Rheology Of Emulsions Research Articles

Investigating the Rheology and Stability of Heavy Crude Oil-in-Water Emulsions Using APG08 Emulsifiers.

This work investigates the performance of isooctyl glucoside (APG08) as an emulsifier for the preparation of a Karamay heavy crude oil-in-water emulsion to facilitate its pipeline transportation. First, various factors affecting the rheology and stability of prepared emulsions were studied. The results revealed that the viscosity and stability of emulsions increased with increasing oil content, surfactant concentration, mixing speed, mixing time, and pH of the aqueous phase. Emulsion viscosity was initially unchanged with the increase in homogenization temperature and then increased while emulsion stability decreased. Meanwhile, the optimal values of key parameters were 75 wt % oil content, 0.5 wt % surfactant concentration, temperature of 30 °C, mixing speed of 750 rpm, mixing time of 10 min, and aqueous phase pH of 11.14, resulting in a viscosity reduction of 88.82% and emulsion stability up to 48 h at 96.27%. In addition, a qualitative relationship between the stability and rheology of emulsions was elaborated by analyzing the experimental results. The findings showed that an increase in emulsion stability was accompanied by an increase in emulsion viscosity. Therefore, emulsion viscosity cannot become very high while improving emulsion stability to ensure proper transportation.

The role of oil concentration on the rheological properties, microstructure, and in vitro digestion of cellulose ether emulsions

The effect of oil concentration (from 5 to 47%) and type of cellulose ether on the rheological properties (flow and linear viscoelasticity), microstructure and oil digestion in o/w cellulose ether emulsions were investigated in the study. Three types of cellulose ethers were used: a hydroxypropyl methylcellulose (HPMC) and two methylcelluloses (MC) with different degrees of methoxyl content. All the emulsions showed shear thinning behaviour. The increase in oil concentration increase the emulsion's viscosity, the viscoelastic moduli G′ and G″, and decreases the loss tangent. The greatest viscosity and viscoelasticity was in the MC with the highest methoxyl content. Oil digestibility was determined by a titration method during in vitro digestion. Compared to a whey protein emulsion (control), the cellulose ether emulsions required a lower NaOH, which indicates lower free fatty acid generation and lower fat digestion. In the cellulose ether emulsions, this decrease in oil digestion was found at all the oil concentrations. A difference in oil digestion kinetics was found between the cellulose ether emulsion (linear) and the control (logarithmic), which was associated to a saturation in the digestive system in the whey protein emulsion. The microstructure after in vitro digestion showed practically no fat globules in the whey protein emulsion, whereas fat globules were observed in the cellulose ether emulsions, which confirms the highest oil digestion in the control emulsion. Cellulose ether emulsions with a wide variety of rheological properties can be obtained by varying cellulose type and oil concentration, with the barrier against fat digestion effective at low and high oil concentrations. • The effect of oil contentin rheology, microstructure and digestion of emulsions were studied. • Viscosity and viscoelasticity increased with oil concentration. • Cellulose ethers showed lower digestibility than a whey protein control. • Different oil digestion kinetics was found among cellulose ether and whey protein control. • Saturation occurs in the whey protein emulsion at higher oil concentration.

Rancidity-induced protein oxidation affects the interfacial dynamic properties and the emulsion rheological behavior of rice bran protein

To improve the practical application of rice bran protein (RBP) prepared from rice bran (RB) with different degrees of rancidity as a stabilizer in emulsion, fresh RB was stored for 0, 1, 5, 7, and 10 d (temperature of 25 °C, relative humidity of 85%) to investigate the effects of RB rancidity on the interfacial dynamic properties and structures of RBP, rheological properties of the O/W emulsion prepared by RBP. RB rancidity-induced moderate oxidation of RBP (prepared from RB storage for 1 d) reduced the particle size (24.36–18.17 nm) and Zeta potential (−13.57 ∼ −14.97 mV) of RBP, while excessive RBP oxidation (prepared from RB storage for 5–10 d) increased the particle size (37.84–68.06 nm) and Zeta potential (−13.40 ∼ −10.6 mV) of RBP. In addition, moderate protein oxidation increased the interfacial pressure, diffusion rate, interfacial expansion modulus of RBP, and emulsion viscoelasticity, while excessive protein oxidation improved the permeability rate and rearrangement rate of RBP. Overall, this study demonstrated that moderate protein oxidation had positive effects on interfacial properties (interfacial dynamic properties and dilatational rheology of interfacial layers) of RBP, which could provide a theoretical basis for mediating the stability and rheology of RBP emulsions by adjusting the degrees of RB rancidity. • Rancidity-induced RBP oxidation changed the K diff , K p and K r of RBP. • RBP oxidation changed the viscoelasticity of interfacial adsorption layers. • RBP oxidation changed the viscosity, G′ and G″ of RBP emulsions.

