Emulsions stabilized with solid nanoparticles: Pickering emulsions

Adding nanoparticles to improve emulsion efficiency and enhance microbial degradation in Pickering emulsions

Interfacial microbial degradation of alkane in Pickering emulsions stabilized by hydrophobic bacterial cells is a new mechanism for microbial degradation of water-insoluble chemicals, where both water-insoluble chemicals in the oil phase and water-soluble nutrients (such as nitrogen and phosphorus) in the water phase are bio-accessible to living microorganisms anchoring onto the oil-water interfaces. In the present work, super-hydrophobic Mycobacterium sp. (contact angle 168.6°) degradation of tetradecane was set up as a model. Addition of fumed SiO2 particles (Aerosil® R974) as a new strategy was developed to enhance tetradecane degradation where the biodegradation rate (based on the accumulated biomass) increased by approximately 80%. The enhanced effect of SiO2 particles on the tetradecane degradation attributed to the synergistic effect of SiO2 particles on the emulsion efficiency of Pickering emulsions stabilized by bacterial cells and then on the enhancement of interfacial microbial degradation in Pickering emulsions. KEY POINTS: • Interfacial microbial degradation in bacterial cells stabilized Pickering emulsions. • Adding fumed SiO2 particles to enhance microbial degradation of tetradecane. • Correlation relationship between emulsion efficiency and interfacial microbial degradation.

Thymol-loaded Zein-pectin composite nanoparticles as stabilizer to fabricate Pickering emulsion of star anise essential oil for improved stability and antimicrobial activity

The aim of the present study was to prepare a new antimicrobial Pickering emulsion of which the star anise essential oil was added to the oil phase, and to investigate the effect of stabilization by bio-based active nanoparticles consisting of zein and pectin loaded with thymol. First, the thymol-loaded zein/pectin composite nanoparticles (ZTNPs) were fabricated as uniformly distributed spherical nanoparticles with an average diameter of 200 nm through antisolvent precipitation. Second, the effects of nanoparticles' concentration, oil phase ratio, and storage time on the stability of emulsions were explored according to particle size potential, interfacial tension, rheology, and micromorphology. Finally, the antibacterial results showed that Pickering emulsion inhibited Escherichia coli and Staphylococcus aureus compared to the control group by nearly 7 log colony-forming unit/g at 36 h, which was twice as much as the inhibition by thymol or star anise essential oils and ZTNPs. Therefore, the proposed Pickering emulsion with star anise essential oil could be used as a green and safe plant-derived antimicrobial agent in the food industry.

Preparation of lauric acid esterified starch by ethanol solvothermal process and its Pickering emulsion

In this paper, the esterification modification of different kinds of starches such as waxy maize, normal maize, high-amylose maize, cassava and potato in high temperature closed system were studied by solvothermal method. The oil-in-water Pickering emulsion were prepared with esterified starches as granule stabilizer. The microscopic state of granules in the emulsion and the physical and oxidation stability of emulsion were studied. The results show that starches are not gelatinized and can be esterified at a temperature (100 °C) much higher than that of gelatinization, and the granule morphology is almost unchanged. DS (degree of substitution) values of esterified starches range from 0.0333 to 0.0512. Pickering emulsion with 50 vol% oil volume fraction prepared with 3.0 wt% granule concentration did not show any instability such as oil-water separation after storage at room temperature for 30 days. Atomic force microscope (AFM) analysis showed that all esterified starch granules had the characteristics of granular cold-water swelling starch (GCWSS). The granules completely swelled into a dense molecular chain in the emulsion, and this three-dimensional network structure improved the stability of emulsion. Therefore, the preparation of esterified starch granules by ethanol solvothermal method is a simple and effective method.

Liquid-Liquid Interfacial Nanoarchitectonics

Science in the small world has become a crucial key that has the potential to revolutionize materials technology. This trend is embodied in the postnanotechnology concept of nanoarchitectonics. The goal of nanoarchitectonics is to create bio-like functional structures, in which self-organized and hierarchical structures are working efficiently. Liquid-liquid interface like environments such as cell membrane surface are indispensable for the expression of biological functions through the accumulation and organization of functional materials. From this viewpoint, it is necessary to reconsider the liquid-liquid interface as a medium where nanoarchitectonics can play an active role. In this review, liquid-liquid interfacial nanoarchitectonics is classified by component materials such as organic, inorganic, carbon, and bio, and recent research examples are discussed. Examples discussed in this paper include molecular aggregates, supramolecular polymers, conductive polymers film, crystal-like capsules, block copolymer assemblies, covalent organic framework (COF) films, complex crystals, inorganic nanosheets, colloidosomes, fullerene assemblies, all-carbon π-conjugated graphite nanosheets, carbon nanoskins and fullerphene thin films at liquid-liquid interfaces. Furthermore, at the liquid-liquid interface using perfluorocarbons and aqueous phases, cell differentiation controls are discussed with the self-assembled structure of biomaterials. The significance of liquid-liquid interfacial nanoarchitectonics in the future development of materials will then be discussed.

Molecular Dynamics Study of Silica Nanoparticles and CO2-Switchable Surfactants at an Oil-Water Interface

Adsorbing CO2-sensitive surfactants on the surface of nanoparticles is an important strategy for preparing stimuli-responsive Pickering emulsions. However, the microscopic mechanisms are still limited, owing to a lack of intuitive understanding at the molecular level on the interactions between nanoparticle and switchable surfactants at the oil-water interface. We employed the molecular dynamics (MD) simulations to explore the mechanism behind the reversible emulsification/demulsification of a Pickering emulsion stabilized by silica nanoparticles (NPs) and CO2-switchable surfactants, named N-(3-(dimethylamino)propyl)alkyl amide (CPMA). MD results show that the protonated surfactant CPMAH+ has strong hydrophilicity, forming an adsorption layer at the oil-water interface. The ionic surfactants can be tightly adsorbed on NP surface through electrostatic interactions. Thus, the formed colloid particle has both hydrophobic and hydrophilic properties, which is a key factor in stabilizing emulsion. When CPMAH+ molecules were deprotonated to CPMA, the hydration activity of the headgroups reduced greatly, inducing a mixture with oil molecules. There are still a certain number of CPMA molecules residing at the oil-water interface due to the hydrophilic amine groups. The results from repeated simulations show that NP can either stay in the water phase or locate at the interface. Even NP was finally adsorbed on the interface and combined with CPMA or oil molecules, the adsorption configuration of CPMA on the NP surface was essentially different from that of CPMAH+. The potential of mean force confirmed that the combination between NP and CPMA is quite unstable due to the disappearance of electrostatic attraction. Different binding configurations and stability between NP and CPMA or CPMAH+ were the fundamental reason for the reversible emulsification/demulsification of Pickering emulsion.

