pH‐Induced Inversion of Water‐in‐Oil Emulsions to Oil‐in‐Water High Internal Phase Emulsions (HIPEs) Using Core Cross‐Linked Star (CCS) Polymer as Interfacial Stabilizer

A pH‐responsive core cross‐linked star (CCS) polymer containing poly(N,N‐dimethylaminoethyl methacrylate) (PDMAEMA) arms was used as an interfacial stabilizer for emulsions containing toluene (80 v%) and water (20 v%). In the pH range of 12.1‐9.3, ordinary water‐in‐oil emulsions were formed. Intermediate multiple emulsions of oil‐in‐water‐in‐oil and water‐in‐oil‐in‐water were formed at pH 8.6 and 7.5, respectively. Further lowering the pH resulted in the formation of gelled high internal phase emulsions of oil‐in‐water type in the pH range of 6.4‐0.6. The emulsion behavior was correlated with interfacial tension, conductivity and configuration of the CCS polymer at different pH.

     

Van der Waals Emulsions: Emulsions Stabilized by Surface‐Inactive,Hydrophilic Particles via van der Waals Attraction

Surface‐inactive, highly hydrophilic particles are utilized to effectively and reversibly stabilize oil‐in‐water emulsions. This is a result of attractive van der Waals forces between particles and oil droplets in water, which are sufficient to trap the particles in close proximity to oil–water interfaces when repulsive forces between particles and oil droplets are suppressed. The emulsifying efficiency of the highly hydrophilic particles is determined by van der Waals attraction between particle monolayer shells and oil droplets enclosed therein and is inversely proportional to the particle size, while their stabilizing efficiency is determined by van der Waals attraction between single particles and oil droplets, which is proportional to the particle size. This differentiation in mechanism between emulsification and stabilization will significantly advance our knowledge of emulsions, thus enabling better control and design of emulsion‐based technologies in practice.     

High‐Internal‐Phase Pickering Emulsions Stabilized Solely by Peanut‐Protein‐Isolate Microgel Particles with Multiple Potential Applications

High‐internal‐phase Pickering emulsions have various applications in materials science. However, the biocompatibility and biodegradability of inorganic or synthetic stabilizers limit their applications. Herein, we describe high‐internal‐phase Pickering emulsions with 87 % edible oil or 88 % n‐hexane in water stabilized by peanut‐protein‐isolate microgel particles. These dispersed phase fractions are the highest in all known food‐grade Pickering emulsions. The protein‐based microgel particles are in different aggregate states depending on the pH value. The emulsions can be utilized for multiple potential applications simply by changing the internal‐phase composition. A substitute for partially hydrogenated vegetable oils is obtained when the internal phase is an edible oil. If the internal phase is n‐hexane, the emulsion can be used as a template to produce porous materials, which are advantageous for tissue engineering.     

Rheological Properties of Particle-Stabilized Emulsions

We have studied the rheological properties of fumed silica particle-stabilized emulsions. Two particles of different polarity were considered, the first more hydrophilic “Aerosil R7200,” the second more hydrophobic “Aerosil R972.” These particles flocculate and probably form a network at the investigated concentration. The flow curves of emulsions stabilized by a single type of particles exhibit yield stress, shear-thinning behavior and thixotropy. Moreover they display rheological features typical of gels. These features are attributed to strengthening of the particle network by droplets. Moreover the rheological properties of w/o emulsions stabilized by hydrophobic are similar to the ones of o/w emulsions stabilized by hydrophilic particles. The rheological properties of o/w emulsions stabilized by mixtures of hydrophilic and hydrophobic particles have then been studied by keeping the total particle concentration constant and varying the mass ratio between particles. The results show that when the hydrophobic particle concentration increases, the viscosity and stability of emulsions decrease establishing evidence that the network is weakened due to preferential orientation of hydrophobic particles towards the oil phase.     

