Emulsion Drop Size Research Articles

Demixing behavior of Pickering emulsions stabilized by Janus particles and uniform Pickering particles at different pH values

This work investigates the demixing behavior of Pickering emulsions consisting of water, n-hexadecane, and two different types of Pickering particles. The first type is uniform, and the second consists of one-side modified Janus particles influencing the emulsion behavior significantly. Both particle types are able to stabilize the emulsions, but lead to clear differences in the emulsion drop size and size distribution. This results in different creaming times varying between minutes and hours and different clearance processes of the water excess phase. Large pH effects were found in addition. At some conditions, non-adsorbed particles were observed that sediment over time in addition to the creaming of the emulsion.

Effect of Salt on the Stability of Vegetable Oil-in-Water Emulsions Stabilized by Soybean Protein and Microgel

The preparation of vegetable oil-water emulsions stabilized by soybean protein and microgel is described. The soybean protein was obtained from n-hexane-defatted soybean powder using a Soxhlet extractor. Using equal volumes of oil and water, vegetable oil-water emulsions were formed either by handshaking the mixture or homogenizing the mixture using a Lab homogenizer. The emulsion was characterized using a drop test and microscopy observation. The drop test shows that the preferred emulsion is vegetable oil-in-water (o/w). The effect of salt and emulsifier concentration on the stability and emulsion drop size was investigated. Emulsions stabilized by soybean protein without addition of salt breakdown after 3 days of preparation because of decomposition of the protein. For emulsions stabilized by microgel in the absence of salt, phase separation occurred within 1 hour. At a fixed salt concentration, it was found that increasing the emulsifier concentration has a significant effect on the stability and drop size of the emulsions stabilized by both protein and microgel. For emulsions stabilized by soybean protein, the stability of emulsions increased with increasing salt concentration without any significant influence on the drop size. The results obtained from the surface tension measurement revealed that different mechanisms of stabilization exist in emulsions stabilized by the protein and microgel.

Effect of Salt on the Stability of Vegetable Oil-in-Water Emulsions Stabilized by Soybean Protein and Microgel

The preparation of vegetable oil-water emulsions stabilized by soybean protein and microgel is described. The soybean protein was obtained from n-hexane-defatted soybean powder using a Soxhlet extractor. Using equal volumes of oil and water, vegetable oil-water emulsions were formed either by handshaking the mixture or homogenizing the mixture using a Lab homogenizer. The emulsion was characterized using a drop test and microscopy observation. The drop test shows that the preferred emulsion is vegetable oil-in-water (o/w). The effect of salt and emulsifier concentration on the stability and emulsion drop size was investigated. Emulsions stabilized by soybean protein without addition of salt breakdown after 3 days of preparation because of decomposition of the protein. For emulsions stabilized by microgel in the absence of salt, phase separation occurred within 1 hour. At a fixed salt concentration, it was found that increasing the emulsifier concentration has a significant effect on the stability and drop size of the emulsions stabilized by both protein and microgel. For emulsions stabilized by soybean protein, the stability of emulsions increased with increasing salt concentration without any significant influence on the drop size. The results obtained from the surface tension measurement revealed that different mechanisms of stabilization exist in emulsions stabilized by the protein and microgel.

Characterization of interfacial interactions and emulsification properties of bicarbonate solutions and crude oil and the effects of temperature and pressure

Abstract An extensive study of fluid/fluid interactions of bicarbonate solutions and crude oil from Danish North Sea has been carried out. Interfacial tension (IFT) measurements, and oil/brine contact tests were conducted. Brine with salinity of 0.05 M was shown to be the optimum salinity in emulsification at basic pH of bicarbonate solution. ATR-FTIR spectra of oil and formed emulsions were recorded to characterize the nature of the emulsion. Information about the content of polar molecules and the water content of the emulsions was provided by the IR analysis. The emulsion structure and drop size which correspond to the optimum salinity were characterized using cryo-scanning electron microscopy (Cryo-SEM) images. The emulsion drop size was comparable to carbonate pore size. This suggests that flow diversion by emulsion formation is possible as a mechanism with an impact on oil recovery. In flow diversion mechanism, formed emulsions will plug fractures and bigger pores and redirect the injected brine to the non-flooded zones. IFT was measured at reservoir pressure (200 bar) and different temperatures (23, 60, 90 and 120 °C). Overall, the change in interfacial tension values in compared to formation water was up to 30% and rarely exceeded that. At each temperature, the IFT has been reduced to the lowest achievable value and no further reduction was observed by increasing the salinity. Furthermore, an increase in temperature led to additional reduction in IFT for each salinity.