Co-delivery of hydrophobic astaxanthin and hydrophilic phycocyanin by a pH-sensitive water-in-oil-in-water double emulsion-filled gellan gum hydrogel

Astaxanthin and phycocyanin were recommended for their bioactivities. However, limited stability and low bioavailability were not conducive to their applications in the food industry. A pH-sensitive double W 1 /O/W 2 emulsion-filled hydrogel loaded concomitantly with astaxanthin and phycocyanin was prepared using the two-step emulsification process. First, the W 1 /O emulsion was fabricated using polyglycerol polyricinoleate as a hydrophobic emulsifier. Second, W 1 /O/W 2 emulsions are typically formed by homogenizing W 1 /O emulsions with an aqueous phase containing sodium caseinate. Later, gellan gum was added to the double emulsion as an additional stabilizer and gelling agent to prepare the double emulsion-filled hydrogel. The influence of gellan gum on the microstructure, rheology, and stability of double emulsions was investigated. The double emulsions remained stable during 30 days’ storage when the content of gellan gum was above 0.4% since the hydrogel formation. The microstructure of double emulsions was maintained under the acidic environment due to the network formed by gellan gum while transformed from hydrogel state to solution state since the disintegration of gellan gum network under neutral conditions. Further, based on the pH-sensitive nature of double emulsion-filled hydrogel, the co-encapsulation of phycocyanin and astaxanthin and the in vitro release behavior were demonstrated. The maximum encapsulation efficiency of phycocyanin and astaxanthin was 94.1% and 90.82%, respectively. In vitro digestion proved their intestinal targeted release ability. These results suggested that the double emulsion-filled gellan gum hydrogel can be used as a pH-sensitive carrier for intestinal targeted delivery of hydrophobic and hydrophilic food bioactive ingredients. • pH-sensitive double emulsion-filled gellan gum hydrogel was prepared. • Co-encapsulation of astaxanthin and phycocyanin was achieved. • Gellan gum improved the encapsulation efficiency of astaxanthin and phycocyanin. • The double emulsions-filled hydrogel achieved intestinal targeting delivery.

The interaction between anionic polysaccharides and legume protein and their influence mechanism on emulsion stability

Legume proteins have excellent emulsification, but the utmost problem is the poor emulsion stability of single protein. In this study, three anionic polysaccharides (xanthan (XG), Willan (WG) and gellan (GG)) were selected to improve stability of protein emulsion (soy protein (SPI), mung bean protein (MPI) and pea protein (PPI)). Molecular interaction, stability, interfacial adsorption, rheology and microstructural characteristics of emulsions were analyzed. The result shown that MPI-polysaccharide emulsion had the smallest particle size and GG-protein emulsion had higher the zeta-potential, and XG-MPI had the best stability. The emulsifying activity and emulsifying stability of GG-SPI were found to be best, the fastest adsorption rate was observed for GG-SPI (AP% 45.23%, Γ 5.03 mg/m 2 ). Fluorescence spectroscopy and gel electrophoresis showed that polysaccharide linked by protein were mainly ascribed to noncovalent interactions and had little effect on the microenvironment. The particle size distributions of SPI group were most homogeneous, and PPI group had obvious aggregation observed by CLSM. All emulsions were pseudo-plastic and shear-thinning properties. XG-MPI and GG-SPI showed better stability and emulsifying properties, polysaccharide promoted the absorption of protein on the oil droplet surface by increasing negative charges repulsive interaction and emulsion viscosity. In brief, the interaction between legume protein and anionic polysaccharide changed the emulsion stability. The research would enriched the emulsions applications in food processing. • Three anionic polysaccharide changed legume protein emulsion stability. • Xanthan-MPI and gellan-SPI showed better stability and emulsion characteristics. • Interaction were noncovalent interaction and had little effect on microenvironment. • Polysaccharide promoted the absorption of protein on the oil droplet surface. • Increasing negative charges repulsive interaction enhanced emulsion viscosity.

