cooled to room temperature, their stability was highly enhanced due to the decrease of collision frequency rate and the enhancement of stabilization of the oil/water interface. Even though, the Ostwald ripening still results in growth of droplets of the nanoemulsions after long-term storage, which limits the practical applications of nanoemulsions. W/O microemulsions are thermodynamic systems. Hence, W/O microemulsions that can form nanoemulsions by simple dilution of water can be used as an alternative to O/W nanoemulsion during storage and transport. Furthermore, biodiesel nanoemulsions could meet the requirements of green chemistry and engineering and be used as new green lubricants in water-based drilling fluid.Keywords: Biodiesel; Green lubricant; Nanoemulsion; W/O microemulsion dilution method

This paper reports the influence of emulsification process on the packing of layered double hydroxide (LDH) particles at the aqueous/oil phase interface and the properties of the resulting Pickering emulsions. Emulsions prepared by ultrasonication display superior long-term stability and gel-like characteristics at the dispersed phase volume fraction well below the random close packing limit, whereas emulsions with same compositions prepared by vortex mixing show some extent of sedimentation and liquid-like behaviors. Rheological measurements demonstrate that the zero-shear elastic modulus and yield stress of gel-like emulsions exhibit power-law dependences on particle concentration and independence on aqueous/oil phase ratio. The microstructural origin of this behavior is investigated by optical microscopy, revealing the droplets become strongly adhesive and a heterogeneous percolating network is formed among neighboring droplets. Fluorescent confocal microscopy measurements further confirm that the droplet adhesion is due to particle layers bridging opposite interfaces. In contrast, homogeneous, isolated, and densely packed droplets are present in emulsions prepared by vortex mixing, which results in these systems being dominantly viscous like the suspending fluid. This study shows that the emulsification process can be used as a trigger to modify long-term stability and rheology of solid-stabilized multiphase mixtures, which greatly expands their potential technological applications.

•Nanographite oxide (NGO) was prepared and used as adsorbent to treat p-nitrophenol.•NGO possessed good adsorption ability to p-nitrophenol with rapid reaction time.•The adsorption of p-nitrophenol onto NGO was physisorption and exothermic.Nanographite oxide prepared by a chemical oxidation method was characterized by SEM, XRD, FT-IR, zeta potential and BET surface area. The use of nanographite oxide as an adsorbent to remove p-nitrophenol from aqueous solutions was investigated. Adsorption experiments were carried out as a function of the contact time, initial p-nitrophenol concentration, pH, adsorbent dosage, and temperature. It was found that the nanographite oxide possessed a large surface area and was particularly effective for the removal of p-nitrophenol. The removal efficiency of p-nitrophenol decreased with an increase of the solution pH from 4.0 to 7.0 and an increase in the temperature. The adsorption of p-nitrophenol onto nanographite oxide reached equilibrium within 2 h. The maximum adsorption capacity of nanographite oxide for p-nitrophenol was 268.5 mg/g at 283 K and a natural pH. The Freundlich isotherm was the best choice to describe the adsorption behavior. The kinetic data were presented by the pseudo-second-order kinetic model. The parameters suggested that the adsorption process of p-nitrophenol onto nanographite oxide occurred via physisorption process and was exothermic in nature. Hydrogen-bonding, electron donor–acceptor and Lewis acid/base interactions were the main mechanisms affecting the adsorption capacity, while dispersive interactions were also found to influence the adsorption of p-nitrophenol through the influence of its deactivating functional groups on the aromatic ring. The results showed that nanographite oxide can be used as a new adsorbent which has higher adsorption capacity and faster adsorption rate for the removal of p-nitrophenol.

•Different alkyl chain length surfactants were used to modify Na-montmorillonite.•The organoclays were used as adsorbents for the removal of chlorophenols.•The adsorption process is complex and involves multiple mechanisms.•Adsorption involves partitioning, electrostatic and van der Waals forces.Organoclays were prepared by replacing exchangeable Na+ ions in Na-montmorillonite (Na-Mt) with dodecyltrimethylammonium bromide (DTAB) and cetyltrimethylammonium bromide (CTAB). Organic modification is important in order to obtain good affinity between organoclays and organic pollutants. Hydrophobic DTAB-montmorillonite (DTAB-Mt) and CTAB-montmorillonite (CTAB-Mt) were studied as adsorbents for 4-chlorophenol and 2,4-dichlorophenol. The morphology, structure, and surface properties of Na-Mt and organoclays were characterized by scanning electron microscopy, X-ray diffraction, Fourier infrared spectroscopy, specific surface area, and zeta potential measurements. Adsorption was determined as a function of adsorbent dosage, pH, contact time, and temperature. It was found that pH and temperature had very important effects on the adsorption of chlorophenols. The Langmuir isotherm was the best choice to describe the adsorption behavior. The maximum adsorption capacities of CTAB-Mt for 4-chlorophenol and 2,4-dichlorophenol were 395.0 and 585.8 mg/g, respectively, whereas the maximum adsorption capacities of DTAB-Mt for 4-chlorophenol and 2,4-dichlorophenol were 331.1 and 458.2 mg/g, respectively. The kinetic data fitted the pseudo-second-order kinetic model. Thermodynamic parameters suggested that the adsorption process of chlorophenols onto organoclays was physisorption and exothermic. The adsorption mechanism is a complex process that involves a combination of partitioning, electrostatic attraction, and van der Waals forces.

