Stabilization of Water‐Soluble Antioxidant in Water‐in‐Oil‐in‐Water Double Emulsions

Abstract

In this study, we are introducing a method that can effectively stabilize antioxidants in water‐in‐oil‐in‐water (W/O/W) double emulsions. Preliminarily, stable W/O/W double emulsions were produced by manipulating the characteristics of internal aqueous phase via two‐stage emulsification, resulting consequently in the formation of fine internal water droplets in the dispersed oil droplets. From conductivity measurements that can determine the elution amount of internal aqueous phase, it was confirmed that the double emulsion stability could be improved by treating the internal aqueous phase with a hydroxypropyl‐beta‐cyclodextrin. In this study, kojic acid, 5‐hydroxy‐2‐(hydroxymethyl)‐4‐pyrone was selected as a model antioxidant. The stabilization of kojic acid was attempted by locating it in the internal water droplets of the stable W/O/W double emulsions. The stability of kojic acid in the double emulsion system could be maintained at 90% for 10 weeks at high temperature. We believe that these stable W/O/W double emulsions could be used meaningfully as a carrier for many unstable antioxidants.     

Factors Affecting the Droplet Size of Water‐in‐Oil Emulsions (W/O) and the Oil Globule Size in Water‐in‐Oil‐in‐Water Emulsions (W/O/W)

Multiple emulsions of the W₁/O/W₂ type are promising tools for encapsulating bioactive ingredients in the inner aqueous droplets. It is necessary, however, to control the factors influencing their encapsulation efficiency. One important factor is the particle size because it determines the surface area available for mass transport. Because of the coexistence of water and oil droplets in multiple emulsions, there are numerous factors that have an impact on particle size, for example, oil phase composition, interfacial properties, and viscosity of the phases. The purpose of this study was to systematically investigate the effect of these factors on particle sizes in multiple emulsions.     

Relationship Between the Polymer Structures and Destabilization of Polymer‐Containing Water‐in‐Oil Emulsions

The viscous properties, scanning electronic microscopy (SEM), and water/oil interfacial tension (IFT) of partially hydrolyzed polyacryamide (HPAM) and hydrophobically associating hydrolyzed polyacryamides modified with N‐dodecylacrylamide were studied with the objective of investigating the influence on destabilization of emulsions. As expected, the copolymers exhibit significant viscosity enhancing capacity and three‐dimensional network structures due to intermolecular hydrophobic associations, and also present high interfacial activities as the IFT decrease with increasing polymer concentration. As a result, the existences of copolymers increased both the viscosity of emulsions and the intensity of interfacial film, in which case slow down the diffusion of demulsifier molecules and enhance the stability of emulsions, finally, the separation of water from oil becomes more difficult.     

Separation of Water‐in‐Oil Emulsions Using Glass Fiber Media Augmented with Polymer Nanofibers

Water‐in‐oil emulsion separations are important to the petrochemical industry for product quality, safety, environmental, and economic reasons. Glass fiber filter media are often used to remove water droplets out of water‐in‐oil emulsions. The experimental results in this work show that 1% by mass of polyamide nanofibers with diameters of about 150 nm added to conventional micron‐sized glass fiber filter media improves the separation efficiency of the filter media from 71 to 84%. The addition of similar amounts of micron‐sized polyamide fibers to the glass fiber media do not improve filter capture efficiency.     

Studies of Kinetics of Coalescence of Water‐in‐Furrial Crude Oil Emulsions by Confocal Microscopy

The kinetic of coalescence of water in Furrial crude oil emulsions (W/O) during the initial stage of demulsification process is showed through of high‐resolution image micrographics by using a confocal microscope. Furrial crude oil from Monagas state is a crude oil extra heavy with severe flocculation/aggregation problems. The kinetic of the initial stage in the coalescence process is critical and of great importance in the definition of the foreword behavior. This information allowed us to characterize the demulsification rate process in a Furrial crude oil. Total W/O emulsion separation was achieved about of 2 hours at 80ºC. The initial fast coalescence is characterized by a short binary coalescence time, which is followed by a large binary coalescence time. Our results demonstrate that the initial coalescence rate determinate the time necessary to achieve a total separation.     

Effect of Emulsification Method on the Properties of Lecithin‐ and PGPR‐Stabilized Water‐in‐Oil‐Emulsions

Water‐in‐oil (w/o) emulsions were prepared with phosphatidylcholine‐depleted lecithin or polyglycerol polyricinoleate (PGPR) as emulsifying agents. The effect of different laboratory emulsification devices and the effect of sodium chloride on particle size distribution, coalescence stability, and water droplet sedimentation were investigated. The properties of lecithin‐stabilized w/o emulsions were found to depend more strongly on the emulsifying method than those prepared with PGPR. The rotor‐stator system was not suitable for preparing stable w/o emulsions with lecithin. Whereas the addition of salt was essential to achieve coalescence‐stable emulsions prepared with PGPR, the presence of NaCl favored the coalescence of water droplets and phase separation in emulsions containing lecithin.     

