Highly Concentrated Emulsions Research Articles

Mechanically robust and anisotropic hydrogel composites for high efficiency steam generation

Solar-driven interfacial evaporation (SDIE) has now become a promising desalination technique to harvest fresh water, and challenges remain to develop high performance solar evaporators that can achieve high performance SDIE while at the same time maintain good mechanical properties. In this work, anisotropic Polydopamine (PDA)/polyvinyl alcohol (PVA)@acidified carbon nanotubes (ACNTs) hydrogels (PPCHs) are prepared for SDIE and dye adsorption. The introduction of PDA and ANCTs improves the overall mechanical properties of the hydrogels and also imparts the hydrogel abundant active adsorption sites. PPCHs possess hierarchically vertical channels and hence powerful water transport capability. The PPCH evaporator with reduced water enthalpy exhibits high evaporation rate and efficiency, up to 3.43 kg m−2 h−1 and 91.6 % even during the long-term evaporation, respectively. In addition, PPCH can also work stably in harsh conditions such as high concentration brine, emulsions, acid and alkali solutions, etc. Due to the electrostatic interaction, PPCHs can effectively adsorb methylene blue (MB) in wastewater. PPCHs show broad application prospects in the field of solar desalination and dye adsorption. This study provides a rational structure design of the hydrogel composites for simultaneous SDIE and organic pollutant removal.

Determination of chiral prothioconazole and its chiral metabolite in water, juice, tea, and vinegar using emulsive liquid–liquid microextraction combined with ultra-high performance liquid chromatography

Emulsive liquid–liquid microextraction (ELLME), a simple, rapid, and environmentally friendly technique, was established to identify chiral prothioconazole and its chiral metabolite in water, juice, tea, and vinegar using ultra-high-performance liquid chromatography (UPLC). Environmentally friendly extractant was mixed with pure water to prepare a high-concentration emulsion, which was added to samples to complete the emulsification and extraction in 1 s. Afterward, an electrolyte solution was added to complete the demulsification without centrifugation. ELLME did not use dispersants compared to the familiar dispersive liquid–liquid microextraction (DLLME), thus reducing the use of toxic solvents and avoiding the effect of dispersants on the partition coefficient. The linear range was from 0.01 to 1 mg/L. The limit of detection was 0.003 mg/L. The extraction recoveries ranged from 82.4 % to 101.6 %, with relative standard deviations of 0.7–5.2 %. The ELLME method developed has the potential to serve as an alternative to DLLME.

Preparation of high complex concentration emulsion stabilized by soy protein/dextran sulfate composite particles.

Soy protein isolate (SPI) could be used as an emulsifier to stabilize emulsions, while SPI is unstable under low acidic conditions. The stable composite particles of SPI and dextran sulfate (DS) could be formed by the electrostatic interaction at the pH was 3.5. And the SPI/DS composite particles were used to prepare the high complex concentration emulsion. The stabilization properties of high complex concentration emulsion were investigated. Compared to uncompounded SPI, the particle size of SPI/DS composite particles was smaller at 1.52 μm, and the absolute value of the potential increased to 19.9 mV when the mass ratio of SPI to DS was 1:1 and the pH was 3.5. With the DS ratio increased, the solubility of the composite particles increased to 14.44 times of the untreated protein at pH 3.5, while the surface hydrophobicity decreased. Electrostatic interactions and hydrogen bonds were the main forces between SPI and DS, and DS was electrostatically adsorbed on the surface of SPI. The emulsion stability significantly enhanced with the increase of complex concentration (38.88 times higher than at 1% concentration), the emulsion average droplet size was the lowest (9.64 μm), and the absolute value of potential was the highest (46.67 mV) when the mass ratio of SPI to DS was 1:1 and the complex concentration of 8%. The stability of the emulsion against freezing was improved. The SPI/DS complex has high solubility and stability under low acidic conditions, and the SPI/DS complex' emulsion has a well stability. This article is protected by copyright. All rights reserved.

