Parameter Selection of Emulsification Processes: Conditions for Nano‐ and Macroemulsions

Beside factors like nature of the emulsifier as well as rheology of the interface and continuous phase, the droplet size distribution of an emulsion governs emulsion properties such as long‐term stability over months or years, texture, and optical appearance. Consequently, emulsions with droplets in nano‐scale are of interest when well‐defined emulsion properties are needed. The formation of emulsions consisting of water, corn oil, and nonionic surfactants using disc systems and high‐pressure homogenizers was studied. The emulsion droplet size distributions were obtained by means of a laser diffraction method. The influence of parameters affecting the emulsion formation, such as emulsification time, viscosity for the disc system, pressure, and homogenizing steps for high‐pressure homogenization, was investigated. Data to determine the effect of the surfactant type and concentration were collected for both systems. The emulsification process using a disc system was evaluated in order to highlight its advantages and limits in comparison to high‐pressure homogenization.     

Influence of Processing on the Physical Stability of Multiple Emulsions Containing a Green Solvent

The influence of the emulsification process on the microstructure and physical stability of model water‐in‐oil‐in‐water (W/O/W) emulsions formulated with a green solvent and a mixture of amphiphilic copolymers as emulsifiers was investigated. Emulsions were prepared by applying a homogenization step with a rotor‐stator device followed by high‐pressure homogenization. Viscous flow tests, transmitted light optical microscopy, globule size distribution (GSD), and multiple light scattering (MLS) measurements were carried out. The GSDs obtained were the result of a recoalescence due to overprocessing and the coalescence of inner droplets with the outer water phase. MLS detected a main destabilization mechanism by creaming. The passing of the emulsion through a high‐pressure homogenizer (HPH) significantly delayed the creaming process.     

High‐Pressure Homogenization as a Process for Emulsion Formation

Emulsions find a wide range of application in industry and daily life. In the pharmaceutical industry lipophilic active ingredients are often formulated in the disperse phase of oil‐in‐water emulsions. Milk, butter, and margarine are examples of emulsions in daily life. In the metal processing industry emulsions are used in the form of coolants. Emulsions can be produced with different systems. In the following, the process of high‐pressure homogenization is briefly compared to other common mechanical emulsification systems. To facilitate the selection of an emulsification system, the influence of the most important parameters of the emulsion formulation on the resulting mean droplet diameter in the most prevalent continuous emulsification systems is outlined. Subsequently, the most common high‐pressure homogenization systems are discussed in detail. On the basis of data from the literature and own experimental results the described high‐pressure homogenization systems will be compared regarding their attainable mean droplet diameter. It shows that homogenizers with a relatively simple geometry like the patented “combined orifice valve” (Kombi‐Blende) attain the smallest mean droplet diameters. The advantage of the “combined orifice valve” compared to other high‐pressure homogenization systems is not more efficient droplet disruption but rather more efficient droplet stabilization against coalescence immediately after the droplet breakup. The greatest research potential concerning the development of new high‐pressure homogenization systems is still to be seen in improvements of droplet stabilization, i.e., the reduction of coalescence.     

A STUDY OF SILICONE OIL-IN-WATER EMULSIONS

Emulsions of silicone oil-in water were formed using a Brinkmann Polytron homogenizer with Igepal CO-530 as an emulsifier. Silicone viscosities ranged from 10 to 33,000 mPa.s at 25°C. Rheological characteristics and particle size analyses of silicone oil-in-water emulsions were studied. At high volume fraction of the dispersed phase (70%-75%), silicone oil-in-water emulsions were stable. At lower volume fractions (50%-60%), emulsions formed were less stable and the two phases easily separated in a few days. The emulsions formed with high volume fraction silicone oil show highly non-Newtonian behavior (shear thinning). Emulsions made with low viscosity oils had lower viscosities than those made from high viscosity oils. Relative viscosity-concentration data could be correlated by the Frankel and Acrivos Equation. Increasing the emulsifier concentration of 70% oil-in-water emulsions resulted in a decrease in mean droplet size and an increase in emulsion viscosity. Increasing the intensity of agitation also resulted in higher viscosity and smaller droplet size until a critical energy input above which droplet size increased. Emulsification with low shear mixing provides more control in decreasing mean droplet size with time.     

