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.     

The Relation Between Phase Behavior and Formation of Narrow Size Distribution W/O Emulsions

Water-in-oil (W/O) emulsions of the water/C₁₂E₅/isooctanol/isooctane system have been prepared at 25° C. Phase behavior studies of the system with constant (2.5 and 6 wt.%) isooctanol concentration showed that the surfactant becomes more lipophilic with the increase in the alkanol concentration. Emulsification was carried out using four low-energy emulsification methods using the slow addition of one or various components to the rest of them, with gentle agitation. Emulsions with low-polydis-persity were obtained when the emulsification process started with a single lamellar liquid crystalline phase. If in addition to a lamellar liquid crystalline phase, other phases, such as excess water phase, were initially present, emulsions with intermediate polydispersity were produced. When a lamellar liquid crystalline phase was not involved and the spontaneous natural curvature of the surfactant was not changed during emulsification, highly polydisperse emulsions were obtained.     

W/O/W多重乳液中水传递的控制

建立了简化的W/O/W(水/油/水)多重乳液乳珠模型——统计平均半径模型, 预测出当W/O/W多重乳液内水相水滴之间以及内外水相之间均达到水传递平衡时的内外水相中盐的浓度, 从而实现对水传递的控制, 以维持W/O/W多重乳液的稳定. 按理论预测制备出了不同稳定态的W/O/W多重乳液, 利用差分扫描量热仪(DSC)检测了多重乳液中水的传递过程, 确定体系在实验状态下的稳定程度, 实验结果与理论预测基本吻合.     

Phase Transitions in Emulsions Formed by Aqueous Emulsifier and its Action on Improving Mobility in Oil Recovery

Transition from oil-in-water (O/W) emulsions to water-in-oil (W/O) emulsions and its action on enhanced oil recovery was investigated by viscosity, morphology, and simulated flooding experiments. This transition can be realized by increasing the volume ratio of oil to water or decreasing the emulsifier concentration. At a mass concentration of 0.3 wt%, the self-developed emulsifier FJ-1 mainly forms O/W emulsions at a volume ratio (oil to water) of 1:1. The emulsions behave as O/W emulsions with a low viscosity when the volume ratio of oil to water is below 2:1. Above 2:1, increasing volume ratio leads to the O/W emulsions transferring into W/O emulsions with high viscosity. For example, at a volume fraction of 4:1, the viscosity of W/O emulsions reaches 229.1 mPa · s, and separated water can hardly be detected. Transition from O/W emulsions to W/O emulsions with high viscosity can also be realized by decreasing the concentration of emulsifier to 0.05 wt% or lower at a volume ratio of 1:1. These may be the critical factors leading to transition from O/W emulsions to W/O emulsions at core conditions. Simulated flooding experiments show that emulsifier fluids can act as an in situ mobility improver and make an improvement of oil recovery even by 20.4%. The results indicate that the water-in-crude-oil emulsions possess great potential in enhancing oil recovery.     

Influence of composition on the encapsulation properties of P/O/W multiple emulsions for Vitamin C

Abstract

The aim of this work was to study the encapsulation properties of polyols-in-oil-in-water (P/O/W) multiple emulsions for Vitamin C (Vc). The influence of formulation factors, including the concentration of lipophilic emulsifier, hydrophilic emulsifier, salt and glycerol had been investigated. The results indicated that the encapsulation stability could be improved by increasing the lipophilic emulsifier concentration which could strengthen the interfacial film. In contrast, the excess of hydrophilic emulsifier destabilized the emulsion. The presence of glycerol in the outer aqueous phase accelerated the phase transfer, thus reduced the encapsulation rate. The addition of salt in inner polyols phase had little effect on encapsulation rate while markedly affected the morphology and stability of this system. P/O/W multiple emulsions showed better encapsulation stability than the W/O/W multiple emulsions as the former’s encapsulation rate could remain more than 75% after 2?weeks while the latter only remained less than 60%. Meanwhile, the P/O/W emulsions exhibited higher storage modulus (G’), bigger loss modulus (G’’) and broaden linear viscoelastic regions than W/O/W emulsions.     

