Mechanism Of Emulsion Stabilization Research Articles

Effect of Polymer Network Architecture on Adsorption Kinetics at Liquid–Liquid Interfaces: A Comparison Between Poly(NIPAM-co-AA) Copolymer Microgels and Interpenetrating Network Microgels

Understanding the adsorption features of polymer microgels with different chemical compositions and structures is crucial in studying the mechanisms of respective emulsion stabilization. Specifically, the use of stimuli-responsive particles can introduce new properties and broaden the application range of such complex systems. Recently, we demonstrated that emulsions stabilized by microgels composed of interpenetrating networks (IPNs) of poly-N-isopropylacrylamide (PNIPAM) and polyacrylic acid (PAA) exhibit higher colloidal stability upon heating compared to PNIPAM homopolymer and other relevant PNIPAM-based copolymer counterparts. In the present work, using pendant drop tensiometry, we studied the evolution of water–tetradecane interfacial tension during the adsorption of PNIPAM-PAA IPN particles, comparing them with single-network P-(NIPAM-co-AA) and PNIPAM microgels. The results showed that, despite having the same chemical composition, copolymer particles exhibit completely different adsorption behavior in comparison to other microgel architectures. The observed disparity can be attributed to the nonuniform distribution of charged acrylic acid groups within the P-(NIPAM-co-AA) network obtained through precipitation polymerization. Oppositely, the presence of IPN architecture provides a uniform distribution of different monomers inside respective microgels. Additionally, hydrogen bonding between PNIPAM and PAA subchains appears to reduce the electrostatic energy barrier, enhancing the ability of IPN particles to successfully cover the liquid interface. Overall, our findings confirm the efficiency of using PNIPAM-PAA IPN microgels for the preparation of oil-in-water emulsions and their stability, even when the temperature rises above the lower critical solution temperature of PNIPAM.

Stability of electrostatically stabilized Pickering emulsion of silica particles and soy hull polysaccharides: Mechanism of pH and ionic strength.

To enhance the surface hydrophobicity and emulsification capacity of silica colloidal particles, a natural surface modification of soy hull polysaccharides (SHP) was conducted. Here, the effects of pH and ionic strength on the stability, microstructure and rheological properties of concentrated Pickering emulsions were investigated. Experimental results show emulsions gelled at pH2, with increasing pH (2-10), SiO2-SHP absolute zeta potential (from -19.6 to -44.7mV) and interfacial tension (from 15.2 to 25.09 mN/m) increased, and viscosity, viscoelasticity and storage stability decreased. Additionally, at low NaCl concentrations (<150mM), SiO2-SHP interfacial tension remained low (21.3 mN/m), promoting stable emulsions (TSI<1.5). In this case, the electrostatic interaction was slightly affected by ions, facilitating the occurrence of composite coagulation. However, as ionic concentration increased (150-300mM), interfacial tension increased (from 20.5 to 27.6 mN/m). Thus, our study presents important insights into the pH and salt ions dependent mechanism of emulsion stabilization by SiO2-SHP.

Investigation of the Surface Activity and Interface Behavior of Hybrid Carbosilane–Cyclosiloxane Dendrimers

This work deals with hybrid carbosilane–cyclosiloxane dendrimers featuring variable tension of rings in the outer layer. The presence of a siloxane bond in the shell of these dendrimers, due to its surface activity, allows the formation of monolayers at the interface. The interfacial energies at a water–hexane interface, measured by the spinning drop method, indicate change in the mechanism of emulsion stabilization with an increase in the generation number of the dendrimers explored.

Insights into the Pickering emulsions stabilized by yeast dietary fiber: Interfacial adsorption kinetics, rheological characteristics, and stabilization mechanisms

This study developed Pickering emulsions based on yeast dietary fiber (YDF) and investigated the interfacial adsorption kinetics of YDF, rheological properties and stabilization mechanisms of emulsions. Results indicated that increasing YDF concentration enhanced its diffusion and rearrangement at the oil-water interface. At a concentration of 8 %, YDF exhibited the highest diffusion rate (0.1406 mN·m−1·s-0.5) and rearrangement rate (18.8 s−1). The emulsion stabilized at this concentration had the smallest droplet size (1.55 μm) and the slowest droplet migration rate (0.34 mm/h), effectively suppressing droplet aggregation due to collisions and thereby improving the overall emulsion stability. Confocal laser scanning microscopy results confirmed that emulsion stability relied on the co-adsorption of proteins and polysaccharides from YDF at the interface, with proteins primarily adsorbed at the oil-water interface and polysaccharides responsible for the continuous phase network formation. This study demonstrates YDF's potential as an emulsion stabilizer and elucidates the stabilization mechanism of YDF-induced emulsion.

