Effects of Salts Containing Mono-, Di-, and Trivalent Ions on Electrical and Rheological Properties of Oil-Water Interface in Presence of Cationic Surfactant: Importance in the Stability of Oil-in-Water Emulsions

Many industrial applications of oil-in-water emulsions involve salts containing ions of different valence. The properties of the oil-water interface (e.g., interfacial tension, zeta potential and interfacial shear viscosity) are strongly influenced by the presence of these salts. This work investigates the role of NaCl, CaCl₂ and AlCl₃ on these properties of the hexane-water interface in presence of a cationic surfactant, viz., hexadecyltrimethylammonium bromide. Addition of salt enhanced the adsorption of surfactant molecules at the hexane-water interface, which increased the interfacial charge density, and consequently, the zeta potential. Interfacial shear viscosity significantly decreased in the presence of salt. The effectiveness of salt at a given concentration was in the sequence: AlCl₃ > CaCl₂ > NaCl. The hexane-in-water emulsions coarsened with time due to the coalescence of hexane droplets. The increase in droplet size with time was analyzed by a model based on the frequency of rupture of the thin aqueous film. The rate constants for coalescence were determined. The rate of coalescence increased in presence of salt.      

Influence of Interfacial Engineering on Stability of Emulsions Stabilized with Soy Protein Isolate

The objectives of this study were to examine the influence interfacial composition on environmental stresses stability of oil in water emulsions. An electrostatic layer-by-layer deposition method was used to create the multilayered interfacial membranes with different compositions: (i) primary emulsion (Soy protein Isolate); (ii) secondary emulsion (Soy protein Isolate – OSA-starch); (iii) tertiary emulsion (Soy protein isolate – OSA-starch – chitosan). Fourier transform-infrared (FTIR) and scanning electron microscopy (SEM) results confirmed the adsorption of charged polyelectrolyte onto oppositely charge polyelectrolyte-coated oil droplets. The stability of primary, secondary, and tertiary emulsions to thermal treatment (30 min at 30–90°C), pH (3–7) and NaCl (0–500 mM) were determined using ζ-potential, particle diameter, and microstructure analysis. Primary emulsions were unstable at pH 4–7, salt concentrations, and thermal treatments. Secondary emulsions were stable to creaming and droplet aggregation at pH 3–5, at ≤50 mM NaCl, and unstable at thermal treatments, whereas tertiary emulsions were stable at all salt concentrations, thermal treatments, and at pH 3–6. These results demonstrate that these polymers can be used to engineer oil in water emulsion systems and improve the emulsion stability to environmental stresses.     

Dependence of emulsion stability on particle size: Relative importance of drop concentration and destabilization rate on the half lifetimes of O/W nanoemulsions

This study reports the behavior of ionic dodecane-in-water nanoemulsions in distinct salt concentrations. Systems of smaller particle size (74–285 nm) were synthesized by a sudden dilution of an equilibrated mixture. Larger size systems (384–670 nm) were obtained from a set of formerly smaller nanoemulsions that evolved unperturbed for 2 weeks. Characteristic destabilization times for flocculation, coalescence, and Ostwald ripening were evaluated. In general, it was observed that stability increases with drop size. However, this size dependence is largely the consequence of the lower particle concentration of the coarser emulsions.     

Transport and Deposition of Alumina Nanoparticles in Water Saturated Porous Media: An Experimental Study

Transport and deposition of nanoparticles (NPs) have drawn great attention in different fields of engineering in recent years because of their potential risk to the environment. In this study, mobility of aluminum oxide NP, one of the most popular metal oxide NPs, was studied in synthetic saturated porous media. The impacts of ionic strength using monovalent (NaCl) and divalent (MgCl₂) salt solution, pH, and NPs concentrations on nano-alumina mobility were investigated. The experimental results showed that the transport of nano-alumina was influenced by ionic strength; the highest mobility was observed at the 0.01 M solution and decreased by increasing ionic strength. Moreover, the suspension containing alumina NPs presented the best mobility behavior in the acidic solution (pH = 2) in comparison with neutral and basic solutions. Consequently, transport of NPs with particle size distribution lower than 100 nm through porous media was facilitated at the acidic, low ionic strength condition. In addition, faster elution occurred when the influent concentration was increased from 0.1 wt% to 0.3 wt%. Finally, it is expected that ionic strength, pH of solution, and NPs concentration will be key parameters to control the nano-alumina mobility.     