Experimental Study on Concentration Effects on the Supercooling of Phase Change Material-in-Water Nanoemulsions

In energy storage, energy transfer and thermal management applications, phase change material (PCM) nanoemulsions are promising; however, supercooling has always been an important issue in the research and application of PCMs. When supercooling occurs, the efficiency of energy storage applications may possibly be reduced. In this study, n-octadecane and n-eicosane (as core materials), and nonionic surfactants (hydrophile-lipophile balance value = 8) were used to prepare n-octadecane and n-eicosane emulsions with a mass concentration of 1–9%. The effects of particle size and operation temperature on emulsion viscosity were investigated, and the relationships between supercooling and the PCM particle size, PCM concentration and process cooling rates were analyzed. The results showed that small PCM particles could form a 2nd freezing point far from the melting point, resulting in a large supercooling degree. As the process cooling rates increased, the supercooling became more pronounced. However, when the high-concentration emulsion was mainly composed of small particles and subjected to low cooling rates, the concentration effect was significant, thereby decreasing the supercooling effect.

Evaluating of the performance of natural mineral vermiculite modified PVDF membrane for oil/water separation by membrane fouling model and XDLVO theory

A novel vermiculite nanoparticles (Verm NPs) modified poly(vinylidene fluoride) (PVDF) ultrafiltration membrane was firstly fabricated via surface coating at pH 7.2–7.3. The dense but porous modified surface formed by controlling the self-polymerization rate of dopamine at relatively weak alkalinity provided both high water flux and rejection rate of BSA, which broke the trade-off between permeability and rejection rate. The contact angle of optimal modified membrane decreased from 69.6° to 45.0°, showing the effectively enhancement of hydrophilicity. By filtrating two kinds of real oil-in-water emulsions, the stable flux of modified membrane was approximately 2 times higher than that of pristine membrane for both low and high concentration oil-in-water emulsions. In addition, the Verm-PVDF membrane also showed a higher removal efficiency of oil and total organic carbon. According to membrane fouling model analysis, the fouling behavior including adsorption, deposition, blockage of membrane pores and formation of cake layer had obviously alleviated after Verm modification for the two kinds of oil-in-water emulsions due to the formation of water layer by isomorphism substitution and surface hydroxylation of Verm NPs. Assessed by extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, Verm-PVDF membrane exhibited a higher energy barrier and an extremely strong repulsive force for foulants to overcome in low and high concentration emulsions during fouling. Overall, the improved antifouling ability and separation performance of modified membrane indicated that the inartificial Verm NPs was a robust material for pH-control membrane modification with potential application value in oil/water separation.

Factors affecting the formation of highly concentrated emulsions and nanoemulsions

Highly concentrated (HC) emulsions and or submicron emulsions arise as an interesting strategy to encapsulate and transport labile lipophilic bioactive compounds such as curcumin to be further incorporated into food formulations. The main factors affecting HC-emulsions formation and stabilization are the homogenization process, the oil volume fraction (φ) and the surfactant to oil ratio (SOR). Therefore, different HC emulsions were prepared by high-shear homogenization (HSH; 11,000 rpm, 2 min), ultrasonication (US; 100 μm, 20–300 s) or microfluidization (MF; 800 bar, 1–5 cycles) varying the φ from 0.4 to 0.7 (40%–70% w/w) and the SOR from 0.01 to 0.2. HSH led to HC emulsions, whose particle sizes decreased from 14.46 to 2.42 μm (d43), as the φ increased from 0.4 to 0.7. However, US and MF provoked the droplet breakup at oil concentrations over 50% w/w. Additionally, the higher the SOR at a fixed φ, the smaller the particle size of the resultant HC emulsions regardless the homogenization procedure applied. Overall, particle size reduction produced a dramatic increase in emulsion viscosity due to a high packing state of droplets that in turn prevented droplets re-coalescence. Moreover, HC emulsions presented a high curcumin encapsulation efficiency (>70%) and release (> 80% after 48 h is). Therefore, this work contributes to demonstrate that the small droplets size is governing the apparent viscosity in HC systems, as well as to elucidate the factors affecting their formation to be used as potential carriers of lipophilic bioactive compounds.