On the shear stability of water-in-water Pickering emulsions stabilized with silica nanoparticles

HypothesisWater-in-water (w/w) emulsions are known for their low interfacial tensions (IFT) which makes their stability to shear questionable. This is because of low particle attachment energies, which can be just a few kT. Therefore, emulsions stabilized with larger particles should display greater stability to shear because of larger attachment energies (10–100 or more kT). This is typically not an issue with traditional oil-in-water Pickering emulsions because particle attachment energies are much larger due to higher interfacial tensions, even when very small particles are used. ExperimentsSilica nanoparticles were silanized with 2-(methoxy(polyethyleneoxy)6-9propyl)trimethoxysilane (PEG-silane) to aid in emulsion stabilization. The phase behavior of an aqueous, two-phase system consisting of 20,000 g mol−1 polyethylene glycol (PEG) and magnesium sulfate (MgSO4) was characterized. Optical microscopy was used to characterize the static properties of the particle stabilized emulsions and shear rheology was used to study the stability of emulsions stabilized with 6 nm and 50 nm PEG-silane functionalized particles. ResultsWe demonstrated that silica nanoparticles silanized with PEG-silane can stabilize MgSO4 drops to produce MgSO4-in-PEG emulsions. We found emulsions stabilized with 6 wt% particles, regardless of particle size (6 nm or 50 nm), had similar viscosities, emulsion drop size, and were statically stable for one week. Emulsion drops stabilized with 6 wt% 50 nm particles doubled in size after 80 min of shear at 10 s−1 whereas those stabilized with 6 wt% 6 nm particles required only 25 min to double in size. We attribute these differences in doubling time to the larger particle attachment energies associated with the 50 nm particles.

Determination of Formulation Conditions Allowing Double Emulsions Stabilized by PGPR and Sodium Caseinate to Be Used as Capsules.

Water-in-oil-in-water (W1/O/W2) double emulsions stabilized by polyglycerol polyricinoleate (PGPR), a lipophilic food grade small polymer, and sodium caseinate, a hydrophilic milk protein, were developed to encapsulate vitamin B12, a model hydrophilic substance easy to titrate. Using rheology, sensitive to drop size evolution and water fluxes, static light scattering, and microscopy both giving the evolution of drops' size and vitamin B12 titration assessing the encapsulation, we were able to detect independently the double emulsion drop size, the encapsulation loss, and the flux of water as a function of time. By differentiating the PGPR required to cover the W1-droplets' surface from PGPR in excess in the oil phase, we built a PGPR-inner droplet volume fraction diagram highlighting the domains where the double emulsion is stable toward encapsulation and/or water fluxes. We demonstrated the key role played by nonadsorbed PGPR concentration in the intermediate sunflower oil phase on the emulsion stability while, surprisingly, the inner droplet volume fraction had no effect on the emulsion stability. At low PGPR concentration, a release of vitamin B12 was observed and the leakage mechanism of coalescence between droplets and oil-water interface of the oily drops (also called globules hereafter), was identified using confocal microscopy. For high enough PGPR content, the emulsions were stable and may therefore serve as efficient capsules without need of an additional gelling, thickening, complexion or interface rigidifying agent. We generalized these results with the encapsulation of an insecticide: Cydia pomonella granulovirus used in organic arboriculture.

CFD-PBM simulation of dense emulsion flows in a high-shear rotor–stator mixer

Computational fluid dynamics (CFD) is coupled to population balance modelling (PBM) for the simulation of turbulent drop dispersion and evolving rheology in concentrated oil–water emulsions flowing through a Silverson 150/250MS mixer. Unsteady Reynolds averaged Navier–Stokes (URANS) simulations on a sliding mesh were performed for the fluid dynamics, linking the k−ω SST turbulence model to the population balance equations. The quadrature method of moments (QMOM) approach is used to solve the population balance equations. Breakage kernels based on the multi-fractal theory of intermittent turbulence have been modified to include the effect of turbulent shear and close packing of drops at high phase volume. A previously developed rheological model is used to calculate the emulsion viscosity. Emulsion drop size is shown to be influenced by rotor speed and phase volume fraction. Flow curves characterising the rheology of the emulsion show shear thinning behaviour and viscosity build after a single pass through the mixer.