Enantioselective Synthesis of anti‐β‐Hydroxy‐α‐Amido Esters by Asymmetric Transfer Hydrogenation in Emulsions

Herein, we present two methods for an asymmetric transfer hydrogenation through the dynamic kinetic resolution of α‐amido‐β‐ketoesters. These procedures yield the corresponding anti‐β‐hydroxy‐α‐amido esters in good yields and with good diastereo‐ and enantioselectivities. First, the scope of the reduction of α‐amido‐β‐ketoesters by using triethylammonium formate azeotrope is examined. Then, an emulsion technology with sodium formate is explored, which allows for broader substrate scope, faster reaction times, and lower catalyst loading. Furthermore, these reactions are operationally simple and can be set up in air.     

Widely Adaptable Oil‐in‐Water Gel Emulsions Stabilized by an Amphiphilic Hydrogelator Derived from Dehydroabietic Acid

A surfactant, R‐6‐AO, derived from dehydroabietic acid has been synthesized. It behaves as a highly efficient low‐molecular‐weight hydrogelator with an extremely low critical gelation concentration (CGC) of 0.18 wt % (4 mm ). R‐6‐AO not only stabilizes oil‐in‐water (O/W) emulsions at concentrations above its critical micelle concentration (cmc) of 0.6 mm , but also forms gel emulsions at concentrations beyond the CGC with the oil volume fraction freely adjustable between 2 % and 95 %. Cryo‐TEM images reveal that R‐6‐AO molecules self‐assemble into left‐handed helical fibers with cross‐sectional diameters of about 10 nm in pure water, which can be turned to very stable hydrogels at concentrations above the CGC. The gel emulsions stabilized by R‐6‐AO can be prepared with different oils (n‐dodecane, n‐decane, n‐octane, soybean oil, olive oil, tricaprylin) owing to the tricyclic diterpene hydrophobic structure in their molecules that enables them to adopt a unique arrangement in the fibers.     

Salt‐Induced Fabrication of Superhydrophilic and Underwater Superoleophobic PAA‐g‐PVDF Membranes for Effective Separation of Oil‐in‐Water Emulsions

Conventional polymer membranes suffer from low flux and serious fouling when used for treating emulsified oil/water mixtures. Reported herein is the fabrication of a novel superhydrophilic and underwater superoleophobic poly(acrylic acid)‐grafted PVDF filtration membrane using a salt‐induced phase‐inversion approach. A hierarchical micro/nanoscale structure is constructed on the membrane surface and endows it with a superhydrophilic/underwater superoleophobic property. The membrane separates both surfactant‐free and surfactant‐stabilized oil‐in‐water emulsions under either a small applied pressure (<0.3 bar) or gravity, with high separation efficiency and high flux, which is one to two orders of magnitude higher than those of commercial filtration membranes having a similar permeation property. The membrane exhibits an excellent antifouling property and is easily recycled for long‐term use. The outstanding performance of the membrane and the efficient, energy and cost‐effective preparation process highlight its potential for practical applications.     

Novel Oil‐in‐Water Emulsions Stabilised by Ionic Surfactant and Similarly Charged Nanoparticles at Very Low Concentrations

Novel oil‐in‐water (O/W) emulsions are prepared which are stabilised by a cationic surfactant in combination with similarly charged alumina nanoparticles at concentrations as low as 10^?5 m and 10^?4 wt %, respectively. The surfactant molecules adsorb at the oil‐water interface to reduce the interfacial tension and endow droplets with charge ensuring electrical repulsion between them, whereas the charged particles are dispersed in the aqueous films between droplets retaining thick lamellae, reducing water drainage and hindering flocculation and coalescence of droplets. This stabilization mechanism is universal as it occurs with different oils (alkanes, aromatic hydrocarbons and triglycerides) and in mixtures of anionic surfactant and negatively charged nanoparticles. Further, such emulsions can be switched between stable and unstable by addition of an equimolar amount of oppositely charged surfactant which forms ion pairs with the original surfactant destroying the repulsion between droplets.     