Effect of Organic Modification on Multiwalled Carbon Nanotube Dispersions in Highly Concentrated Emulsions.

Highly concentrated water-in-oil emulsions incorporating multiwalled carbon nanotubes (MWCNTs) are prepared. Homogeneous and selective dispersions of MWCNTs throughout the oil phase of the emulsions are investigated. The practical insolubility of carbon nanotubes (CNTs) in aqueous and organic media necessitates the disentanglement of CNT “agglomerates” through the utilization of functionalized CNTs. The design and synthesis of two tetra-alkylated pyrene derivatives, namely, 1,3,6,8-tetra(oct-1-yn-1-yl)pyrene (TOPy) and 1,3,6,8-tetra(dodec-1-yn-1-yl)pyrene (TDPy), for the noncovalent organic modification of MWCNTs are reported. The modifier molecules are designed in such a manner that they facilitate an improved dispersion of individualized MWCNTs in the continuous-oil phase of the highly concentrated emulsion (HCE). Transmission electron microscopic analyses suggest that the alkylated pyrene molecules are adsorbed on the MWCNT surface, and their adsorption eventually results in the debundling of MWCNT agglomerates. Fourier transform infrared, Raman, and fluorescence spectroscopic analyses confirm the π–π interaction between the alkylated pyrene molecules and MWCNTs. The noncovalent modification significantly improves the effective debundling and selective dispersion of MWCNTs in HCEs.

A Combined XRD, Solvatochromic, and Cyclic Voltammetric Study of Poly (3,4-Ethylenedioxythiophene) Doped with Sulfonated Polyarylethersulfones: Towards New Conducting Polymers.

Despite the poor solubility in organic solvents, poly (3,4-ethylenedioxythiophene) (PEDOT) is one of the most successful conducting polymers. To improve PEDOT conductivity, the dopants commonly used are molecules/polymers carrying sulfonic functionalities. In addition to these species, sulfonated polyarylethersulfone (SPAES), obtained via homogeneous synthesis with different degrees of sulfonation (DS), can be used thanks to both the tight control over the DS and the charge separation present in SPAES structure. Here, PEDOTs having enhanced solubility in the chosen reaction solvents (N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and N-methyl-2-pyrrolidone) were synthesized via a high-concentration solvent-based emulsion polymerization with very low amounts of SPAES as dopant (1% w/w with respect to EDOT monomer), characterized by different DS. The influence of solvents and of the adopted doping agent was studied on PEDOT_SPAESs analyzing (i) the chemical structure, comparing via X-ray diffraction (XRD) the crystalline structures of undoped and commercial PEDOTs with PEDOT_SPAES’ amorphous structure; (ii) solvatochromic behavior, observing UV absorption wavelength variation as solvents and SPAES’ DS change; and (iii) electrochemical properties: voltammetric peak heights of PEDOT_SPAES cast onto glassy carbon electrodes differ for each solvent and in general are better than the ones obtained for neat SPAES, PEDOTs, and glassy carbon.

Fabrication and Characterization of Quinoa Protein Nanoparticle-Stabilized Food-Grade Pickering Emulsions with Ultrasound Treatment: Interfacial Adsorption/Arrangement Properties.

The natural quinoa protein isolate (QPI) was largely reflected in the nanoparticle form at pH 7.0 (∼401 nm), and the ultrasound at 20 min progressively improved the contact angle (wettability) and surface hydrophobicity of the nanoparticles. Ultrasound process also modified the type of intraparticle interaction, and the internal forces of sonicated particles were largely maintained by both disulfide bonds and hydrophobic interaction forces. In emulsion system, the ultrasound progressively increased the emulsification efficiency of the QPI nanoparticles, particularly at high protein concentration ( c > 1%, w/ v) and higher emulsion stability against coalescence. As compared with the natural QPI-stabilized emulsions, the 20 min sonicated emulsions exhibited higher packing and adsorption at the protein interface. The microstructure of emulsions that occurs is bridging flocculation of droplets at low c (≤1%, w/ v), while the amount of protein particles could be high enough to cover the droplet surface at high c ( >1%, w/ v) with hexagonal array model arrangement. Thus these results illustrated that both natural and sonicated QPI nanoparticles could be performed as effective food-grade stabilizer for Pickering emulsion; however, the sonicated QPI nanoparticles exhibited much better emulsifying and interfacial properties.