•The salt stability of MMT dispersions is improved slightly by adsorbing M1000.•M1000 maintains the stability of the high temperature treated MMT suspensions.•PEO causes a weak bridging flocculate for MMT suspensions at high temperature.In this work, a systematical evaluation of a polyetheramine (Jeffamine M1000) and polyethylene oxide (PEO), which have a similar number of ethylene oxide units and molecular weight, on modulating colloidal stability of montmorillonite suspensions after the high temperature treatment (120 °C, 16 h) or in the presence of salt was performed at 25 °C. A varied of methods including measurement of adsorption, X-ray diffraction (XRD), zeta potential, transmission electron microscopy (TEM), settlement experiments and rheology measurements were used to illustrate the difference. Results indicate that M1000 molecules adsorb onto the particles mainly through an ion exchange mechanism and adopt a densely packed mushroom configuration on the clay surface. Because of the adsorption properties of M1000, the salt tolerance is improved slightly (from 10 mmol/L to 50 mmol/L NaCl) and the colloidal stability of the high temperature treated suspensions is maintained. Meanwhile, PEO molecules adsorb onto clay via hydrogen bonding and take a compact conformation on the clay surface, which could not improve the salt tolerance effectively and leads to a weak bridge flocculation at high temperature. Thus, this finding not only provides some new guidance on modulating the colloidal stability of dispersions but also would be very useful in specific applications, such as drilling fluids and water treatment.

•PIC method at elevated temperature was applied to prepare W/O nanoemulsions.•The obtained highly concentrated nanoemulsions have high stability.•Current study discloses an option to prepare W/O nanoemulsions.Phase inversion composition (PIC) method is generally used to prepare nanoemulsions because of its relatively low energy costs and ease of formation. Most of the reported nanoemulsions are usually oil-in-water nanoemulsions. In this work, water-in-oil nanoemulsions in water/Span 80-Brij 35/paraffin oil system were prepared by the PIC method at elevated temperature. This method allows the formation of finely dispersed W/O nanoemulsions in this system. However, macroemulsions rather than nanoemulsions were prepared by PIC method at room temperature. As a result of the significant change of interfacial tension with temperature, the emulsion droplet size decreases from 50 μm to 82 nm with the increase in temperature from 25 °C to 80 °C. The droplet size of nanoemulsions prepared at 80 °C was in the range of 70–200 nm and the internal phase content could reach as high as 60 wt%. The obtained nanoemulsions were stable without obvious change in droplet size in two months. This study provides significant information for optimizing the formation of W/O nanoemulsions.Highly stable concentrated W/O nanoemulsions can be prepared by PIC method at elevated temperature.

The wettability of montmorillonite could be in situ modified by cationic surfactant cetyltrimethylammonium bromide (CTAB). The type and stability of emulsions prepared from montmorillonite with different concentrations of cationic surfactant were investigated, and a double phase inversion of emulsions was observed. The adsorption of CTAB on montmorillonite particles was studied by surface tension and zeta potential measurements, and the variation of the wettability of particles with the concentration of CTAB was characterized by the contact angle measurements. The adsorption of particles at the surface of emulsion droplets was observed by laser-induced confocal scanning microscopy. At low surfactant concentrations, the adsorption of CTAB on montmorillonite increased the hydrophobicity of the particles, and the stability of oil-in-water emulsions was enhanced. With the increase of the CTAB concentration, montmorillonite particles changed from hydrophilic to hydrophobic, and water-in-oil emulsions were obtained. However, at higher surfactant concentrations, the emulsions inverts to O/W again because montmorillonite particles were reconverted into hydrophilic due to the formation of CTAB bilayer on the surface of montmorillonite.

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.

