Low-energy formation of edible nanoemulsions: Factors influencing droplet size produced by emulsion phase inversion

Nanoemulsions can be used for the encapsulation and oral delivery of bioactive lipophilic components, such as nutraceuticals and pharmaceuticals. There is growing interest in the utilization of low-energy methods to produce edible nanoemulsions. In this study, we examined the influence of system composition and preparation conditions on the formation of edible nanoemulsions by the emulsion phase inversion (EPI) method. The EPI method involves titrating an aqueous phase (water) into an organic phase (oil + hydrophilic surfactant). The influence of oil type, surfactant type, surfactant-to-oil ratio (SOR), and initial surfactant location on the particle size distributions of the emulsions was studied. The droplet size produced by this method depended on: (i) oil type: medium chain triglycerides (MCT) < flavor oils (orange and limonene) < long chain triglycerides (olive, grape, sesame, peanut and canola oils); (ii) surfactant type: Tween 80 < Tween 20 < Tween 85; (iii) surfactant concentration: smaller droplets were produced at higher SOR; (iv) surfactant location: surfactant initially in oil < surfactant initially in water. The low energy method (EPI) was also compared to a high energy method (microfluidization). Small droplets (d < 160 nm) could be produced by both methods, but much less surfactant was needed for the high energy method (SOR ? 0.1) than the low energy method (SOR ? 0.7).     

The effect of NaCl and Na2SO4 concentration in aqueous phase on the phase inversion temperature O/W nanoemulsions

The effect of NaCl and Na₂SO₄ concentrations in aqueous phase on the phase inversion temperature (PIT) in nanoemulsions of water/Brij30/n-hexadecane system has been studied separately, and then compared. The variation of conductivity with temperature was measured by Cyber Scan PC510 conductivity meter for emulsions with 20 wt% hexadecane and 8 wt% Brij30 concentration and different concentrations of NaCl and Na₂SO₄ in aqueous phase. The results showed that with increasing concentrations of NaCl and Na₂SO₄ in aqueous phase, the PIT of nanoemulsions decreases. The effect of the elevation of concentration on the decrease of PIT was more for Na₂SO₄ in aqueous phase than NaCl with equal concentrations.     

Role of liquid crystal in the emulsification of a gel emulsion with high internal phase fraction

A gel emulsion with high internal oil phase volume fraction was formed via an inversion process induced by a water–oil ratio change. The process involved the formation of intermediate multiple emulsions prior to inversion. The multiple emulsions contain a liquid crystal formed by the surfactant with water; this was both predicted by the equilibrium phase diagram as well as observed using polarization microscopy. These multiple emulsions were more stable compared to alternative multiple emulsions prepared in the same way with a surfactant that does not form liquid crystals. While the formation of a stable intermediate multiple emulsion may not be a necessary condition for the inversion to occur, the transitional presence of a liquid crystal proved to be a significant factor in the stabilization of the intermediate multiple emulsions. The resulting gel emulsion contained a small fraction of the liquid crystal according to the phase diagram, and it exhibited excellent stability.     

Thermal analysis of phase change emulsion

This paper presents some results obtained by Differential Scanning Calorimetry (DSC) for characterizing the phase transition within an emulsion. The dispersed substances are either hexadecane, octadecane, water or binary solution. A non-equilibrium model taking into account the inter-phase heat transfer between the emulsifying medium and the dispersed droplet is proposed and explains the main experimental features.     

磺化聚苯乙烯离聚体水基微乳液乳化过程中相反转机理的研究

将聚苯乙烯改性制成磺化聚苯乙烯离聚体，溶解在甲苯／甲醇混合溶剂中，缓慢加水将聚苯乙烯乳化成稳定的水包油的水基微乳液。本文通过研究在乳化过程中体系粘度和导电性的变化，研究了聚苯乙烯离聚体溶液乳化过程的相反转机理和离子含量对乳化过程和相反转机理的影响。     

Morphology development and phase inversion during dynamic vulcanisation of EPDM/PP blends

