Surfactant-Free High Internal Phase Emulsions Stabilized by Cellulose Nanocrystals

Food-grade rapeseed cake particles: Production, physicochemical characteristics, and emulsifying properties

Rapeseed cake is rich in dietary fibers and proteins, but is predominantly used as fertilizer, with limited utilization in other applications. This study aimed to develop a food-grade holo-cellulose rapeseed cake fibrous particles stabilizer using hush pre-treatment (sequential alkali-acid, and heat), followed by ultrasonic cavitation (USC) or high-pressure microjet (HPM) processing. The pretreatment improved particle suspension stability (ζ-potential: -1.9 ± 1.5 mV to -42.5 ± 2.0 mV) and hydrophobicity (contact angle: 59.6 ± 1.9° to 81.3 ± 2.2°), endowing the particles with excellent emulsifying properties. Subsequent USC and HPM treatments decreased particle size and improved suspension stability further. The treated particles showed an octopus-like entangled enabling stable anchoring at the interface of oil and water. These particles formed a rigid network, contributing to the formation of robust emulsion gels. This study provides a feasible strategy for the advanced processing of rapeseed cake, expanding its potential applications in gel-based food industry and, promoting its high-value applications.

Pickering stabilization of double emulsions: Basic concepts, rationale, preparation, potential applications, challenges, and future perspectives

Double emulsions (DEs) offer unique compartmentalized structures but are inherently unstable, prompting significant scientific and industrial efforts to enhance their stability. One promising strategy is the use of solid particles-known as Pickering stabilization-resulting in Pickering double emulsions (PDEs), which overcome many limitations of conventional low-molecular-weight (LMW) surfactants. However, the term "Pickering" is often misused in the literature to describe any formulation containing particles, regardless of whether the interface is fully stabilized by them. This review aims to clarify the concept of Pickering stabilization, outline the rationale for its application to DEs, and examine preparation mechanisms, interfacial approaches, potential applications, and current challenges. Particles with dual wettability and high desorption energy irreversibly adsorb at interfaces, forming robust mechanical barriers that inhibit coalescence and reduce diffusion or escape of internal droplets. PDEs can be prepared via two-step emulsification, one-step processes, or advanced microfluidic methods. A variety of Pickering approaches have been developed to engineer particles capable of dual interfacial stabilization, enabling sophisticated functions such as (co-)encapsulation, controlled release, and the formation of hierarchical structures like microspheres, colloidosomes, and antibubbles. To unlock the full potential of PDEs for industrial applications, future research should prioritize eliminating surfactant use, developing safe and sustainable particles, and advancing scalable production methods without compromising emulsion stability or performance.

High internal phase Pickering emulsions stabilized by surface-modified dialdehyde xylan nanoparticles

Polysaccharide-based particles have attracted considerable attention for stabilizing Pickering emulsions due to their sustainability and biocompatibility. In this study, we developed a novel approach utilizing hemicellulose-based nanoparticles for the stabilization of high internal phase Pickering emulsions (HIPPEs). Polyethylenimine-modified dialdehyde xylan nanoparticles (PEI-DAXNPs) were prepared through periodate oxidation of xylan nanoparticles obtained from esparto pulp, followed by a Schiff base reaction with polyethylenimine (PEI). Oil-in-water HIPPEs were fabricated using PEI-DAXNPs as the sole stabilizer through a one-time homogenization method and exhibited long-term stability after 180 days of storage. Furthermore, gel-like HIPPEs were obtained with a minimum concentration of 0.1 wt% PEI-DAXNPs in the continuous phase and exhibited shear-thinning behavior and promising viscoelastic properties, indicating good processability in the fabrication of soft materials and porous scaffolds. Therefore, the produced PEI-DAXNPs demonstrated significant potential as HIPPE stabilizers, providing inspiration for the valorization of hemicellulose-based nanoparticles.

PDMS-in-water emulsions stabilized by cellulose/chitin/starch nanoparticles for fabrication of oil adsorbents: A comparison study

Pickering emulsion template has aroused attention in the fabrication of porous composite materials. In this work, six nanoparticles including cellulose nanofiber/nanocrystal (CNF/CNC), chitin nanofiber/nanocrystals (ChNF/ChNC) and waxy/normal corn nanocrystal (WSNC/CSNC) were comparatively studied for their performance in fabricating porous composites with PDMS via Pickering emulsion templates. Among all, CNF and ChNF exhibited best emulsion stabilizing ability, while ChNF and ChNC at optimized concentrations enabled the formation of high internal phase emulsions with long-term stability of over 300 days. WSNC and CSNC with poorest emulsion stabilizing ability failed to obtain porous composites while the other four particles all formed porous composites with PDMS. The ChNF and ChNC composites displayed highest hydrophobicity, followed by the CNC composite. As adsorbents for diesel oil, the ChNF composite showed the highest adsorption capacity and adsorption selectivity, which could be easily recycled by simple mechanical squeezing. At optimized PDMS fractions, the ChNF composite could achieve continuous oil-water separation under vacuum with a highest separation efficiency of 98.9 % at high flux of 8862 L/h·m2. This study revealed the association between nanoparticles and their composite materials fabricated from Pickering emulsion template, hopefully broadening the application of natural polymers in water treatment and related fields.