Emulsification of viscous alkyd resin by catastrophic phase inversion with nonionic surfactant

The addition of water to hydrophobic alkyd resin containing a hydrophilic nonionic surfactant (polyethoxylated-20-oleyl alcohol) was used to produce the emulsion morphology change from W/O to O/W in a small thermostated reactor (50mL). The so-called catastrophic phase inversion of the water/alkyd resin system was detected by monitoring both, the viscosity by torque measurement and the electrical conductivity, until an equal weight fraction of water and resin is attained (fw=0.5). The two methods provide similar values of the phase inversion point (PIP). Although the determination of the PIP exhibits a small inaccuracy, it is clear that different torque profiles and PIP are observed depending on the resin neutralization level, the surfactant concentration and the water addition rate. For the non-neutralized resin, both, PIP and emulsion drop size, decrease with surfactant concentration increase. The completely neutralized resin could be emulsified using a minimum of 2wt% of surfactant in the final emulsion. In such a case the water fraction at which inversion occurs (fw,Inv=0.36) is independent of the surfactant concentration and a small resin drop diameter (<200nm) can be obtained. A more precise study of the reached drop size of the emulsion versus resin neutralization (0, 25, 50, 75, 100 and 125%) indicates that a minimum diameter is obtained around 90–100% neutralization, with no effect of over-neutralization. For non-neutralized resin a maximum fw,Inv (0.25) can be obtained by reducing water addition rate allowing the production of 0.5μm droplets in a longer process.

Relating emulsion stability to interfacial properties for pharmaceutical emulsions stabilized by Pluronic F68 surfactant

We explore mechanisms of emulsion stability for several systems using Pluronic F68 and a range of oils commonly used in pharmaceutics and cosmetics. We report measurements of dynamic emulsion drop size, zeta potential, and creaming time, as well as dynamic interfacial tension and interfacial viscoelasticity. Experiments show that with 1wt% Pluronic F68, soybean oil emulsions were the most stable with no creaming over six months, followed by isopropyl myristate, octanoic acid, and then ethyl butyrate. The eventual destabilization occurred due to the rising of large drops which formed through Ostwald ripening and coalescence. While Ostwald ripening is important, it is not the dominant destabilization mechanism for the time scale of interest in pharmaceutical emulsions. The more significant destabilization mechanism, coalescence, is reduced through surfactant adsorption, which decreases surface tension, increases surface elasticity, and adds a stearic hindrance to collisions. Though the measured values of elasticity obtained using a standard oscillatory pendant drop method did not correlate to emulsion stability, this is because the frequencies for the measurements were orders of magnitude below those relevant to coalescence in emulsions. However, we show that the high frequency elasticity obtained by fitting the surface tension data to a Langmuir isotherm has very good correlation with the emulsion stability, indicating that the elasticity of the interface plays a key role in stabilizing these pharmaceutical formulations. Further, this study highlights how these important high frequency elasticity values can be easily estimated from surface isotherms.

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

AbstractThe 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.

Injection of Dilute Oil-in-Water Emulsion as an Enhanced Oil Recovery Method for Heavy Oil: 1D and 3D Flow Configurations

Unfavorable mobility ratio and reservoir heterogeneities contribute to water fingering phenomenon that leads to relatively low oil recovery factors in heavy oil fields. Experiments have shown that injection of oil-in-water emulsions can be used as an effective enhanced oil recovery (EOR) method, leading to substantial increase in the volume of oil recovered. Capillary-driven mobility alteration of the water phase by emulsion drops leads to not only more uniform macroscopic reservoir sweep, but also a pore scale reduction in the residual oil saturation. Despite recent developments, fundamental aspects of dilute oil-in-water emulsion flow through porous media and its application as an EOR method are still not clear. Experiments were performed in a 1D flow configuration using silica sandpacks and sandstone cores to determine the effect of permeability, emulsion drop size, dispersed phase concentration and size of injected emulsion bank on the volume of displaced oil, a crude heavy oil from Campos Basin (\(20^{\circ }\) API). X-ray computerized tomography images obtained during experiments in a Castlegate sandstone block in a 1/4 5-spot configuration revealed that emulsion acts both in the macroscale and pore scale, improving the macroscopic sweep and lowering the residual oil saturation.