Morphology development and phase inversion were investigated during dynamic vulcanisation of ethylene–propylene–diene terpolymer (EPDM)/polypropylene (PP) blends. The effects of viscosity ratio and cross-linking reactions were also addressed. EPDM/PP blends were dynamically vulcanised in a Haake batch mixer using resole and SnCl₂ as cross-linking agents. The morphology development and cross-linking degree with reaction time were followed by morphology analysis (SEM and TEM) and measurement of EPDM gel content, respectively. For the same reaction time, it was found that the EPDM gel content decreased when the low-molecular-weight EPDM was used. As a result, the morphological development was delayed and the phase-inversion point was shifted to higher reaction times, allowing us to monitor morphological development during a thermoplastic vulcanisate (TPV) preparation. Using the low-molecular-weight EPDM and increasing the PP viscosity accelerated the morphological development, shifting phase-inversion to lower reaction times. While blend composition influenced final TPV morphology, it had a minor effect on the mechanism of morphological development. A correlation between cross-linking degree and morphology development was established. The results obtained allowed to propose a mechanism of morphology development during dynamic vulcanisation of the EPDM/PP blends, including phase inversion.     

磺化聚苯醚离聚体微乳化过程相反转的研究

以乙酰磺酸为磺化剂制备了磺化度为 3%～ 1 7%mol的磺化聚苯醚 (SPPO)并中和成盐 ,在一定的温度和搅拌速度下 ,加水将SPPO乳化成水包油的稳定水基微乳液。用乳化过程中的体系的电导率、粘度和表面张力的变化表征了乳化相反转过程。另外还研究了溶剂的极性和离子含量对SPPO溶液可乳化性和乳化过程的影响     

Modification of porous poly(vinylidene fluoride) membrane using amphiphilic polymers with different structures in phase inversion process

Three kinds of amphiphilic polymers, including the tri-block copolymer of (polyethylene oxide)–(polypropylene oxide)–(polyethylene oxide) (I, EPTBP), the comb-like copolymer of polysiloxane with polyethylene oxide and polypropylene oxide side chains (II, ACPS) and the hyperbranched star copolymer of polyester-g-methoxyl polyethylene glycol (III, HPE-g-MPEG), were blended with PVDF to fabricate porous membranes via a phase inversion process, respectively, and the effects of the different structures of the amphiphilic polymers on the properties of the blend membranes were compared. The membranes were characterized by scanning electron microscopy (SEM), elemental analysis, X-ray photoelectron spectroscopy (XPS) analysis, mercury porosimetry, water contact angle measurements, etc. The anti-fouling properties of the prepared membranes were evaluated by static and dynamic bovine serum albumin (BSA) adsorptions. Specially, the stabilities of these amphiphilic polymers in the final membranes were estimated by continuous leaching tests. At the same time, the properties of the membranes using the amphiphilic polymers as modifiers were compared with those of the membrane using poly(ethylene glycol) (PEG) as modifier.     

Incomplete phase inversion W/O/W emulsion and formation mechanism from an interfacial perspective

Water-in-oil-in-water (W/O/W) double emulsion can be prepared by incomplete phase inversion method using both medium chain triglycerides (MCT) and isopropyl myristate (IPM) as oil phase, Span 85-Tween 80 (HLB values of 2.5-3.0) as mixed emulsifiers. The preparation method was simple, and the final double emulsions were proved of good microstructure and particle size distribution. Owning to the addition of Tween 80 to Span 85, interfacial tension, interfacial viscosity and modulus decreased, which contributed to the phase inversion. Furthermore, formation of reverse micelles under high-speed dispersion may be a hypothesis to explain the incomplete phase inversion phenomenon.     

Mathematical modeling of silver extraction by an emulsion liquid membrane process

A general physical model of a typical batch extraction system employing an emulsion liquid membrane process for the extraction of silver has been developed. The model takes into account the extraction reaction between the silver ion and the carrier molecules at the external interface, the diffusion of the complex in the membrane phase, the stripping reaction at the internal interface and the reaction of silver ion with the reagent, HCL, in the internal phase to yield silver chloride incapable of permeating through the membrane phase. In addition, the leakage of the internal aqueous phase to the external aqueous phase due to membrane breakage has been incorporated in this model. The batch extraction of silver using D2EHPA as a carrier has been carried out under various experimental conditions. The experimental data can be well explained by the present model.     

催化剂对乳液模板法制备碳材料形貌的影响

以液体石蜡为油相,间苯二酚和甲醛的水溶液为水相,吐温80和司班80为乳化剂,获得油/水(O/W)型乳状液.将该乳状液聚合、碳化去除模板后制得了碳材料,研究了不同催化剂对所得碳材料形貌的影响.结果表明:选择NaOH为催化剂时,制得的碳材料是一种具有孔壁和孔洞的多孔碳泡沫,典型样品的孔径约为1-2μm;当氨水为催化剂时,所得碳材料是由微球或者相互缠绕的蠕虫状粒子组成的块体材料,这些微球或粒子的直径主要集中在1-2μm,与NaOH为催化剂时所得碳泡沫的孔径尺寸相当.研究发现,氨水的加入使得乳液体系发生了相转化,由原来的O/W型乳液逐渐转变为W/O型高内相乳液.从分子间氢键出发,应用内聚能理论探讨了催化剂导致的乳液相变以及不同形貌碳材料的形成过程.     

