W/O/W emulsions with high internal droplet volume fraction

Thermoresponsive Phase Change Oleogel Microcapsules for Coencapsulation of Hydrophilic and Hydrophobic Actives

To address the concurrent needs of the personal care industry for simultaneous protection of active ingredients and enhancement of product functionality, this study employs a microfluidic technique to fabricate EstoGel M-based oleogel microcapsules capable of coencapsulating both hydrophilic and hydrophobic actives. The oleogels exhibit gel-like characteristics with a melting point of approximately 70 °C, ensuring high encapsulation efficiency for hydrophilic and hydrophobic actives within aqueous environments. The oleogel microspheres encapsulating hydrophobic actives are prepared using microfluidic technology with robust elasticity, which can be ruptured by a force of less than 15 mN, contributing to a favorable tactile sensation upon application. The structural integrity of these microspheres is preserved within a temperature range up to 70 °C, indicating their thermodynamic stability. In addition, oleogel microcapsules are prepared using microfluidic technology, and their effectiveness in coencapsulating hydrophilic and hydrophobic active ingredients is successfully demonstrated, along with excellent skin feel and temperature stability. The exceptional tactile properties of EstoGel M-based oleogel microcapsules offer a promising strategy for creating innovative personal care products that integrate high encapsulation efficiency with multifunctional attributes.

The Preparation of W/O/W High-Internal-Phase Emulsions as Coagulants for Tofu: The Effect of the Addition of Soy Protein Isolate in the Internal Water Phase

Tofu quality is determined by a controlled coagulation process using a W/O/W emulsion coagulant. The impact of adding soy protein isolate (SPI) to the inner water phase on the stability of W/O/W high-internal-phase emulsions (HIPEs) and its application as a coagulant for tofu was assessed. No creaming occurred during 7-day storage with SPI concentrations up to 0.3%, while the emulsion droplets aggregated with 0.5% and 0.7% SPI. Emulsions containing 0.3% SPI maintained a constant mean droplet size after 21 days of storage and exhibited the lowest TURBISCAN stability index value. HIPE stability against freeze-thaw cycles improved after heating. HIPEs with SPI concentrations above 0.3% demonstrated an elastic gel-like behavior. The increased viscosity and aggregation of the protein around droplets indicated that the interaction among emulsion droplets could enhance stability. W/O/W HIPE coagulants significantly increased tofu yield, reduced hardness, and produced a more homogenous tofu gel compared to a MgCl2 solution. The HIPE with 0.3% SPI was found to be optimal for use as a coagulant for tofu.

Development of edible nanoemulsions containing vitamin E using a low-energy method: Evaluation of particle size and physicochemical properties for food and beverage applications

Pasta, a globally popular dish, serves as a complete meal around the world. This research aims to improve the nutritional value of pasta by enriching it with vitamin E. Firstly, vitamin E and sesame oil were mixed in different ratios (1:10, 1:5, 10:10) and dissolved in an aqueous medium at 50 °C with different concentrations of Tween 80 (10 %, 20 %, 30 %). Coarse emulsions were formed by gradual addition of the oil phase to the aqueous phase, followed by equilibration using an Ultratrax mixer at 15,000 rpm for 5 min. The target nanoemulsions were then produced using an ultrasonic system. After 30 days of storage, the most stable nanoemulsions containing 10 % Tween 80 and a 1:10 ratio of vitamin E to sesame oil showed minimal changes. In addition, nanoemulsions with 10 % Tween 80 and a 10:10 ratio of vitamin E to sesame oil showed less turbidity than those with 20 % and 30 % Tween 80. Evaluation of enriched pasta for physical, chemical and sensory properties compared to non-enriched samples showed no significant differences in properties such as pH, ash, total solids, texture and colour characteristics (P < 0.05). Enriched pasta samples showed an increase in moisture content of 0.94 % and a decrease in weight loss of 2.13 % compared to the control, with improved brightness (L) and yellowness (b) due to the addition of nanoemulsion. Sensory evaluation showed higher scores for pasta samples enriched with nanoemulsions containing vitamin E compared to control samples. This pioneering study introduces nanoemulsion technology to improve the nutritional profile of pasta by enriching it with vitamin E. The research demonstrates the successful formulation of stable nanoemulsions and their positive effects on pasta properties, suggesting promising avenues for improving public health through innovative pasta enrichment methods.