Production of high-oleic palm oil nanoemulsions by high-shear homogenization (microfluidization)

Abstract Nanoemulsions present benefits such as an increase in the bioavailability, solubility and targeted delivery of encapsulated substances, and thus, they are a method of incorporating high nutritional value oils, such as high-oleic palm oil (HOPO). In this work, O/W nanoemulsions were obtained by microfluidization using HOPO (1–20% w/w) in the oily phase along with whey (1–20% w/w), Tween 20 (1:1 w/w ratio) and water in the aqueous phase following a surface response design methodology. The response variables were the average drop size (ADS), the polydispersity index (PDI), the zeta potential (ζ), CIELAB color parameters and viscosities of the fresh nanoemulsions (0 days) and nanoemulsions stored at two temperatures (5 and 19 °C) for 4 days. The ADS, PDI and ζ values varied between 163 and 2268 nm, 0.2 and 1, and − 29.7 and − 47.2 mV, respectively. The viscosity was affected by the storage temperature; after 4 days at 19 °C, it increased almost 6-fold compared to the viscosity of the fresh sample. With regards to the color parameters, significant changes were observed based on the concentrations of HOPO and whey. In addition, the prediction equations only presented errors below 7% for the evaluated variables, with R 2 values above 0.85. Finally, the influence of whey protein denaturation at 60 °C on the stabilities of the two most stable nanoemulsions, according to the optimization process, was observed. Industrial relevance Among its many benefits, nanoencapsulation is characterized by increasing the bioavailability of the encapsulated active compound and by the protection that it grants against environmental and processing effects, as micronutrients (for example vitamins) can be susceptible to chemical, enzymatic and/physical instability prior, during and after the processing of food products that contain. One of the techniques studied in recent decades for obtaining nanoemulsions is microfluidization. Microfluidization is a high-energy method that uses high pressure to force the fluid through microchannels that have a specific configuration, emulsifying the fluid by the combined effects of cavitation, shear and impact, thus showing an excellent emulsifying efficiency. However, in food industries the use of microfluidization is not popular and other kind of high shear homogenization are used. In this work, the development of stable emulsions using microfluidization, calls for the use of other types of materials that can provide emulsifying characteristics, such as whey, a compound that is currently one of the main effluents of dairy processes, depending on the type of product. Obtaining nanoemulsions for encapsulation purposes has been studied in many functional products, but to the best of our knowledge, it has not been reported with high-oleic palm oil. This oil contains approximately 50% saturated, 10% di-unsaturated and 40% monounsaturated fatty acids, with oleic acid in sn-2 position in triacylglycerols. This composition makes palm oil as soluble as olive oil. In addition, high-oleic palm oil (HOPO), in particular, has a high stability because it is an oleic acid-rich oil, which has been introduced to replace trans fats and has presented a healthy alternative to such fats in food formulations and the fried food industry. It is also important to highlight that oleic acid has a range of health benefits, such as a decrease in the total cholesterol, an increase in HDL (high-density lipoprotein) and a decrease in LDL (low-density lipoprotein). Oleic acid also retards the development of heart diseases, promotes the formation of antioxidants in the body and reinforces the integrity of the cell wall. In addition, red palm oil (crude) contributes significant nutritional value because it is rich in β-carotenes, α-tocopherol and tocotorienols, supplying vitamins and provitamins that are important for but not produced by the human body. Finally, this work demonstrates that emulsion drop size does not affect the stability of the nanoemulsion if it formulation is designed. Therefore, the goal of this work was to evaluate the most favorable conditions for the microfluidization, formulation and storage of HOPO nanoemulsions using whey powder to produce stable nanoemulsions.

