Stabilization of CO2‐in‐water emulsions with high internal phase volume using PVAc‐b‐PVP and PVP‐b‐PVAc‐b‐PVP as emulsifying agents

Two newly‐designed hydrocarbon surfactants, that is, poly(vinyl acetate)‐block‐poly(1‐vinyl‐2‐pyrrolidone) (PVAc‐b‐PVP) and PVP‐b‐PVAc‐b‐PVP, were synthesized using reversible addition–fragmentation chain transfer polymerization and used to form CO₂/water (C/W) emulsions with high internal phase volume and good stability against flocculation and coalescence up to 60 h. Their structures were precisely determined by nuclear magnetic resonance, gel permeation chromatography, thermal gravimetric analysis, and differential scanning calorimetry. Besides low temperature and high CO₂ pressure, the surfactant structures were the key factors affecting the formation and stability of high internal phase C/W emulsions, including the polymerization degrees of CO₂‐philic block (PVAc) and hydrophilic block (PVP), as well as the number of hydrophilic tail. The surface tension of the surfactant aqueous solution and the apparent viscosity of the C/W emulsions were also measured to characterize the surfactants efficiency and effectiveness. The surfactants with double hydrophilic tails showed stronger emulsifying ability than those with single hydrophilic tail. The great enhancement of the emulsions stability was due to decrease of the interface tension as well as increase of the steric hindrance in the water lamellae, preventing a frequent collision of CO₂ droplets and their fast coalescence. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46351.     

Effects of Surfactant Headgroups on Oil-in-Water Emulsion Droplet Formation: An Experimental and Simulation Study

Nonpolar oils such as kerosene and diesel oil are common collectors in coal flotation. Surfactants are usually added to the pulp to emulsify the oil collectors. The present study used dodecane as the oil collector and anionic sodium dodecyl sulfonate (SDS) and nonionic tetraethylene glycol monododecyl ether (C₁₂EO) with different headgroups and identical chain alkyls to investigate the effect of the surfactant headgroups on oil-in-water emulsion droplet formation. The morphology and stability of dodecane emulsions were determined experimentally. Density functional theory (DFT) and molecular dynamics (MD) simulations were used to explain the microscopic mechanism. The results of DFT indicated a larger interaction between SDS and the water molecules than that between C₁₂EO and water molecules. The results obtained by MD suggested that the SDS headgroup exhibited a loose arrangement and a relatively large gap size, thereby weakening the interaction between SDS and water molecules at the dodecane/water interface. In contrast, the headgroups of C₁₂EO were bent and interwoven with others to form a tight reticulation at the interface. According to the simulation results, the ability of the surfactant to form dodecane-in-water emulsion droplets depends on the arrangement of the surfactants at the oil–water interface rather than on the interaction strength between the headgroups of the surfactants and water molecules. The presented microscopic mechanism of the surfactant headgroup formation of oil-in-water emulsion droplets offers surfactant selection and design references.     

Relation of Supersaturation Ratio in Mixed Anionic Surfactant Solutions to Kinetics of Precipitation with Calcium

One synergism of using surfactant mixtures is the reduction in the equilibrium extent of and rate of precipitation. The overall time required for calcium-induced precipitation of mixed sodium dodecyl sulfate (SDS) and sodium octylbenzene sulfonate (SOBS) over a particular range of ratios has been found to increase dramatically when compared to either SDS or SOBS alone. In this study, light transmission and isoperibol calorimetry were used to measure the delay in the precipitation reaction, while scanning electron and optical micrographs of crystals formed give insight into the precipitation mechanism. The smaller the difference in the supersaturation ratio of the two precipitating surfactants, the longer the induction time is. The delay in the extent of precipitation is due to the interruption of crystal formation from dissimilar precipitating surfactants.     

Use of a Nonionic Surfactant to Inhibit Precipitation of Anionic Surfactants by Calcium

One synergism of using surfactant mixtures is the reduction in the equilibrium extent of and rate of precipitation. The overall time required for calcium-induced precipitation of mixed sodium dodecyl sulfate (SDS) and sodium octylbenzene sulfonate (SOBS) over a particular range of ratios has been found to increase dramatically when compared to either SDS or SOBS alone. In this study, light transmission and isoperibol calorimetry were used to measure the delay in the precipitation reaction, while scanning electron and optical micrographs of crystals formed give insight into the precipitation mechanism. The smaller the difference in the supersaturation ratio of the two precipitating surfactants, the longer the induction time is. The delay in the extent of precipitation is due to the interruption of crystal formation from dissimilar precipitating surfactants.     