Rotor‐Stator and Disc Systems for Emulsification Processes

Emulsions now find a wide range of applications in industry and daily life. In the pharmaceutical industry lipophilic active ingredients as well as many nutritional products such as vitamins are often formulated in the dispersed phase of oil‐in‐water emulsions. Emulsions can be produced with different mechanical emulsification techniques. In the following review, the process of rotor‐stator systems and disc systems are compared to other popular mechanical emulsification systems. On the basis of experimental results from the authors' laboratory, a discontinuous gear‐rim dispersing system, discontinuous disc system, and a continuous high pressure system are compared with regard to their attainable mean droplet diameter and drop size distribution in an oil‐in‐water emulsion. It can be shown that dissolver discs with a very simple geometry attain very small mean droplet diameters and a very narrow droplet size distribution, comparable to the emulsions obtained with established rotor‐stator systems such as gear‐rim dispersers.     

Factors affecting droplet size of sodium caseinate‐stabilized O/W emulsions containing β‐carotene

This work was initiated to prepare an oil‐in‐water (O/W) emulsion containing β‐carotene by microfluidization. The β‐carotene was dissolved in triolein and microfluidized with an aqueous phase containing sodium caseinate (SC) as the emulsifier. Microfluization at 140 MPa resulted in O/W emulsions with a mean droplet diameter of ca. 120 nm, which was further confirmed by transmission electron microscopy analysis. The influences of SC concentration and microfluidization parameters on the droplet size of the emulsions were studied. The results showed that the mean droplet diameter decreased significantly (p <0.05) from 310 to 93 nm with the increase in SC concentration from 0.1 to 2 wt‐%. However, a further increase in SC concentration did not much change the droplet diameter, although the polydispersity of the emulsions was slightly improved. The droplet diameter of the emulsions was found to decrease from 200 to 120 nm with increasing microfluidization pressure, with narrower droplet size distribution. The storage study showed that the emulsions were physically stable for about 2 weeks at 4 °C in the dark. The results provide a better understanding of the performance of SC in stabilizing the O/W emulsions.     

Preparation of spherical yttrium oxide powders using emulsion evaporation

Water-in-oil type emulsions were used to prepare yttrium oxide powders by evaporation of the yttrium-containing aqueous phase in a hot oil bath. Emulsions were characterized with respect to emulsion type, droplet size distribution and stability. Y₂O₃ powders obtained by this method consisted of small (1–3 μm) spherical granules made up of 0·1 μm crystallites. The effects on the powder of emulsifier concentration, yttrium ion concentration, evaporation temperature and atmosphere were studied.     

Effectiveness of Polyoxyethylene Nonionic Emulsifiers in Emulsification Processes Using Disc Systems

Additives such as emulsifiers and stabilizers (viscosity enhancers or polymers) are needed to stabilize emulsion systems against coalescence and creaming. A way to reduce emulsifier input by determining the effectiveness of different emulsifiers is described. Only disc systems with optimized configuration are applied for emulsification. Polysorbates are taken as an example for emulsifiers. The viscosity was increased with pectin as a viscosity enhancer to allow higher energy inputs by the disc systems and, therefore, to improve droplet disruption. The attainable mean diameters of oil droplets stabilized only by pectin were compared with the resulting mean diameters of oil droplets of emulsions containing polysorbates. Polysorbate 20, the emulsifier with the highest water solubility of all here described emulsifiers, proved to be the most effective in decreasing the mean diameter of the disperse phase when using disc systems. An optimal emulsifier concentration of 2 wt‐% for emulsions at low viscosities is observed for all polysorbates and for the whole range of oil concentration.     

Stabilization of liquid water-in-oil emulsions by modifying the interfacial interaction of glycerol monooleate with aqueous phase ingredients