Achieving Target Emulsion Drop Size Distributions Using Population Balance Equation Models of High-Pressure Homogenization

Population balance equation (PBE) models have been used extensively to predict drop size distributions (DSDs) of dispersed phase systems. In our previous publications, we have used the PBE framework to develop increasingly sophisticated process models for oil-in-water emulsification in high-pressure homogenizers. The goal of this study was to utilize these PBE models for integrated emulsion product and process design through the formulation and solution of homogenizer optimization problems. For a specified number of homogenization passes, the initial amount of surfactant and the pressure of each pass were determined by solving a nonlinear least-squares optimization problem such that the target DSD were achieved. Three alternative objective functions that differed with respect to the distribution specification and the penalty on surfactant usage were formulated and solved for different target DSDs. The model predictions were successfully validated by performing homogenization experiments using the optimized formulation and homogenization variables.

HLD–NAC and the Formation and Stability of Emulsions Near the Phase Inversion Point

It is well-known that surfactant–oil–water (SOW) emulsions undergo substantial changes in drop size (10-fold or more) and stability (up to 4 orders of magnitude) near the phase inversion point. Predicting these changes is important in numerous applications. However, the complex connection between composition, formulation properties, and hydrodynamic conditions limits the ability to predict the outcome of emulsification and demulsification processes. To address this gap, the hydrophilic–lipophilic deviation (HLD) was used to quantify the proximity to the inversion point, considering the composition of the formulation, temperature, and electrolyte concentration. The net-average-curvature (NAC) equations combined with the HLD predicted the density, interfacial tension, interfacial rigidity, and viscosity for the sodium dihexyl sulfosuccinate (SDHS)–toluene–water system. The predicted properties were incorporated in hydrodynamic models to predict the initial emulsion drop size. The calculated properties and i...

Concentrated Emulsion Characterization in Flowing Conditions

Concentrated emulsions (dispersed phase fractions greater than 1 vol %) have applications in a wide variety of industries. In the energy industry, these emulsions are encountered in every stage of crude oil processing. Characterizing such concentrated emulsions in the presence of surfactants and/or solid particles and in flowing conditions will help develop strategies for managing these complex systems. In this work, an experimental flow loop equipped with an inflow microscope was used to quantify emulsion drop size distributions as a function of the water concentration, flow rate, temperature, and stabilizing agent type. The solid-stabilized emulsions indicated that only the water concentration had an overall impact on the drop size distributions. This work showed that the drop size distribution is a function of the temperature, water concentration, and flow rate for surfactant-stabilized emulsions. The direct, unique experimental insight gained about concentrated emulsions in this work provides a fundam...

Cellulose nanofibrils for one-step stabilization of multiple emulsions (W/O/W) based on soybean oil

Cellulose nanofibrils (CNF) were incorporated in water-in-oil (W/O) microemulsions and emulsions, as well as water-in-oil-in-water (W/O/W) multiple emulsions using soybean oil. The addition of CNF to the aqueous phase expanded the composition range to obtain W/O/W emulsions. CNF also increased the viscosity of the continuous phase and reduced the drop size both of which increased the stability and effective viscosity of the emulsions. The effects of oil type and polarity on the properties of the W/O/W emulsions were tested with limonene and octane, which compared to soybean oil produced a smaller emulsion drop size, and thus a higher emulsion viscosity. Overall, CNF are a feasible alternative to conventional polysaccharides as stability enhancers for normal and multiple emulsions that exhibit strong shear thinning behavior.

A model for the prediction of droplet size in Pickering emulsions stabilized by oppositely charged particles.

Colloidal particles irreversibly adsorb at fluid-fluid interfaces stabilizing what are commonly called "Pickering" emulsions and foams. A simple geometrical model, the limited coalescence model, was earlier proposed to estimate droplet sizes in emulsions. This model assumes that all of the particles are effective in stabilization. The model predicts that the average emulsion drop size scales inversely with the total number of particles, confirmed qualitatively with experimental data on Pickering emulsions. In recent years, there has been an increasing interest in synthesizing emulsions with oppositely charged particles (OCPs). In our experimental study, we observed that the drop size varies nonmonotonically with the number ratio of oppositely charged colloids, even when a fixed total number concentration of colloids is used, showing a minimum. We develop a mathematical model to predict this dependence of drop size on number ratio in such a mixed particle system. The proposed model is based on the hypothesis that oppositely charged colloids form stable clusters due to the strong electrostatic attraction between them and that these clusters are the effective stabilizing agents. The proposed model is a two-parameter model, parameters being the ratio of effective charge of OCPs (denoted as k) and the size of the aggregate containing X particles formed due to aggregation of OCPs. Because the size of aggregates formed during emulsification is not directly measurable, we use suitable values of parameters k and X to best match the experimental observations. The model predictions are in qualitative agreement with experimentally observed nonmonotonic variation of droplet sizes. Using experiments and theory, we present a physical insight into the formation of OCP stabilized Pickering emulsions. Our model upgrades the existing Wiley's limited coalescence model as applied to emulsions containing a binary mixture of oppositely charged particles.