Study on the flow of highly concentrated emulsions

ABSTRACTAn investigation was performed into the flow of highly concentrated water-in-oil emulsions. The viscosity of the low shear rate region in the downward curve was much higher than the viscosity of the upward curve due to the refining effect of the intensive shear. However, this refining effect lasted for just a short time. After that, the structure of highly concentrated emulsion (HCE) can return to its original state. The flow of HCE depends on the shear rate and droplet size of the dispersed phase. The viscosity curve of HCE, which is measured in the initial upward shearing sweep, had two platforms, whereas the region of shear rate was 10−4 s−1 ∼ 103 s−1. The water-in-oil structure was destroyed by intensive shear and much solid ammonium nitrate (AN) was observed in the image of HCE. The small droplets can enhance the capacity of HCE to prevent the breakage of structure under shearing. The microstructure of HCE was closer to its original situation when the droplet size was small.

Method for controlling mean droplet size in the manufacture of phase inversion bituminous emulsions

The most important factors related to the manufacture of phase inversion bitumen in water emulsions are discussed in this paper. The distribution and average droplet diameter of an emulsion depends on formulation variables such as the volume fraction, the concentration and type of surfactant and the temperature of the dispersed phase employed, the type of bitumen used, and mechanical variables as the rotational speed and time used. The emulsions for this study are prepared according to the High Internal Phase Ratio (HIPR) procedure, which requires that the initial dispersion is conducted with internal phase fractions higher than the critical packing (φ>0.74). The bitumen used in this paper are 15/25, 35/50, 50/70 and 70/100. This procedure allows the manufacture of high concentration emulsions, with a small average droplet size, and narrow particle size distribution. Results show that both the droplet size and the particle size distribution obtained can be controlled by changing the parameters of the formulation. Specially one of the most important parameters to consider in the emulsion formulation if we want to obtain the smallest mean droplet size is the penetration grade bitumen used, such as the results presented in this paper.

Preparation and investigation of emulsion explosive matrix based on gas oil for mining process

Six emulsifiers derived from polyisobutylene succinic anhydride (PIBSA) were obtained (E1 to E6) with different Hydrophile-Lipophile Balance (HLBs). Interfacial tension measurements were evaluated for the prepared emulsifiers. The emulsifier (E3 and E6) exhibited the lowest interfacial tension value. Two highly concentrated emulsions (HCE) were prepared. And its stability was scanned form point of HLB, rheology and aging. It was found that, the maximum stability was exhibited by E3 and E6 HLBs, Further the rheological measurement was investigated for (E3 and E6). From the rheological measurement, it was found that, the Bingham yield values (σB) were 1244.4 and 1917.7Pa for the E3, E6 and the Herschel Bulkley values (σH) were 432.66 and 699.66Pa for the E3, E6 respectively. Aging indications the changes in the rheological properties and the aged emulsions fits Cross model. Stability of these emulsions was determined.