Flocculation of Bacillus amyloliquefaciens H Disintegrates with Cationized Starch and Aminated Hydroxyethylcellulose

The ability of cationized hydroxyethylated starch (CHES) and aminated hydroxyethylcellulose (DEAE-HEC) to flocculate cell disintegrate of Bacillus amyloliquefaciens H (BamHI) was investigated. The efficiency of flocculation was compared to that of synthetic polymer polyethyleneimine (PEI) and natural polysaccharide chitosan. The influence of salt concentration and biomass concentration on flocculation efficiency was investigated. It was found that the efficiency of flocculation with CHES and DEAE-HEC was similar to that of PEI but better compared to chitosan. Recovery of total soluble proteins at higher than 0.3% concentration of flocculant decreased by more than 18.8% and 42.3% compared to PEI and chitosan, respectively. The yield of BamHI restriction endonuclease activity with all flocculants was similar except for chitosan where 13.1% lower yield was obtained. Meanwhile, efficiency of flocculation with CHES and DEAE-HEC depends drastically on the salt concentration, that is, flocculation diminishes if NaCl concentrations higher than 0.2 M (for CHES) or 0.1 M (for DEAE-HEC) are used. The results have shown that CHES and DEAE-HEC are promising flocculants of cell disintegrates if higher yield of protein is of great concern.     

Effect of Nanoparticle Hydrophobicity on Stability of Highly Concentrated Emulsions

The effect of hydrophobicity index (HI) of fumed nanosilica specimens on stability of water-in-oil (W/O) highly concentrated emulsions (HCE with ? = 90 vol%) with an overcooled dispersed phase was studied. A series of five silica with HI in the 0.60–1.34 range and HI > 3 were used separately and in combination with a low molecular weight traditional surfactant, Sorbitan MonoOleate (SMO). First, it was shown that SMO alone can stabilize W/O HCE whereas only silica nanoparticles with intermediate HI in the range 0.97 ≤ HI ≤ 1.34 could form W/O emulsions only up to 77–79 vol%. Then, on the contrary to SMO-based emulsions, Pickering emulsions are unstable under shearing. When mixed (silica plus SMO) emulsifier systems were used, firstly a thermodynamic consideration revealed that only SMO is likely to adsorb at the W/O interface and controls the emulsifying process by the decrease in the interfacial tension. Then, interestingly, all different kinds of emulsion stability investigated in this study demonstrate a breaking point (BP) at HI = 0.97. Below the BP the emulsions were found to be very unstable on shelf as well as under shear. Above the BP, a clear synergy between colloidal silica and SMO surfactant has been found.      

Cinnamoyl Pluronic F127 as a Stimuli-Sensitive Amphiphile

Cinnamoyl Pluronic F127 (CP F127) was prepared by reacting cinnamoyl chloride and Pluronic F127. On the ¹H NMR spectrum of CP F127, 1.2 moiety of cinnamoyl group was found to be attached to one molecule of CP F127. Using pyrene as a fluorescence probe, it was found that not only Pluronic F127 but also CP F127 could be readily assembled into micelles, and the critical micelle concentration was around 0.015 mg/ml and 0.03 mg/ml, respectively. Pluronic F127 in aqueous solution (2% w/v) could form no particles in 10–20°C, but particles (ca. 30 nm in diameter) were detected on a dynamic light scattering machine in 25–40°C possibly due to the thermal micellization. However, CP F127 was assembled into particles (ca. 230 nm) even in the lower temperature range, possibly because of the intermolecular hydrophobic interaction of the cinnamoyl group. The particle size of CP F127 strongly depended on the medium temperature and UV irradiation time. CP F127 was a good emulsifier for the preparation of O/W emulsions. The oil droplet size markedly increased upon UV irradiation (254 nm, 6 W), possibly because of the photo-dimerization of cinnamoyl group, but it was little affected by the temperature change (10–40°C).     

Experimental Investigation of Asphaltenes Flocculation Threshold in Crude Oils Using Different Methods: Comparative Study

Despite some recent progress trustworthy methods to predict the flocculation onset in crude oils are still needed. In this article, different experimental methods, like the density measurement method, the optical and the spot techniques based on the mixture of crude oil + toluene or cyclohexane + n-heptane, respectively, are applied to assess changes of aggregation occurring in crude oil under influence of physical and chemical factors as well as under variable temperature conditions. The solubility parameters of Hildebrand have also been used to predict the flocculation threshold. It turned out that the findings achieved by the spot method and the optical technique are in excellent agreement with break points of the reduced density curves obtained by the density measurement method for crude oils of different geographical origins. Using the solubility parameters of Hildebrand leads to comparable results. All these achievements confirm the density measurement method as a new possibility for reliably determining the flocculation onset in crude oils systems. With respect to temperature effects, changes of the oil microstructure could be detected as function of the temperature by means of the differential scanning calorimetry. In particular the thermal curves behavior of certain crude oils confirmed the existence of aggregation processes.      