Prediction of emulsion drop size distributions in colloid mills

Colloid mills are the most common emulsification devices used in industry for products with high oil content. Drop breakage occurs when the emulsion is flowed through a small gap between rotor and stator under laminar shear conditions. In this paper, we have developed the first full population balance equation (PBE) model for colloid mills and used the model to better understand the relevant drop breakage mechanisms. The PBE model accounted for both drop breakage and coalescence and generated predictions of the drop size distribution after each pass of the emulsion through the colloid mill. Drops were assumed to break due to capillary instability with the distribution of drop sizes resulting from each breakage event studied in detail. A viscosity model was developed to predict the emulsion viscosity as function of the oil fraction and the high shear rates commonly used. Nonlinear optimization was used to estimate adjustable parameters in the breakage and coalescence functions to minimize the least-squares difference between predicted and measured drop size distributions for high oil-to-surfactant emulsions. We concluded that experimentally observed drop volume distributions could not be predicted with daughter drop distribution functions reported in the literature. Improved predictions were obtained using a new bimodal distribution function which captured drop breakage into multiple, nearly uniform daughter drops with a large number of small satellite drops. We also investigated model extensibility for changes in the oil fraction, emulsion flow rate and rotor speed.

Dynamic flow response of crude oil-in-water emulsion during flow through porous media

Injection of crude oil-in-water emulsion in tertiary mode has been recognized as a potential method to increase oil recovery. Better understanding of emulsion flow through porous media is needed to develop practical improved oil recovery processes based on emulsion flooding mechanisms. In this study, two sets of experiments were carried out to further investigate the flow of emulsion in consolidated sandstone core plugs. First, the efficiency of emulsion injection to improve oil recovery was evaluated in two-phase flow experiments. Second, single-phase flow experiments were designed to understand the flow of emulsion at pore scale. In these experiments, a crude oil-in-water emulsion with known drop-size distribution was injected in water-saturated Berea sandstone cores followed by water injection at increasing flow rate. The overall pressure drop and its Fast Fourier Transform were analyzed to unveil potential connections to pore level flow. The pore throat blockage-release mechanism was inferred to be linked to the acquired pressure drop oscillation. The pore-scale dynamics has been shown to depend on local capillary number and emulsion drop size. The blockage-release mechanism of the trapped drops becomes less effective as the water flow rate or equivalently, the capillary number, increases above a critical value. Also, a larger drop-to-pore size ratio results in higher required capillary number, i.e. larger viscous force to mobilize the drops in the porous media.

Microencapsulation of Aqueous Compounds Using Hexamethylenediamine and Trimesoyl Chloride: Monodisperse Capsule Formation and Reaction Conditions on Membrane Properties

Efficient microencapsulation of aqueous compounds for dispersion in aqueous media remains challenging. To prepare aqueous microcapsules, we employed interfacial polymerization with hexamethylenediamine (HMDA) and trimesoyl chloride (TMC), which are commonly used for the formation of impermeable reverse-osmosis membranes. We employed an emulsification technique based on a high-viscosity external phase and uniform shear fields to produce monodisperse aqueous drops on the order of 10 μm. The effects of shear stress and HMDA concentration on the drop sizes were studied. The HMDA amount and emulsion drop size were both found to be important for subsequent capsule formation. The stoichiometric ratios of amine to acid chloride affected both the redispersibility of the microcapsules and the release rates of Coomassie Brilliant Blue (Coomassie Blue). Although high encapsulation efficiencies were achieved, the release rate varied with the sizes of the encapsulated molecules/ions. Optimum capsule formation and control of release were obtained with a stoichiometric ratio [c(NH2)/c(COCl)] of 5.