Effect of emulsification parameters on the rheology, texture, and physical stability of cosmetic emulsions: A multiscale approach

This study presents a multiscale approach for the production of cosmetic emulsions to evaluate the influence of emulsification on the macroscopic and microscopic properties of the product. This study evaluates the effects of the impeller pumping capacity and tip velocity on the rheological and textural properties of the cosmetic emulsions at the macroscopic scale as well as the effect of these parameters on the average drop size and the drop size distribution at the microscopic scale. This study also considers the influence of the pumping capacity and tip velocity on the physical stability of cosmetic emulsions. Two dispersed phase concentrations were used in this study (i.e., 30 % and 80 % w/w) to evaluate the effect of the product formulation on the performance of the cosmetic emulsions. The results showed that the impeller pumping capacity and the tip velocity are key parameters to control the energy demand and drop formation during the emulsification process (mean drop size and drop size distribution). These parameters also govern the microscopic structure of the emulsions, which has a strong influence on the macroscopic performance of the product. Thus, the tip velocity and pumping capacity are proposed as appropriate scale-up factors for the emulsification process.

Rheology of Emulsions Thickened by Starch Nanoparticles.

The rheology of oil-in-water (O/W) emulsions thickened by starch nanoparticles is investigated here. The starch nanoparticle concentration is varied from 0 to 25 wt% based on the matrix aqueous phase. The oil concentration is varied from 0 to 65 wt%. At a given nanoparticle concentration, the emulsions are generally Newtonian at low oil concentrations. The emulsions become shear-thinning at high oil concentrations. The increase in nanoparticle concentration at a given oil concentration increases the consistency of the emulsion and enhances the shear-thinning behavior of emulsion. The rheological behavior of emulsions is described reasonably well by a power-law model. The consistency index of the emulsion increases with the increases in nanoparticle and oil concentrations. The flow behavior index of emulsion decreases with the increases in nanoparticle and oil concentrations, indicating an increase in the degree of shear-thinning in emulsion.

Erratum: “Shear rheology of a dilute emulsion of ferrofluid droplets dispersed in a non-magnetizable carrier fluid under the influence of a uniform magnetic field” [J. Rheol. 65, 925 (2021)

Erratum: “Shear rheology of a dilute emulsion of ferrofluid droplets dispersed in a non-magnetizable carrier fluid under the influence of a uniform magnetic field” [J. Rheol. 65, 925 (2021)

Effect of humectants and Zygosaccharomyces bailii inoculation on the physical stability of oil-in-water emulsions modeling salad dressings.

Salad dressing formulations include a pH within 3.2-4.1, salt and other solutes to depress water activity. The interaction between hydrocolloids and other components such as humectants determines their physical and microbiological stability. To our knowledge, the effect of commonly used solutes on physical stability and rheological characteristics of oil-in-water emulsions stabilized by xanthan gum has not been reported, and neither has the effect of a spoilage yeast on physical stability been evaluated. The effect of different humectants (sodium chloride, glucose and xylitol) and Zygosaccharomyces bailii inoculation on the stability of oil-in-water emulsions containing different levels of xanthan gum to emulate different types of salad dressings was investigated by means of droplet size, zeta potential, rheological measurements and confocal laser scanning microscopy (CLSM). Generally, the addition of humectants strengthened the weak or strong emulsion structure, especially xylitol. Glucose or xylitol acted as stabilizers since they decreased Sauter and De Broucker diameter. On the contrary, NaCl destabilized the emulsions since it increased droplet size and exhibited the lowest absolute values of zeta potential. Inoculation with Z. bailii destabilized some emulsions since it increased Sauter and De Broucker diameter. Emulsion droplet size, polydispersity, and xanthan gum and yeast location were confirmed by CLSM imaging. This study highlights the key role of humectants and xanthan gum level on physical characteristics and stability of oil-in-water emulsions. Addition of xylitol leads to an enhancement in emulsion rheology and physical stability, suggesting that it is a potential low-calorie multifunctional additive for salad dressings. © 2022 Society of Chemical Industry.