Application potential of wheat bran cellulose nanofibers as Pickering emulsion stabilizers and stabilization mechanisms

In this paper, cellulose nanofibers (CNF) were prepared from wheat bran (WB) and the structure of CNF was determined. Fourier transform infrared spectra and X-ray diffractograms showed the groups such as hydroxyl and carboxyl groups and cellulose type 1 structure possessed by CNF, respectively. Scanning electron microscopy exhibited that CNF was filamentous and intertwined. In addition, Pickering emulsions were prepared using CNF and the physicochemical properties of the emulsions were characterized. The results showed that CNF was able to increase the zeta potential and viscosity of the emulsions, thus improving the stability of the emulsions. Moreover, CNF formed a physical barrier by adsorbing at the oil-water interface and near the oil droplets and CNF dispersed in the aqueous phase formed a network structure to restrict the movement of oil droplets, thus improving the stability of the emulsions. These findings may provide some new insights for the potential applications of WB.

Mechanisms of Pickering emulsion formation and stabilization by composite arabinoxylan–whey protein isolate particles

Few systematic studies were performed into the properties of arabinoxylan (AX) and protein composite particles, and their mechanisms of action in an emulsion remain largely unknown. In this study, composite particles based on different concentrations of AX and whey protein isolate (WPI) were constructed, and a systematic characterization was conducted to determine their functional properties. A good compatibility was found between WPI and AX, and the composites exhibited an enhanced thermal stability and consistent particle sizes. Molecular interactions, including hydrogen bonds, were detected between WPI and AX, and the composite particles containing 4% AX exhibited the lowest interfacial tension and the strongest emulsification ability. AX promoted protein adsorption on the oil phase surface, and the desorption energy of the composite particles at the oil/water interface increased accordingly. The stability of an emulsion stabilized by AX–WPI was confirmed by rheological and microstructural investigations. This study therefore provides theoretical support for the application of such emulsions.

An investigation of the mechanism of emulsion stabilization in octenyl succinic anhydride-modified tamarind seed polysaccharide

Previous studies have shown that octenyl succinic anhydride-modified tamarind seed polysaccharide (OTSP) is an effective emulsion stabilizer. In this study, the fine structure and interfacial behavior of OTSP were investigated using a variety of methods to elucidate its mechanism for stabilizing emulsions. First, the results of nuclear magnetic resonance indicated that the esterification reaction occurred at the 6th carbon atom of glucose, which was not replaced by xylose in the main chain of TSP. Then, the studies of the interfacial behavior showed that OTSP adsorbed more at the oil-water interface than TSP, and that the intermolecular interactions of OTSP were stronger than those of TSP. The adsorption of OTSP at the interface was dominated by diffusion. Compared to TSP, OTSP formed a denser and more flexible interfacial layer and was resistant to large deformations and high-frequency perturbation. Molecular dynamics simulations revealed the presence of an Ω-like structure in the OTSP molecule. This structure reduced the degree of ordering of its molecular chains, resulting in a more flexible and looser structure that facilitated the rearrangement of OTSP molecules at the interface. The hydrophobic groups anchored the OTSP to the surface of the oil droplets, fixing them in the network structure, further restricting droplet movement and thus improving emulsion stability. The results of this study contribute to the understanding of the mechanism of polysaccharide-stabilized emulsion, which is of great significance in promoting the application of TSP in the food industry.