Stabilization of highly concentrated emulsions with oversaturated dispersed phase: Effect of surfactant/particle ratio

Currently, there is considerable interest in highly concentrated emulsions (HCE) due to both the variety of rheological effects that are observed in their deformation and flow and to their practical application in the mining, pharmaceutical, cosmetics and food industries. The material investigated is highly concentrated water-in-oil emulsion with a dispersed phase volume fraction of approximately 90%. The dispersed phase is a super-cooled solution of inorganic salts. Instability of such emulsions arises either from crystallization of the dispersed phase in the system during ageing or under high shear conditions. Here, we report a new approach to stabilize this highly concentrated water-in-oil emulsion by adding colloidal particles in combination with short amphiphilic molecules. A series of five fumed silica nanoparticles, each with a different hydrophobicity index (HI) in the ranges 0.60–1.34 and >3, were mixed with sorbitan monooleate (SMO) into the oil phase prior to emulsification. The refinement time, rheological properties and stability of the resulting emulsions were investigated for varying SMO/particle ratios. At low surfactant-to-particle ratio, the silica content controls emulsion stability, but above some critical level (transitional point) SMO dominates over particles. The relationship between shear modulus and SMO-to-particle ratio shows the same transition point related to the same SMO-to-particle ratio found with the refinement time. Interestingly, for each HI, the emulsions are most stable in terms of both shelf life and under high shear when prepared with a SMO-to-particle ratio equaling exactly the value at this transitional point. Using the relationship between the zero modulus of particle dispersions in oil and the SMO-to-particle ratio, we show that the most stable emulsions are formed from dispersions having maximum particle flocculation, induced by SMO reverse micelles, in line with the SMO-to-particle ratio transitional point.

Effects of sulfate chitosan derivatives on nonalcoholic fatty liver disease

Sulfate chitosan derivatives have good solubility and therapeutic effect on the cell model of NAFLD. The aim of this study was to examine the therapeutic effect of sulfate chitosan derivatives on NAFLD. The male Wistar rats were orally fed high fat emulsion and received sulfate chitosan derivatives for 5 weeks to determine the pre-treatment effect of sulfate chitosan derivatives on NAFLD. To evaluate the therapeutic effect of sulfate chitosan derivatives on NAFLD, the rats were orally fed with high concentration emulsion for 5 weeks, followed by sulfate chitosan derivatives for 3 weeks. Histological analysis and biomedical assays showed that sulfate chitosan derivatives can dramatically prevent the development of hepatic steatosis in hepatocyte cells. In animal studies, pre-treatment and treatment with sulfate chitosan derivatives significantly protected against hepatic steatohepatitis induced by high fat diet according to histological analysis. Furthermore, increased TC, ALT, MDA, and LEP in NAFLD were significantly ameliorated by pre-treatment and treatment with sulfate chitosan derivatives. Furthermore, increased TG, AST, and TNF-α in NAFLD were significantly ameliorated by treatment with sulfate chitosan derivatives. Sulfate chitosan derivatives have good pre-treatment and therapeutic effect on NAFLD.

Study on Integration Treatment Technology of Waste Emulsion from Machining Processing

The study studied the treatment technology of high concentration emulsion wastewater in metal machining plant. By analyzing the properties of emulsion wastewater, the author used the combination process of membrane technology + Fe-C micro-electrolysis + membrane bioreactor to treat the wastewater. Through the ceramic membrane, the removal rate of CODCr can reach 95%. Fe-C micro-electrolysis treatment can improve the biodegradability of wastewater, lastly through the membrane bioreactor treatment systems; CODCr of the effluent is less than 100 mg/L, which meets the requirements of The First Grade of the National Discharge Standard (GB8978-1996).

The rheology of binary mixtures of highly concentrated emulsions: Effect of droplet size ratio

Binary mixtures of highly concentrated emulsions (HCE) with three droplet size ratios and different compositions were prepared. It was found that by the proper selection of droplet size ratio and composition of binary mixtures, the shear modulus, viscosity, yield stress, and yield strain can be dropped lower than mixing rules and even primary HCE. This effect is similar to what is known for dispersions with volume fraction less than 0.7 but has not been described for HCE. For such formulations, the caged mechanism of droplets dynamics is not dominant due to the provided free volume that can be occupied by smaller droplets during flow. This is originated from the increase in maximum closest packing and thus more efficient spatial packing. By studying the scaling behavior of shear modulus and yield stress, the significance of interdroplet interaction was distinguished.