Emulsion Inversion in an Oil‐Surfactant‐Water System Based on Model Naphthenic Acids under Alkaline Conditions

Emulsion inversion has been studied in a system based on oil (toluene/heptane), 5β‐cholanic acid, and an alkaline brine solution by varying the concentration of sodium hydroxide. At an intermediate pH w/o emulsions were formed, and in the high pH region o/w emulsions were formed. Emulsion inversion occurred in the pH range 8.5–10. The w/o emulsions were consistently more stable compared to the o/w emulsions. Increasing the amount of acid enhanced the stability of the emulsions. Maximum stability was observed close to pH 8, where the ratio between the undissociated and dissociated acid was approximately 1.5. From light microscopy, it can be seen that the emulsions are stabilized by a liquid gel phase. At equilibrium the system consists of an oil phase, a liquid gel phase, and an aqueous phase. Increasing the oil fraction eventually gave only w/o emulsions in the pH range between 7 and 14. For these emulsions, no obvious difference in stability was observed at pH 8, while the stability of the emulsions in the high pH region was significantly enhanced. An increase of the ratio between toluene and heptane gave no obvious difference in either stability or type of emulsion while varying the pH. Use of a less lipophilic acid, such as 4‐octylbenzoic acid, gave very unstable w/o emulsions in the intermediate pH region, while stable o/w emulsions were found in the high pH region.     

Kinetics of the Oxidation of Phenylhydrazine by [Fe(CN)6]3− in Water‐in‐Oil Microemulsions

The oxidation reaction of phenyl hydrazine (Phh) by hexacyanoferrate ([Fe(CN)₆]^3?) has been studied in water‐in‐oil (w/o) microemulsion media. The kinetic profile of the reaction was investigated as a function of [Phh], droplet size, and droplet concentration. Comparison of the kinetic profiles of the reaction in microemulsion, water‐urea, and water‐AOT‐urea media indicates that the kinetic profile of the reaction in microemulsion shows a behavior similar to that of the reaction in water‐AOT‐urea medium at 4 M urea. An initial increase and then a decrease in k_obs is observed with increasing molar ratio, W_o(=[H₂O]/[AOT]) at constant [AOT] (=0.4 M), whereas k_obs decreases upon increasing the AOT concentration at constant molar ratio.     

Viscoelastic Properties of Crude Oil Components at Oil‐Water Interfaces. 2: Comparison of 30 Oils

The dilational properties of diluted (0.7 vol/vol in toluene) and undiluted crude oil‐water interfaces have been studied using the oscillation drop method with the objective of understanding the properties contributing to the overall stability of crude oil emulsions. The importance of working with undiluted crude oils instead of model systems when dilational properties of real oil‐water systems are going to be reproduced in the laboratory setting has been discussed. For such studies, molecular exchange mechanisms and the aggregation state of asphaltenes are too dependent on concentration to justify the use of model compounds, i.e. fractionated asphaltenes diluted in a solvent. As expected in the low frequency range (0.01–1 Hz), molecular exchange from the bulk oil phase strongly affected the measured dilational parameters. For the diluted crude oils, the frequency dependence of the dilational modulus increased with its magnitude. The systems that exhibited particularly low magnitude of the dilational modulus were of the heaviest crude oils in the sample set, whereas the systems with greatest dilational modulus were among the lightest crude oils. The overall characteristic time of relaxation of the crude oil‐water interfaces was in the range below 10 seconds. The undiluted crude oil‐water interfaces had similar interfacial properties as the diluted samples except for slightly reduced magnitude of the dilational modulus. The crude oil‐water interfaces appeared to be soluble, but some observations pointed to intrinsic rheological properties of the interfaces. Intrinsic elasticity and viscosity of the films should be studied outside the frequency range used here at low (ω～0 Hz) and high (ω→500 Hz), respectively.     

Water‐in‐oil Emulsions Stabilized by Hydrophobized Microfibrillated Cellulose

The properties of water‐in‐toluene emulsions stabilized solely by hydrophobized microfibrillated cellulose (MFC) were investigated. By varying the degree of surface substitution (DSS), the wettability of the MFC was altered. All emulsions prepared with MFC displayed excellent stability to coalescence. The stability to gravity‐induced sedimentation increased with increasing MFC concentration, the highest stability being obtained with MFC of moderate hydrophobicity. Drop sizes increased with increasing DSS, with a corresponding decrease in stability to sedimentation. An increase in the toluene:water ratio at constant MFC concentration resulted in a decrease in the average drop size. For all emulsions, the polydispersity in drop size decreased with decreasing average drop diameter.     