Catastrophic phase inversion of abnormal emulsions in the vicinity of the locus of transitional inversion

This paper deals with the phase behaviour of model abnormal emulsions of cyclohexane/water/polyethoxylated surfactant in the vicinity of the locus of transitional inversion (optimum formulation). Abnormal emulsions are formed under dynamic conditions if the phase containing the soluble surfactant becomes the dispersed phase. Phase maps have been suggested in the literature that define the boundaries of emulsion morphologies. On these maps, only one transformation can be observed for any formulation scan. Furthermore, the morphology of emulsions in the vicinity of the locus of transitional inversion is rather vague. One might assume that by changing the HLB of the surfactant used in an abnormal emulsion to favour the continuous phase, that abnormal emulsion will gradually transform to a normal emulsion of the same type. A new experimental procedure was adopted in which emulsification was started with abnormal emulsions. To transform the abnormal emulsions to the normal emulsion of the same type, they were exposed to variations in temperature, the surfactant HLB, or water–oil phase ratio. As the optimum formulation was approached, the abnormal emulsions became so unstable that could not exist anymore in the un-favoured morphology and inverted to the normal emulsion of the opposite type. Further variation in the formulation along the route led to a transitional inversion to the normal emulsion of the original type. The result indicates an important finding that the transformation of abnormal emulsions to normal ones of the same type occurred via two successive inversions of catastrophic and transitional nature. It appears that the boundaries of catastrophic inversion correspond to the emulsions with the finest drop size. A modification to the phase behaviour maps, to include the locus of catastrophic phase inversion in the vicinity of the transitional inversion, was thus suggested.     

One-step synthesis of self-healable hydrogels by the spontaneous phase separation of linear multi-block copolymers during the emulsion copolymerization

Self-healable polyacrylamide-based hydrogels were prepared at room temperature via a one-step emulsion copolymerization of acrylamide(AM),dodecyl 2-methacryIate(DM),and 5-acetylaminopentyl acrylate(AAPA) using sodium dodecyl sulfonate(SDS) as the emulsifier and ammonium persulfate(APS)as the initiator.The produced linear multi-block copolymer chains are composed of randomly-linked hydrophilic polyacrylamide segments(PAM) and hydrophobic segments constituted by DM and AAPA units(P(DM-co-AAPA)).The P(DM-co-AAPA) segments will self-aggregate into hydrophobic microdomains during the polymerization process driven by the hydrophobic interactions,and finally separate from water phase,acting as the crosslinks and leading to the formation of strong hydrogels with a storage modulus as high as 400 Pa.These hydrophobic microdomains will be dissolved in water when the temperature increases to 70℃,resulting in a temperature-responsive reversible sol-gel transition of the prepared hydrogels.Furthermore,the prepared hydrogels have excellent self-healing ability.The broken hydrogels can be automatically healed into a body with a same strength within 2-min's contact.This work provides a new simple way to prepare reversible physical crosslinked hydrogel with high strength and self-healing efficiency.     

Electrochemical studies on poly(vinylidene fluoride-hexafluoropropylene) membranes prepared by phase inversion method

The copolymer membranes, poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) were prepared by phase inversion method using poly(ethylene glycol) (PEG) as an additive with acetone or dimethyl formamide as solvent. The morphology of the membranes has been greatly varied with the composition of the polymer and solvent. The ionic conductivity of the membranes were measured at various temperatures (−30 to 50 °C). The prepared membranes have been employed as separators in LiCoO₂/Li cells and were subjected to charge-discharge studies at 0.2 C - rate. The polymer membrane prepared with a ratio of PVdF-HFP (50):PEG (50) using dimethyl formamide as solvent delivered higher discharge capacity than the membranes prepared with acetone as solvent.     