Application of a Laser Diffraction Method for Determination of Stability of Dispersion Systems in Food and Chemical Industry

Laser diffraction was used for determination of particle size of various emulsions. Mean particle size, fractions' number, and dispersion coefficients of tested systems are presented. Stability of greasing emulsions in relation to their pH was also tested. It was found out that determination of droplet size distribution in fat emulsions allows prediction of their properties (stability). The parameter may be helpful in selection of appropriate production process parameters, composition, and control of marketed emulsion systems during their storage. The purpose of the study was to determine applicability of a laser diffraction method for evaluation of stability of selected dispersion systems in food and chemical industry.     

Comparison of the Rheological Behavior of Solutions and Formulated Oil-in-Water Emulsions Containing Carboxymethylcellulose (CMC)

In this study, it was aimed to compare the rheological properties of carboxymethylcellulose (CMC) in aqueous solutions and their corresponding emulsions containing 0.05, 0.1, 0.25, and 0.5% CMC in the aqueous phase. Samples with 0.05 and 0.1% CMC showed Newtonian behavior, but shear-thinning behavior was observed in CMC solutions and emulsions with increasing CMC concentrations to 0.25% and 0.5%. Rheological behavior of all samples were modeled by Power law (R ² = 0.986–197) and Casson models (R ² = 0.968–1). According to the Ostwald–de Waele model, the consistency index of all samples was increased and the flow behavior index decreased with increasing CMC concentration. Comparison of our data with four predicting models (Einstein, Larson, Pal, and Dougherty-Krieger equations) showed that the viscosity of continuous phase controls the viscosity of emulsions with high CMC concentrations and these models are not applicable for such situations. Addition of CMC increased the emulsion stability of O/W emulsions. This stability was increased with increasing CMC concentrations.     

Thermo- and pH-Responsiveness of Emulsions Stabilized with Acidic Thermosentive Polymers

A temperature- and pH-responsive polymeric surfactant was prepared by copolymerizing N-isopropylacrylamide, methacrylic acid, and octadecylacrylate. Poly(N-isopropylacrylamide-co-methacrylic acid-co-octadecylacrylate) (P(NIPAM-MAA-ODA) was used as an emulsifier for the preparation of water-in-oil emulsions. The mean droplet size at room temperature was almost constant for 50 hours at pH 5.0, 7.0, and 9.0. However, the size markedly increased for 50 hours at pH 3.0, possibly because of the low hydrophilicity of the copolymer and the small interfacial area one molecule of the copolymer can stabilize at a low pH value. The droplet size markedly decreased from 4.7 to 1.8 µm, when the pH of medium increased from 5.0 to 9.0 with the temperature kept constant. This may be ascribed to that the hydrophilicity of the copolymer and the interfacial area one molecule of copolymer can stabilize will be higher at a higher pH value. When the temperature increased over 35°C with the pH kept constant, the droplet size significantly increased probably because the NIPAM segment of the copolymer becomes hydrophobic with increasing the temperature so the copolymer would poorly act as an emulsifier.     

Surface and Structural Properties of Gold Nanoparticles and Their Biofunctionalized Derivatives in Aqueous Electrolytes Solution

Gold nanoparticles reduced by sodium citrate (d ～ 10 nm) and purchased gold colloid particles (d ～ 500 nm) were examined and compared. The properties of both gold particles and their biofunctionalized derivatives with L-cysteine and L-glutathione were studied in the presence of sodium nitrate. The structural investigations indicated an aggregated inner structure.

The isoelectric points of pure gold, citrate reduced gold, and functionalized gold were measured and compared. The low isoelectric point of pure gold/water interface was explained by considering the distribution and accumulation of H⁺ and OH^? ions within the interfacial water layer, being more pronounced for OH^? ions.      