The beeswax-based fish oil oleogels adjusting the stabilization mechanism and lipid digestion of bi-layer emulsions: Spatial conformation and molecular interaction

Fish oil contains omega-3 polyunsaturated fatty acids, but their poor oxidation stability and gastrointestinal digestion rate led to the low bioavailability. Oleogels could improve the stability of EPA and DHA, so the effect of beeswax (BW)-based fish oil oleogels (FOGs) on the stabilization mechanism and lipid digestion of bi-layer emulsions was investigated. The results showed that the enhanced BW crystals lowered the myofibrillar protein (MP) unfolding along with the decrease in β-sheets, hydrophobic force and disulfide bond, thus reducing the interfacial adsorption capacity and emulsion stability. The enhanced BW formed the rigid crystal network structure and improved the crystal size in the inner layer. The suitable FOG addition (4 wt%) enhanced the unfolding of advanced structures in the outer layer, and the exposure of more hydrophobic groups and disulfide bonds facilitated the interfacial adsorption, thus reducing the size. The final release rate of FFAs significantly decreased with the increasing BW, and significantly increased and decreased with the increasing FOG. BW and FOGs could induce the changes in spatial conformation, and the exposure of hydrophobic groups and disulfide bonds affected the lipase contact at the interface. BW and FOG could adjust the crystal network structure in the inner layer and spatial conformation in the outer layer, thus improving the stabilization and lipid digestion of bi-layer emulsions. This study can provide a theoretical basis for developing DHA and EPA food.

Interfacial Cooperative Assembly of Surfactants and Opposite Wettability Nanoparticles Stabilizes Water-in-Oil Emulsions at High Temperature.

Pickering emulsions have promising applications in the development of unconventional oil and gas resources. However, the high-temperature environment of the reservoir is not conducive to the stabilization of Pickering emulsions. In addition, the preparation of Pickering emulsions under low-energy emulsification and low-concentration emulsifier conditions is a difficult challenge. Here, we report a high-temperature resistant water-in-paraffin oil Pickering emulsion, which is synergistically stabilized by polyglycerol ester (PGE) and nanoparticles with opposite wettability (lipophilic silica and hydrophilic alumina). This emulsion can be prepared under mild stirring (500 rpm) conditions and can be stable at 140 °C for at least 30 days. The synergistic effects of surfactant, silicon nanoparticles (MSNPs) with different wettability, and alumina nanoparticles (AONPs) on the stability of both emulsions and water-oil interfacial membranes were investigated through bottle experiments, cryogenic scanning electron microscopy (cryo-SEM), optical microscopy, fluorescence microscopy, etc. The results showed that both hydrophobic MSNPs and hydrophilic AONPs are adsorbed together at the water-oil interface to stabilize the W/O emulsion, which can be prepared by 500 rpm stirring. The stability of emulsions strongly depends on the wettability of MSNPs, and the MSNP with moderate hydrophobicity (for example, aqueous phase contact angle of 136°) makes the emulsion exhibit the highest stability against aggregation and settling at elevated temperatures. The emulsion stabilization mechanism was revealed in terms of the adsorption capacity of the surfactant by MSNPs, the adsorption morphology and desorption energy of nanoparticles at the water-oil interface adsorption layer, and emulsion rheology. These findings demonstrate a novel and simple strategy to prepare Pickering W/O emulsions with high-temperature stability at low shear strength.

Effect of stigmasterol and polyglycerol polyricinoleate concentrations on the preparation and properties of rapeseed oil-based gel emulsions

Emulsion gels mimic the rheological properties of solid and semi-solid fats, offering a viable solution to replace conventional fats in low-fat food formulations. In this study, gel emulsions stabilized with stigmasterol (ST) and polyglycerol polyricinoleate (PGPR) complexes were prepared. Initially, we examined the effect of the ST/PGPR complex on the mechanism of gel emulsion stabilization. Our findings revealed that the gel emulsion formulated with 3% PGPR and ST exhibited a robust structure, effectively stabilizing the entire system and ensuring uniform distribution, and increasing ST concentration led to greater stability of the gel emulsion system. Stability assessments demonstrated that gel emulsions containing 3% PGPR and varying ST concentrations exhibited remarkable thermal stability and effectively delayed oil oxidation. These results underscore the high stability of gel emulsions stabilized with the ST/PGPR complex, highlighting their potential as a margarine substitute.