•Low-temperature viscosity of organoclay dispersions can be reduced by PIBSI.•Low-temperature dispersibility of organoclay was largely improved by PIBSI.•PIBSI has little impact on the long-term stability of montmorillonite.•PIBSI adsorbs on the surface of organoclay by hydrogen bonding.•PIBSI provides steric effect and modifies the Hamaker constant of organoclay.In the process of deepwater drilling, maintaining proper low-temperature rheological properties of oil-based drilling fluids and controlling the viscosity of clay dispersions in nonpolar solvents are of great importance. In this work, a dichain polyisobutylenesuccinimide with sufficient viscosity lowering performance was synthesized. The effects of polyisobutylenesuccinimide on low-temperature rheology and dispersibility of organoclay particles in mineral oil were investigated by rheological measurements, sedimentation experiments, optical microscopic observation and transmission electron microscopy. The results indicate that the polyisobutylenesuccinimide is an effective rheological modifier and dispersant at low temperatures in nonpolar solvents. The dispersion mechanism was investigated by Fourier transform infrared spectroscopy, adsorption measurements and X-ray diffraction. The results suggest that the polyisobutylenesuccinimide molecules adsorb on the surface of organoclay particles by hydrogen bonding interactions. The combination of steric stabilization and modification of the Hamaker constant of the particles leads to stable organoclay dispersions. In contrast, polyisobutylenesuccinimide has no significant impact on the long-term dispersibility of unmodified montmorillonite in mineral oil, because of the lower surface coverage.Polyisobutylenesuccinimide (PIBSI) can significantly reduce the viscosity and improve dispersibility of organoclay dispersions in mineral oil at low temperatures. In contrast, PIBSI has no significant effect on long-term stability of montmorillonite. In these figures, OM represents organoclay and MMT indicates montmorillonite.

The roles of a fluorescent dye, methyl orange (MO) in the emulsions stabilized by layered double hydroxide (LDH) particles have been investigated in detail. The hydrophilic LDH particles are rendered partially hydrophobic by the in situ surface modification with MO, leading to the enhanced stability of emulsions. The variation of contact angle, zeta potential and emulsion stability demonstrates the amphiphile-like behaviors of MO. Exploiting the fluorescence of MO, we have shown in situ microscopic images of MO-modified particle adsorption onto droplet surface using confocal fluorescence microscopy. Furthermore, the adsorption of MO-modified LDH on liquid droplet surface has also been exploited to produce hollow colloidosomes, the morphology of which has been observed with SEM.Methyl orange molecules act as fluorescent amphiphiles in emulsions stabilized by layered double hydroxide (LDH) particles.Highlights► Methyl orange acts as a fluorescent amphiphile in Pickering emulsions. ► Methyl orange enhances particle hydrophobicity and improve the emulsion stability. ► In situ microscopic imaging reveals particle adsorption onto the emulsion droplets. ► Hollow colloidosomes have been fabricated with obtained emulsions as templates.

•LDHs-SDS has a hydrophobic surface and great affinity toward organic dyes.•LDHs-SDS effectively remove anionic, cationic and nonionic dyes from wastewater.•The treatment of LDHs-SDS to an actual dye wastewater proved to be favorable.Organic dyes are an important class of pollutants in wastewater, and it is necessary to find a broad-spectrum adsorbent that can effectively remove different kinds of organic dyes. Through the organic modification of layered double hydroxides (LDHs), the surface properties of the LDHs change from hydrophilic to hydrophobic, resulting in a greater affinity for organic pollutants. Dodecylsulfate-intercalated layered double hydroxide (LDHs-SDS) was prepared with a Mg/Al molar ratio of 2:1 using a co-precipitation method, and was characterized by X-ray diffraction and Fourier transform infrared spectroscopy. The synthesized LDHs-SDS was used as an adsorbent to remove anionic (direct blue G-RB (DB), reactive yellow 4GL (RY), acid red GR (AR)), cationic (basic blue (BB)) and nonionic dyes (disperse red 3B (DR)) from aqueous solution. The sorption was found to be independent of pH from 5 to 10. The maximum removal capacities for DB, RY, AR, DR and BB were 707.76, 392.88, 137.33, 249.24 and 165.11 mg/g, respectively, at 298 K. The adsorption isotherm for AR fitted the Freundlich model well, and data for the other dyes fitted the Langmuir model. The sorption kinetics of all five dyes were well described by the pseudo-second-order model. After treating actual dye wastewater with LDHs-SDS, the results indicate that this could be a potentially effective adsorbent for dye effluent treatment.

•Surface modification of Na-MMT in alkane solvents results in its dispersion.•OMMT has been prepared in alkane solvents based on ion exchange reaction.•This dispersion method is proposed to be used for rheology control.The surface properties of a natural sodium montmorillonite (Na-MMT) was dramatically altered by a cationic surfactant dioctadecyldimethylammonium chloride (DODMAC) through an intercalation and ion exchange reaction in alkane solvents. Optical micrographs show that in situ organo-modification with surfactant DODMAC significantly improves the dispersibility of Na-MMT in alkane solvents. Changes in the structure and surface properties of the organophilic montmorillonite (OMMT) formed in octane, a volatile alkane, were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), thermogravimetric analysis (TGA/DTG) and Fourier transform infrared spectroscopy (FTIR). It is shown that organo-modification of Na-MMT surfaces based on ion exchange reaction in alkane solvents results in dispersion of the hydrophilic Na-MMT in the organic medium. And most importantly, viscosity curves of the clay suspensions suggest a potential method to control the rheological behavior of dispersions in alkane solvents instead of using organophilic montmorillonites. Furthermore, dispersion approaches and mechanism presented here will be useful for choosing compatibilizer and optimizing processing conditions especially in developing pristine-clay polymer nanocomposites.