Tannic acid enhanced the emulsion stability, rheology and interface characteristics of Clanis Bilineata Tingtauica Mell protein stabilised oil‐in‐water emulsion

SummaryClanis Bilineata Tingtauica Mell Protein (CBTMP) was one of the new natural insect protein resources. However, due to its strong surface hydrophobicity and poor emulsion stability, its application has greatly been limited. In this study, Pickering emulsions were prepared by CBTMP–Tannic acid (CBTMP–TA) particles and soybean oil (φ = 50%). The presence of TA significantly increased the zeta‐potential (from −23.5 ± 0.73 to −29.23 ± 0.58 mV) and three‐phase contact angle (from 129.9 ± 4.53° to 87.27 ± 3.20°) of complex, especially the concentration of TA was 0.4 mm. Besides, the stability of emulsions was significantly improved according to the results of the droplet size and static multiple light scattering. Furthermore, rheological properties including viscosity, thixotropy and creep recovery were significantly enhanced, which indicated the formation of a more stable network structure. Interfacial behaviour (Interfacial tension, interfacial film viscoelasticity and diffusion rate) of emulsions was significantly changed, forming a more stable interfacial layer as TA content increased. The CBTMP–TA complex was adsorbed at the interface and the adsorption rate was also mainly affected by the content of TA. The study indicated CBTMP–TA compositions to enhance stability, rheological behaviours and interfacial characteristics, and demonstrated the potential applications of insect protein resources in food emulsion systems.

Rheology of dispersions and emulsions composed of chia mucilage and the application of chia in food.

Chia mucilage (CM) is an emerging resource in food applications. However, the mechanism of this biopolymer as a stabilizer/emulsifier ingredient has not yet been well defined. A non-uniform viscoelastic tridimensional network was observed on emulsions with CM, while the surface activity of the CM ingredient has been associated with its protein content. To understand its functionality in food, this review focused on discussing and summarizing the rheological properties of dispersions and emulsions composed of CM under different conditions, such as pH, temperature, salt content, and mucilage content. For example, emulsions and dispersions with CM showed pseudoplastic behavior. An increase in the CM concentration increased the viscosity and the consistency index and decreased the behavior index. The consistency index of dispersions with CM increased with pH. The future evaluation of emulsions and dispersions properties, such as viscoelastic properties and microstructure, is particularly important for the successful use of CM in the food industry. The principal studies have evaluated the use of CM in dairy and meat systems as an emulsifier, stabilizer, or lipid replacer. The nutritional quality of the products with CM was maintained or improved, but sometimes an undesirable darkening was observed. Future evaluation of the cold extraction method of CM might improve the color and overall sensory acceptability of food products with CM. Integrated chia seed processing, including mucilage, oil, and protein extraction could be carried out to make chia seed industrial processing viable. © 2022 Society of Chemical Industry.

Ethanol-tolerant pickering emulsion stabilized by gliadin nanoparticles

In this paper, ethanol-tolerant Pickering emulsion was prepared using gliadin nanoparticles (NPs) based on pH adjustment coupled heat treatment. The effects of gliadin NPs concentration on ethanol-tolerant Pickering emulsions in terms of emulsion size, microstructure, and rheology were investigated. The results indicated that gliadin NPs exhibited an elliptical appearance. At pH 7, the particle size was 600.04 ± 4.80 nm, and the polydispersity coefficient was 0.18 ± 0.29. Fluorescence spectra showed that this method destroyed the tertiary structure of the protein and initiated the self-assembly of gliadin. With the increase of particle concentration, the size of the Pickering emulsion decreased, and the emulsion gradually became gelatinized. The increase of particle concentration made the oil-water interface in emulsion more robust. This study showed that the preparation of gliadin NPs based on pH regulation coupled heat treatment could stabilized the emulsion in the presence of ethanol. The structural and functional properties of Pickering emulsion could be regulated by the concentration of particle stabilizers, thus providing a theoretical basis for constructing structured and functionalized Pickering emulsions.