Nanoporous zirconium oxide prepared using the supramolecular templating approach

Hexagonal (Hx-ZrO₂) and lamellar (L-ZrO₂) phases of zirconium oxide have been prepared using the supramolecular templating approach. Long chain primary alkyl amines led to the formation of lamellar phases, while quaternary ammonium surfactants gave hexagonal phases. The materials have been characterized by XRD, TG/DTG, IR, XPS, SEM and EDX techniques. The influence of various synthesis parameters such as (i) the ZrO₂ surfactant ratio, (ii) the surfactant/water ratio, (iii) the nature of surfactant, (iv) the crystallization temperature and (v) the crystallization time have been investigated. The final solid products were found to be thermally unstable regardless of their structure. Removal of the surfactant from the mesopores by solvent extraction without damaging the structure was not possible.     

Development of novel cosmetic base using sterol surfactant. I. Preparation of novel emulsified particles with sterol surfactant+

We have developed various kinds of ultrafine emulsifying methods using random copolymer of polyoxyethylene (POE)/polyoxypropylene (POP) dimethyl ether [EPDME]. Among ultrafine emulsions made by these methods, it was revealed that an O/W type emulsion, which had prepared with EPDME, sterol surfactant, and polar oils, had a unique structure that had a lamellar structure on the surface of emulsified particles. To clarify the character of the particles and the mechanism of the emulsification, investigation using small angle X-ray scattering (SAXS) measurement and the phase diagram of the emulsion system was done. FF-TEM observation indicated that a few lamellar layers were deposited from the oily ingredients on the surface of the emulsified particle. It was also presumed that the lamellar structure was formed with sterol surfactant and polar oil. The phase diagram analysis suggested that EPDME could form emulsified particles having lamellar structure on the surface of the particle with hydrophilic sterol surfactant in polar oils.     

Solid-state complexes of poly(N-vinyl-pyrrolidone) and dodecyl benzene sulfonic acid: Self-assembled structure and thermal properties

Solid-state complexes of flexible polymers with long-tail surfactants (surf) exhibit mesomorphic phase and microphase-separated lamellar morphology consisting of alternating polymer and surf layers. The alkyl tails in the surf layers are highly stretched and closely packed due to the excluded volume effect. In this study, the self-assembled structure of a new polymer(surf) complex system based on complexation between poly(N-vinyl pyrrolidone) (PVP) and dodecyl benzene sulfonic acid (DBSA) was investigated by optical microscopy and small-angle X-ray scattering (SAXS). Both mesomorphic phases and microphase-separated lamellar morphology were observed in PVP(DBSA) complexes. The thicknesses of polymer and surf layers were determined from the one-dimensional correlation function. Both types of thickness are dependent on complex composition. The interplay between chain conformational entropy and interaction energies (repulsive and attractive) is suggested to control the self-organized structure in the complexes. Complexation with DBSA reduced the thermal stability of PVP, which was in contrast with poly(ethyleneimine)-DBSA complexes reported previously.     

The phase behaviors of cationic and anionic aqueous mixtures and the usage as templates for synthesis of mesoporous materials

Liquid crystals formed in aqueous mixtures of cationic and anionic surfactants were used as structure- directing templates for preparation of mesoporous silicas. For this purpose, micellar particle sizes and liquid crystal regions in the mixed system containing cetyl trimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) were investigated by Melvin laser particle size analyzer and polarizers, respectively. The formation of large organized assemblies was closely related to both the total surfactant concentrations and mixing ratios. Micelles formed at low total concentration while liquid crystals formed at high total concentration. The mixtures of CTAB and SDS favored the formations of large organized assemblies when the molar fraction of CTAB was 0.30 or 0.70. Using tetraethoxysilane as precursor and liquid crystals as templates, mesoporous silicas were prepared at different total concentrations of surfactants when molar fraction of CTAB was fixed at 0.70. Transmission electron microscopy results revealed that ordered mesoporous silicas with lamellar pore channels were prepared. Nitrogen adsorption-desorption determinations showed that these materials exhibited a pore size about 4.5 nm. In addition, the surface areas increased significantly with the increase of total surfactant concentrations. This work provided a simple and effective approach to synthesize lamellar mesoporous silicas.     