The rheology of highly concentrated emulsions stabilized with different surfactants

An investigation was performed into the effect of surfactants on the rheology of water-in-oil highly concentrated emulsions (HCE). The surfactants were oligomers of the PIBSA-type with different headgroups and low-molecular-weight sorbitan monooleate (SMO). The rheological properties of HCE are presented by flow curves with clearly expressed yield stress and dynamic modulus which does not depend on frequency but does on the amplitude of deformations. The changes in modulus and the yield stress depend on the nature of the headgroups as well as the addition of low molecular weight surfactant. It was shown that an increase in the surfactant concentration results in the decrease in the rheological parameters. This shows the significance of micellar structure on the rheological behaviour of HCE. The dependencies of elastic modulus as well as the yield stress on droplet size are deviated from scaling by Laplace pressure. This means that some additional arguments to explain the elasticity of “compressed” HCE emulsions should be included for comparison with the classical models based on the conception of increase in the surface area of droplets. Finally, it was found that the scaling of shear modulus with reciprocal squared droplet size fulfil the zero intercept condition for this variation.

Compositional Characterization of Bitumen/Water Emulsion Films by Negative- and Positive-Ion Electrospray Ionization and Field Desorption/Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

By means of electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT−ICR MS) and automated field desorption/ionization (FD) FT−ICR MS, we identify nonvolatile nonpolar, polar acidic, and basic water-in-bitumen emulsion film stabilizers. Highly condensed aromatic basic, nonpolar, and acidic asphaltene multilayered films stabilize emulsions near or at critical bitumen concentration for asphaltene flocculation. Solvent diluent added beyond the critical dilution concentration precipitates highly condensed acidic, all basic, and most neutral species from the oil/water interface. The most abundant classes in high bitumen concentration emulsion films include neutral pure hydrocarbons and S, acidic O2 and O2S, and basic N and NS heteroatom classes. Highly abundant low bitumen concentration emulsion film stabilizers include acidic O2, O4, and O3S classes.

Highly electrically conductive poly(3,4-ethylenedioxythiophene) prepared via high-concentration emulsion polymerization

Poly(3,4-ethylenedioxythiophene) (PEDOTh) with high electrical conductivity was prepared by oxidative polymerization of 3,4-ethylenedioxythiophene under high-concentration emulsion conditions in the presence of 2-naphthalenesulfonic acid sodium salt acting as an emulsifier and a doping agent and Fe 2(SO 4) 3 as an oxidant. PEDOTh with electrical conductivity as high as 165 S cm −1 was obtained with good yield. XRD analysis indicated that the PEDOTh had a face-to-face stacking distance of 3.3 Å between the polythiophene planes in the solid. The SEM image revealed that the PEDOTh particles formed a layered structure. The packing structure, morphology, and electrical conductivity of the obtained PEDOTh were compared with those of PEDOTh synthesized via a usual emulsion polymerization.

Competitive adsorption of protein and surfactants in highly concentrated emulsions: effect on coalescence mechanisms

The effect of the addition of low-molecular-weight surfactants on the coalescence-stability of emulsions stabilized by the protein β-lactoglobulin was studied in highly-concentrated emulsions. Although Tween-20 and Span 80 are both able to displace the protein from the droplet interface, only with Span 80 does this lead to coalescence by spontaneous rupture of thin films between the emulsion droplets. This suggests that this mechanism of coalescence is only enhanced if the adsorbed protein layer is displaced by a surfactant that is by itself not effective in stabilizing O/W-emulsions. Flow-induced coalescence, another important mechanism for coalescence in highly-concentrated protein-stabilized emulsions, was reduced after the addition of SDS and Tween-20 at concentrations where they are able to displace the adsorbed protein. Span 80 and a sucrose monoester of fatty acids did not reduce flow-induced coalescence at the concentrations applied, which is probably due to their moderate ability to displace adsorbed protein. The above observations give new insight into the function of added surfactant in protein-stabilized emulsions.