High throughput study of phase inversion parameters for polyimide-based SRNF membranes

High throughput (HT) techniques were applied for the first time for a detailed study of parameters involved in a phase inversion process. The synthesis of integrally skinned asymmetric polyimide (Matrimid^®) membranes was investigated. In spite of being one of the most important materials of reference in solvent resistant nanofiltration (SRNF), a detailed study of the phase inversion parameters for this system is still missing. Phase inversion parameters were selected both on the level of the composition of the casting solution (polymer concentration, solvent type, co-solvent/solvent weight ratio, non-solvent content) as on the level of the post-casting (evaporation time) and immersion (composition coagulation medium) conditions. The study of this extensive parameter space was conducted in a HT-fashion, in which the entire membrane preparation and testing process was miniaturized, parallellized and automated. Thanks to the availability of reliable HT techniques at all levels (i.e. preparation of polymer solutions, membrane casting and membrane testing), 145 membranes were prepared and tested (in triplicate) in the separation of the dye rose Bengal from 2-propanol within a time frame of a few months, meaning a dramatic improvement in time- and cost-efficiency. An attempt was made to link the SRNF performances of the prepared membranes and their SEM-observed morphologies more fundamentally to the phase inversion parameters through the use of Hansen solubility parameters and viscosity measurements.     

Phase inversion of UV-curable anionic polyurethane in the presence of acetone solvent

UV-curable self-emulsified polyurethane acrylates were synthesized in acetone and then dispersed in water. The effect of acetone’s ratio on the emulsification of the polyurethane acrylate was investigated. With a proper amount of acetone as a solvent, stable emulsion with small particle size and narrow particle size distribution was successfully produced and the viscosity during the process of emulsification was greatly reduced. However, stable emulsion could not be obtained when the acetone level was larger than a critical value. A ternary phase diagram was mapped. It was found that only those systems experiencing a phase inversion process lead to a stable emulsion. The carboxylic content is another important factor influencing the properties of emulsion and the process of emulsification. The effect of the carboxylic content on the emulsification was also studied in the experiment. There was another critical carboxylic content for stability. Stable emulsions with small drop sizes less than 50 nm were produced.     

Observations on the dynamics of nonsolvent-induced phase inversion

The diffusion and gelation dynamics of nonsolvent-induced phase inversion in several polyethersulfone (PES)/solvent/nonsolvent systems are observed using a dark-ground optical technique. The observed dynamics are correlated with the resultant morphologies of the solidified gels obtained via scanning electron microscopy. In situ dynamic measurements show that rapid precipitations result in finger formation and delayed precipitations result in sponge formation. Rapid precipitations for some systems also exhibit an initial region of high, anomalous diffusion front motion which correlates well with the appearance of finger-like macrovoids in the film sublayer. Micrographs of both thin (200–300 μm) and thick (3 mm) films formed by liquid-liquid demixing clearly show that the overall morphologies scale with initial film thickness. However, as observed for the cellulose acetate (CA)/dimethylsulfoxide (DMSO)/H₂O system, the possibility of crystallization can complicate the scaling analysis. A ternary diffusion model is also employed to describe the isothermal diffusion encountered during the formation of PES membranes. Binary thermodynamic and kinetic parameters needed for computations are determined from experimental data. Model results agree well with experimental observations. The model accurately predicts the transition from finger-to-sponge formation, as well as other observed trends in dynamics and morphology. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys, 35: 569–585, 1997     

Preparation of P(AN–MMA) microporous membrane for Li-ion batteries by phase inversion

A novel process was proposed for preparation of microporous poly(acrylonitrile–methyl methacrylate) (P(AN–MMA)) membranes by phase inversion techniques using ultrasonic humidifier. Being prepared by dissolving the polymer (PAN–MMA) in the N,N-dimethylformamide (DMF) solution with mechanical stirring, the homogenous casting solution was cast onto a clean glass plate. Successively, the glass plate was exposed to the water vapor produced by ultrasonic humidifier, inducing the phase inversion. It is found the pore size is much more uniform across the cross-section of the membrane than that of the porous membrane prepared by conventional water bath coagulation technique. The microporous membranes were directly obtained after the washing and drying. It had about 1–5 μm of pores and presented an ionic conductivity of 2.52 × 10⁻³ S/cm at room temperature when gelled with 1 M LiPF₆/EC-DMC (1:1 vol.%) electrolyte solution. The test cells with the gel electrolytes prepared from as-prepared microporous membranes showed stable cycling capacities, indicating that the microporous membrane, which was prepared from cheap starting materials acrylonitrile and methyl methacrylate, can be used for the gel electrolyte of lithium batteries.