This paper focuses on the influence of Ca2+ binding and temperature on the molecular size and hydrophilicity of sulfonic acid type polymers. Two different molecule structural polymers employed were sodium polystyrene sulfonate and poly(2-acrylamido-2-methyl-1-propane-sulfonic acid). The effect of CaCl2 and high temperatures on the polymer molecules was explored with gel permeation chromatography, calcium ion selective electrodes, Fourier transform infrared spectroscopy, transmission electron microscopy, dynamic light scattering, rheology, and surface tension measurements. The results indicate that high temperatures promote the binding of calcium ions with the two polymers and also lead to dehydration of the polymer chains. The variation rule of molecular size, apparent viscosity and surface tension of the two sulfonic acid type polymers depended on their molecular structure.Graphical abstractPossible explanation for the effect of heat treatment and CaCl2 addition on the structure and distribution of PSS in aqueous solution. The black curves represent the PSS molecules and the orange circles indicate the calcium ions.Highlights► The combination of Ca2+ on PSS increased with temperatures and salt concentrations. ► The effect of Ca2+ and temperatures on polymers depended on the molecular structure. ► The hydrophobicity of PSS increased with concentrations of salt and temperatures. ► Some aggregates formed in the PSS system with high salt by heated treatment.

A novel Ca2+ ion responsive particulate emulsifier, which is based on copolymer nanoaggregates, is reported in this work. Results from dynamic light scattering (DLS) and cryo-transmission electron microscopy (cryo-TEM) indicate that the formation of poly (4-styrenesulfonic acid-co-maleic acid) sodium salt (PSSMA) nanoaggregates is strongly dependent on Ca2+ concentration. The PSSMA copolymer only aggregates above a critical Ca2+ concentration (0.2 M) with an average diameter of 10–40 nm. After dilution with water, PSSMA nanoaggregates are rapidly redissolved again. On the basis of the properties of PSSMA nanoaggregates, Ca2+ ion responsive Pickering emulsions were successfully prepared. At high Ca2+ concentrations, the emulsions with high stability against coalescence can be prepared with the size in the submicrometer range as determined by DLS. Cryo-TEM and dynamic interfacial tension results confirm the adsorption of PSSMA nanoaggregates at the interface, which is the key to the stability of the emulsions. More importantly, rapid demulsification can be achieved by dilution with water on demand. It is because, upon dilution with water, PSSMA nanoaggregates undergo a transition from stable nanoaggregates to individual polymer chains, which leads to interfacial desorption of nanoaggregates and rapid demulsification of emulsions. Thus, this finding presents a new manipulation on emulsion stability and is expected to provide a useful guidance in the fields of oil recovery, food science, environment protection, and so on.

Oil-in-water nanoemulsions were produced in the system water/Span 80–Tween 80/paraffin oil via the phase inversion composition (PIC) method at elevated temperature. With the increase of preparation temperature from 20 to 70 °C, we found that the emulsion droplet diameter decreases from 10.3 μm to 51 nm, proving the formation of nanoemulsions. The viscosity of nanoemulsions clearly increases with droplet volume fraction, φ, but the droplet size changes less. Significantly, at φ ≤ 0.5, the size distribution of nanoemulsions can be kept unchangeable more than 5 months. These results proved that the highly viscous paraffin oil can hardly be dispersed by the PIC method at 25 °C, but the increase in preparation temperature makes it possible for producing monodisperse nanoemulsions. Once the nanoemulsion is produced, the stability against Ostwald ripening is outstanding due to the extremely low solubility of the paraffin oil in the continuous phase. The highly stable nanoemulsions are of great importance in practical applications.

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.

Dispersion stability of organoclay (surfactant-modified montmorillonite) in nonpolar solvents can be dramatically improved by adding nonionic surfactants sorbitan monoleate (Span 80), sorbitan trioleate (Span 85) and 1-oleoyl-rac-glycerol (GMO). The effects of the surfactants on the basal spacing, size and surface potential of organoclay were investigated. The increase of the basal spacing of organoclay indicated that the surfactants have intercalated into the organoclay interlayer, which promoted the exfoliation of organoclay. Correspondingly, the reduction of the size of organoclay particles was observed. We also measured the surface potential of organoclay and found it increased with the surfactant concentration and then reached a constant value. The adsorption behavior of surfactants on the particles and the variation of the surface potential of the particles were in consistent with the dispersion stability of organoclay in nonpolar solvents. We believe that the improvement of the dispersion stability caused by adding a nonionic surfactant is the result of the combination of steric and electrostatic effects.Graphical abstractThe adsorption of Span 80 on organoclay in octane could increase the particle surface potential and improve the dispersion stability.Highlights► Dispersion of organoclay in octane could be stabilized by nonionic surfactants. ► Nonionic surfactant adsorbed at the surface and entered the interlayer of organoclay. ► The adsorption of nonionic surfactants increased the surface potential of particles. ► The stability is improved by a combination of steric and electrostatic effects.