Intestine-targeted high internal phase Pickering emulsion formulated using silkworm pupa protein via ultrasonic treatment

High internal phase Pickering emulsions (HIPPEs) stabilized by food grade particles have received much attention as deliver vehicles for bioactives in recent years. In this study, ultrasonic treatment was conducted to regulate the size of silkworm pupa protein (SPP) particles, fabricating oil-in-water (O/W) HIPPEs with intestinal releasability. Briefly, the pretreated SPP and SPP-stabilized HIPPEs were characterized, and the targeting release was investigated using in vitro gastrointestinal simulations and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Results revealed ultrasonic treatment time was the key factor regulating emulsification performance and stability of HIPPEs. Optimized SPP particles were obtained based on their size and zeta potential of 152.67 nm and 26.77 mV, respectively. With ultrasonic treatment, the hydrophobic groups in the secondary structure of SPP were exposed, facilitating the formation of a stable oil-water interface for HIPPEs. Additionally, SPP-stabilized HIPPE showed high stable against the gastric digestion. The SPP with 70 kDa molecular weight, which was the major interfacial proteins of the HIPPE, can be hydrolyzed by intestinal digestive enzymes, enabling the intestine-targeted release of the emulsion. Overall, in the present study, a facile method was developed to stabilize HIPPEs using solo SPP with ultrasonic treatment to protect and deliver hydrophobic bioactive ingredients.

CO2 responsive self-standing Pickering emulsion gel stabilized with rosin-based surfactant modified cellulose nanofibrils

Emulsion gel was developed to provide desirable texture, palatability and functionality to food products. Tunable stability of emulsions is often desired, as in certain situations, the chemical content release usually relies on emulsion induced destabilization of the droplet. However, the destabilization for emulsion gel is difficult because of the formation of highly entangled networks. To address this issue, a fully biobased Pickering emulsion gel stabilized by cellulose nanofibrils (CNF) modified with a CO2 responsive rosin-based surfactant, maleopimaric acid glycidyl methacrylate ester 3-dimethylaminopropylamine imide (MPAGN) was reported. The emulsification/de-emulsification can be reversibly regulated because this surfactant has sensitive CO2 responsive property. MPAGN can be reversibly between active cationic (MPAGNH+) and inactive nonionic (MPAGN) responsive to CO2 and N2. The microstructure of the emulsion gel was observed and compared before and after the response. The rheological properties of emulsion gel stabilized by different concentrations of MPAGNH+ and different contents of CNF were studied separately. As 0.2 wt% CNF was dispersed in 1 mM MPAGNH+ solution, the obtained emulsion can be self-standing for long duration. The rheology study indicated that these emulsions show typical gel characteristics with shear-thinning behavior. The stabilization mechanism of these gel emulsion is a synergistic effect caused by the combination of CO2 responsive Pickering emulsion and intertwined network caused by the hydrogen-bond interaction among CNF.

Banana biomass waste: A prospective nanocellulose source and its potential application in food industry - A review

Bananas are among the most produced and consumed fruit all over the world. However, a vast amount of banana biomass is generated because banana trees bear fruit only once in their lifetime. This massive amount of biomass waste is either disposed of in agricultural fields, combusted, or dumped at plantations, thus posing environmental concerns. Nanocellulose (NC) extraction from this source can be one approach to improve the value of banana biomass. Owing to its superb properties, such as high surface area and aspect ratio, good tensile strength, and high thermal stability, this has facilitated nanocellulose application in the food industry either as a functional ingredient, an additive or in food packaging. In this review, two different applications of banana biomass NC were identified: (i) food packaging and (ii) food stabilizers. Relevant publications were reviewed, focusing on the nanocellulose extraction from several banana biomass applications as food additives, as well as on the safety and regulatory aspects. Ultimately, further research is required to prompt a perspicuous conclusion about banana biomass NC safety, its potential hazards in food applications, as well as its validated standards for future commercialization.

Investigation on physicochemical properties, sensory quality and storage stability of mayonnaise prepared from lactic acid fermented egg yolk

In this research, the physicochemical properties, sensory quality, and storage stability of mayonnaise prepared from egg yolk fermented for different times (0, 3, 6, and 9 h) have been investigated. Compared with control mayonnaise (3.50 μm and 92.88%), mayonnaise prepared from fermented egg yolk possessed significantly lower particle size (3.32-3.41 μm) and higher emulsion stability (97.26-98.72%). Meanwhile, texture, color, and gas chromatography-mass spectrometry (GC-MS) analysis revealed that the fermented egg yolk significantly enhanced the firmness, consistency and cohesiveness, lightness and redness, and flavor profile of mayonnaise. Sensory evaluation showed that mayonnaise with 3 h-fermented egg yolk exhibited the highest sensory scores. And the microscopic and appearance characteristics revealed that fermented egg yolk endowed mayonnaise with a more stable appearance after 30 days of storage. These results indicated that lactic acid fermentation of egg yolk is a feasible way to improve consumer acceptability and shelf life of mayonnaise.

Epoxy Phase-Change Materials Based on Paraffin Wax Stabilized by Asphaltenes

The usual problem of meltable phase-change agents is the instability in their form upon heating, which can be solved by placing them into a continuous polymer matrix. Epoxy resin is a suitable medium for dispersing molten agents, but it is necessary to make the obtained droplets stable during the curing of the formed phase-change material. This work shows that molten paraffin wax forms a Pickering emulsion in an epoxy medium and in the presence of asphaltenes extracted from heavy crude oil. Theoretical calculations revealed the complex equilibrium in the epoxy/wax/asphaltene triple system due to their low mutual solubility. Rheological studies showed the viscoplastic behavior of the obtained dispersions at 25 °C, which disappears upon the heating and melting of the paraffin phase. Wax and asphaltenes increased the viscosity of the epoxy medium during its curing but did not inhibit cross-linking or reduce the glass transition temperature of the cured polymer. As a result of curing, it is possible to obtain phase-change materials containing up to 45% paraffin wax that forms a dispersed phase with a size of 0.2-6.5 μm. The small size of dispersed wax can decrease its degree of crystallinity to 13-29% of its original value, reducing the efficiency of the phase-change material.

Pickering emulsions stabilised with oligoglycine-functionalised nanodiamond as a model system for ocular drug delivery applications

Oil-in-water emulsions, stabilised with conventional surfactants, are commonly used in eye drops for ocular drug delivery. However, the presence of surfactants can sometimes irritate tissues. Furthermore, conventional emulsions often have poor retention on ocular tissue. Pickering emulsions stabilised with nanoparticles have been gaining attention in recent years for a range of biomedical applications because of their biocompatibility. Here, Pickering emulsions were evaluated for the first time for the confinement of organic components for potential application in ocular drug delivery. For a model system, we used nanodiamond (ND) nanoparticles functionalised with covalently-bonded two-tail (2T) oligoglycine C10(NGly4)2 to make Pickering oil-in-water emulsions, which were stable over three months of storage under neutral pH. We proved the non-toxicity of ND-2T Pickering emulsions, comparable to buffer solution, via an ex vivo bovine corneal permeability and opacity test. The retention of the oil phase in the ND-2T stabilised emulsions on corneal tissue is significantly increased because of the mucoadhesive properties arising from the positively-charged terminal amino groups of 2T. Our formulated emulsions have a surface tension, pH and salt concentration comparable to that of tear fluid. The high retention of the ND-2T-stabilised emulsions on the corneal surface, in combination with their non-toxicity, gives them distinct advantages for ocular drug delivery. The principles of this model system could be applied in the future design of a range of formulations for drug delivery.