Rheology and stability of concentrated emulsions fabricated by insoluble soybean fiber with few combined-proteins: Influences of homogenization intensity

Insoluble soybean fiber with few proteins, which is extracted from defatted okara by homogeneous combined with alkali treatment, was used to prepare concentrated emulsions. Firstly, insoluble soybean fiber extracted under pH12 was used to fabricate concentrated emulsions containing various particle concentrations and oil volume fractions and the optimized condition was obtained. Subsequently, insoluble soybean fiber extracted under pH12 followed by different homogeneous strengths were utilized. Concentrated emulsions stabilized by insoluble soybean fiber that was subjected to stronger homogenization presented lower absolute values of the ζ-potential about −47.7 mV and average droplet sizes of 37.0 μm approximately. Moreover, these emulsions exhibited a higher viscosity and elastic modulus, thereby providing better stability and less pronounced environmental sensitivities towards either pH 5 or 100 mM NaCl. Overall, results revealed that insoluble soybean fiber with few protein, especially subjected to homogenization during fiber extraction, was well suited to fabricate concentrated emulsions.

Nanocellulose from bamboo shoots as perfect Pickering stabilizer: Effect of the emulsification process on the interfacial and emulsifying properties

In this work, the medium internal phase O/W Pickering emulsions stabilized with bamboo shoots nanocellulose (BSNC) was successfully fabricated. The nanocellulose extracted from bamboo shoots with an average width of 56.37 nm and height of 7.44 nm showed great potential as an emulsifier in the Pickering emulsions. The effects of BSNC content, oil-water ratio and emulsification process on the structure, stability and rheology of the resultant Pickering emulsions was explored. The obtained emulsion with the BSNC content of 0.5 wt% at the oil to water volume ratio of 5:5 had a lower particle size of around 25 μm. With the increasing BSNC content, the emulsions presented increased droplet size, and even demulsification occurred. Interestingly, the physicochemical properties of the emulsions could be significantly improved through twice shearing, which effectively reduced droplet size. The surface coverage was above 100% for the Pickering emulsions stabilized with the BSNC content of 0.5%–1.1%. With the increasing BSNC content, the apparent viscosity was increased first and then decreased, and all emulsions showed elastic behaviors. This work would provide theoretical guidance for preparing medium or high internal phase Pickering emulsions stabilized with nanocellulose.

Responsive Telechelic Block Copolymers for Enhancing the Elasticity of Nanoemulsions

The rheology of emulsions dictates their performance in many scientific and industrial applications. Here, we demonstrate that high-molecular-weight telechelic triblock copolymers composed of polystyrene end blocks with a poly(ethylene oxide) midblock effectively modify the rheology of a suspension of cyclohexane nanodroplets. Because of their telechelic structure, these polymers bridge between droplets to generate elastic networks with shear moduli on the order of 1000 Pa. The network elasticity increases with polymer concentration and molecular weight as the polymers more effectively form bridges. Furthermore, we tune the nanoscale interactions that control the polymer partitioning by decreasing the temperature below the cloud point of the system. At low temperatures, the polystyrene end blocks no longer preferentially partition into the cyclohexane droplets, and the emulsions begin to exhibit terminal viscous relaxations. These results identify key properties of telechelic block copolymers that can be exploited to significantly enhance nanoemulsion elasticity to improve the processability and transport of complex fluids in applications ranging from 3D printing to functional hydrogels.

Influence of Aqueous Phase Composition on Double Emulsion Stability and Colour Retention of Encapsulated Anthocyanins.

Water-in-oil-in-water (W1/O/W2) emulsions (double emulsions) have often been used for the encapsulation of bioactive compounds such as anthocyanins. Instability of both anthocyanins and double emulsions creates a need for a tailored composition of the aqueous phase. In this work, double emulsions with a gelled internal water phase were produced and monitored over a 20-day storage period. The effect of the electrolyte phase composition (varying electrolyte components, including adipic acid, citric acid, and varying concentration of potassium chloride (KCl)) on anthocyanin and double emulsion stability was analysed using colour analysis, droplet sizing, and emulsion rheology. The effect of electrolytes on colour retention was shown to differ between the primary W1/O emulsion and the secondary W1/O/W2 emulsion. Furthermore, droplet size analysis and emulsion rheology highlighted significant differences in the stability and structural behaviour of the emulsions as a function of electrolyte composition. In terms of colour retention and emulsion stability, a citrate-buffered system performed best. The results of this study highlight the importance of strict control of aqueous phase constituents to prevent anthocyanin degradation and maximise double emulsion stability. Additional experiments analysed the effect of pectin chemistry on the anthocyanin colour retention and leakage, finding no conclusive difference between the unmodified and amidated pectin.