Stereoselective Synthesis of cis‐1‐Aryl‐2‐benzoyl‐3,3‐dicyanocyclopropanes in Water

The highly stereoselective preparation of cis‐1‐aryl‐2‐benzoyl‐3,3‐dicyanocyclopropanes with arsonium salt and olefin in water is described. It is simple, efficient, and environmentally benign.     

Isolation and Characterization of Naphthenic Acids from a Metal Naphthenate Deposit: Molecular Properties at Oil‐Water and Air‐Water Interfaces

Naphthenic acids from a West African metal naphthenate deposit have been isolated and characterized by infrared (IR), nuclear magnetic resonance (NMR), and Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR MS). The sample has been shown to comprise a narrow group of 4‐protic naphthenic acids of molecular weight ～1230 Da. The determined mass of 1230.0627 Da suggests a compound with the elemental composition C₈₀H₁₄₂O₈. The NMR data show no sign of carbon‐carbon multiple bonds. Hence, the elemental composition indicates the presence of six saturated hydrocarbon rings. The naphthenic acids have proved to be highly oil‐water (o/w) interfacially active. On elevation of the pH from 5.6 to 9.0, interfacial activity increases gradually due to a higher degree of dissociation of the carboxylic groups. At pH 9.0, the interfacial tension (IFT) between water and toluene‐hexadecane (1–9 vol.) is lowered by ～40 mN/m at concentrations of only 0.0050–0.010 mM naphthenic acid. The time rate of decrease of the IFT (dγ/dt) is also concentration‐dependent, and a well‐defined IFT is attained at long observation periods.

The C₈₀ naphthenic acids form relatively unstable Langmuir monolayers. The stability decreases further with increasing pH as more monomers become dissociated and dissolve into the aqueous phase. The stability is altered upon addition of calcium ions into the subphase due to formation of calcium naphthenate at the surface. In the undissociated state, the acids have a molecular area of ～160 Å²/molecule in the noninteracting region. The high area reflects an extended molecular structure comprising four carboxylic head groups, which are likely to be separated by hydrocarbon chains.     

Characterization and Evaluation of Electrolyte Influence on Canola Oil/Water Nano‐Emulsion

Emulsion stability is controlled by the physicochemical properties of the adsorbed layers formed on the surface of the droplets. Zeta potential and droplet size measured initially and during storage can estimate O/W emulsion stability. The aim of this study was to characterize and evaluate the effects of different hydrolyzable compounds employed in pharmaceutical and cosmetic preparations on the zeta potential and droplet size of canola O/W nano‐emulsions and, consequently, the emulsion stability. The samples containing additives demonstrated significant change in zeta potential, but in spite of that, no macroscopic instability was observed. Yet the droplet size values did not undergo significant change.     

Mesoscopic Simulation of Aggregates in Surfactant／Oil／Water Systems

The aggregates in sodium dedecylsulphate(SDS)/dimethylbenzene/water systems have been investigated using dissipative particles dynamic(DPD) simulation method.Through analyzing three-dimensional structures of aggregates,three simulated results are found.One is the phase separation,which is clearly observed by water density and the aggregates in the simulated cell;another is the water morphology in reverse micelle,which can be found through the isodensity slice of water including bound water,trapped water and bulky water;the third is about the water/oil interface,i.e.,ionic surfactant molecules,SDS,prefer to exist in the interface between water and oil phase at the low concentraion.     

An Electrorheological Study on the Behavior of Water‐in‐Crude Oil Emulsions Under Influence of a DC Electric Field and Different Flow Conditions

The influence of an applied DC electric field on viscosity and droplet size distribution of different water‐in‐crude oil emulsions was monitored in order to investigate the induction of coalescence of the water droplets. The effects caused by the voltage imposition were studied by rheological analysis and the validity of the obtained results was discussed, comparing with the features of real electrocoalcscer systems. A low field NMR technique (CPMG NMR) and digital video microscopy (DVM) were used to elucidate the behavior of the emulsions. Experiments performed at low shear rate with increasing electric field magnitude showed an increase in viscosity until a critical value. E_CRIT was reached. Thereafter coalescence occurred and viscosity decreased irreversibly below its initial value. The electrorheological behavior of the emulsions can be attributed to the organization (flocculation) of water droplets induced by the electric field, accompanied by an increase in viscosity. The structure breaks down as the shear rate is increased, leading to a decrease in viscosity. Experiments performed at high shear showed only a small decline in the viscosity. Although it was evident that coalescence took place, it did not involve the whole sample, because the electrodes were uncoated. As a direct consequence, the mean value of the droplet size within the emulsion did not change noticeably. Nonetheless this mean value was less recurrent and the formation of droplets of very large diameter occurred.     