Assessing and Predicting Physical Stability of Emulsion-Based Topical Semisolid Products: A Review

The emulsion-based topical semisolid dosage forms present a high degree of complexity due to their microstructures which is apparent from their compositions comprising at least two immiscible liquid phases, often times of high viscosity. These complex microstructures are thermodynamically unstable, and the physical stability of such preparations is governed by formulation parameters such as phase volume ratio, type of emulsifiers and their concentration, HLB value of the emulsifier, as well as by process parameters such as homogenizer speed, time, temperature etc. Therefore, a detailed understanding of the microstructure in the DP and critical factors that influence the stability of emulsions is essential to ensure the quality and shelf-life of emulsion-based topical semisolid products. This review aims to provide an overview of the main strategies used to stabilize pharmaceutical emulsions contained in semisolid products and various characterization techniques and tools that have been utilized so far to evaluate their long-term stability. Accelerated physical stability assessment using dispersion analyzer tools such as an analytical centrifuge to predict the product shelf-life has been discussed. In addition, mathematical modeling for phase separation rate for non-Newtonian systems like semisolid emulsion products has also been discussed to guide formulation scientists to predict a priori stability of these products.

Construction and characterization of Pickering emulsions stabilized by soy protein hydrolysate microgel particles and quercetin-loaded performance in vitro digestion

Food-grade Pickering emulsions stabilized by protein microgel particles have received increasing attentions owing to their potential applications in the food industry. Herein, soy protein hydrolysate microgel particles (SPHMs) produced at various pH (3, 5, 7, and 9) with and without ultrasonication were used to stabilize Pickering emulsions. Compared with those prepared using ultrasonication at pH 3-7, SPHMs prepared using ultrasonication at pH 9 showed excellent amphiphility at the oil-water interface and a superior ability to reduce interfacial tension. The Pickering emulsion stabilized by the latter SPHMs displayed a small particle size and a high net charge on the droplet surface, formed a dense honeycomb network interfacial layer with high viscoelasticity and adsorbed protein content, and experienced no visually detectable creaming during storage for 21 days, i.e., exhibited optimum colloidal stability. Furthermore, the above emulsion featured a quercetin encapsulation efficiency of 89.45 % and was capable of sustainable release, achieving a low free fatty acid release efficiency of 61 % and a relatively high quercetin bioaccessibility of 65 % in in vitro simulated digestion experiments. Thus, this work inspires the use of SPHMs in emulsion-based functional foods.

Phase Diagram of Pickering Emulsions Stabilized by Cellulose Nanocrystals

Cellulose is a promising renewable and biocompatible biopolymer for stabilizing Pickering emulsions (PEs). In the present study, PEs were produced by low-frequency ultrasounds with cellulose nanocrystals (CNCs) and caprylic/capric triglycerides. Phase diagrams allowed to understand mechanisms of formation and long-term stabilization of PEs. Emulsion type, continuous phase viscosity, and yield of oil incorporation were studied after PEs formation. Droplet size, oil release, and stability were measured weekly up to 56 days of storage. Results showed that oil mass fraction above 70% w/w led to unstable W/O PEs. Lower oil mass fraction formed O/W PEs of stability depending on CNC content and oil mass fraction. Droplet size stability increased with CNCs/oil ratio. A very low CNCs/oil ratio led to phase separation and oil release. High CNC content stabilized oil droplets surface, increased aqueous phase viscosity, and prevented creaming. Highly stable PEs were produced for CNC content above 3% (w/w) and oil mass fraction below 50% (w/w). Mechanisms for PEs formation and stabilization were proposed for various CNC contents and oil mass fractions.

Advances in Starch Nanoparticle for Emulsion Stabilization

Starch nanoparticles (SNPs) are generally defined as starch grains smaller than 600-1000 nm produced from a series of physical, chemical, or biologically modified starches. Many studies have reported the preparation and modification of SNPs, which are mostly based on the traditional "top-down" strategy. The preparation process generally has problems with process complexity, long reaction periods, low yield, high energy consumption, poor repeatability, etc. A "bottom-up" strategy, such as an anti-solvent method, is proven to be suitable for the preparation of SNPs, and they are synthesized with small particle size, good repeatability, a low requirement on equipment, simple operation, and great development potential. The surface of raw starch contains a large amount of hydroxyl and has a high degree of hydrophilicity, while SNP is a potential emulsifier for food and non-food applications.

Controlling polyHIPE Surface Properties by Tuning the Hydrophobicity of MOF Particles Stabilizing a Pickering Emulsion

Metal-organic frameworks (MOFs) show promise for the capture of greenhouse gases. To be used at a large scale in fixed-bed processes, their shaping under a hierarchical structure is mandatory and remains a major challenge, while keeping available their high specific surface area. For that purpose, we propose herein an original method based on the stabilization of a paraffin-in-water Pickering emulsion by a fluorinated Zr MOF (UiO-66(F4)) with polyHIPEs (polymers from high internal phase emulsions) strategy consisting of the polymerization of monomers in the external phase. After polymerization of the continuous phase and elimination of the paraffin, a hierarchically structured monolith is obtained with the UiO-66(F4) particles embedded in the polymer wall and covering the internal porosity. To avoid the pore blocking induced by the embedment of the MOF particles, our strategy was to modify their hydrophilic/hydrophobic balance with a controlled adsorption of hydrophobic molecules (perfluorooctanoic acid, PFOA) on the UiO-66(F4) particles. This will induce a displacement of the MOF position at the paraffin-water interface in the emulsion and then make the particles less embedded into the polymer wall. This leads to the formation of hierarchically structured monoliths integrating UiO-66(F4) particles with higher accessibility, maintaining their original properties and allowing their application in fixed-bed processes. This strategy was demonstrated by N₂ and CO₂ capture, and we believe that such original strategy could be applied to other MOF materials.

Pickering emulsions stabilized with differently charged particles

For addressing health issues and ecological concerns, the cosmetic and pharmaceutical industries are facing the challenge of designing emulsions without the use of surfactants. Emulsions stabilized by colloidal particles, known as Pickering emulsions, are promising in this matter. In this article, three different types of particles (neutral, anionic and cationic) are used alone or in binary mixtures as stabilizers of Pickering emulsions. The influence of the particles' charge on the emulsions' properties and the synergies between the different types of particles are studied. It is demonstrated that the kinetics of adsorption of the particles at the water/oil interface control the coverage and their organization at the droplet surface, rather than their interactions after adsorption. Binary mixtures of differently charged particles are a powerful way to control the droplet coverage and the particle loading in the emulsions. In particular, the combination of anionic and cationic particles led to smaller droplets and higher particle coverage of emulsion droplets.