Different from traditional methods for preparing pH-switchable Pickering emulsifiers, a simple and straightforward approach is established on the basis of a reversible process between in situ formation and dissolution of Mg(OH)2 nanoparticles (MHp). It was found that when pH value was above 9.5, emulsions of liquid paraffin-in-water can be stabilized by the resulting surface-active particles. Below this pH, emulsions demulsify, resulting in a reversible Pickering emulsifier. Based on the strongly pH-dependent precipitation of metal hydroxide nanoparticles, this procedure offers a new way to design pH-switchable emulsifiers without aid of any other organic matters.Graphical abstractIn situ formed magnesium hydroxide nanoparticles could be used not only as a excellent emulsifier but also with excellent pH-switchability.Research highlights► In situ formed magnesium hydroxide nanoparticles (MHp) could served as a excellent emulsion stabilizer. ► Owing to strong pH dependence during precipitation of MHp, MHp shows excellent pH-dependent and reversibility, which make it with pH-switchability for emulsion stability. ► The key rule for such phenomenon is a pH reversibility between ionic form and particle form, which may be applied to other metal hydroxide nanoparticles.

Herein we offer a simple method to produce non-spherical emulsion droplets stabilized by freshly formed Mg(OH)2 nanoparticles (MPs). The non-spherical degree of droplets as a function of experiment conditions was investiged and the origins of the presence of non-spherical dropelts were discussed. The results of optical microscope images show that stable spherical droplets can be fused into non-spherical at given aging temperature. It is also recognized that particle concentration, oil/water ratio and aging time significantly affect droplet fusion and excess particles that are not adsorbed on the oil/water interface are helpful in restraining droplet fusion. Based on the TEM, XRD and Fluorescence confocal microscopy results, the origins of droplet fusion are inferred from the presence of vacant holes in the particle layer. Because of Oswald ripening, particles on droplet surfaces grow larger than the freshly precipitated ones under a given aging temperature. The growth of particles results in the reduction of total cover area of particle layer and thus creates vacant holes in the particle layer which would cause partial coalescence of droplets once they collide. Thus, these findings can offer a simple alternative to obtain a large amount of non-spherical emulsion droplets but also can help the preparation of non-spherical colloid particles.Graphical abstractAging temperature induces the formation of non-spherical emulsion droplets and the origins are attributed to the partial coalescence which is resulted from the particle size growth and the decrease of particle coverage on the droplet surface.Highlights► Non-spherical emulsion droplets could be obtained by aging spherical emulsion droplets stabilized by freshly precipitated magnesium hydroxide nanoparticles at certain temperature. ► Particle concentration, oil/water ratio, aging temperature and aging time remarkably influence the formation of non-spherical emulsion droplets. ► The decrease of particle coverage on the droplet surface is the origin of non-spherical emulsion droplet formation.

Paraffin oil/water nano-emulsions stabilized by Tween 80/Span 80 were prepared using the phase inversion temperature (PIT) method in the presence of inorganic salts. The influence of different kinds of inorganic salts on the PIT, electrophoretic properties and long-term stability of the nano-emulsions was studied by conductivity measurements, zeta potential measurement and dynamic light scattering. It was found that, for a system with high PIT, an optimum PIT can be obtained in the presence of salting-out salts, and thus a stable emulsion can be prepared. The salts reduce the absolute value of the zeta potential of the nano-emulsion droplets and influence their long term stability. By analyzing the evolution of emulsion droplet size with time, the main instability mechanisms of the nano-emulsions were found to be Ostwald ripening and/or coalescence.Graphical abstractResearch highlights▶ Paraffin oil/water nano-emulsions stabilized by a mixture of Tween 80 and Span 80 were prepared using the PIT method in the presence of inorganic salts. ▶ For a system with high PIT, an optimum PIT can be obtained by adding appropriate amounts of salting-out salts. ▶ The influence of inorganic salts on zeta potential and long term stability of nano-emulsions prepared by the PIT method was firstly studied.