A microfluidic and Langmuir approach to unveil the interplay between hydroxypropyl methylcellulose and zein nanoparticles on the stability of Pickering emulsions

Utilizing microfluidic technology and Langmuir trough, the study investigated how hydroxypropyl methylcellulose (HPMC) interact with zein nanoparticles (ZNPs) at interfaces and their collective impact on emulsion stability. Herein, microchips were designed with varying adsorption channel lengths to study the effect of adsorption kinetics on the coalescence stability, while Langmuir assessments provided insights into particle adsorption kinetic and film properties of emulsion stabilization mechanisms. Results suggested that HPMC's incorporation expedited ZNPs' rearrangement rates at the interface, especially at low concentrations, resulting in a synergistic reduction in interfacial tension. However, at high HPMC concentration, a competitive adsorption scenario emerged between ZNPs and HPMC, leading to increased interfacial tension and instability. Microfluidic analyses of droplet coalescence, alongside Langmuir-derived interfacial rheology data, revealed that while a small amount of HPMC significantly bolstered emulsion stability by enhancing viscoelastic properties of interfacial film, an excess of HPMC inversely affected these parameters, diminishing film elasticity and thus, the emulsion's coalescence resistance. The adsorption kinetic and the interaction on interface of HPMC and zein particles were analyzed via microfluidic and LB technology in this study, which will not only expand our current strategies for interface engineering of emulsions, but also deepens our understanding of the interplay between mixed particle system adsorption properties, interfacial rheology, and Pickering composite emulsion stability.

Adsorption mechanism of asphaltenes and surfactants at oil-water interface: based on dissipative particle dynamics method

The study of emulsion stabilization mechanisms is of great importance in the field of crude oil extraction, transportation and processing. In order to further investigate the roles of asphaltenes and surfactants in the emulsion stabilization process, the adsorption mechanisms of asphaltenes and surfactants at the oil-water interface were investigated using dissipative particle dynamics. The results show that: the asphaltene interfacial film gradually becomes thicker before the saturation adsorption of asphaltene molecules at the oil-water interface, and the interfacial tension decreases with the increase of the number of molecules until it reaches the equilibrium state; different surfactant molecules have different influences on the interface, and the calculations of the radial distribution function and the interfacial tension show that H2T4 molecules have a stronger effect than H4T4 at the oil-water interface and have stronger surface activity. H2T4 reaches saturation adsorption capacity faster than H4T4 and has higher interfacial efficiency. The asphaltene-surfactant composite system can stabilize the oil-water interface more effectively. Competitive and synergistic effects of asphaltene and surfactant in the process of interfacial adsorption. When the concentration of surfactant in the composite system is low, there is a synergistic effect between the two in the interfacial adsorption process; when the concentration of surfactant is high, there is a competitive effect between the two in the synergistic adsorption process. The surfactant H4T4 has both interfacial adsorption and self-aggregation in the competitive adsorption process. This paper provides ideas for exploring the kinematic laws of molecular behavior in the stabilization mechanism of crude oil emulsions.

Potato starch/naringenin complexes for high-stability Pickering emulsions: Structure, properties, and emulsion stabilization mechanism

In this study, potato starch (PS)/naringenin (NAR) complex was prepared, and its properties and emulsification behavior were evaluated. The experimental results demonstrated that NAR successfully formed a complex with PS molecules through hydrogen bonds and other non-covalent interactions. The emulsifying capacity (ROV) of PS/NAR complex with 16 % composite ratio was 0.9999, which was higher than PS (ROV = 0.3329) (p < 0.05). Based on particle property analysis and molecular dynamics simulation, the mechanism of improving the emulsification performance might be the action of the benzene ring of NAR and intermolecular hydrogen bonding. In addition, the stability of the Pickering emulsions with PS/NAR complexes as emulgators was significantly improved. The emulsifying and rheological behavior of starch-based Pickering emulsions could be adjusted by changing the proportion of the complexes. Results demonstrated that the PS/NAR complexes might be a prospective stabilizer of Pickering emulsions based on starch material and might expand the use of PS in edible products.