Oscillations Produced From Acidity Hydrolysis of Triglyceride in Emulsion

A new type of oscillating reaction was found from the systematic design of the chemical oscillator in water in oil (W/O) emulsions. It is an acidity hydrolysis reaction of long chain triglyceride in W/O emulsion at 25.0 ± 0.1°C in a bath stirring reactor. During the process of reaction, there were periodic and semi‐periodic changes lasting more than 10 hours both in electrolytic conductivity and electric potential. Microscope also revealed that the emulsion structure changed regularly and quickly. Because of the large difference in the solubility of the hydrolyzed products, it could be thought, that the different redistribution in the two phases of water and oil induces the regular changes. Marangoni effect of interface membrane made oscillation to form. The oscillating reaction can be used to explain the periodic change in the living system produced from coupling between reaction and diffusion.     

Phase transitions and microstructure of emulsion systems prepared with acylglycerols/zinc stearate emulsifier

The emulsification processes, during which acylglycerols/zinc stearate emulsifier, water, and oil phase formed ternary systems, such as water-in-oil (W/O) emulsions, oil-in-water (O/W) dispersions, and unstable oil-water mixtures, were investigated in order to characterize the progressive transformations of the dispersed systems. The type, structure, and phase transitions of the systems were found to be determined by temperature and water phase content. Crystallization of the emulsifier caused the destabilization and subsequent phase inversion of the emulsions studied, at a temperature of 60-61 degrees C. The observed destabilization was temporary and led, at lower temperature, to W/O emulsions, "O/W + O" systems, or O/W dispersions, depending on the water content. Simultaneous emulsification and cooling of 20-50 wt % water systems resulted in the formation of stable W/O emulsions that contained a number of large water droplets with dispersed oil globules inside them ("W/O + O/W/O"). In water-rich systems (60-80 wt % of water), crystallization of the emulsifier was found to influence the formation of crystalline vesicle structures that coexisted, in the external water phase, with globules of crystallized oil phase. Results of calorimetric, rheological, and light scattering experiments, for the O/W dispersions obtained, indicate the possible transition of a monostearoylglycerol-based alpha-crystalline gel phase to a coagel state, in these multicomponent systems.     

Origins of two surfactant phases (D and Dp′) in a temperature-composition space of water/C12EO6 / propanol / heptane system: tricritical point and critical double end point

The origins of middle surfactant phases (D and Dp′) were investigated in the composition-temperature (49–73 °C) space of a water/hexaethyleneglycol dodecyl ether (C₁₂EO₆)/propanol/heptane system at atmospheric pressure. Two types of three-phase bodies exist in the dilute C₁₂EO₆ region of the four-component composition tetrahedron at 49.0 °C. A cone-like three-phase body consisting of aqueous (W), Dp′, and oil (O) phases becomes thinner with increasing temperature, and collapses into the superimposed critical tie lines (CTL) at 51.7 °C. One end of the superimposed CTL is a critical double end point where the closed-loop coexistence curve of the Dp′ and O phases disappears. The chiral three-phase body consisting of W, D, and O phases shrinks with increasing temperature, and finally vanishes at the tricritical point near 72.5 °C. The roles of C₁₂EO₆ and propanol are discussed and the conditions for the middle surfactant phases are discussed on the basis of the whole series of three-phase behavior. Received: 9 July 1998 Accepted in revised form: 25 August 1998     

Fabrication of macroporous foam and microspheres of polystyrene by Pickering emulsion polymerization

Poly(styrene-co-methacrylic acid) (PS-co-MAA) particles were synthesized via surfactant-free emulsion polymerization and then used as particulate emulsifiers for preparation of Pickering emulsions. Our results showed that adjusting the solution pH can tune the wettability of PS-co-MAA particles to stabilize either water-in-oil (W/O) or oil-in-water (O/W) Pickering emulsions. Stable W/O emulsions were obtained with PS-co-MAA particles at low pH values due to their better affinity to the dispersed oil phase. In contrast, increasing the pH value significantly changed the stabilizing behavior of the PS-co-MAA particles, leading to the phase inversion and formation of stable O/W emulsions. We found that the oil/water ratio had a significant influence on pH value of the phase inversion. It decreased with decreasing the oil/water ratio, and no phase inversion occurred when the styrene volume fraction reduced to 10 %. Additionally, macroporous polystyrene (PS) foam and PS microspheres were obtained via polymerization of Pickering high internal phase emulsion (Pickering HIPE) and O/W Pickering emulsion, respectively.     