The inhibition of hydration and dispersion of drilling cuttings and maintaining of proper flow properties of drilling fluids play a significant role in a successful drilling process. In this work, we show that low molecular weight polyetheramine provides sufficient inhibiting performance while it has no effect on the rheological properties of clay dispersions. The inhibition mechanism was explored with adsorption, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), contact angle, sedimentation and rheology measurements. The results indicate highly affinitive Langmuir type adsorption behaviors of polyetheramine on clay particles. The expansion of clay gallery height suggests that polyetheramine molecules intercalate into MMT interlayers. The adsorption of polyetheramine increases the hydrophobicity of MMT particle surface. The formation of a hydrophobic shell on the particle surfaces and the intercalation of polyetheramine in the clay gallery are believed to be the main inhibition mechanism of polyetheramine. Rheological measurement demonstrates that polyetheramine has no effect on the viscosity of prehydrated clay dispersions, which further proves this kind of polyetheramine can be used as superior inhibitors in water based drilling fluids.Graphical abstractHighlights► The adsorption of poly(oxypropylene)diamine (D230) on montmorillonite inhibits the dispersion of clay particles into aqueous solution. ► The increase of the surface hydrophobicity and the intercalation of D230 in the interlayer are believed to be the main inhibition mechanism. ► D230 has no effect on the viscosity of prehydrated montmorillonite dispersion, which proves that it can be used as superior inhibition additive in water based drilling fluids.

The addition of salt promotes the adsorption of layered double hydroxide (LDH) particles onto the air–water interface, but stable foams cannot be prepared from LDH dispersions at all the concentration of NaCl or sodium acetate. We generated stable foams using positively charged plate-like LDH particles in the presence of sodium butyrate. The effects of adding sodium butyrate to LDH on the particle zeta potential, adsorption behavior and the adsorption of modified particles at the air–water interface were studied. At a fixed LDH particle concentration, adding of a trace amount of sodium butyrate maximizes flocculation of the aqueous particle dispersion. Foams prepared under this condition of particle dispersion are most stable to coalescence and halt completely disproportionation. Also, the size of the bubbles is the smallest. The bubbles are stable when drying at 80 °C with little change in size. Laser-induced fluorescent confocal micrographs and scanning electron microscopy observations clearly confirm the adsorption of LDH particles on the foam surfaces, and the bubbles are armored by an interfacial particle multilayer.SEM images of foams stabilized by butyrate anions-modified LDH particles at low and high sodium butyrate concentrations. The initial sodium butyrate concentrations are (a) 25 mM (b) 100 mM.

Liquid paraffin−water emulsions were prepared by homogenizing oil phases containing sorbitan oleate (Span 80) and aqueous phases containing layered double hydroxide (LDH) particles or Laponite particles. While water-in-oil (w/o) emulsions are obtained by combining LDH with Span 80, the emulsions stabilized by Laponite−Span 80 are always o/w types regardless of the Span 80 concentration. Laser-induced fluorescent confocal micrographs indicate that particles are absorbed on the emulsion surfaces, suggesting all the emulsions are stabilized by the particles. The difference of the particle-stabilized emulsion type may be explained by comparing particle contact angles and the oil−water interfacial tensions, indicating that more Span 80 molecules are adsorbed on the LDH particles than on Laponite. Apparently, the LDH particles are rendered more hydrophobic by Span 80, resulting in the formation of w/o emulsions. The long-term stability of the emulsions was also compared. Emulsions stabilized by Span 80 alone completely separate into two bulk phases of oil and water after 3 months. However, emulsion stability is greatly enhanced with the addition of LDH or Laponite particles. This synergism was accounted for by an increase of the dilational viscoelasticity modulus of the oil−water interface after particles were added to the aqueous phase. This increase indicates that the gel-like particle layer stays at the oil−water interface and resists emulsion coalescence. Scanning electron microscope (SEM) images display the presence of a firm layer surrounding the emulsion droplets and a three-dimensional particle network which extends into the bulk phase aiding emulsion stability.

Liquid paraffin–water emulsions were prepared which were stabilized by Laponite particles in situ modified with poly(oxypropylene)diamines in the absence of electrolytes. First, the characteristics of the Laponite dispersions in the presence of increasing concentrations of diamines were studied in detail. Infrared absorption spectra and zeta potential measurements confirm the adsorption of diamines on the Laponite particles. Adsorption isotherms further indicate highly affinitive L-type behaviors and the diamine molecules are deduced to lie with both end groups anchored on the particle surface and the poly(oxypropylene) chain exposed to the aqueous solution. Then, emulsions were prepared using the diamine-modified particles. Diamines and Laponite particles alone are ineffective emulsifiers, but a strong synergism is exhibited between them. Laser-induced fluorescent confocal micrographs and TEM observations demonstrate the arrangement of the particles on the emulsion surfaces and also reveal the stability mechanisms. The emulsion stability was also explored with optical microscopy and droplet size measurements. As the diamine concentration increases, the extent of emulsion creaming decreases and the droplet size correspondingly decreases. At a certain low diamine concentration, the extent of emulsion creaming decreases down to a minimum and the corresponding droplet size is the smallest. This optimal emulsion state is unchanged when the diamine concentration is further increased.