The influence of α and α′ subunits on SPI Pickering emulsions based on natural hybrid breeding varieties

In this study, food-grade protein nanoparticles (Wild-NPs, α-lack-NPs, α′-lack-NPs, and (α + α′)-lack-NPs) were organized as emulsion stabilizers via thermal induction. The effects of α and α′ subunits in soybean protein isolate (SPI) on Wild nanoparticle Pickering emulsion (Wild-NPPEs), α-lack nanoparticle Pickering emulsion (α-lack-NPPEs), α′-lack nanoparticle Pickering emulsion (α′-lack-NPPEs) and (α + α′)-lack nanoparticle Pickering emulsion ((α + α′)-lack-NPPEs) were investigated. The Pickering emulsion stabilization mechanism indicated that the α′-lack-NPs particle size, surface hydrophobicity, and contact angle were mostly comparatively large. Therefore, the absence of the α′ subunit made the desorption of protein nanoparticles at the oil and water interface require higher energy. Through the hydrophobic interaction between molecules, the structure and properties of the emulsion were improved, showing good stability. The existence of α′-lack-NPPEs leads to the formation of a gel-like network in the emulsion, which increases the viscosity of the emulsion and makes the network structure of the emulsion more uniform and denser.

PH and redox dual-responsive Pickering emulsion based on silica nanoparticles and novel ferrocene surfactant

Responsive Pickering emulsions capable of responding to external stimuli have been extensively studied, however, there are few studies on double-responsive Pickering emulsions. Here in, a novel ferrocene surfactant (FcACUa) was synthesized and combined with aminated silica nanoparticles (0.5 wt%) to stabilize pH and redox sensitive smart Pickering emulsions. The carboxyl groups act as pH-sensitive parts, while ferrocene serves as the redox-responsive center. Stability and pH/redox response performance of the emulsions were investigated through various methods, such as the contact angle, macroscopic states, creaming index, microscopic images, droplet size distributions, etc. All atom molecular dynamics and dissipative particle dynamics simulations were used to probe the distribution of nanoparticles and surfactant at the water-oil interface, as well as to reveal the stabilization and pH/redox response mechanisms of the Pickering emulsions. Pickering emulsions can be reversibly switched between stable and unstable by adding HCl and NaOH or adding H2O2 and N2H4·H2O. After five pH-induced cycles, the emulsion shows no significant degradation or morphological changes. However, for the redox induced emulsification demulsification process, the size of the emulsion drops increases with the increase of the number of cycles. This work provides insights into the Pickering emulsion stabilization mechanism and the regulation mechanisms of pH and redox stimulation, which may have potential value in emulsion polymerization, biphasic catalysis, and oil and gas transportation.

Correlationship between self-assembly behavior and emulsion stabilization of pea protein-high methoxyl pectin complexes treated with ultrasound at pH 2.0

This study investigated the effects of ultrasound on the self-assembly behavior of pea protein (PP)-high methoxyl pectin (HMP) complexes at pH 2.0 through transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and intrinsic fluorescence analysis. The emulsion stabilization mechanism of PP-HMP treated with ultrasound (PP-HMP-US) was also elucidated. The results indicated that ultrasound increased the emulsifying activity index (EAI) and emulsifying stability index (ESI) of PP-HMP. Moreover, PP-HMP-US-based emulsions formed small, dispersed oil drops, which were stable during storage. PP-HMP- and PP-HMP-US-based emulsions did not demonstrate any creaming. The TEM results revealed that ultrasound can regulate the self-assembly behavior of PP and HMP to form spherical particles with a core–shell structure. This structure possessed low turbidity, a small particle size, and high absolute zeta potential values. The FTIR and intrinsic fluorescence spectra demonstrated that ultrasound increased the α-helix and β-sheet contents and exposed the tryptophan groups to more hydrophilic environments. Ultrasound also promoted the PP-HMP self-assembly through electrostatic interaction and improved its oil–water interfacial behavior, as indicated by the EAI and ESI values of PP-HMP-US-based emulsions. The current results provide a reference for the development of an innovative emulsifier prepared by ultrasound-treated protein–pectin complexes at low pH.