Pickering Emulsion Stabilized by β-Cyclodextrin and Cinnamaldehyde/β-Cyclodextrin Composite

A Pickering emulsion was prepared using β-cyclodextrin (β-CD) and a cinnamaldehyde (CA)/β-CD composite as emulsifiers and corn oil, camellia oil, lard oil, and fish oil as oil phases. It was confirmed that Pickering emulsions prepared with β-CD and CA/β-CD had good storage stability. The rheological experiments showed that all emulsions had G' values higher than G″, thus confirming their gel properties. The results of temperature scanning rheology experiments revealed that the Pickering emulsion prepared with β-CD and CA/β-CD composites had high stability, in the range of 20-65 °C. The chewing properties of Pickering emulsions prepared by β-CD and corn oil, camellia oil, lard, and herring oil were 8.02 ± 0.24 N, 7.94 ± 0.16 N, 36.41 ± 1.25 N, and 5.17 ± 0.13 N, respectively. The chewing properties of Pickering emulsions made with the CA/β-CD composite and corn oil, camellia oil, lard, and herring oil were 2.51 ± 0.05 N, 2.56 ± 0.05 N, 22.67 ± 1.70 N, 3.83 ± 0.29 N, respectively. The texture properties confirmed that the CA/β-CD-composite-stabilized-emulsion had superior palatability. After 28 days at 50 °C, malondialdehyde (MDA) was detected in the emulsion. Compared with the β-CD and CA + β-CD emulsion, the CA/β-CD composite emulsion had the lowest content of MDA (182.23 ± 8.93 nmol/kg). The in vitro digestion results showed that the free fatty acid (FFA) release rates of the CA/β-CD composite emulsion (87.49 ± 3.40%) were higher than those of the β-CD emulsion (74.32 ± 2.11%). This strategy provides ideas for expanding the application range of emulsifier particles and developing food-grade Pickering emulsions with antioxidant capacity.

A Bioactive Compound-Loaded Zinc-Aminoclay Encapsulated, Pickering Emulsion System for Treating Acne-Inducing Microbes

Acne is a common skin condition caused by the growth of certain bacteria. Many plant extracts have been investigated for their potential to combat acne-inducing microbes, and one such plant extract is microwave-assisted Opuntia humifusa extract (MA-OHE). The MA-OHE was loaded onto zinc-aminoclay (ZnAC) and encapsulated in a Pickering emulsion system (MA-OHE/ZnAC PE) to evaluate its therapeutic potential against acne-inducing microbes. Dynamic light scattering and scanning electron microscopy were used to characterize MA-OHE/ZnAC PE with a mean particle diameter of 353.97 nm and a PDI of 0.629. The antimicrobial effect of MA-OHE/ZnAC was evaluated against Staphylococcus aureus (S. aureus) and Cutibacterium acnes (C. acnes), which contribute to acne inflammation. The antibacterial activity of MA-OHE/ZnAC was 0.1 and 0.025 mg/mL to S. aureus and C. acnes, respectively, which were close to naturally derived antibiotics. Additionally, the cytotoxicity of MA-OHE, ZnAC, and MA-OHE/ZnAC was tested, and the results showed that they had no cytotoxic effects on cultured human keratinocytes in a range of 10-100 μg/mL. Thus, MA-OHE/ZnAC is suggested to be a promising antimicrobial agent for treating acne-inducing microbes, while MA-OHE/ZnAC PE is a potentially advantageous dermal delivery system.

Impacts of crosslinking conditions on Pickering emulsions stabilized by genipin-crosslinked chitosan-caseinophosphopeptides nanocomplexes

Polysaccharide-polypeptide nanocomplexes are promising colloidal Pickering stabilizers. The resulting Pickering emulsions, however, are susceptible to pH and ionic strength changes. This phenomenon was also observed in our recently developed Pickering emulsions stabilized by the chitosan (CS)-caseinophosphopeptides (CPPs) nanocomplexes. To improve the stability of these Pickering emulsions, we herein crosslinked the CS-CPPs nanocomplexes with a natural crosslinker genipin. The genipin-crosslinked CS-CPPs nanocomplexes (GCNs) were used to prepare Pickering emulsions. The impacts of genipin concentration, crosslinking temperature, and duration on the characteristics of GCNs and the GCNs-stabilized Pickering emulsions (GPEs) were systemically investigated. GCNs showed crosslinking strength-dependent variations in their physical properties. Crosslinking at a weak or strong condition weakened the emulsification ability of GCNs at low concentrations. A strong crosslinking condition also compromised the capacity of GCNs to stabilize a high fraction of oil. GPEs were oil-in-water type and gel-like. GCNs crosslinked at a lower temperature and for a shorter crosslinking duration stabilized stronger gel-like GPEs. Moreover, GPEs had high pH and ionic strength stabilities. This work provided a feasible way to enhance the stability and regulate the physical properties of Pickering emulsions stabilized by polysaccharide-polypeptide nanocomplexes.

All-oil Constructs Stabilized by Cellulose Nanocrystal Surfactants

Constructing all-oil systems with desired geometries and responsiveness would produce a new class of reconfigurable materials that can be used for applications that are not compatible with water or aqueous systems, a fascinating goal to achieve but severely limited by the lack of surfactants. Here, we demonstrate an efficient strategy to stabilize oil-oil interfaces by using the co-assembly between the cellulose nanocrystal and amine-functionalized polyhedral oligomeric silsesquioxane (POSS-NH₂). Cellulose nanocrystal surfactants (CNCSs) form and assemble in situ at the interface, showing significantly enhanced binding energy and acid-dependent interfacial activity. When CNCSs jam at the interface, a robust assembly with exceptional mechanical properties can be achieved, allowing the 3D printing of all-oil devices on demand. Using CNCSs as emulsifiers, oil-in-oil high internal phase emulsions can be prepared by one-step homogenization and, when used as templates, porous materials that require water-sensitive monomers can be synthesized. These results open a new platform for stabilizing and structuring all-oil systems, providing numerous applications for microreactors, encapsulation, delivery, and tissue engineering scaffolds.

Oscillatory and Relaxation Study of the Interfacial Rheology of Star Polymers with Low-Grafting-Density PEO Arms and Hydrophobic Poly(divinylbenzene) Cores

Star polymers have been gaining interest due to their tunable properties. They have been used as effective stabilizers for Pickering emulsions. Herein, star polymers were synthesized via activators regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP). Poly(ethylene oxide) (PEO) with terminal α-bromoisobutyrate ATRP functionality was used as a macroinitiator and divinylbenzene as a crosslinker for the arm-first star synthesis. Stars with PEO arms with a molar mass of either 2 or 5 kDa had a relatively low density of grafted chains, i.e., ca. 0.25 chain/nm². The properties of PEO stars adsorbed at oil-water interfaces were investigated using interfacial tension and interfacial rheology. The magnitude of interfacial tensions at oil-water interfaces depends on the nature of the oil phase, being lower at the m-xylene/water interface than at the n-dodecane/water interface. Small differences were observed for stars with different molecular weights of PEO arms. The overall behavior of PEO stars adsorbed at an interface can be considered as an intermediate between a particle and a linear/branched polymer. Obtained results offer an important insight into the interfacial rheology of PEO star polymers in the context of their application as stabilizers for Pickering emulsions.

Stabilization of high internal phase Pickering emulsions with millimeter-scale droplets using silica particles

High internal phase emulsions stabilized with colloidal particles (Pickering HIPEs) have recently been studied intensively because of their great stability achieved by the irreversible adsorption of particles onto the oil-water interface and their usage as a template for synthesizing porous polymeric materials, called PolyHIPEs. In most cases, Pickering HIPEs with microscale droplets ranging from tens of micrometers to hundreds of micrometers have been successfully achieved, but the stabilization of Pickering HIPEs with millimeter-sized droplets is rarely reported. In this study, we report for the first time that, by using shape-anisotropic silica particle aggregates as a stabilizer, successful stabilization of Pickering HIPEs with millimeter-sized droplets can be achieved, and the size of droplets can be simply controlled. Additionally, we demonstrate that stable PolyHIPEs with large pores can be readily converted to PolyHIPEs with millimeter-scale pores, which have advantages in absorbent materials and biomedical engineering applications.