We investigated the behavior of foams stabilized by Laponite nanoparticles combined with alkylammonium bromides with different alkyl chain lengths. A four-region model based on electrostatic and hydrophobic interactions adequately explains the adsorption of the cationic surfactants on the negatively charged Laponite particles. The results indicate that chain length has a minimal influence on surfactant adsorption via cation exchange, but a longer alkyl chain length can induce a stronger hydrophobic interaction among the adsorbed alkylammonium molecules and hence a higher surfactant adsorption. Adsorption of surfactants on the Laponite particles is crucial to foam stability. Surfactant addition initially transforms particles from anionic to uncharged and hydrophobic and subsequently to cationic as a result of adsorption. The foam experiments indicate that the most hydrophobic particles, possessing an adsorbed monolayer of surfactant, yield foams which are completely stable to disproportionation and coalescence. As the surfactant chain lengths increase from C12 to C16, the characteristic features of the adsorption isotherm are lowered by approximately an order of magnitude. For surfactants with longer alkyl chain surfactants, stable foams are obtained at lower concentrations.

Paraffin wax-in-water submicron emulsions stabilized by Span 80/Tween 80 were prepared by the emulsion inversion point (EIP) method. Stable emulsions with droplet diameters about 700 nm could be formed when the hydrophilic–lipophilic balance (HLB) values are between 9.5 and 10.3 and the surfactant-to-oil ratio is above 0.2. Increased emulsification temperature and cooling rate were found to improve the emulsion properties. Either mixing all components together or addition of oil to the aqueous surfactant dispersion could not produce stable emulsions. Optical microscopy and scanning electron microscopy (SEM) were used to study the morphology of the emulsion droplets. The droplets were solid at room temperature, showing bright spots under polarized light and an irregular spheres shape under SEM. Due to homogeneous nucleation in the finely dispersed emulsion droplets, the emulsion shows a large degree of undercooling (15 °C) in the differential scanning calorimetry (DSC) thermogram. The emulsions became unstable with heating, but remained stable under cooling. The electrophoretic properties of emulsion droplets showed a negative zeta potential, which was increased with the pH of the system due to the adsorption of hydroxyl groups.

The foamability and foam stability of hydrophilic silica particles (A200) and cationic surfactant cetyltrimethylammonium bromide (CTAB) dispersion in the presence and absence of liquid paraffin were evaluated by interface tension, zeta potential and dilatational rheology. At low surfactant concentration, both the foamability and foam stability of A200/CTAB dispersion in the presence of liquid paraffin are decreased, due to the low coverage degree of silica particles on the air/water interface of the foam films. At the intermediate surfactant concentration, in the absence of liquid paraffin, the foam stability is enhanced by the adsorption of silica particles on the air/water interface. In the presence of liquid paraffin, there is a synergistic stabilization by the adsorption of hydrophobically modified silica particles and oil droplets on the air/water monolayer of foam film. At the same surfactant concentration range, the foamability increases until a plateau value is reached. At high surfactant concentration, the surface of silica particles is hydrophilic and so the silica particles become to disperse in the aqueous phase again. In this case, both the air/water and oil/water interfaces are mainly covered by CTAB molecules, resulting in a slight decrease of foam stability.

In this paper, we report the preparation of aqueous suspensions of Ni/Al layered double hydroxide (LDH) nanoparticles by a non-steady co-precipitation followed by peptization. By choosing suitable peptization temperature and time, well-dispersed suspensions were obtained. Meanwhile, the particle size, shape and size polydispersity can be efficiently controlled. Nematic ordering is observed in colloidal Ni/Al LDH suspensions and confirmed by birefringence observations and SAXS measurements. Furthermore, we showed that the sol–gel transition takes place after a liquid crystalline phase transition in concentrated Ni/Al LDH suspensions. The absence of isotropic–nematic phase separation can be attributed to the fact that the nematic phase droplets are too small to settle to the bottom of the cuvette.Well-defined Ni/Al LDH nanoparticles were prepared and nematic ordering confirmed by birefringence observations and SAXS measurements is observed in concentrated Ni/Al LDH suspensions.

Stable foams have been generated in low concentration aqueous dispersions of hexylamine-modified Laponite particles. The particles are of primary size 30 nm, modified with hexylamine molecules to render them partially hydrophobic or moderate flocculants. Infrared adsorption spectra and zeta potential measurements confirm the adsorption of hexylamine molecules on the Laponite particles. The foamability, drainage behavior and microstructure of wet foams were studied in terms of their dependence on the content of Laponite particles and the concentration of hexylamine. Laser-induced confocal microscopy observations confirm that stable bubbles appear to be surrounded by a thin layer of hexylamine-modified Laponite particles, which is crucial to the stability of foams. The interfacial rheology of the same systems has been also investigated by measuring the dilational viscoelasticity as a function of hexylamine concentrations. The adsorption of particles at the air–water interface has the effect of increasing dilational surface elasticity, indicating that the gel-like layer at the interface inhibits foam drainage and bubble coalescence.