High internal phase double emulsions stabilized by modified pea protein-alginate complexes: Application for co-encapsulation of riboflavin and β-carotene

The application of many hydrophilic and hydrophobic nutraceuticals is limited by their poor solubility, chemical stability, and/or bioaccessibility. In this study, a novel Pickering high internal phase double emulsion co-stabilized by modified pea protein isolate (PPI) and sodium alginate (SA) was developed for the co-encapsulation of model hydrophilic (riboflavin) and hydrophobic (β-carotene) nutraceuticals. Initially, the effect of emulsifier type in the external water phase on emulsion formation and stability was examined, including commercial PPI (C-PPI), C-PPI-SA complex, homogenized and ultrasonicated PPI (HU-PPI), and HU-PPI-SA complex. The encapsulation and protective effects of these double emulsions on hydrophilic riboflavin and hydrophobic β-carotene were then evaluated. The results demonstrated that the thermal and storage stabilities of the double emulsion formulated from HU-PPI-SA were high, which was attributed to the formation of a thick biopolymer coating around the oil droplets, as well as thickening of the aqueous phase. Encapsulation significantly improved the photostability of the two nutraceuticals. The double emulsion formulated from HU-PPI-SA significantly improved the in vitro bioaccessibility of β-carotene, which was mainly attributed to inhibition of its chemical degradation under simulated acidic gastric conditions. The novel delivery system may therefore be used for the development of functional foods containing multiple nutraceuticals.

Encapsulation Properties of Mentha piperita Leaf Extracts Prepared Using an Ultrasound-Assisted Double Emulsion Method

Double emulsions (W1/O/W2) have long been used in the food and pharmaceutical industries to encapsulate hydrophobic and hydrophilic drugs and bioactive compounds. This study investigated the effect of different types of emulsifiers (plant- vs. animal-based proteins) on the encapsulation properties of Mentha piperita leaf extract (MLE) prepared using the double emulsion method. Using response surface methodology, the effect of ultrasound-assisted extraction conditions (amplitude 20-50%; time 10-30 min; ethanol concentration 70-90%) on the total phenolic content (TPC) and antioxidant activity (percent inhibition) of the MLE was studied. MLE under optimized conditions (ethanol concentration 76%; amplitude 39%; time 30 min) had a TPC of 62.83 mg GA equivalents/g and an antioxidant activity of 23.49%. The optimized MLE was encapsulated using soy, pea, and whey protein isolates in two emulsifying conditions: 4065× g/min and 4065× g/30 s. The droplet size, optical images, rheology, and encapsulation efficiency (EE%) of the different encapsulated MLEs were compared. The W1/O/W2 produced at 4065× g/min exhibited a smaller droplet size and higher EE% and viscosity than that prepared at 4065× g/30 s. The higher EE% of soy and pea protein isolates indicated their potential as an effective alternative for bioactive compound encapsulation.

Optimization of preparation conditions and in vitro sustained-release evaluation of a novel nanoemulsion encapsulating unsaturated guluronate oligosaccharide

Unsaturated guluronate oligosaccharide (GOS) was prepared from alginate-derived homopolymeric blocks of guluronic acid by alginate lyase-mediated depolymerization. In this study, a GOS-based water-in-oil-in-water (W1/O/W2) nanoemulsion was prepared, and different influencing factors were investigated. First, linseed oil was selected as the optimal carrier oil. Then, other optimal conditions of the GOS nanoemulsion were determined based on response surface methodology (RSM). Under the optimal conditions, the obtained GOS nanoemulsion showed a spherical structure with an average particle size of 273.93 ± 8.91 nm, and its centrifugal stability was 91.37 ± 0.45 %. Moreover, the GOS nanoemulsion could achieve the aim of sustained release in vitro and be stably stored at 4°C for at least 5 days. This work prepared a novel GOS-based W1/O/W2 nanoemulsion that may effectively address the storage difficulties of unsaturated GOS and provides a valuable contribution to the application of GOS in the food and medicine fields.