Gemini型表面活性剂在离子液体中构筑的溶致液晶

通过差示扫描量热仪(DSC)、X射线衍射仪(XRD)、热台偏光显微镜(POM)和红外光谱仪等手段研究了Gemini表面活性剂在硝酸乙基铵(EAN)中构筑的溶致液晶体系(lyotropic liquid crystal,LLc)的性质。结果表明,在液晶区内,所形成的溶致液晶均为层状介晶A相(SmA),且EAN主要存在于液晶相分子层的极性亚层中;液晶相稳定存在的温度区间随Gemini表面活性剂的浓度、尾链长度的增加而变大,随联接链的增加表现出先增大再减小的趋势;羟基削弱了离子头基与反离子间的相互作用,进而缩小了液晶相稳定存在的温度区间。     

Making homogeneous and fine droplet O/W emulsions using nonionic surfactants

In many emulsion systems, creaming occurs during the first stage of emulsion breakdown. To reduce the rate of creaming, emulsions having small and uniform droplets are desirable. In this work, types and HLB of nonionic surfactants, emulsification methods, and combinations of oils and nonionic surfactants were investigated in order to make stable and homogeneous emulsions. Emulsification was attained by dissolving the surfactants in the oil phases. The addition speed and volume of water to the oil phases were important factors affecting the emulsion droplet size. The change of the solute state in the process of emulsification was observed stage by stage, and the mechanism of emulsification was elucidated. Homogeneous emulsions were formed in the HLB region, showing liquid crystalline and gel phases in the emulsifying process. The addition speed of water to the oil phase was very important in forming the liquid crystalline and gel phases. Polyoxyethylene(n)sorbitan monostearate could emulsify three kinds of oils (hydrocarbon, fatty acid ester and triglyceride). Polyoxyethylene(n)alkyl ether could emulsify hydrocarbon and fatty acid ester. Polyoxyethylene(n)-monostearate could emulsify only hydrocarbon. Surfactants with proper HLB which were soluble in the oil phase and in the presence of a very small amount of water formed a stable emulsion. The solubility state of oil and surfactant was the key to making a fine emulsion.     

Phase inversion of polyacrylamide‐based inverse‐emulsions: Influence of inverting‐surfactant type and concentration

The phase inversion of polymeric water‐in‐oil emulsions has been systematically studied by employing nonylphenol and alcohol ethoxylates with various chemistries as well as physical chemical characteristics. A combination of thermodynamics, phase diagrams, and rheometry were used to investigate the behavior of the inverting surfactants as well as the inverted, acrylamide‐based, cationic emulsions. Polymeric inverse‐emulsions containing the inverting surfactant showed no evidence of low‐shear thinning, though they did thin as hydrodynamic forces increased (0.01 to 100 s^?1) prior to reaching a chemistry‐ and concentration‐independent plateau, as is typical for emulsions. The viscosity of emulsions containing inverting surfactants reached a minimum at 1.2% of the “emulsion breaker”. The efficiency of inversion was optimized at 2 wt % of nonylphenols, expressed as a percentage of the total emulsion mass, and increased with the degree of ethoxylation. Interestingly, the viscosity of the polymer inverted in water was maximized at an inverting‐surfactant level corresponding to the CMC of the pure surfactant in water. The alcohol ethoxylates required a higher concentration for inversion (3 wt %), though they provided a higher ultimate inverse viscosity of the polymeric emulsion in water. Therefore, while the inversion process was less efficient with alcohol ethoxylates, the ultimate dilution solution properties of the polyelectrolytes liberated were improved relative to the nonylphenols. Overall, the process of adding a water‐in‐oil emulsion, containing an emulsion breaker, to an excess of water involves a catastrophic inversion mechanism. To be effective under such circumstances, an inverting surfactant should have a partition coefficient between the aqueous an organic phases greatly exceeding unity as well as a hydrophilic–lipophilic balance (HLB) above 12. Effectiveness increases linearly with the partition coefficient. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3567–3584, 2007     