Glycerol monooleate (GMO)-stabilized liquid water-in-vegetable oil emulsions are difficult to stabilize due to the desorption of GMO from the water-vegetable oil interface toward the oil phase. This work improved the stability of GMO-stabilized liquid 20 wt% water-in-canola oil (W/CO) emulsion by modifying the dispersed aqueous phase composition with hydrogen bond-forming agents. As a control, 20 wt% water-in-mineral oil (W/MO) emulsion was also utilized. Different concentrations of hydrogen bond-forming agents (citric acid (CA), ascorbic acid (AA), low methoxyl pectin (LMP)) with and without salts (sodium chloride (S) or calcium chloride (Ca)) were added to the aqueous phase before emulsification, which enhanced emulsifier binding to the water–oil interface. W/CO emulsion without any aqueous phase additive destabilized instantly, whereas W/MO emulsion stayed stable during the week-long observation. The addition of hydrogen bond-forming agents and salts significantly improved emulsion stability. LMP, with many hydrogen bond-forming groups, was able to provide the highest emulsion stability after 7 days in both oils compared to AA, CA and their mixtures with S. Emulsions with both oils formed weak gels due to the formation of an extensive network of water droplet aggregates. Overall, the hydrogen bond-forming agents interacted with GMO at the interface, thereby favoring their presence at the water droplet surface and significantly improving the stability of liquid W/CO emulsions. The knowledge developed in this research can be useful in utilizing GMO to stabilize liquid water-in-oil emulsions without using any fat crystal network.     

Zum Mechanismus der Stabilisierung von Emulsionen

Mechanism of Stabilization of Emulsions The known mechanisms of stabilization of emulsions by the use of interface-active substances are explained. In emulsions which contain relatively small proportion of the emulsifier, the latter is effective exclusively at the interface between the emulsion droplet and the continuous liquid. In this case the emulsifier causes the formation and stabilization of either an o/w-or a w/o-emulsion, depending on its constitution. The physical and chemical background of the aforesaid phenomenon is discussed. Based on these considerations one can explain the HLB-system as well as the Bancroft's rule governing the relationship between partition equilibrium of the emulsifier and the type of emulsion formed. In emulsions which contain relatively large proportions of the emulsifier, the type of emulsion and its stability may also be influenced by the formation of liquid crystalline mixed phases composed of all the components. A special case is the so called ?Micro-Emulsions”?, which can be considered as micellar solutions of solubilized polar and unpolar oil.     

Preparation and characterization of highly stable monodisperse argan oil‐in‐water emulsions using microchannel emulsification

Argan oil is well known for its nutraceutical properties. Its specific fatty acid composition and antioxidant content contribute to the stability of the oil and to its dietetic and culinary values. There is an increasing interest to use argan oil in cosmetics, pharmaceutics, and food products. However, the formulation of highly stable emulsions with prolonged shelf life is needed. In this study, argan oil‐in‐water (O/W) emulsions were prepared using microchannel (MC) emulsification process, stabilized by different non‐ionic emulsifiers. The effects of processing temperature on droplet size and size distribution were studied. Physical stability of argan O/W emulsions was also investigated by accelerated stability testing and during storage at room temperature (25 ± 2°C). Highly monodisperse argan O/W emulsions were produced at temperatures up to 70°C. The obtained emulsions were physically stable for several months at room temperature. Furthermore, emulsifier type, concentration, and temperature were the major determinants influencing the droplet size and size distribution. The results indicated that a suitable emulsifier should be selected by experimentation, since the interfacial tension and hydrophilic–lipophilic balance values were not suitable to predict the emulsifying efficiency. Practical applications: MC emulsification produces efficiently monodisperse droplets at wide range of temperatures. The findings of this work may be of great interest for both scientific and industrial purposes since highly stable and monodisperse argan oil‐in‐water emulsions were produced which can be incorporated into food, cosmetic, or pharmaceutical formulations.     

Influence of Disperse Phase Characteristics on Stability, Physical and Antimicrobial Properties of Emulsions Containing Cinnamaldehyde

Cinnamaldehyde was delivered in emulsion form using Acetem 90-50K as a carrier and Tween 60 as emulsifier. Cinnamaldehyde interacted with Acetem 90-50K by forming H-bonds. The effect of disperse phase characteristics on storage stability, physical and antimicrobial properties was investigated. A storage test of emulsions was carried out for 15 days at two temperatures (22 and 4 °C). Emulsions and nano-emulsions showed higher stability at 22 °C than at 4 °C. Nano-emulsions displayed excellent stability versus creaming and coalescence after 15 days storage at 22 °C (z-avg <100 nm). Physical properties were greatly affected by droplet size and concentration. Emulsions became less viscous, more transparent and darker as the droplet size or concentration decreased. The antimicrobial activity was measured against Listeria monocytogenes and Escherichia coli. Escherichia coli was highly resistant to cinnamaldehyde compared to L. monocytogenes. Incubation with cinnamaldehyde at 2.5 mM caused the complete inactivation of L. monocytogenes after 1 day and of E. coli after 9 days. There was no difference in the antimicrobial effect of cinnamaldehyde due to different droplet sizes (~80 and ~5,000 nm).     