Tea polyphenols encapsulated in W/O/W emulsions with xanthan gum-locust bean gum mixture: Evaluation of their stability and protection

Herein, improvement of the stability of the water-in-oil-in-water (W/O/W) emulsions by addition of xanthan gum (XG)/locust bean gum (LBG) mixture in the inner water phase was aimed. The impact of XG/LBG mixture on the physical stability, microstructure and rheological properties of W/O/W emulsions was investigated. It was found that, compared with the control emulsions, the presence of XG/LBG mixture could improve the stability of W/O/W emulsions against coalescence. The tea polyphenols (TPPs) and XG/LBG mixture were simultaneously included in the internal aqueous phase of the double emulsion and stored at 25 and 40 °C in the dark for 28 d. The results showed that XG/LBG mixture not only had a protective role for TPPs encapsulated in the internal water phase, but also maintained more than 50% of the antioxidant capacity of TPPs.

Fabrication and characterization of double (W1/O/W2) emulsions loaded with bioactive peptide/polysaccharide complexes in the internal water (W1) phase for controllable release of bioactive peptide

The objective of this study was to develop food-grade double emulsions containing bioactive peptide (BP)/polysaccharide (P) complexes and to investigate their thermal stability (e.g., BP release) at different temperatures. The BP/P complexes were formed via electrostatic interactions, and successfully encapsulated into the internal water phase of double emulsions with different oil phases. All emulsions clearly showed temperature dependence during storage. BP/P complex-loaded double emulsions showed higher thermal stability and lower release of encapsulated BP (45 °C: < 1%, 65 °C: < 30%) over time, which effectively prevented BP release within the emulsion system. For the effect of the oil phase, the BP released from double emulsions was in the order of MCT > coconut > canola oil. Thus, we concluded that BP release can be controlled in double emulsions by differently charged polysaccharides and oil types and that BP/P-loaded double emulsions can be utilized as functional ingredients for developing heat-sensitive food products.

Strategy to improve crude oil biodegradation in oligotrophic aquatic environments: W/O/W fertilized emulsions and hydrocarbonoclastic bacteria

We studied petroleum biodegradation by biostimulation by using water in oil in water (W/O/W) double emulsions. These emulsions were developed using seawater, canola oil, surfactants, and mineral salts as sources of NPK. The emulsions were used in the simulation of hydrocarbon bioremediation in oligotrophic sea water. Hydrocarbon biodegradation was evaluated by CO2 emissions from microcosms. We also evaluated the release of inorganic nutrients and the stability of the emulsion's droplets. The double emulsions improved CO2 emission from the microcosms, suggesting the increase in the hydrocarbon biodegradation. Mineral nutrients were gradually released from the emulsions supporting the hydrocarbon biodegradation. This was attributed to the formation of different diameters of droplets and therefore, varying stabilities of the droplets. Addition of the selected hydrocarbonoclastic isolates simulating bioaugmentation improved the hydrocarbon biodegradation. We conclude that the nutrient-rich W/O/W emulsion developed in this study is an effective biostimulation agent for bioremediation in oligotrophic aquatic environments.