Pickering emulsions stabilized by inside/out Janus nanotubes: Oil triggers an evolving solid interfacial layer

HYPOTHESIS

In the field of Pickering emulsion, original inside/ouside Janus clays nanoparticles are investigated for their emulsification properties. Imogolite is a tubular nanomineral of the clay family having both inner and outer hydrophilic surfaces. A Janus version of this nanomineral with an inner surface fully covered by methyl groups can be obtained directly by synthesis (Imo-CH₃, hybrid imogolite). The hydrophilic/hydrophobic duality of the Janus Imo-CH₃ allows the nanotubes to be dispersed in an aqueous suspension and enables emulsification of non-polar compounds due to the hydrophobic inner cavity of the nanotube.

EXPERIMENTS

Through the combination of Small Angle X-ray Scattering (SAXS), interfacial observations and rheology, the stabilization mechanism of imo-CH₃ in oil-water emulsions has been investigated.

FINDINGS

Here, we show that interfacial stabilization of an oil-in-water emulsion is rapidly obtained at a critical Imo-CH₃ concentration as low as 0.6 wt%. Below this concentration threshold, no arrested coalescence is observed, and excess oil is expelled from the emulsion through a cascading coalescence mechanism. The stability of the emulsion above the concentration threshold is reinforced by an evolving interfacial solid layer resulting from the aggregation of Imo-CH₃ nanotubes that is triggered by the penetration of confined oil front into the continuous phase.

Synthesis and characterization of sago starch nanocrystal laurate as a food grade particle emulsifier

Starch nanocrystals (SNCs) are tiny particles that possess unique qualities due to their small size, such as increased crystallinity, thin sheet structure, low permeability, and strong resistance to digestion. Although sago starch nanocrystals (SNCs) are naturally hydrophilic, their properties can be modified through chemical modifications to make them more versatile for various applications. In this study, the esterification process was used to modify SNCs using lauroyl chloride (LC) to enhance their surface properties. Three different ratios of LC to SNC were tested to determine the impact on the modified SNC (mSNC). The chemical changes in the mSNC were analyzed using FTIR and ¹H NMR spectroscopy. ##The results showed that as the amount of LC increased, the degree of substitution (DS) also increased, which reduced the crystallinity of the mSNC and its thermal stability. However, the esterification process also improved the hydrophobicity of the SNC, making it more amphiphilic. The emulsification capabilities of the mSNC were investigated using a Pickering emulsion, and the results showed that the emulsion made from mSNC-1.0 had better stability than the one made from pristine SNC. This study highlights the potential of SNC as a particle emulsifier and demonstrates how esterification can improve its emulsification capabilities.

Pickering emulsions stabilized with a spirulina protein-chitosan complex for astaxanthin delivery

Astaxanthin (AXT) is a lipid-soluble carotenoid with good anti-oxidation, hepatic steatosis reduction, anti-inflammation, and intestinal microbiota regulation ability, whose poor stability and pH vulnerability limit its bioavailability. Spirulina protein (SP) derived from spirulina has good emulsifying ability with potential application in nutraceuticals, medicines, and cosmetics. In this study, Pickering emulsions were prepared using a SP-chitosan (CS) complex as an emulsifier. The particle size, zeta potential, and three-phase contact angle of the SP-CS complex with different SP to CS ratios were investigated. A mass ratio of 1 : 2.5 SP-CS complex showed a good emulsifying ability in preparing Pickering emulsion. A higher storage modulus and viscoelasticity were observed with higher SP-CS complex concentrations and oil fractions. The SP-CS Pickering emulsion significantly improved the stability of AXT in different environments. The lipid release rate and AXT bioavailability after digestion of 3 wt% SP-CS complex-stabilized Pickering emulsion reached 70.54 ± 1.59% and 36.60 ± 3.44%, respectively. The results indicated that the SP-CS complex could act as a Pickering emulsion stabilizer and had the potential to deliver protective hydrophobic AXT.

Preparation and emulsification properties of cationic starch-xanthan gum composite nanoparticles

In this work, nanoparticles were prepared by the composite of cationic starch (CS) and xanthan gum (XG) through gelatinization and alcohol precipitation for the first time. Physicochemical properties, micromorphology, and emulsification properties of CS/XG nanoparticles were measured. SEM showed that after compositing with XG, the diameter size of the CS/XG nanoparticles was increased from about 50 nm to 150-300 nm. FT-IR, XRD and ¹³C CP/MAS NMR confirmed that XG was successfully complexed with CS. Besides, the visual observation indicated emulsions stabilized by CS/XG nanoparticles had excellent storage and thermal properties. Additionally, the rheological and stability results of emulsions show that pH and NaCl had effects on the rheological and stability properties of emulsions, which means that the prepared emulsions had environmental responsiveness. Thus, this work provides an efficient method to prepare CS and GX composite nanoparticles with efficient emulsifying properties.

Observation of curcumin-encapsulated Pickering emulsion stabilized by cellulose nanocrystals-whey protein isolate (CNCs-WPI) complex under in vitro lipid digestion through INFOGEST model

Curcumin-encapsulated Pickering emulsion (Cur-PE) was successfully prepared using cellulose nanocrystals (CNCs)-whey protein isolate (WPI) complex as a stabilizer to control the size and stability of the Cur-PE. Firstly, needle-like CNCs were prepared by acid hydrolysis, and the mean particle size, polydispersity index (PDI), zeta potential, and aspect ratio of the CNCs were 100.7 nm, 0.32, -43.6 mV, and 20.8, respectively. The Cur-PE-C_0.5W_0.1, prepared with 0.5 wt% CNCs and 0.1 wt% WPI at pH 2, had a mean droplet size of 230.0 nm, PDI of 0.275, and zeta potential of +53.5 mV. The Cur-PE-C_0.5W_0.1 prepared at pH 2 exhibited the highest stability during storage for 14 days. FE-SEM revealed that the droplets of the Cur-PE-C_0.5W_0.1 prepared at pH 2 were spherical and fully covered by CNCs. The adsorption of CNCs at the oil-water interface increases the encapsulation efficiency (89.4 %) of curcumin in the Cur-PE-C_0.5W_0.1 and protects curcumin from pepsin digestion in the gastric phase. However, the Cur-PE-C_0.5W_0.1 was sensitive to release curcumin in the intestine phase. The CNCs-WPI complex developed in this study could serve as a promising stabilizer to make Pickering emulsions stable at pH 2 for the encapsulation and delivery of curcumin to the expected target area.