偶联阳离子表面活性剂和常用阴离子表面活性剂混合溶液的相分离和微观结构

The properties of aqueous two-phase system (ATPS) of mixed solution containing gemini cationic surfactant trimethylene-l,3-bis(dodecyldimethyl ammonium) bromide (12-3-12, 2Br-) and traditional anionic surfactant sodium dodecyl sulfate (SDS) with or without added salt have been studied. An ATPS is formed in a narrow region of the ternary phase diagram different from that of traditional aqueous cationic-anionic surfactant systems. In ATPS region, the lowest total concentration of surfactants varies with the mixing ratio of geminis to SDS. Photographs obtained from freeze-etching, negative-staining and transmission electron microscopy show that the microstructures of two phases are different from each other. Micelles and vesicles can coexist in a single phase. The addition of salts can change the phase diagram of ATPS. Furthermore, the added salts promote the aggregation of rod-like micelles to form coarse network structure that increase the viscosity of solutions. The negative ions of the added salts are the determining factor.     

Adsorption,Electrokinetic and Stabilizing Properties of the Guar Gum/Surfactant/Alumina System

The adsorption of non‐ionic polysaccharide guar gum (GG) in the presence of surfactants (anionic SDS, non‐ionic TX‐100, cationic CTAB and their equimolar mixtures) from their NaCl solutions onto an alumina surface (Al₂O₃) was studied spectrophotometrically. This study is important in light of the many disagreements concerning the structure and behaviour of mixtures containing polymers and surfactants at the surface of an adsorbent. The presence of surfactant caused an increase in the GG adsorption in all studied systems as a consequence of the formation of complexes. Among the single surfactants the highest increase in the GG adsorption was observed in the presence of CTAB. However, the usage of mixtures of the surfactants caused a much more effective increase in the GG adsorption on the alumina surface because of the synergistic effect of the surfactants. In order to get some information on the structure of the electrical double layer (edl), the surface charge density of alumina was determined and zeta potential measurements were conducted. The obtained data showed that the adsorption of GG or GG/surfactant complexes on the metal oxide surface strongly influences a diffused part of the edl, whereas a compact part of the edl is not affected. The colloidal stability of the alumina suspensions was measured in the presence and absence of GG and surfactants. It was found that GG and the mixtures of GG and surfactants can improve the stability of the suspensions.     

Structural Analyses of Hydrated Crystals in Mixed Green Surfactant Systems: α‐Sulfonated Fatty Acid Methyl Ester Salt and Fatty Acid Soap Mixtures

α‐Sulfonated fatty acid methyl ester salts (MES), synthesized from renewable plant resources, are an example of green surfactants used in eco‐friendly washing detergents because of their excellent detergent properties, biodegradability, and enzyme stability. Although various physicochemical properties of MES crystals and micelles have been studied, mixed systems composed of MES and other surfactants have not been well studied. We investigated the crystalline structures of hydrated solids in mixed systems containing MES and soaps, which have been utilized as detergents, using small‐ and wide‐angle X‐ray scattering (SWAXS), differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy techniques. The minimum dissolution temperature, determined by visual observation, of a 4:1 M ratio of the sodium salt of α‐sulfonated palmitic acid methyl ester (C₁₆MES‐Na) and sodium palmitate (C₁₆‐Na), is indicative of a eutectic mixture. SWAXS measurements reveal that C₁₆MES‐Na and C₁₆‐Na crystals are formed separately in this system. Eutectic mixtures were also observed for the C₁₆MES‐Na/C₁₆MES‐K (α‐sulfonated palmitic acid methyl ester potassium salt) system and in the C₁₆MES‐K/C₁₆‐Na system. Furthermore, in addition to C₁₆MES‐K and C₁₆‐Na crystals, C₁₆MES‐Na crystals were also formed in the C₁₆MES‐K/C₁₆‐Na system, through counterion exchange during crystallization.     