Ultrasound-assisted production of palm oil-based isotonic W/O/W multiple nanoemulsion encapsulating both hydrophobic tocotrienols and hydrophilic caffeic acid with enhanced stability using oil-based Sucragel

In this work, the effects of thickeners and tonicity towards producing stable palm oil-based water-in-oil-in-water (W/O/W) multiple nanoemulsion using ultrasound and microfluidizer were investigated. Palm oil, Sucragel, polyglycerol polyricinoleate, Tween 80, Xanthan gum, and NaCl were used. W/O/W was formed under the optimized conditions of ultrasound at 40% amplitude and for 180 s of irradiation time, whereas for the microfluidizer, the optimized conditions were 350 bar and 8 cycles. This is the first work that successfully utilized Sucragel (oil-based thickener) in imparting enhanced stability in W/O/W. W/O/W with isotonic stabilization produced the lowest change in the mean droplet diameter (MDD), NaCl concentration, and water content by 1.5%, 2.6%, and 0.4%, respectively, due to reduced water movement. The final optimized W/O/W possessed MDD and dispersity index of 175.5 ± 9.8 and 0.232 ± 0.012, respectively. The future direction of formulating stable W/O/W would be by employing oil phase thickeners and isotonicity. The observed ~12 times lesser energy consumed by ultrasound than microfluidizer to generate a comparable droplet size of ~235 nm, further confirms its potential in generating the droplets energy-efficiently.

Impact of fat crystallization on the resistance of W/O/W emulsions to osmotic stress: Potential for temperature-triggered release

Water-in-oil-in-water (W/O/W) emulsions can be designed to encapsulate, protect, and release both hydrophilic and hydrophobic functional compounds. In this study, we examined the impact of crystallizing the fat phase on the resistance of W/O/W emulsions to osmotic stress, with the aim of developing osmotic-responsive systems. Polyglycerol polyricinoleate (PGPR) was used as a hydrophobic surfactant to stabilize the inner water droplets, while Quillaja saponin and whey protein isolate (WPI) were used as hydrophilic surfactants to coat the oil droplets. The impact of fat crystallization was examined by using either a liquid (soybean oil, SO) or semi-solid (hydrogenated soybean oil, HSO) fat as the oil phase. An osmotic stress was generated by establishing a sucrose concentration gradient between the internal and external water phases. Alterations in the droplet size, morphology, and stability of the W/O/W emulsions was measured when the sucrose concentration gradient was changed. The W/O droplets in the SO-emulsions swelled/shrank when the external sucrose concentration was below/above the internal sucrose concentration, which is indicative of water diffusing into/out of the droplets. Conversely, there was no change in the size of the W/O droplets in the HSO-emulsions under the same conditions, which was attributed to the mechanical strength of the fat crystal network resisting swelling or shrinking. HSO-emulsions did exhibit swelling when they were heated above a critical temperature, due to melting of the fat crystals and disruption of the crystal network. Our results demonstrate that crystallization of the oil phase of W/O/W emulsions can prevent water transport due to osmotic stress, which may be useful for developing temperature-triggered delivery systems for application in foods, cosmetics, pharmaceuticals, or personal care products.

Evaluating the Stability of Double Emulsions—A Review of the Measurement Techniques for the Systematic Investigation of Instability Mechanisms

Double emulsions are very promising for various applications in pharmaceutics, cosmetics, and food. Despite lots of published research, only a few products have successfully been marketed due to immense stability problems. This review describes approaches on how to characterize the stability of double emulsions. The measurement methods are used to investigate the influence of the ingredients or the process on the stability, as well as of the environmental conditions during storage. The described techniques are applied either to double emulsions themselves or to model systems. The presented analysis methods are based on microscopy, rheology, light scattering, marker detection, and differential scanning calorimetry. Many methods for the characterization of double emulsions focus only on the release of the inner water phase or of a marker encapsulated therein. Analysis methods for a specific application rarely give information on the actual mechanism, leading to double emulsion breakage. In contrast, model systems such as simple emulsions, microfluidic emulsions, or single-drop experiments allow for a systematic investigation of diffusion and coalescence between the individual phases. They also give information on the order of magnitude in which they contribute to the failure of the overall system. This review gives an overview of various methods for the characterization of double emulsion stability, describing the underlying assumptions and the information gained. With this review, we intend to assist in the development of stable double emulsion-based products.