Study by Differential Scanning Calorimetry of Water-in-Oil Emulsions Stabilized by Clays and CTAB

In this work, we have tested various formulations in order to get emulsions containing pure water, Tunisian olive oil, Tunisian clays, and an ammonium salt. Two different types of clays: smectite and kaolinite and the cethyltrimethylamonium bromide (CTAB) were tested. CTAB is used as surfactant and a compound modifying the clays properties. The amount of CTAB being fixed at 0.66 w/w, the proportions of clays were varied from 0 to 9% for each of the following proportions of water: 10, 20, 30%. To the aqueous phase obtained by mixing two separate aqueous phases: water + CTAB and water + clay, the oil was added drop by drop, the agitation being maintained at 5000 rpm. The obtained mixtures were analyzed by Differential Scanning Calorimetry (DSC), optical microscopy and bottle tests. An optimized formulation containing water (30%), smectite clay (5.3%) and CTAB (0.66%) was found to give W/O emulsions which kinetic stability is greater than 75 days regarding coalescence and greater than 700 hours regarding sedimentation.     

The transition of three types of three-phase behavior in a temperature-composition space of water/C12EO6/propanol/heptane system

 The change of three-phase behavior of a water/hexaethylene-glycol dodecyl ether (C₁₂EO₆)/propanol/heptane system was studied with increasing temperature (30.0–48.9 °C). A cone-like three-phase body consisting of aqueous (W), surfactant (D_p), and oil (O) phases is formed in the composition tetrahedron at lower temperatures. The body is expanded with increasing temperature, and touches the water–C₁₂EO₆–heptane triangle (the base) at 44.8 °C. At about 45.6 °C the loci of the D_p and O phases meet and cut off at a critical double end point and the three-phase body separates into two bodies: one has a chiral shape and the other is unclosed. The unclosed body is transformed with the change of shape of the tie triangle on the base as temperature increases and leaves from the base at 48.9 °C. A closed-loop miscibility gap between middle surfactant (D^′ _p) and O phases or a cone-like three-phase body is formed inside the composition tetrahedron at higher temperatures. The roles of C₁₂EO₆ and propanol are also discussed. Received: 14 April 1998 Accepted: 15 July 1998     

Optimization of Oil-in-Water Emulsion Stability: Experimental Design,Multiple Light Scattering,and Acoustic Attenuation Spectroscopy

To find an optimal formulation of oil-in-water (O/W) emulsions (φ_o = 0.05), the effect of emulsifier nature and concentration, agitation speed, emulsifying time, storage temperature and their mutual interactions on the properties and behavior of these dispersions is evaluated by means of an experimental design (Nemrodw software). Long-term emulsion stability is monitored by multiple light scattering (Turbiscan ags) and acoustic attenuation spectroscopy (Ultrasizer). After matching surfactant HLB and oil required HLB, a model giving the Sauter diameter as a function of emulsifier concentration, agitation speed and emulsification time is proposed. The highest stability of C₁₂E₄-stabilized O/W emulsions is observed with 1% emulsifier.     

An origin of a middle surfactant phase (Dp): A critical double end point in a water/polyoxyethylene alkyl ether/propanol/heptane system

 Phase behavior of water/hexaethyleneglycol dodecyl ether (C₁₂EO₆)/propanol/heptane system was investigated in a composition–temperature space (25–30 ^°C) at atmospheric pressure. A cone-like three-phase body consisting of aqueous (W), surfactant (Dp), and oil (O) phases is formed in the two-phase body of Wm (aqueous micellar phase)+O at 30.0 ^°C. With decreasing temperature the three-phase body becomes thinner and finally disappears at a critical double end point (CDEP) where the two critical end points of W and Dp phases are merged. The CDEP exists at about 26.2 ^°C (T _CDEP). The hydrophile–lipophile balance (HLB) of the mixed amphiphile changes towards lipophilic on addition of propanol. As a result, the Wm phase separates into two phases W+Dp above the T _CDEP. Further addition reduces the lipophobicity of aqueous media (or the solvophobicity of the mixed amphiphile), and the W and Dp phases are merged again. Below T _CDEP, since C₁₂EO₆ becomes much hydrophilic, the change of HLB lurks and a middle phase (Dp) cannot be observed. Received: 19 June 1997 Accepted: 20 March 1998     

The Stability of Highly Concentrated Water-in-Oil Emulsions and Structure of Highly Porous Polystyrene Produced from Them