Influence of Different Factors on the Particle Size Distribution and Solid Fat Content of Water-in-Oil Emulsions

The influence of the variation of different parameters on the particle size distribution and solid fat content (SFC) of water‐in‐oil emulsions was studied. The use of solid fat instead of liquid oil, higher polyglycerol polyricinoleate (PGPR) concentration, or higher homogenization energy led to smaller mean particle sizes. The decrease of the emulsifier/water ratio turned the particle size distribution of the emulsions from bimodal to trimodal. The increase of PGPR concentration increased the SFC of the fat in the absence of water, but it did not produce the same effect in the emulsion. This result suggested that the presence of dispersed aqueous phase prevented the modifying action of the emulsifier on the crystallization of the continuous lipid phase. The experimentation indicated that the adsorption of the surfactant at the interface would reduce its availability to affect crystallization in bulk fat, as the SFC in lipid phase decreased with increasing interfacial area.     

Use of pulsed nuclear magnetic resonance to predict emulsion stability

Pulsed nuclear magnetic resonance (NMR) was used to measure extent of oil solidification during cooling of oil-in-water emulsions. “Percent interaction,” derived from these measurements, was found to correlate well with actual resistance of the emulsion to creaming and phase separation during storage. Average oil droplet size gave a fair correlation with stability, but the correlation of required Hydrophile-Lipophile Balance (HLB) with stability was poor. Pulsed NMR cooling curve measurements on emulsions offer an improved method for prediction of emulsion stability. Presented at the AOCS Meeting in Chicago, September 1976.     

Emulsifier type,metal chelation and pH affect oxidative stability of n‐3‐enriched emulsions

Recent research has shown that the oxidative stability of oil‐in‐water emulsions is affected by the type of surfactant used as emulsifier. The aim of this study was to evaluate the effect of real food emulsifiers as well as metal chelation by EDTA and pH on the oxidative stability of a 10% n‐3‐enriched oil‐in‐water emulsion. The selected food emulsifiers were Tween 80, Citrem, sodium caseinate and lecithin. Lipid oxidation was evaluated by determination of peroxide values and secondary volatile oxidation products. Moreover, the zeta potential and the droplet sizes were determined. Tween resulted in the least oxidatively stable emulsions, followed by Citrem. When iron was present, caseinate‐stabilized emulsions oxidized slower than lecithin emulsions at pH 3, whereas the opposite was the case at pH 7. Oxidation generally progressed faster at pH 3 than at pH 7, irrespective of the addition of iron. EDTA generally reduced oxidation, as evaluated by volatiles formation in all emulsions, irrespective of pH and emulsifier type, except in the lecithin and caseinate emulsions where a pro‐oxidative effect was observed for some volatiles. The different effects of the emulsifier types could be related to their ability to chelate iron, scavenge free radicals, interfere with interactions between the lipid hydroperoxides and iron as well as to form a physical barrier around the oil droplets.     

Preparation of alumina microshells by the emulsion evaporation technique

Spherical hollow alumina powders (alumina microshells) were prepared from evaporation of water-in-oil (w/o) type emulsions by employing an aqueous Al(NO₃)₃ solution as water, mineral oil as the organic phase and a non-ionic surfactant, Arlacel 83, as the emulsifier. It was found that 65% mineral oil, 30% aqueous Al(NO₃)₃ and 5% Arlacel 83 composition produced stable, w/o type emulsions by mechanical stirring at 20°C. The aluminum ion concentration was varied between 0·25 and 2·0 to investigate its effect on the emulsion droplet size. Alumina microshells obtained from the evaporation of w/o emulsions were characterized with respect to size and distribution. The influence of aluminum ion concentration on these properties was also studied.     