Bioaccessibility study of calcium and vitamin D3 co-microencapsulated in water-in-oil-in-water double emulsions

Calcium and vitamin D₃ were co-encapsulated in three types of water-in-oil-in-water (W/O/W) double emulsions stabilized with biopolymers: gum arabic, sodium alginate (Alg) and chitosan (Ch). Three calcium salts with different solubility were used: calcium carbonate (CaC), tricalcium phosphate (CaP) and calcium gluconate (CaG). In order to study the bioavailability of calcium and vitamin D₃, the W/O/W double emulsions were subjected to digestion in simulated conditions using in vitro gastrointestinal models. The size of the oil droplets of all double emulsions increased in oral phase and decreased in gastric and intestinal phases. In the intestinal phase, the average diameter of oil globules in the W/O/W(Alg) and W/O/W(Ch) was d₂₃ = 6.56 ± 0.09 and d₂₃ = 5.33 ± 0.01 and the electro-kinetic potential was: ζ ≈ -25 mV and ζ ≈ -17 mV, respectively. Presence of calcium ions in the intestinal fluid decreased the free fatty acids content and decreased the bioaccessibility of vitamin D₃ due to the inhibition of micellization process.

Water-in-oil-in-water double emulsions loaded with chlorogenic acid: release mechanisms and oxidative stability

Chlorogenic acid (CA) is a natural compound used as an antioxidant in the preparation of food, drugs, and cosmetics. Due to their low stability and bioavailability, many researchers have studied the encapsulation of CA in various delivery colloidal systems. The aim of this study was to evaluate the stability of water-in-oil-in-water (W/O/W) double emulsions loaded with CA and its antioxidant capacity. For this purpose, CA-W/O/W double emulsions were prepared using Span 80 and lecithin as lipophilic emulsifiers, and Tween 20 as a hydrophilic emulsifier. The influence of nature of lipophilic emulsifiers, the presence of chitosan (CH) in the internal and external aqueous phases, pH, temperature and the storage time of W/O/W double emulsions were also investigated. Depending on the preparation conditions, the W/O/W double emulsions showed the droplet size in the range 9.13 ± 0.55 μm-38.21 ± 1.87 μm, the creaming index 34%-78% and the efficiency encapsulation 79.45 ± 1.5%-88.13 ± 1.9%. Zeta potential values were negative for the W/O/W double emulsion without CH (-36.8 ± 2.02mV; -27.3 ± 1.75mV) and positive for the W/O/W double emulsions with CH in the external aqueous phase (+6.5 ± 0.42mV; 28.6 ± 0.92mV). The study of the release of CA from W/O/W double emulsions has highlighted two mechanisms: one based on the coalescence between the water inner droplets or between the oil globules as well as a diffusion releasing mechanism. The oxidative stability parameters of the W/O/W double emulsions, such as the peroxide value (POV) and the conjugated diene content (CD) were measured.

Effect of outer water phase composition on oil droplet size and yield of (w1/o/w2) double emulsions

In this study the effect of various emulsifiers (whey protein isolate (WPI), Na-caseinate, and Tween 20) and thickeners (xanthan and pectin) present in the outer water phase, w₂, on oil droplet size and yield of the inner water phase, w₁, of (w₁/o/w₂) double emulsions was investigated. Double emulsions stabilized by Tween 20 had smaller oil droplet sizes and higher yields in comparison to emulsions stabilized by WPI and Na-caseinate. Gelation of the inner water droplets w₁ increased yield by 20% for all emulsifiers. Upon the addition of thickeners, the increasing viscosity of the outer water phase, w₂, facilitated oil droplet breakup. This resulted in smaller oil droplets and lower yields. When pectin was used as a thickener, in comparison to xanthan, an additional decrease in yield was observed. The yield decreased to values close to zero indicating that all inner water droplets w₁ were lost during emulsification. We conclude that type of hydrophilic emulsifier, properties of inner water droplets, viscosity ratio of continuous and dispersed phase, as well as type of thickener influence oil droplet size and yield of w₁ phase of double emulsions. This work provides a better understanding of how composition influences the properties of double emulsions and how this can be used to design double emulsions as fat replacers in more complex food systems.