Tailoring of High‐Order Multiple Emulsions by the Liquid–Liquid Phase Separation of Ternary Mixtures

Multiple emulsions with an “onion” topology are useful vehicles for drug delivery, biochemical assays, and templating materials. They can be assembled by ternary liquid phase separation by microfluidics, but the control over their design is limited because the mechanism for their creation is unknown. Herein we show that phase separation occurs through self‐similar cycles of mass transfer, spinodal decomposition or nucleation, and coalescence into multiple layers. Mapping out the phase diagram shows a linear relationship between the diameters of concentric layers, the slope of which depends on the initial ternary composition and the molecular weight of the surfactant. These general rules quantitatively predict the number of droplet layers (multiplicity), which we used to devise self‐assembly routes for polymer capsules and liposomes. Moreover, we extended the technique to the assembly of lipid‐stabilized droplets with ordered internal structures.     

A Physicochemical Study of the Effects of Acidity on the Distribution and Antioxidant Efficiency of Trolox in Olive Oil‐in‐Water Emulsions

The efficiency of antioxidants to inhibit the oxidation of lipid‐based emulsions depends on several factors including their nature and their concentration at the reaction site. Here, we have analyzed the effects of acidity and of surfactant concentration on the distribution and efficiency of the vitamin E analog Trolox (TR) in stripped olive oil‐in‐water emulsions stabilized with Tween 20. The distribution was assessed in the intact emulsions by employing a kinetic method that exploits the reaction between the hydrophobic 4‐hexadecylbenzenediazonium ions and TR. Kinetic results are interpreted on the grounds of the pseudophase model. The effects of TR on the oxidative stability of the emulsion were determined at different pH values by monitoring the formation of conjugated dienes over time. The results show that the efficiency of TR increases upon increasing pH even though its concentration in the interfacial region decreases.     

纳米粒子稳定乳液及其在纳米结构合成中的应用*

本文在介绍常规乳状液、微乳液和固体稳定乳液的基础上,着重综述了纳米粒子稳定乳液的特点及其在纳米结构合成中的应用进展,并对目前该研究领域亟待解决的问题进行了分析。纳米粒子稳定乳液具有独特的油、水、固三相环境和水油、水固、油固三个相界面,分散相液滴尺寸可以在微米、亚微米乃至纳米尺度调节,因而可以作为合成组成、结构和性能极为丰富多样的纳米结构的介质。纳米粒子对乳液稳定作用的机理,以及纳米粒子稳定乳液中化学反应的特殊规律还有待深入研究。本文在介绍固体稳定乳液的基础上,着重综述了纳米粒子稳定乳液的特点及其在纳米结构合成中的应用进展,并对目前该研究领域亟待解决的问题进行了分析。纳米粒子稳定乳液具有独特的油、水、固三相环境和水油、水固、油固三个相界面,分散相液滴尺寸可以在微米、亚微米乃至纳米尺度调节,因而可以作为合成组成、结构和性能极为丰富多样的纳米结构的介质。纳米粒子对乳液稳定作用的机理,以及纳米粒子稳定乳液中化学反应的特殊规律还有待深入研究。     

Thixotropy in Native Petroleum Emulsions

Native water in crude oil emulsions, stabilized by indigenous surfactants, exhibit both positive thixotropy (PT) and negative thixotropy (NT) in Couette flow. PT is associated with microscopic processes, local break-up of droplet clusters in emulsions with low and moderate volume fractions of water φ, or fracturing of emulsion-gels with φ > 0.7. The latter process involves the coalescence of water droplets along a fracture plain, which results in vorticity banding of emulsion flow. NT reflects evolution of the macroscopic radial banding in flow of emulsions with 0.18 < φ < 0.58 and is dictated by the displacement of the interface between the sheared and unsheared regions.