We investigated the effect of nonadsorbing polymer on the phase behavior of suspensions of positively charged Mg2Al layered double hydroxide (LDH) platelets by birefringence observations and rheological measurements. We show that the depletion attraction, induced by the addition of a high-molecular-weight polyvinyl pyrrolidone (PVP), enriches the phase behavior of these electrostatically stabilized suspensions. At intermediate LDH and polymer concentration, two isotropic phases (I1−I2) coexist, nematic−nematic (N1−N2) demixing occurs, and a sediment phase is observed, with the appearance of two-, three-, four-, and even six-phase coexistence. Upon increasing the polymer concentration, the I−N phase transition and the sol−gel transition shift to lower LDH concentrations; meanwhile, the I−N coexistent samples enter the purely nematic phase. We explain the richness of the phase behavior in such LDH−PVP mixtures by discussing the interactions among PVP-induced depletion attraction, particle polydispersity, and particle sedimentation.

A liquid paraffin−water emulsion was investigated using layered double hydroxide (LDH) particles and sodium dodecyl sulfate (SDS) as emulsifiers. Both emulsifiers are well-known to stabilize oil-in-water (o/w) emulsions. Surprisingly, a double phase inversion of the emulsion containing LDH particles is induced by the adsorption of SDS. At a constant LDH concentration, the emulsion is o/w type when SDS concentrations are low. At intermediate SDS concentrations, the first emulsion inversion from o/w to w/o occurs, which is attributed to the enhanced hydrophobicity of LDH particles caused by the desorption of the second layer of surfactant, leaving a densely packed SDS monolayer on the LDH exterior surfaces. The second inversion from water-in-oil (w/o) to o/w occurs at higher SDS concentrations, which may be due to the competitive adsorption at the oil/water interfaces between the LDH particles modified by the SDS bilayers and the free SDS molecules in the bulk solution, but the free SDS molecules dominate and determine the emulsion type. Laser-induced fluorescent confocal micrographs clearly confirm the adsorption of LDH particles on the surfaces of the initial o/w and intermediate w/o emulsion droplets, whereas no LDH particles were adsorbed on the final o/w emulsion droplet surfaces. Also, transmission electron microscopy (TEM) observations indicate that the shape of the final o/w emulsions is similar to that of the monomeric SDS-stabilized emulsion but different from that of the initial o/w emulsions. The adsorption behavior of SDS on LDH particles in water was investigated to offer an explanation for the emulsion double phase inversion. The zeta potential results show that the particles will flocculate first and then redisperse following surfactant addition. Also, X-ray diffraction (XRD) measurements indicate that SDS adsorption on the LDH interior surfaces will be complete at intermediate concentrations.

Fe3O4 nanoparticles coated with oleic acid bilayer (a diameter about 12 nm) were synthesized. The structure and composition of the particles were analyzed by TEM, FTIR and TGA. The TGA experiments of the bilayer-coated particles show a distinct two-stage mass loss. Partition experiments show that the modified Fe3O4 nanoparticles are affected by aqueous dispersion pH and ion strength. Accordingly, the Pickering emulsions stabilized by modified Fe3O4 particles are also sensitive to pH and ion strength. The phase inversion of the emulsions occurs when 1.0013.50pH>13.50. The phase inversion of emulsions also can be adjusted by the ion strength. In interfacial adsorption experiments, the hydrophobic Fe3O4 nanoparticles form particle clusters, while the hydrophilic particles form uniform multilayers.The stability of Pickering emulsions stabilized by 1.0 wt% modified Fe3O4 nanoparticles. The emulsion types change from W/O to O/W, then to W/O with increasing pH.

HypothesisHydrophobic modification can influence interparticle interaction, their interfacial adsorption, and stability of particle-stabilized emulsions. Emulsions stabilized by rodlike particles are more stable than those prepared with spherical particles even at low concentrations. Moreover, interfacial adsorption of particles will be tuned by controlling the modification. Thus, it is possible to prepare stable W/O emulsions with in-situ modified rodlike particles.ExperimentsRodlike sepiolite particles were in-situ modified in oil using dimethyldioctadecylammonium chloride (DODMAC). High salinity solution (water) in paraffin oil (W/O) emulsion was prepared with the modified particles. Stability of emulsions at room temperature and after aging at 160 °C for 24 h was studied. Mechanism of emulsion stability was explored by rheological measurements and confocal fluorescent microscopy.FindingsRemarkable stability against coalescence was found at high temperature. The enhanced stability is due to the high viscosity of continuous phase. Moreover, modification of sepiolite particles at high DOMDAC concentrations enhances particle adsorption at water-oil interfaces and network in continuous phase, which improve the stability against sedimentation and coalescence of the W/O emulsions.