Tayloring W/O/W emulsion composition for effective encapsulation: The role of PGPR in water transfer-induced swelling

The role of the lipophilic surfactant, polyglycerol polyricinoleate (PGPR) in water transfer in food-grade double emulsions was investigated, and related to physical emulsion stability. Double (W/O/W) emulsions were prepared with various PGPR concentrations (0.5-5.0 wt%) in the oil phase, at initial osmotic pressure differences of up to 1.1 MPa between the water phases. At high PGPR concentrations (>2 wt%), emulsions showed good physical stability, with encapsulation efficiency close to 100%. It was found that PGPR is involved in water transfer between the water phases through reverse micelle formation by PGPR molecules or hydrated monomers of PGPR, and this allows for controlled swelling. Emulsions that are initially of low viscosity (milk-like emulsions), obtain an apparent viscosity of up to 3 Pa·s, and this effect can be used to tune the emulsion properties to the targeted application, whithout the need to gel either the internal or external phase.

Bulk double emulsification for flow cytometric analysis of microfluidic droplets

Droplet microfluidics is valuable for applications in chemistry and biology, but generates massive numbers of droplets that must be analyzed and sorted. Here, we describe a simple approach to bulk double emulsify microfluidic emulsions for analysis and sorting with commercial flow cytometers. We illustrate the method by using it to identify droplets based on nucleic acid content. Though simple, our method provides a general approach for analyzing and sorting microfluidic droplets without custom microfluidic double emulsifiers or sorters.

Water fluxes and encapsulation efficiency in double emulsions: impact of emulsification and osmotic pressure unbalance

We study the influence of the emulsification process on encapsulation efficiency of drugs in double water-in-oil-in-water emulsions. Two drugs were used, first vitamin B12 which can be considered as a model drug and secondly a suspension of Cydia pomonella Granulovirus (CpGV), a virus used in organic agriculture to protect fruits against the Carpocapse insect. Encapsulation is measured by classical UV-Vis spectroscopy method. Additionally we show that rheology is a useful tool to determine water exchanges during emulsification. In a two-step emulsification process, using rotor-stator mixers, encapsulation reaches high levels, close to 100% whatever the flowing regime. This encapsulation decreases only if two conditions are fulfilled simultaneously: (i) during the second emulsification step the flow is turbulent and (ii) it leads to excessive fragmentation inducing formation of too small drops. We also investigate the effect of a deliberate loss of osmotic pressure balance on the encapsulation and characterize the induced water fluxes. We show that encapsulation of vitamin B12 is not affected by the osmotic pressure unbalance, while water exchanges, if they exist, are very fast and aim at restoring equilibrium. As a consequence, the emulsification efficiency is not very sensitive to osmotic stresses provided that the interfaces resist mechanically.

Modulating the release of Escherichia coli in double W1/O/W2 emulsion globules under hypo-osmotic pressure

Bacterial release from double W₁/O/W₂ emulsion globules under hypo-osmotic pressure is described for the first time.

Crocin loaded nano-emulsions: Factors affecting emulsion properties in spontaneous emulsification

Spontaneous emulsification may be used for encapsulating bioactive compounds in food and pharmaceutical industry. It has several advantages over high energy and other low energy methods including, protecting sensitive compounds against severe conditions of high energy method and its ability to minimize surfactant, removal of cosurfactant and thermal stability compared with other low energy methods. In this study, we examined possibility of encapsulating highly soluble crocin in W/O micro-emulsions using spontaneous method which further could be used for making double emulsions. Nonionic surfactants of Span 80 and polyglycerol polyricinoleate (PGPR) were used for making micro-emulsions that showed the high potential of PGPR for spontaneous method. Surfactant to water ratio (SWR%) was evaluated to find the highest amount of aqueous phase which can be dispersed in organic phase. Droplet size decreased by increasing SWR toward the SWR=100% which had the smallest droplet size and then increased at higher levels of surfactant. By increasing SWR, shear viscosity increased which showed the high effect of PGPR on rheological properties. This study shows in addition to W/O micro-emulsions, spontaneous method could be used for preparing stable O/W micro-emulsions.