Double inversion of emulsions induced by salt concentration

The effects of salt on emulsions containing sorbitan oleate (Span 80) and Laponite particles were investigated. Surprisingly, a novel double phase inversion was induced by simply changing the salt concentration. At fixed concentration of Laponite particles in the aqueous phase and surfactant in paraffin oil, emulsions are oil in water (o/w) when the concentration of NaCl is lower than 5 mM. Emulsions of water in oil (w/o) are obtained when the NaCl concentration is between 5 and 20 mM. Then the emulsions invert to o/w when the salt concentration is higher than 50 mM. In this process, different emulsifiers dominate the composition of the interfacial layer, and the emulsion type is correspondingly controlled. When the salt concentration is low in the aqueous dispersion of Laponite, the particles are discrete and can move to the interface freely. Therefore, the emulsions are stabilized by particles and surfactant, and the type is o/w as particles are in domination. At intermediate salt concentrations, the aqueous dispersions of Laponite are gel-like, the viscosity is high, and the transition of the particles from the aqueous phase to the interface is inhibited. The emulsions are stabilized mainly by lipophilic surfactant, and w/o emulsions are obtained. For high salt concentration, flocculation occurs and the viscosity of the dispersion is reduced; thus, the adsorption of particles is promoted and the type of emulsions inverts to o/w. Laser-induced fluorescent confocal micrographs and cryo transmission electron microscopy clearly confirm the adsorption of Laponite particles on the surface of o/w emulsion droplets, whereas the accumulation of particles at the w/o emulsion droplet surfaces was not observed. This mechanism is also supported by the results of rheology and interfacial tension measurements.     

Comparison of droplet flocculation in hexadecane oil-in-water emulsions stabilized by beta-lactoglobulin at pH 3 and 7

The influence of surface and thermal denaturation of adsorbed beta-lactoglobulin (beta-Lg) on the flocculation of hydrocarbon oil droplets was measured at pH 3 and compared with that at pH 7. Oil-in-water emulsions (5 wt % n-hexadecane, 0.5 wt % beta-Lg, pH 3.0) were prepared that contained different levels of salt (0-150 mM NaCl) added immediately after homogenization. The mean particle diameter (d43) and particle size distribution of diluted emulsions were measured by laser diffraction when they were either (i) stored at 30 degrees C for 48 h or (ii) subjected to different thermal treatments (30-95 degrees C for 20 min). In the absence of salt, little droplet flocculation was observed at pH 3 or 7 because of the strong electrostatic repulsion between the droplets. In the presence of 150 mM NaCl, a progressive increase in mean particle size with time was observed in pH 7 emulsions during storage at 30 degrees C, but no significant change in mean particle diameter with time (d43 approximately 1.4 +/- 0.2 microm) was observed in the pH 3 emulsions. Droplet aggregation became more extensive in pH 7 emulsions containing salt (added before thermal processing) when they were heated above 70 degrees C, which was attributed to thermal denaturation of adsorbed beta-Lg leading to interdroplet disulfide bond formation. In contrast, the mean particle size decreased and the creaming stability improved when pH 3 emulsions were heated above 70 degrees C. These results suggest that the droplets in the pH 3 emulsions were weakly flocculated at temperatures below the thermal denaturation temperature of beta-Lg (T < 70 degrees C) but that flocs did not form so readily above this temperature, which was attributed to a reduction in droplet surface hydrophobicity due to protein conformational changes. The most likely explanation for the difference in behavior of the emulsions is that disulfide bond formation occurs much more readily at pH 7 than at pH 3.     

Micronization of Iron Oxide Particles Using Gas Antisolvent Process

Iron oxide particles were micronized by supercritical carbon dioxide (CO₂) as an antisolvent in a batch gas antisolvent (GAS) process. In the present study, the feasibility of GAS process to micronize the iron oxide particles using dimethyl sulfoxide (DMSO) as a solvent was investigated. In this direction, particle size and morphology changes were investigated with changing solution pressure (80–150 bar), temperature (308.15–328.15 K), and concentration (1.5–6 g/l). Based on the different experimental conditions, the particle size of the original iron oxide was decreased in the range of 17.25 to 4.23 µm, which shows a the success of the GAS process to reduce the particle size of the intact iron oxide particles. Simultaneously, morphology changes were observed starting from the irregular morphology for synthesized particles to more regular shapes that included fused and spherical-fused particles.     

Preparation and Characterization of Polymeric Nanocapsules Produced by in Situ Polymerization From Nanoemulsions Produced by Direct Emulsification

Polymeric nanoparticles constitute an important drug delivery system with controlled release profile. This article describes a new way to produce polymeric nanocapsules using a vegetable oil nanoemulsion as template. The process occurs in two steps: First, a nanoemulsion was obtained with a low-energy method based on phase inversion emulsification, using 2-ethylhexyl acrylate as lipophilic monomer. The in situ polymerization of the nanoemulsion droplets is induced by the addition of polymerization catalyzers. The mean size of the polymeric nanoparticles was evaluated by photon correlation spectroscopy and atomic force microscopy. Both techniques showed the formation of polymeric nanocapsules with a mean particle size less than 300 nm.     