Segregative phase separation of gelatin and tragacanth gum solution and Mickering stabilization of their water-in-water emulsion with microgel particles prepared by complex coacervation

This study aimed to investigate the segregative interaction of gelatin (G) and tragacanth gum (TG) and the stabilization of their water-in-water (W/W) emulsion by G-TG complex coacervate particles. Segregation was studied at different pHs, ionic strengths and biopolymer concentrations. Results showed that incompatibility was affected by increasing the biopolymer concentrations. So, three reigns were demonstrated in the phase diagram of the salt-free samples. NaCl significantly changed the phase behavior via enhancement of self–association of polysaccharide and changing solvent quality due to the charge screening effect of ions. The W/W emulsion prepared from these two biopolymers and stabilized with G-TG complex particles was stable for at least one week. The microgel particles improved emulsion stability by adsorption to the interface and creating a physical barrier. A fibrous and network-like structure of the G-TG microgels was observed by scanning electron microscopy images suggesting the Mickering emulsion stabilization mechanism. It was confirmed that the bridging flocculation between the microgel polymers led to phase separation after the stability period. Biopolymer incompatibility investigation is a useful tool to obtain beneficial knowledge for preparation new food formulation, especially no contain oil emulsions for low- calorie diets.

Determination of the Emulsion Stabilization Mechanisms of Quaternized Glucan of Curdlan via Rheological and Interfacial Characterization

Interfacial-active quaternized glucan of curdlan (QCD) with different degrees of substitution (DS) was prepared and used as stabilizers of oil-in-water (O/W) emulsions at different concentrations. The adsorption behavior of QCDs, rheology of bulk emulsions and interfacial films, emulsion morphology, and stability were investigated. The emulsifying capacity of QCD was essentially related to the viscoelastic features of the interfacial film and the continuous phase and the electrostatic repulsion among oil droplets. QCD molecules with different DS form structurally different interfacial films. The high-DS QCD formed a viscously predominant interfacial film with certain hydrophobicity, whereas the low-DS QCD molecules formed an elastically predominant film characterized by hydrogen bonds among adsorbed chains. The structuralization of low-DS QCD molecules through physical cross-linking in bulk and interfacial films at high concentrations was conducive to emulsion stability. Excess QCD chains in the bulk formed a weak gel-like network, further hindering the movement of droplets in the emulsions. Relevant emulsification and stability mechanisms were proposed. Finally, the stability of curcumin encapsulated in O/W emulsions was evaluated.

Interfacial characteristics of artificial oil body emulsions (O / W) prepared using extrinsic and intrinsic proteins: Inspired by natural oil body

In order to explore the stabilization mechanisms of intrinsic protein (IP) and extrinsic protein (EP) in natural oil-bodies, the effects of adding EP and IP in different relative proportions on the stability, interfacial characteristics, and digestibility of artificial oil body (AOB) emulsions were studied. The stability test results showed that the AOB emulsion prepared using 40% EP/60% IP exhibited the highest ζ-potential (−36.3 mV) and storage stability. According to the results of interface properties, competitive adsorption occurred at the interface in the emulsions prepared using IPs and EPs. Furthermore, by measuring the bioavailability of free fatty acids and curcumin during the digestion process, it was elucidated that 40% EP/60% IP developed a stable interfacial membrane, which facilitated the targeted release of curcumin in the intestine and yielded higher bioavailability. These results lay the foundation for clarifying the stabilization mechanism of natural oil body emulsions from an interfacial perspective.

Emulsifying and emulsion stabilization mechanism of pectin from Nicandra physaloides (Linn.) Gaertn seeds: Comparison with apple and citrus pectin

The emulsifying and emulsion stabilization mechanism of three kinds of pectin (Nicandra physaloides (Linn.) Gaertn seeds pectin-NP, apple pectin-AP, and citrus pectin-CP) were compared in terms of emulsions system, interface layer and pectin structure. The results showed the emulsifying properties of NP was superior to AP and CP, which attributed to lower interfacial tension (∼15.57 mN/m) and better long-term stability to prepared emulsion. The long-term stability of NP emulsion ascribed to the higher emulsion viscosity, more uniform droplet size distribution, stronger electrostatic repulsion, and thicker interfacial layer. Structurally, the emulsifying activity of NP was mainly provided by acetyl and methyl groups, and the emulsifying stabilization was provided by the neutral monosaccharide side chains and ionized carboxyl groups. Therefore, the protein in pectin was not essential for the stabilization of oil-water interface, and the carbohydrate components played a crucial role in when especially lack of protein. Consider that the emulsifying properties of NP were independent of protein, it may be a potential natural emulsifier in resisting acid, ions, and heat.