Encapsulation, protection, and release of hydrophilic active components: potential and limitations of colloidal delivery systems

There have been major advances in the development of edible colloidal delivery systems for hydrophobic bioactives in recent years. However, there are still many challenges associated with the development of effective delivery systems for hydrophilic bioactives. This review highlights the major challenges associated with developing colloidal delivery systems for hydrophilic bioactive components that can be utilized in foods, pharmaceuticals, and other products intended for oral ingestion. Special emphasis is given to the fundamental physicochemical phenomena associated with encapsulation, stabilization, and release of these bioactive components, such as solubility, partitioning, barriers, and mass transport processes. Delivery systems suitable for encapsulating hydrophilic bioactive components are then reviewed, including liposomes, multiple emulsions, solid fat particles, multiple emulsions, biopolymer particles, cubosomes, and biologically-derived systems. The advantages and limitations of each of these delivery systems are highlighted. This information should facilitate the rational selection of the most appropriate colloidal delivery systems for particular applications in the food and other industries.

Understanding and controlling the release mechanism of Escherichia coli in double W1/O/W2emulsion globules in the presence of NaCl in the W2phase

The results suggest that release of bacteria from W₁/O/W₂emulsion can be controlled by varying the formulation. Release occurs due to oil globule bursting independent to diffusion.

Synergistic combination therapy using a lipid shell-droplet core nanosphere with tunable thickness

A newly-designed drug carrier composed of an internal droplet core and a thickness-controllable shell was successfully developed. By co-delivering paclitaxel, doxorubicin and quantum dots simultaneously, this combinational drug delivery system could achieve in vitro fluorescence imaging, chemotherapeutic and oxidation therapy.

Breaking of the Bancroft rule for multiple emulsions stabilized by a single stimulable polymer

We investigated emulsions of water and toluene stabilized by (co)polymers consisting of styrene (S) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) monomer units with different compositions and structures such as a PDMAEMA homopolymer, a P(S-co-DMAEMA) random copolymer and various PS-b-PDMAEMA and PS-b-(S-co-DMAEMA) block copolymers. The model system is used to study the fundamental conditions under which the different kinds of polymer-stabilized emulsions (direct oil in water, inverse water in oil and multiple emulsions) are stabilized or destabilized by pH change (at constant temperature). Polymer properties like chain conformation at the toluene-water interface as probed by SANS and neutron reflectivity at the liquid-liquid interface, the oil-water partitioning of the polymer chains (Bancroft's rule of thumb) as determined by UV spectroscopy and interfacial tensions measured by the rising and spinning drop techniques are determined. Overall, results evidence that the curvature sign, as defined by positive and negative values as the chain segments occupy preferentially the water and toluene sides of the interface respectively, reliably predicts the emulsion kind. In contrast, the Bancroft rule failed at foreseeing the emulsion type. In the region of near zero curvature the crossover from direct to inverse emulsions occurs through the formation of either unstable coexisting direct and inverse emulsions (i) or multiple emulsions (ii). The high compact adsorption of the chains at the interface as shown by low interfacial tension values does not allow to discriminate between both cases. However, the toluene-water partitioning of the polymeric emulsifier is still a key factor driving the formation of (i) or (ii) emulsions. Interestingly, the stabilization of the multiple emulsions can be tuned to a large extent as the toluene-water polymer partitioning can be adjusted using quite a large number of physico-chemical parameters linked to polymer architecture like diblock length ratio or polymer total molar mass, for example. Moreover, we show that monitoring the oil-water partitioning aspect of the emulsion system can also be used to lower the interfacial tension at low pH to values slightly higher than 0.01 mN m(-1), irrespective of the curvature sign.