Spectrophotometric Determination of Gold in Water and Ore with 2‐Carboxyl‐1‐Naphthalthiorhodanine

Abstract

This paper reports on the synthesis of a new chromogenic reagent, 2‐carboxyl‐1‐naphthalthiorhodanine (CNTR). A high sensitive, selective, and rapid method for the determination of gold based on the rapid reaction of gold with CNTR and the solid phase extraction of the colored chelate with a reversed phase polymer‐based C₁₈ cartridge was developed. In the presence of 0.05–0.5 mol L^?1 of phosphoric acid solution and emulsifier‐OP medium, CNTR reacts with gold to form a red chelate of a molar ratio 1∶3 (gold to CNTR). This chelate was enriched by the solid phase extraction with a polymer‐based C₁₈ cartridge and the retained chelate was eluted from the cartridge with dimethyl formamide (DMF). The enrichment factor of 100 was achieved. In the DMF medium, the molar absorptivity of the chelate is 1.35×10⁵ L · mol^?1 · cm^?1 at 540 nm. Beer's law is obeyed in the range of 0.01～2 µg mL^?1 in the measured solution. The relative standard deviation for 11 replicates sample of 0.5 µg L^?1 level is 2.05%. The detection limit, based on three times the standard deviation is 0.02 µg L^?1 in the original sample. This method was applied to the determination of gold in water and ore with good results.     

Temperature Effect on the Phase Behavior of the Systems Water/Sucrose Laurate/Ethoxylated‐mono‐di‐glyceride/Oil

The phase behavior of the systems water/sucrose laurate/ethoxylated mono‐di‐glyceride/oil was investigated as function of temperature and the weight ratio of EMDG in the mixed surfactants. The oils were R (+)‐limonene, isopropylmyristate, and caprylic‐capric triglyceride. This study demonstrates that the phase inversion temperature (PIT) decreases and the efficiency of the mixed surfactants (γ¯) increase as the weight ratio of the EMDG in the mixed surfactants increases. R (+)‐limonene gave lower phase inversion temperatures and higher efficiencies compared to isopropylmyristate, and caprylic‐capric triglyceride. The solubilization capacity of the system water/sucrose laurate/oil increased upon the addition of ethoxylated mono‐di‐ glyceride which stabilize the surfactant layer and increase the interfacial area.     

Salt‐Induced Micellization of Pluronic F88 in Water

The effect of potassium chloride on the micellization of a poly(ethylene oxide)‐poly(propylene oxide)‐poly(ethylene oxide) (PEO‐PPO‐PEO) triblock copolymer (Pluronic F88: EO₁₀₃PO₃₉EO₁₀₃.) in water was studied by fluorescence, FTIR, ¹H NMR, dynamic light scattering, and dye solubilization. The critical micellization temperature (CMT) values of the copolymer decreased with an increase of KCl concentration while micellar core gets progressively dehydrated. The results reveal the leading role of salt‐water interaction in promoting the micellization of PEO‐PPO‐PEO copolymer by the addition of salt. No significant micellar growth was seen even at temperatures close to cloud point.     

Phase Transition of Acrylamide‐Based Polyampholyte Gels in Water

The swelling behavior of acrylamide (AAm)–based polyampholyte hydrogels in water and in aqueous salt (NaCl) solutions was investigated. [(Methacrylamido)propyl]trimethyl‐ammonium chloride (MAPTAC) and acrylic acid (AAc) were used as the ionic comonomer in the hydrogel preparation. Three sets of hydrogels containing 70 mol% AAm and 30 mol% ionic comonomers of varying mole ratios were prepared. The variations of the hydrogel volume in response to changes in pH, and salt concentration were measured. As pH increases from 1, the hydrogel volume V _eq in water first increases and reaches a maximum value at a certain pH. Then, it decreases again with a further increase in pH and attains a minimum value around the isoelectric point (IEP). After passing the collapsed plateau region, the gel reswells again up to pH=7.1. The reswelling of the collapsed gels containing 10 and 4% MAPTAC occurs as a first‐order phase transition at pH=5.85 and 4.35, respectively, while the hydrogel with 1% MAPTAC reswells continuously beyond its IEP. Depending on pH of the solution, the hydrogels immersed in salt solutions exhibit typical polyelectrolyte or antipolyelectrolye behavior. The experimental swelling data were compared with the predictions of the Flory‐Rehner theory of swelling equilibrium including the ideal Donnan equilibria. It was shown that the equilibrium swelling theory qualitatively predicts the experimental behavior of polyampholyte hydrogels.     

Facile and Efficient Deoxygenation of Amine‐N‐oxides with Gallium in Water

Abstract

A facile and efficient procedure for the deoxygenation of amine‐N‐oxides with gallium metal in water is described. The experimental procedure is quite simple and the products are obtained in high yields without any activating agent.