玉米油W1/O/W2型多重乳状液稳定性的研究

高脂食品严重危害着人类健康,这引起人们对低脂食品的的不断追求,因此脂肪替代品的开发越来越受到人们重视。本试验以玉米油和生物高聚物为主要原料通过两步乳化法制备W1/O/W2多重乳状液作为脂肪替代品(FS),以离心稳定性为衡量标准,用显微镜直接观察,探讨了初复乳乳化工艺、各相相对体积比对玉米油W1/O/W2型多重乳状液体系稳定性的影响。结果表明:1.影响玉米油多重乳状液稳定性的主要因素有:复乳的乳化工艺,内水相与油相体积之比等。2.两步乳化工艺中第二步乳化工艺对复乳稳定性影响较大,其规律是随着乳化强度的提高,粒径减小,稳定性呈上升趋势,适宜的乳化条件为7200 r.min.1,13 min,而第一步乳化工艺对复乳稳定性几乎没有影响。3.内水相与油相、初乳与外水相均是影响复乳稳定性的主要因素,前者主要是依靠改变初乳黏度来影响复乳稳定性,后者主要是乳滴间范德华力与电排斥力共同作用的结果,适宜的体积比分别为1:4和1:1。     

Facile synthesis of one‐to‐one copy of monomer droplet to latex particle via equilibrium stabilized miniemulsion polymerization

Miniemulsion polymerization has been traditionally used to synthesize latex particles with a high homogenization energy to prepare an oil/water miniemulsion followed by further polymerizations. However, the exact copy of monomer droplets to latex particles depends critically on emulsion formulation, homogenization condition as well as the stability of the miniemulsified droplets after homogenization. In this study, we demonstrated experimentally for the first time that one‐to‐one copy of monomer droplets to latex particles can be synthesized via polymerization of a miniemulsion prepared from a less stringent preparation process including formulation without costabilizer and low homogenization energy. The criterion to obtain narrow size distribution of monomer droplets was established by equilibration of a low energy homogenized emulsion for different keeping time and the bulk homogenized emulsion subsequently phase separated into two layers. Top layer is the polydispersed monomer‐rich phase. The bottom layer is the equilibrium‐stabilized monomer droplet emulsion, in which the size distribution of droplets is narrow. The equilibrium‐stabilized emulsion is stable for days and subsequent polymerization exhibits nearly 100% droplet nucleation. Furthermore, the effect of surfactant/costabilizer and initiator on the one‐to‐one feature for the synthesis of latex particles was investigated in details. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Influence of Nanoparticles and Drop Size Distributions on the Rheology of w/o Pickering Emulsions

The rheological behavior of particle/oil suspensions and w/o Pickering emulsions consisting of water, 1‐dodecene and different fumed silica nanoparticles was investigated. The particles varied in hydrophobicity and specific surface area. The influence of particle concentration and water content on rheology was determined and the emulsion drop size distributions were examined. Emulsions with different drop sizes were created by either varying the particle concentration or the water content. It was found that the particles in the continuous oil phase and not the drop size distribution seem to be the major influencing factor on the Pickering emulsion rheology.     

Emulsifying and self‐emulsified properties of siloxane polymer grafted with easy hydrophile

A series of siloxane polymers (SHE) with varying weight percents of simple nonionic hydrophilic groups have been synthesized and characterized by FTIR and ¹³C‐NMR. Emulsions have been made by self‐emulsification of those polymers in pure water and also by emulsifying silicone oil using those polymers as oil‐in‐water type emulsifiers. The stability of those emulsions have been examined apparently from the phase separation and also from the particle size increase on storage by Transmission Electron Microscopy (TEM) and photo microscopy. The results reviled that SHE 40, having 40 wt % grafted hydrophile, formed the most stable self‐emulsified emulsion, and SHE30 and SHE40 could be used as effective emulsifiers for silicone oil emulsification. The possible use of those emulsions as a defoamer for water‐borne systems has also been investigated by measuring the reduction of foam height of a strongly foamed aqueous solution of sodium lauryl sulfate (SLS). The defoaming ability decreases with the increase in hydrophile wt % in the polymer backbone; however, it increases with the emulsion (defoamer) concentrations. When compared with respect to the total wt % of hydrophobe contents in the emulsion defomer, the self‐emulsified emulsion has shown better defoaming than the silicone oil emulsion, and the results are well in accord with the difference in size of the respective emulsion particles. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2408–2415, 2002