Phase behavior in liquid crystallization for diblock copolymers consisting of rubbery amorphous and side-chain liquid crystalline components

Phase behavior in liquid crystallization was studied for a series of liquid crystalline (LC) diblock copolymers consisting of rubbery amorphous and side-chain liquid crystalline components, poly(n-butyl acrylate) (PBA) and poly[11-(4′-cyanophenyl-4″-phenoxy)undecyl acrylate] (PLC), respectively, using a time-resolved small-angle X-ray scattering (SAXS) techniques, DSC and polarized optical microscopy (POM). The block copolymers used had three kinds of copolymer compositions, 44, 20 and 15 wt% of PLC compositions (BLC44, BLC20 and BLC15, respectively). BLC44 showed a smectic liquid crystalline structure. In the process of liquid crystallization for BLC44, the SAXS peak due to the microphase separation structure existing before liquid crystallization was changed continuously to be at a smaller angular side, and at almost the same time, a new peak appeared at a further smaller angular side and developed. The former peak disappeared with the development of liquid crystallization. The behavior of these SAXS peaks suggests that the microphase separation structure was changed discretely at the transition from isotropic to smectic and that two phases coexist in the early stage of the liquid crystallization. The coexistence of two peaks in the early stage of the liquid crystallization corresponded to the POM observation. In the isotropization process, coexistence of two phases was not observed. For BLC20 exhibiting a cylindrical structure in both isotropic and liquid crystalline states, the liquid crystalline structure was not smectic but probably nematic, and the spacing was changed continuously in liquid crystallization. No liquid crystallization was observed in SAXS, POM and DSC for BLC15. The orientation of smectic layers within lamellar domains was investigated using 2D-SAXS images. The smectic layer was aligned perpendicularly to the lamellar interface.     

The Impact of Polyoxyethylene Sorbitan Surfactants in the Microstructure and Rheological Behaviour of Emulsions Made With Melted Fat From Cupuassu (<Emphasis Type="Italic">Theobroma grandiflorum</Emphasis>)

Cupuassu fat is a good candidate for partial substitution of cocoa butter in many products, including emulsions. However, for such use it is necessary to know the characteristics of the products prepared with cupuassu fat. Therefore, the main goal of this work is to characterize emulsions prepared with cupuassu fat using the surfactants Tween^® 60, Tween^® 80 and Tween^® 85 as emulsifiers. The emulsions were prepared at 43 °C with addition of 0.5 or 1.5 % (w/v) of surfactant and compared with an emulsion without surfactant. All emulsions were analysed by conductivity, stability, pH, optical microscopy, rheology and oxidative stability. It was verified that the emulsions prepared with Tween^® 60 and Tween^® 80 have higher stability, smaller droplet size and higher apparent viscosity. Also, these properties are positively influenced by the concentration of the surfactant. On the other hand, emulsions prepared with Tween 85 or without surfactant reached unsatisfactory results. The rheological behaviour of the emulsions was adequately described by both Herschel-Bulkley and Mizhari-Berki models revealing pseudoplastic character. These emulsions also present strong gel behaviour, with storage modulus higher than loss modulus. In conclusion, cupuassu fat can be used as oil phase for emulsions products and this characterization helps to understand their behaviour in order to increase their use in food industry.     

Thin layer concentrated emulsion copolymerization of PUASi/Styrene/Methyl methacrylate

Stable concentrated emulsions of polymerizable polysiloxane‐containing polyurethane (PUASi)/Styrene (St)/Methyl methacrylate (MMA) were prepared using sodium dodecyl sulphate (SDS)/nonyl polyoxyethylene ether (OS15)/polyvinyl alcohol (PVA) as composite surfactant and azobisisobutyronitrile (AIBN) as initiator. A novel polymerization method, thin layer polymerization was used to carry out the concentrated emulsion copolymerization at 55°C. The effects of TDI/PPG molar ratio, surfactant concentration, different kinds of surfactants, and temperature on polymerization stability were studied. The effects of the thickness of the thin layer, the outside temperature of the reactor, as well as polymerization environment on the volatilization rate of water, and monomer in the system were investigated. The conversion‐time relationships of the thin layer polymerization and the tube polymerization, as well as the effect of polymerization environment on the polymerization rate were also investigated. The morphology of latex particles was determined with transmission electron microscope (TEM). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and properties of novel alkyl sulfate gemini surfactants