Dynamics of prolate spheroids in the vicinity of an air-water interface

In this article, we present the mobilities of prolate ellipsoidal micrometric particles close to an air-water interface measured by dual wave reflection interference microscopy. Particle's position and orientation with respect to the interface are simultaneously measured as a function of time. From the measured mean square displacement, five particle mobilities (3 translational and 2 rotational) and two translational-rotational cross-correlations are extracted. The fluid dynamics governing equations are solved by the finite element method to numerically evaluate the same mobilities, imposing either slip and no-slip boundary conditions to the flow at the air-water interface. The comparison between experiments and simulations reveals an agreement with no-slip boundary conditions prediction for the translation normal to the interface and the out-of-plane rotation, and with slip ones for parallel translations and in-plane rotation. We rationalize these evidences in the framework of surface incompressibility at the interface.

Smart antimicrobial Pickering emulsion stabilized by pH-responsive cellulose-based nanoparticles

Responsive antimicrobial materials can control and slow the release of antimicrobial agents smartly by responding to the stimulation of environmental conditions. In this study, we designed the pH-responsive cellulose-based nanoparticles (TOCNC-g-PEI) with amino and carboxyl groups by grafting polyethyleneimine (PEI) to carboxylated cellulose nanocrystals. Finally, the Pickering emulsion was endowed with smart antimicrobial properties by emulsifying the oregano essential oil (OEO) with nanoparticles. The TOCNC-g-PEI₂₅₀₀₀ had uniform size, greater dispersion, and excellent antimicrobial properties. The contact angles of nanoparticles were 78.70 ± 1.13°, 55.80 ± 1.58° and 55.35 ± 1.56° at neutral conditions, pH 4.0 and 8.0, respectively. The nanoparticles were responding to pH stimulation. The developed emulsion (4:6, 1.30 wt%) had exceptionally stabilized and encapsulated 98.56 ± 1.22 % of the oil phase. The OEO released rapidly within 0-12 h and slowly at 12-36 h. The cumulative release rates quickly reached 93.60 ± 3.73 % (pH 4.0) and 83.25 ± 0.36 % (pH 8.0) and stabilized gradually. The antimicrobial rates of emulsion stimulated for 4 h reached 100 % at pH 4.0, and both of them exceeded 96.10 ± 2.49 % at pH 8.0. The response of Pickering emulsion to pH stimulating controlled release antimicrobial agents and achieved smart antimicrobial.

Starch physical treatment, emulsion formation, stability, and their applications

Pickering emulsions are increasingly preferred over typical surfactant-based emulsions due to several advantages, such as lower emulsifier usage, simplicity, biocompatibility, and safety. These types of emulsions are stabilized using solid particles, which produce a thick layer at the oil-water interface preventing droplets from aggregating. Starch nano-particles (SNPs) have received considerable attention as natural alternatives to synthetic stabilizers due to their unique properties. Physical formulation processes are currently preferred for SNP production since they are environmentally friendly procedures that do not require the use of chemical reagents. This review provides a thorough overview in a critical perspective of the physical processes to produce starch nano-particles used as Pickering emulsion stabilizers, fabricated by a 2-step process. Specifically, the reviewed physical approaches for nano-starch preparation include high hydrostatic pressure, high pressure homogenization, ultrasonication, milling and antisolvent precipitation. All the essential parameters used to evaluate the effectiveness of particles in stabilizing these systems are also presented in detail, including the hydrophobicity, size, and content of starch particles. Finally, this review provides the basis for future research focusing on physical nano-starch production, to ensure the widespread use of these natural stabilizers in the ever-evolving field of food technology.

Evaluating the Emulsifying Capacity of Cellulose Nanofibers Using Inverse Gas Chromatography

Cellulose nanofibers (CNFs) are attracting increasing attention as emulsifiers owing to their high emulsifying capacity, biocompatibility, and biodegradability. The emulsifying capacity has been experimentally shown to depend not only on the type of oil but also on the chemical structure of the CNF surface. However, the theoretical relationship between these two factors and emulsification remains unclear, and therefore, industrial applications are limited. Here, we assess the desorption energy (DE) of CNFs from the oil surface in o/w emulsion for various CNF/oil combinations to understand the mechanism of emulsification. Two types of surface-carboxylated CNFs having different cationic counterions, namely, sodium and tetrabutylammonium ions, were used as emulsifiers. The surface free energies of the CNFs were evaluated using inverse gas chromatography, and the nonpolar Lifshitz-van der Waals γ^LW, electron-acceptor γ⁺, and electron-donor γ^- components were obtained from the chromatography profiles based on the van Oss-Chaudhury-Good theory. CNF with tetrabutylammonium ions was found to have a higher γ⁺ component than CNF with sodium ions. Therefore, the emulsion stability improved with oils having high γ^- components owing to the increase in the DE value; this was verified through both theoretical calculations using a fibrous model and experimental dynamic interfacial tension measurements. Our approach is useful for predicting the emulsifying capacity of CNFs, and it should contribute toward the design of novel CNF-based emulsions.

Targeting Interfacial Location of Phenolic Antioxidants in Emulsions: Strategies and Benefits

It is important to have larger proportions of health-beneficial polyunsaturated lipids in foods, but these nutrients are particularly sensitive to oxidation, and dedicated strategies must be developed to prevent this deleterious reaction. In food oil-in-water emulsions, the oil-water interface is a crucial area when it comes to the initiation of lipid oxidation. Unfortunately, most available natural antioxidants, such as phenolic antioxidants, do not spontaneously position at this specific locus. Achieving such a strategic positioning has therefore been an active research area, and various routes have been proposed: lipophilizing phenolic acids to confer them with an amphiphilic character; functionalizing biopolymer emulsifiers through covalent or noncovalent interactions with phenolics; or loading Pickering particles with natural phenolic compounds to yield interfacial antioxidant reservoirs. We herein review the principles and efficiency of these approaches to counteract lipid oxidation in emulsions as well as their advantages and limitations.

Pickering Emulsions Stabilized With Biodegradable Nanoparticles For The Co-Encapsulation Of Two Active Pharmaceutical Ingredients

Innovative Pickering emulsions co-encapsulating two active pharmaceutical ingredients (API) were formulated for a topical use. An immunosuppressive agent, either cyclosporine A (CysA) or tacrolimus (TAC), was encapsulated at high drug loading in biodegradable and biocompatible poly (lactic-co-glycolic acid) (PLGA) nanoparticles (NP). These NP stabilized the oil droplets (Miglyol) containing an anti-inflammatory drug, calcitriol (CAL). The influence of the API on the physico-chemical properties of these emulsions were studied. Emulsions formulated with or without API had a similar macroscopic and microscopic structure, as well as interfacial properties, and they exhibited a good stability for at least 55 days. The emulsions did not alter the viability of human keratinocytes (HaCaT cell line) after 2 and 5 days of exposure to NP concentrations equivalent to efficient API dosages. Thus, these new Pickering emulsions appear as a promising multidrug delivery system for the treatment of chronical inflammatory skin diseases.

pH-Switchable Pickering miniemulsion enabled by carbon quantum dots for quasi-homogenized biphasic catalytic system

A quasi-homogenized miniemulsion system enabled by carbon quantum dot solid nanoparticles for biphasic catalysis is proposed, which breaks existing limits for an immiscibly biphasic system and overcomes issues for large-sized solid particle-stabilized emulsion droplets. The presented Pickering miniemulsion features pH-responsive behavior, finally triggering facile product separation and catalyst recycling in one reaction vessel.