The porosity of polymer materials produced by polymerizing dispersion media of highly concentrated emulsions may be predicted, provided that the emulsions are stable. The study of the stability of water-in-oil (W/O) emulsions containing styrene as a dispersion medium at 25 and 65°C has shown that emulsions with a dispersed phase fraction of 0.75 and sorbitan monooleate concentrations of 1.5–20.0 vol % are stable to coalescence but are unstable to sedimentation. Emulsions with a dispersed phase fraction of 0.95 are stable to both coalescence and sedimentation at sorbitan monooleate concentrations of 10–20 vol %. Open-pore polymer materials are formed from emulsions with dispersed phase fractions of 0.75 and 0.95 at sorbitan monooleate concentrations of 2.0–3.5 and 10–12 vol %, respectively. At a dispersed phase fraction of 0.75 and a sorbitan monooleate concentration of <2 vol %, a multiple O/W/O emulsion is formed, the polymerization of which yields a porous polymer material containing spherical polystyrene particles inside pores. At higher surfactant concentrations in emulsions with dispersed phase fractions of 0.75 and 0.95 partly destroyed porous materials are formed.     

Preparation characteristics of water-in-oil-in-water multiple emulsions using microchannel emulsification

Microchannel (MC) emulsification is a novel technique for preparing monodispersed emulsions. This study demonstrates preparing water-in-oil-in-water (W/O/W) emulsions using MC emulsification. The W/O/W emulsions were prepared by a two-step emulsification process employing MC emulsification as the second step. We investigated the behavior of internal water droplets penetrating the MCs. Using decane, ethyl oleate, and medium-chain triglyceride (MCT) as oil phases, we observed successful MC emulsification and prepared monodispersed oil droplets that contained small water droplets. MC emulsification was possible using triolein as the oil phase, but polydispersed oil droplets were formed from some of the channels. No leakage of the internal water phase was observed during the MC emulsification process. The internal water droplets penetrated the MC without disruption, even though the internal water droplets were larger than the resulting W/O/W emulsion droplets. The W/O/W emulsion entrapment yield was measured fluorometrically and found to be 91%. The mild action of droplet formation based on spontaneous transformation led to a high entrapment yield during MC emulsification.     

Preparation and characterization of W/O/W double emulsions containing MgCl2

The aim of present study is to design food-grade W/O/W double emulsions encapsulating Mg²⁺ and investigate their stability and release properties. Prepared emulsions were characterized in terms of global stability, particle size, rheological properties, and interfacial tension. The double emulsions were sensitive to the presence of magnesium salt. The mean droplet size and viscosity of emulsions was positively correlated to MgCl₂ concentration. The microscopic pictures confirmed that the water transfer between two aqueous phases caused the reduced stability of double emulsions. It was suggested that swelling breakdown was the main mechanism in controlling the release of encapsulated Mg²⁺.     

Solubilization of Styrene and Acrylamide Monomers in Microemulsions

Abstract

Phase diagrams of sodium dodecyl sulfonate (DS)/n‐butanol/styrene/water systems with variable amounts of styrene were constructed at 40°C, and the effects of styrene on microemulsion stability were studied. The solubilization of styrene in these O/W microemulsion systems was investigated by ¹H NMR methods. The results show that the solubilization site shifts from the palisade layer to the inner core of microemulsion droplets when the molar fraction of styrene reaches 0.312. The solubilization of acrylamide in cetyltrimethylmethyl ammonium bromide (CTAB)/n‐butanol/10% n‐octane/water reverse microemulsions (W/O) was studied with a ¹³C NMR method. It was found that the acrylamide was mainly solubilized in the Stern layer of droplets at low acrylamide levels. However, when the mole fraction of acrylamide approaches 0.428, the acrylamide penetrates into the palisade layer and is distributed along the hydrocarbon chain of the surfactant.     

Emulsion stability in sucrose monoalkanoate system with addition of cosurfactants

The hydrophile-lipophile property of the sucrose monododecanoate changes from hydrophilic to lipophilic by adding an alcohol as a cosurfactant. With the addition of a short-alkyl-chain alcohol (pentanol, hexanol), the surfactant forms the middle-phase microemulsion whereas a lamellar liquid crystal (L_!) appears with a medium- or long-chain alcohol (heptanol, octanol, decanol) at the balanced state in water/ SE/ cosurfactant/ decane system. The effect of changing oil was also studied in the presence of a middle-chain cosurfactant (heptanol). A short-chain aromatic oil (m-xylene) forms middle-phase microemulsion whereas a longer aliphatic one (hexadecane) forms lamellar liquid crystalline phase in a dilute region when the HLB of surfactant is balanced in a given system. O/W emulsions become stable on the hydrophilic-surfactant-rich side whereas W/O emulsions are stable on the cosurfactant-rich side. Emulsions are very unstable in the three-phase regions. However, when the lamellar phase is produced, emulsions become stable at the balanced state because water and oil are incorporated in L_! phase in the longer cosurfactant systems such as water/ SE/ octanol/ decane and water/ SE/ decanol/ decane.     