The emulsion flocculation stability of protein-carbohydrate diblock copolymers

The effect of the steric layer thickness on the flocculation stability of beta-lactoglobulin-carbohydrate diblock copolymers was assessed. The diblock copolymers were created by conjugating beta-lactoglobulin to maltose or a series of different M(n) maltodextrins using the Maillard reaction. The thickness and spatial arrangement of the interfacial layers were assessed via latex adsorption and selective enzymatic digestion studies. An increase in the molecular weight of the maltodextrin (900, 1900 and 3800 Da) increased the interfacial thickness (1.1, 2.5 and 7.3 nm, respectively). No detectable change to interfacial thickness was observed upon the attachment of maltose. The increase in the interfacial layer thickness scaled with the hydrodynamic size of the carbohydrate. The beta-lactoglobulin-maltodextrin conjugates were found to have a diblock architecture, with the protein anchored at the surface and the carbohydrate protruding into the aqueous continuous phase. The stability of oil-in-water emulsions formed using the conjugates was assessed by exposing them to salt (150 mM NaCl or 0-20 mM CaCl(2)), heat alone or heat in the presence of 150 mM NaCl. Conjugation of a 900 Da maltodextrin provided sufficient steric stabilization to prevent flocculation in high salt environments. The effect of the (number) density of the steric layer was also assessed by controlling the average number of maltodextrins attached per beta-lactoglobulin molecule. The steric layer density at which emulsions became unstable was a function of carbohydrate M(n). Emulsions made from the 900 Da maltodextrin conjugate became unstable below a steric layer density of one tail per 7.5 nm(2), whilst emulsions made from the 1900 Da maltodextrin were unstable below a steric layer density of one tail per 9.5 nm(2). This trend was expected and can be explained by the stronger van der Waals attraction that arises from the closer interdroplet separations that are permissible with the shorter maltodextrins. The excellent flocculation stability of Maillard conjugate emulsions is thought to arise from the combined effects of weak electrostatic repulsion from the screened protein surface charge and steric repulsion from the attached carbohydrate layer. This means that attachment of a relatively thin steric layer is enough to stabilize the emulsions against flocculation. These findings have important implications for the development of commercial processes to manufacture protein-carbohydrate Maillard conjugate emulsifiers. Furthermore the work provides a greater empirical understanding of the relationship between interfacial architecture and colloidal stability, and may provide the means for greater theoretical understanding of biopolymer stabilization of interfaces.     

Janus Emulsion Drops: Equilibrium Calculations

Experimental results indicated the contact angles in the drops of Janus emulsions formed in a one-step mixing process to be invariant within a significant range the oil volume ratios, similar to the results from microfluidics emulsification. Since this result points to a connection between the kinetically formed emulsions and the local equilibrium topology of emulsion drops, the effect of interfacial tensions on the morphology of Janus emulsions was estimated from the equilibrium interfacial tensions at the line of contact. Realistic values of the tensions revealed the limited range of these to obtain Janus drops and also offered correlation between the equilibrium entities and the curvature of the interface between the two oils.     

Physical and Rheological Characteristics of Emulsion Model Structures Containing Iranian Tragacanth Gum and Oleic Acid

The physical and rheological properties of oil in water model emulsion systems containing Iranian tragacanth gum (TG) (0.5, 1 g/100 ml emulsions), whey protein isolate (WPI) (2, 4 g/100 ml emulsions), and oleic acid (5, 10 ml/100 ml emulsions) were investigated for droplet-size distribution, creaming index, and rheological properties of emulsions. The shear-thinning behavior of all dispersions was modeled using power law, Cross, and Ellis models. The power law model described the flow behavior of dispersions for its lowest standard error (0.29) and highest determination coefficient (R²) (0.99). Rheological investigation showed that both loss (G″) and storage (G′) modules increased as gum and oil content increased. Delta degree was 0.1 and increased as frequency increased, indicating that liquid-like viscose behavior dominated solid-like elastic behavior. Droplet-size distribution was measured by light scattering and microscopic observations revealed a flocculated system. Gum, WPI, and oil contents decreased the emulsion creaming index with gum concentration having the greatest effect.