Pickering Emulsions Based in Inorganic Solid Particles: From Product Development to Food Applications

Pickering emulsions (PEs) have attracted attention in different fields, such as food, pharmaceuticals and cosmetics, mainly due to their good physical stability. PEs are a promising strategy to develop functional products since the particles’ oil and water phases can act as carriers of active compounds, providing multiple combinations potentiating synergistic effects. Moreover, they can answer the sustainable and green chemistry issues arising from using conventional emulsifier-based systems. In this context, this review focuses on the applicability of safe inorganic solid particles as emulsion stabilisers, discussing the main stabilisation mechanisms of oil–water interfaces. In particular, it provides evidence for hydroxyapatite (HAp) particles as Pickering stabilisers, discussing the latest advances. The main technologies used to produce PEs are also presented. From an industrial perspective, an effort was made to list new productive technologies at the laboratory scale and discuss their feasibility for scale-up. Finally, the advantages and potential applications of PEs in the food industry are also described. Overall, this review gathers recent developments in the formulation, production and properties of food-grade PEs based on safe inorganic solid particles.

Is there a difference between surfactant-stabilised and Pickering emulsions?

What measurable physical properties allow one to distinguish surfactant-stabilised from Pickering emulsions? Whereas surfactants influence oil/water interfaces by lowering the oil/water interfacial tension, particles are assumed to have little effect on the interfacial tension. Here we perform interfacial tension (IFT) measurements on three different systems: (1) soybean oil and water with ethyl cellulose nanoparticles (ECNPs), (2) silicone oil and water with the globular protein bovine serum albumin (BSA), and (3) sodium dodecyl sulfate (SDS) solutions and air. The first two systems contain particles, while the third system contains surfactant molecules. We observe a significant decrease in interfacial tension with increasing particle/molecule concentration in all three systems. We analyse the surface tension data using the Gibbs adsorption isotherm and the Langmuir equation of state for the surface, resulting in surprisingly high adsorption densities for the particle-based systems. These seem to behave very much like the surfactant system: the decrease in tension is due to the presence of many particles at the interface, each with an adsorption energy of a few k_BT. Dynamic interfacial tension measurements show that the systems are in equilibrium, and that the characteristic time scale for adsorption is much longer for particle-based systems than for surfactants, in line with their size difference. In addition, the particle-based emulsion is shown to be less stable against coalescence than the surfactant-stabilised emulsion. This leaves us with the conclusion that we are not able to make a clear distinction between the surfactant-stabilised and Pickering emulsions.

Destabilization of Pickering emulsions by interfacial transport of mutually soluble solute

HYPOTHESIS

Pickering emulsions (PEs) once formed are highly stable because of very high desorption energies (∼10⁷ k_BT) associated with particles adsorbed to the interfaces. The destabilization of PEs is required in many instances for recovery of valuable chemicals, products and active compounds. We propose to exploit interfacial instabilities develop by the addition of different types of solutes to PEs as a route to engineer their destabilization.

EXPERIMENTS

PEs stabilized by (i) spherical particles, (ii) non-spherical particles, (iii) oppositely charged particle-particle mixtures, and (iv) oppositely charged particle-polyelectrolyte mixtures are formulated. Different types of solutes are added to these highly stable PEs and the macroscopic as well as microscopic changes induced in the PEs is recorded by visual observation and bright field optical microscopy.

FINDINGS

Our results point to a simple yet robust method to induce destabilization of PEs by transiently perturbing the oil-water interface by transport of a mutually soluble solute across the interface. The generality of the method is demonstrated for different kind of solutes and stabilizers including particles of different sizes (nm to µm), shapes (sphere, spheroids, spherocylinders) and types (polystyrene, metal oxides). The method works for both oil-in-water (o/w) and water-in-oil (w/o) PEs with different kinds of non-polar solvents as oil-phase. However, the method fails when the solute is insoluble in one of the phases of PEs. The study opens up a new approach to destabilization of particle stabilized emulsions.

Biopolymer-based pickering high internal phase emulsions: Intrinsic composition of matrix components, fundamental characteristics and perspective

Pickering HIPEs have received tremendous attention in recent years due to their superior stability and unique solid-like and rheological properties. Biopolymer-based colloidal particles derived from proteins, polysaccharides and polyphenols have been demonstrated to be safety stabilizers for the construction of Pickering HIPEs, which can meet the demands of consumers for "all-natural" products and provide "clean-label" foods. Furthermore, the functionality of these biopolymers can be further extended by forming composite, conjugated and multi-component colloidal particles, which can be used to modulate the properties of the interfacial layer, thereby adjusting the performance and stability of Pickering HIPEs. In this review, the factors affecting the interfacial behavior and adsorption characteristics of colloidal particles are discussed. The intrinsic composition of matrix components and fundamental characteristics of Pickering HIPEs are emphatically summarized, and the emerging applications of Pickering HIPEs in the food industry are reviewed. Inspired by these findings, future perspectives concerning this field are also put forward, including (1) the exploration of the interactions between biopolymers used to produce Pickering HIPEs and target food ingredients, and the influence of the added biopolymers on the flavor and mouthfeel of the products, (2) the investigation of the digestion properties of Pickering HIPEs under oral administration, and (3) the fabrication of stimulus-responsive or transparent Pickering HIPEs. This review will give a reference for exploring more natural biopolymers for Pickering HIPEs application development.

Pickering emulsion stabilized by modified pea protein-chitosan composite particles as a new fat substitute improves the quality of pork sausages

Pickering emulsion is a potential substitute for animal fat due to high stability and solid-like properties. Therefore, the effect of replacing 25%-100% pork backfat with Pickering emulsion (75% corn oil volume fraction) stabilized by modified pea protein-chitosan composite particles on the quality of sausages was studied. All meat pastes exhibited a strong gel-like rheological character (G' > G"). The incorporation of Pickering emulsion in sausages enhanced the textural properties (hardness, springiness, chewiness, cohesiveness and resilience) and the uniformity and compactness of micromorphology, as well as suppressed the cooking loss and TBARS content. In particular, the sausages with a backfat substitution ratio of 100%, showing a similar overall sensory acceptability to the backfat sausage, revealed the best rheological properties, texture properties and micromorphology and the lowest cooking loss and fat oxidation (P < 0.05). The results showed that Pickering emulsion stabilized by modified pea protein-chitosan composite particles is a potential fat substitute for meat products with the desirable characteristics.

A Robust Switchable Oil-In-Water Emulsion Stabilized by Electrostatic Repulsions between Surfactant and Similarly Charged Carbon Dots

How to control the stability of oil-in-water (O/W) emulsions is one of the main topics for scientists working in colloidal systems. Recently, carbon dots (CDs) have received great interest as smart materials because of their excellent physicochemical properties and versatile applications. Herein, for the first time, advanced and switchable O/W emulsions are presented that are stabilized by the synergistic effect of cationic surfactant cetyltrimethylammonium bromide CTAB (emulsifier) and similarly charged CDs (stabilizer). In the formulated emulsion, the cationic surfactant molecules are adsorbed at the oil and water interface to decrease the interfacial tension and enrich the drops with a positive charge to ensure intensive electrostatic repulsions among them. On the contrary, cationic CDs are distributed in the water phase among the droplets to reduce the water secretion and prevent flocculation and droplet coalescence. The stabilizing effect is found to be universal for emulsions of a range of oil phases. Furthermore, the formulated emulsion is found to be switchable between "stable" and "unstable" modes by adding an equivalent of anionic surfactant sodium dodecyl benzene sulphonate (SDBS). The stabilized and switchable O/W emulsions are believed to have wide practical applications in water purification, pharmaceuticals, protein recognition, as well as catalysis.