Microemulsion polymerization of acrylamide and styrene: Effect of the structures of reaction media

Isothermal phase diagrams of the system cetyltrimethylammonium bromide (CTAB)/n‐butanol/n‐octane/water were constructed, and the effect of the oil (n‐octane) contents on the microemulsions was studied at 40 °C. We determined the microemulsion structures of two systems, CTAB/n‐butanol/10% n‐octane/water and sodium dodecyl sulfonate (As)/n‐butanol/20% styrene/water, by conductivity measurements to investigate the polymerization of acrylamide and styrene in the two microemulsion systems. The polymerization kinetics of the water‐soluble monomer acrylamide in CTAB micelles and the different CTAB/n‐butanol/10% n‐octane/water microemulsion media [water‐in‐oil (W/O), bicontinuous (BC), and oil‐in‐water (O/W)] were studied with water‐soluble sodium bisulfite as the initiator. The maximum polymerization rate in CTAB micelles was found at the second critical micelle concentration. A mechanism of polyacrylamide formation and growth was proposed. A connection between the structures of the microemulsions and the polymerization rates was observed; the maximum polymerization rate occurred at two transition points, from W/O to BC and from BC to O/W, and the polyacrylamide molecular weights, which depended on the structures of the microemulsions, were also found. A square‐root dependence of the polymerization rates on the initiator concentrations was obtained in CTAB micelles and O/W microemulsion media. The polymerization of the oil‐soluble monomer styrene in different As/n‐butanol/20% styrene/water microemulsion media (W/O, BC, and O/W) was also investigated with different initiators: water‐soluble potassium persulfate and oil‐soluble azobisisobutyronitrile. A similar connection between the structures of the microemulsions and the conversions of styrene in CTAB/n‐butanol/10% n‐octane/water for the polymerization of acrylamide was observed again. The structures of the microemulsions had an important role in the molecular weights and sizes of polystyrene. The polystyrene particles were 10–20 nm in diameter in BC microemulsion media and 30–60 nm in diameter in O/W microemulsion media according to transmission electron microscopy. We determined the solubilization site of styrene in O/W microemulsion drops by ¹H NMR spectra to analyze the results of the microemulsion polymerization of styrene. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3320–3334, 2001     

Thermo- and UV Photo-Triggerable Monoolein Cubic Phase Bearing Poly(Hydroxyethyl Acrylate-co-Coumaryl Acrylate-co-Octadecyl Acrylate)

Thermo- and UV photo-triggerable monoolein (MO) cubic phases were developed by incorporating poly(hydroxyethyl acrylate-co-coumaryl acrylate-co-octadecyl acrylate) (P(HEA-CA-ODA)) in the cubic phases. P(HEA-CA-ODA)s, for which the HEA/CA/ODA molar ratio was 98.6:0:1.4, 96.7:2.0:1.3, 96.2:2.6:1.2, 95:3.8:1.2, and 92.8:6.1:1.1, calculated on the ¹H NMR spectra, were prepared by a free radical reaction. The air–water interfacial tension was inversely proportional to the CA content of the copolymer. The copolymers for which the CA content was 2.6%, 3.8%, and 6.1% exhibited their phase transition temperature in an aqueous solution in the temperature range from 25°C to 40°C. As the CA content was more, the temperature sensitivity was higher and the phase transition temperature was lower. The UV light (254 nm, 6 W)-induced dimerization degree of CA was proportional to its content in the copolymers. The release of fluorescein isothiocyanate-dextran from cubic phases containing P(HEA/CA/ODA)s was promoted by UV light irradiation, possibly due to the photo-induced collapse of the copolymer chains. The release from cubic phases incorporating copolymers, for which the CA content was 3.8% and 6.1%, was enhanced by increasing the releasing medium temperature from 23°C to 37°C, possibly due to the thermal collapse of the copolymer chains.