Comparative Study of Physicochemical Properties of Nanoemulsions Fabricated with Natural and Synthetic Surfactants

This work aims to evaluate the effect of two natural (whey protein isolate, WPI, and soy lecithin) and a synthetic (Tween 20) emulsifier on physicochemical properties and physical stability of food grade nanoemulsions. Emulsions stabilized by these three surfactants and different sunflower oil contents (30% and 50% w/w), as the dispersed phase, were fabricated at two levels of homogenization pressure (500 and 1000 bar). Nanoemulsions were characterized for droplet size distribution, Zeta-potential, rheological properties, and physical stability. Dynamic light scattering showed that droplet size distributions and D50 values were strongly affected by the surfactant used and the oil content. WPI gave similar droplet diameters to Tween 20 and soy lecithin gave the larger diameters. The rheology of emulsions presented a Newtonian behavior, except for WPI-stabilized emulsions at 50% of oil, presenting a shear-thinning behavior. The physical stability of the emulsions depended on the surfactant used, with increasing order of stability as follows: soy lecithin < Tween 20 < WPI. From our results, we conclude that WPI is an effective natural replacement of synthetic surfactant (Tween 20) for the fabrication of food-grade nanoemulsions.

Bulk rheology of sticky DNA-functionalized emulsions.

We measure by experiment and particle-based simulation the rheology of concentrated, non-Brownian droplet emulsions functionalized with surface-bound single-stranded (ss), "sticky," DNA. In the absence of ssDNA, the emulsion viscosity increases with the dispersed phase volume fraction ϕ, before passing through a liquid-solid transition at a critical ϕ_{c} related to random close packing. Introducing ssDNA leads to a liquid-solid transition at ϕ<ϕ_{c}, the onset being set by the droplet valency N and the ssDNA concentration (or simulated binding strength ε). Using insight from simulation, we identify three key behaviors: (i) jammed suspensions (ϕ>ϕ_{c}≈0.64) show weak effects of functionalization, with elastic rheology instead governed by droplet stiffness; (ii) suspensions with ϕ<ϕ_{c} and N=1, 2 always exhibit viscous rheology, regardless of functionalization; and (iii) for ϕ<ϕ_{c} and N>3, functionalization leads to a controllable viscous-elastic transition. We present state diagrams showing the range of rheological tuning attainable by these means.

Influence of the composition of macromolecular diols on the rheology and water absorption of polyurethane acrylate emulsions

AbstractWaterborne modified polyurethane (PU) dispersions with different macromolecular diols as soft segments were prepared by the self‐emulsifying method, and then compounded with the acrylate monomers, the polyurethaneacrylate composite emulsion (PUA) with the core‐shell structure was prepared by emulsifier free emulsion polymerization. The effects of the type and ratio of macromolecular diols in the soft segment on the particle size and distribution, rheological properties, adhesion, water absorption and thermal properties of the PUA emulsion were studied. The results showed that the particle size of PUA decreased, and the shear resistance and heat resistance of PUA were enhanced with the addition of polypropylene glycol. According to the water absorption rate of PUA emulsion, it was found that adding poly‐1,4‐butanediol adipate glycol and poly(caprolactone) diol with more hydrophobic groups could improve the water resistance of PUA dry film, and the minimum water absorption value was 0.68%.

Study on the rheology of a dilute emulsion of surfactant-covered droplets using the level set and closest point methods

In this work, we study the effects of surfactant elasticity (E), coverage factor (X), and Péclet number (Pe) on the droplet shape and emulsion rheology. Our analysis considers a single two-dimensional surfactant-covered droplet in an immiscible liquid submitted to a simple shear flow. The numerical methodology combines the level set, to capture the interface, and the closest point method to solve the surfactant transport equation. We separate the dilute phase contribution to the bulk stress tensor in the capillary stress, associated with the normal stress jump, and the Marangoni stress, related to the stress tangent to the interface. Our results show that E and X affect the droplet shape more intensely than the Pe. On the other hand, Pe directly affects the emulsion's bulk viscosity. For Pe≫1, the capillary viscosity decreases with X, while the Marangoni viscosity grows with X. Such a compensation mechanism allows the increase in the bulk viscosity with X. We also present results for the first normal stress difference.