Four anionic gemini surfactants of the sulfate type C₁₂C_nC₁₂, where n is the spacer chain length (n = 3, 4, 6, and 10) were synthesized. The structures of these surfactants were confirmed by FT‐IR, ¹H NMR, ESI mass spectra (ESI‐MS), and elemental analysis. The surface‐active properties of these compounds were investigated by means of surface tension, electrical conductivity, and fluorescence measurements. Premicellar aggregations were found for the four gemini surfactants, as revealed by the conductivity measurement. The formation of premicellar aggregates may account for the discrepancy between the critical micelle concentration (cmc) obtained by the surface tension and conductivity measurement. The cmc values of these gemini surfactants were much lower than that of sodium dodecylsulfate (SDS) and decreased monotonously with the increase of spacer chain length from 3 to 10. The effect of spacer chain length on the performance properties like foaming, emulsion stability, and lime soap dispersing ability were also studied and discussed. Practical applications : Alkyl sulfate surfactants are one of the most widely used surfactants. The new alkyl sulfate gemini surfactants synthesized in our study are more surface‐active than sodium dodecylsulfate. These gemini surfactants possess low critical micelle concentrations, high emulsion stability, and excellent lime soap dispersing ability. They have potential applications in the fields of cosmetics, detergents, etc.     

Enhancing storage stability of emulsions by binding detergents with soy protein isolate and its hydrolysates

Sodium dodecyl sulfate (SDS) is a frequently used anionic detergent, and proteins are among the widely used minor ingredients in cosmetic products. Proteins may enhance the detergent functions and protect human skin from irritation caused by detergents. Soy protein hydrolysates (SPH) were prepared by modifying soy protein (SP) with papain. Varying concentrations of SP or SPH were mixed with various concentrations of SDS at different pH values to determine: (i) molecular characteristics, degree of hydrolysis (DH), and surface hydrophobicity (S ₀) of SP and SPH; (ii) the effect of SDS concentrations on the S ₀ of SP; (iii) the storage stabilities of oil-in-water emulsions formed by SDS, SP, SPH, SP-SDS, and SPH-SDS; and (iv) the effect of protein concentration (0.01 to 1.5%), DH (1.2 to 12.5%), and pH (3.0, 5.0, 7.0, and 9.0) on storage stabilities of emulsions formed by SP-SDS or SPH-SDS. An increase in emulsion stability (ES) with increasing protein concentration was observed. The ES values of emulsions formed by SPH-SDS complexes were significantly higher than those formed by SP-SDS at pH 7.0 and 9.0. The ES of emulsions formed by the complexes were low at pH 5.0 and increased with increasing pH. At pH 3.0 the emulsions formed by SP-SDS at 1 to 1.5% protein concentration and by SPH-SDS at 1.5% protein concentration were very stable. The results indicate that at least one-half of SDS content can be replaced by SP or SPH while maintaining emulsion stability.     

The effects of ethanol content and emulsifying agent concentration on the stability of vegetable oil-ethanol emulsions

In vegetable oil-ethanol emulsions ethanol is the polar phase and vegetable oil is the nonpolar phase. The primary advantage of vegetable oil-ethanol emulsions over conventional water-oil emulsions is that they enable the incorporation of water-and oil-insoluble or poorly soluble functional compounds and/or drugs into emulsions. A number of nonionic surfactants were used to select appropriate stabilizers for stable vegetable oil-ethanol emulsions. We found decaglycerol mono-oleate (MO750) to be the best stabilizer for ethanol-in-oil (E/O) emulsions. The effects of ethanol content and of emulsifying agent concentration on the stability of vegetable oil-ethanol emulsions were examined with MO750. After emulsification, two turbid layers formed simultaneously when ethanol content exceeded 20 wt%. The top layers (oil-in-ethanol emulsions; O/E emulsions) were very unstable, whereas the stability of the bottom layers (E/O emulsions) depended on the ethanol content. The stability of E/O emulsions is closely related to the effective concentration of MO750 aggregates, which play an important role in the film thickness stability of interfacial films formed by surfactant aggregates. Instability of E/O emulsion at 5 wt% MO750 is probably due to the polydispersity (i.e., nonuniform size and shape) of MO750 aggregates at high MO750 concentration. E/O emulsions prepared with 0.1, 0.5, and 1 wt% MO750 were stable, suggesting that the interfacial films formed were effective in protecting the droplets against coalescence and Ostwald ripening.