Water-in-water emulsion stabilized by cellulose nanocrystals and their high enrichment effect on probiotic bacteria

HYPOTHESIS

The effect of the molecular weight and polymer concentration on the partition behavior of aqueous two-phase systems (ATPs) is significant for constructing water-in-water (W/W) emulsions. Hence, a long-term stable W/W emulsion system might be obtained through selecting the appropriate stabilizer and component phases, which could be a possible carrier for probiotics.

EXPERIMENTS

Compared with the reported molecular weight difference between polyethylene oxide (PEO) and dextran (DEX) systems, PEO and dextran with lower molecular weight had been used for constructing the water in water (W/W) emulsion system. The W/W emulsions were stabilized using cellulose nanocrystals (CNCs), and the potential application of the W/W emulsion for the encapsulation of Lactobacillus was explored.

FINDINGS

Emulsion stability exhibited a "dose-effect" relationship with the CNCs concentration and was decreased with the increase of the DEX concentration. The emulsion phase separation rate was increased with increasing ionic strength and temperature. Both Lactobacillus Plantarum and Lactobacillus helveticus were highly inclined to the DEX phase, and the emulsion droplets were deformed and aggregated when the encapsulation amount was increased. This long-term stability would provide a promising approach for designing high-density culture and fermentation of probiotics.

Water Droplets Tailored as Wax Crystal Carriers to Mitigate Wax Deposition of Emulsion

This study explores how the micro-distribution change of wax crystals from the continuous oil phase to the oil-water interface mitigates the macro wax deposition of an emulsion. Two types of interfacial actions between wax crystals and water droplets, interfacial adsorption and interfacial crystallization, which were induced by two different emulsifiers, sorbitan monooleate (Span 80) and sorbitan monostearate (Span 60), respectively, were detected by differential scanning calorimetry and microscopy observation. The wax interfacial crystallization promoted by Span 60 resulted in the wax being nucleated directly at the oil-water interface prior to the continuous oil phase, conferring the nascent wax crystals and water droplets to be combined as coupled particles. The utilization of the wax interfacial crystallization behavior to hinder wax deposition of an emulsion was further explored. When the coupled wax crystal-water droplet particles were formed during the wax deposition process, water droplets acted as wax crystal carriers, entraining these nascent wax crystals to disperse in the emulsion, which significantly reduced the amount of wax crystals available to form the network of the deposit. In addition, this change also led to the basic structural units in the wax deposit evolving from wax crystal clusters/networks to water droplet flocs. The study elucidates that through adjusting the dispersion of wax crystals from the oil phase to the oil-water interface, water droplets could act as a functional component to tailor the properties of the emulsion or resolve related flow and deposition problems in pipeline transportation.

Unique Fiber Morphologies from Emulsion Electrospinning—A Case Study of Poly(ε-caprolactone) and Its Applications

The importance of electrospinning to produce biomimicking micro- and nano-fibrous matrices is realized by many who work in the area of fibers. Based on the solubility of the materials to be spun, organic solvents are typically utilized. The toxicity of the utilized organic solvent could be extremely important for various applications, including tissue engineering, biomedical, agricultural, etc. In addition, the high viscosities of such polymer solutions limit the use of high polymer concentrations and lower down productivity along with the limitations of obtaining desired fiber morphology. This emphasizes the need for a method that would allay worries about safety, toxicity, and environmental issues along with the limitations of using concentrated polymer solutions. To mitigate these issues, the use of emulsions as precursors for electrospinning has recently gained significant attention. Presence of dispersed and continuous phase in emulsion provides an easy route to incorporate sensitive bioactive functional moieties within the core-sheath fibers which otherwise could only be hardly achieved using cumbersome coaxial electrospinning process in solution or melt based approaches. This review presents a detailed understanding of emulsion behavior during electrospinning along with the role of various constituents and process parameters during fiber formation. Though many polymers have been studied for emulsion electrospinning, poly(ε-caprolactone) (PCL) is one of the most studied polymers for this technique. Therefore, electrospinning of PCL based emulsions is highlighted as unique case-study, to provide a detailed theoretical understanding, discussion of experimental results along with their suitable biomedical applications.

Self-healing waterborne polyurethane coatings with high transparence and haze via cellulose nanocrystal stabilized linseed oil Pickering emulsion

Protection coatings with self-healing ability can significantly enhance their anti-corrosion properties and service life. In this study, self-healing waterborne polyurethane (WPU) coatings with high transparence and haze were facile fabricated via cellulose nanocrystal (CNC) stabilized linseed oil (LO) Pickering emulsion. Sustainable CNCs displayed outstanding emulsifying ability and stability to stabilize LO Pickering emulsion. The size of LO Pickering emulsion droplets decreases with the CNC concentration, while the emulsion fraction and surface coverage by CNCs increase with CNC concentration, leading to a more stable Pickering emulsion. The self-healing rates of WPU coatings at varied time, temperature, CNC and catalyst concentration were investigated. Higher temperature, larger emulsion droplets, and with driers employed as catalysts generally lead to faster self-healing rate. The WPU self-healing coatings displayed much better abrasion resistance and mechanical properties than pristine WPU due to the incorporation of CNCs. Moreover, the WPU self-healing coatings show a high transparence and haze due to light scattering, and their applications as coatings of lamp covers and glass to achieve uniform light distribution and privacy protection with high light transmission were further demonstrated.

Comparison of cellulose and chitin nanofibers on Pickering emulsion stability-Investigation of size and surface wettability contribution

There is an increasing concern about developing biobased colloid particles for Pickering stabilization due to the environment-friendliness and health-safety needs. In this study, Pickering emulsions were formed by using TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidized cellulose nanofibers (TOCN) and chitin nanofibers prepared by TEMPO-mediated oxidation (TOChN) or partial deacetylation (DEChN). The physicochemical characterizations of Pickering emulsions demonstrated that the higher cellulose or chitin nanofiber concentrations, surface wettability, and zeta-potential, the higher effectiveness in Pickering stabilization. Specifically, even though DEChN was at a shorter size (with a length of 254 ± 72 nm) as compared to TOCN (with a length of 3050 ± 1832 nm), it showed an excellent stabilization effect on emulsions at the concentration of 0.6 wt% due to its higher affinity to soybean oil (water contact angle of 84.38 ± 0.08°) and large electrostatic repulsion between oil particles. Meanwhile, when the concentration was 0.6 wt%, long TOCN (water contact angle of 43.06 ± 0.08°) formed a three-dimensional network in the aqueous phase, which produced a superstable Pickering emulsion resulting from the limited moving of droplets. These results provided important information on the formulation of Pickering emulsions stabilized by polysaccharide nanofibers with suitable concentration, size and surface wettability.