Study about the effect of cellulose nanocrystals on a polyacrylate miniemulsion

Cellulose nanocrystals (CNC) are widely used due to their biodegradability, high strength, large surface area, and functional versatility. This study investigates the interaction between CNC and acrylate emulsions, which mainly focuses on their impact on emulsion characteristics, polymerization behaviour, and storage stability. CNC was incorporated into an acrylate miniemulsion system at varying concentrations, followed by the systematic study of its effects on particle size, interfacial tension, zeta potential, yield, and viscosity. The morphology of CNC-acrylate systems was analysed using infrared spectroscopy and scanning electron microscopy (SEM). The results demonstrated that CNC effectively co-stabilized acrylate miniemulsions and enhanced their stability before polymerization. Although CNC did not directly participate in polymerization or affect yield or reaction rates, it slowed the diffusion of free radicals. However, CNC concentrations higher than 1 wt% negatively impacted post-polymerization storage stability and caused aggregation of droplets. These findings reveal the dual role of CNC as both a stabilizing and aggregating agent, offering new insights into its potential for the design of advanced polymer systems.

Highly Persistent and Robust Emulsion Stabilized by Hierarchical Cellulose Microgel through Stereo-hindrance under Extreme Conditions

Emulsion stabilization oil-in-water under harsh conditions (e.g., hypersaline, acid and alkali, and high temperature) is a great challenge for conventional emulsion stabilizers, including surfactants or particles. Herein, a persistent and robust emulsion under harsh conditions is achieved via a sustainable solution based on a hierarchical cellulose microgel (h-CMG). h-CMG in aqueous suspension establishes stable 3D networks by its nanotentacles and microbody, which can spatially hinder the approach and coalescence of droplets to each other and stabilize the emulsion. Unlike the emulsion stabilized by minimizing the interfacial energy and protecting the water/oil interface, the emulsion spatially stabilized by h-CMG exhibits extensive tolerance to extreme conditions and the feature of stable high internal phase emulsion (80%, v/v). The related droplet size and emulsion volume are almost unchanged in the pH range of 1 to 14, in NaCl aqueous solution of 2 mol/L, or even at 80 °C for 12 h. This genuine biobased emulsifier is highly favorable to the food, cosmetics, and pharmaceutical industries without the risk of nanotoxicity, and it also can provide a reliable emulsifier for the chemical and drilling industries involving harsh operation circumstances.

Stabilization of Oil-in-Water Pickering Emulsions by Surface-Functionalized Cellulose Hydrogel

An amphiphilic cellulose (CLH) hydrogel was synthesized via grafting of quaternary ammonium groups onto cellulose. The structural properties of CLH were characterized via Fourier transform infrared (FTIR)/13C solid-state NMR spectroscopy, elemental (CHN) analysis, particle size distribution (PSD), thermogravimetric analysis (TGA), and wettability was assessed through contact angle measurements. Pickering emulsions of apolar oils in water were prepared using variable weights of the CLH hydrogel as the stabilizing agent, along with different methods of agitation (mechanical shaking and sonication). The characterization results for CLH provide support for the successful grafting of quaternary ammonium groups onto cellulose to produce hydrogels. Different methods of agitation of an oil/water mixture revealed the formation of an oil-in-water (O/W) Pickering emulsion that was stable to coalescence for over 14 days. The resulting emulsions showed variable droplet sizes and stability according to the dosage of CLH in the emulsion and the agitation method, where the emulsion droplet size is related to the particle size of CLH. The addition of methyl orange (MO), a probe to evaluate the phase partitioning of the dye, had minor effects on the emulsion droplet size, and the emulsion prepared with 0.8 wt.% of CLH and agitated via sonication exhibited the smallest droplet size and greatest stability. This study is anticipated to catalyze further research and the development of low-cost and sustainable biopolymer hydrogels as stabilizers for tunable Pickering emulsion. Grafted cellulose materials of this type represent versatile stabilizing agents for foods, agrochemicals, and pharmaceutical products and technologies.

Antiscaling Pickering Emulsions Enabled by Amphiphilic Hairy Cellulose Nanocrystals

Nucleation and growth of sparingly soluble salts, referred to as scaling, has posed substantial challenges in industrial processes that deal with multiphase flows, including enhanced oil recovery (EOR). During crude oil extraction/recovery, seawater is injected into oil reservoirs and yields water-in-oil (W/O) emulsions that may undergo calcium carbonate (CaCO3) scaling. Common antiscaling macromolecules and nanoparticles have adverse environmental impacts and/or are limited to functioning only in single-phase aqueous media. Here, we develop a novel antiscaling cellulose-based nanoparticle that enables scale-resistant Pickering emulsions. Cellulose fibrils are rationally nanoengineered to yield amphiphilic hairy cellulose nanocrystals (AmHCNC), bearing hydrophilic dicarboxylate groups and hydrophobic alkyl chains on disordered cellulose chains (hairs) protruding from nanocrystal ends. The unique chemical and structural properties of AmHCNC render them the first dual functional antiscaling and emulsion stabilizing nanoparticle. AmHCNC stabilize W/O Pickering emulsions at a concentration of 1.00 wt % for 1 week while inhibiting CaCO3 scale formation up to 70% by mass at a supersaturation degree of ∼101 compared with the synthetic surfactant Span 80. To the best of our knowledge, this study presents the first biopolymer-based solution for the long-lasting scaling challenge in multiphase media, which may set the stage for developing sustainable scale-resistant multiphase flows in a broad spectrum of industrial sectors.

Enhanced stability and biocompatibility of HIPEs stabilized by cyclodextrin-metal organic frameworks with inclusion of resveratrol and soy protein isolate for β-carotene delivery

High internal phase Pickering emulsions (HIPEs) constitute a significant research domain within colloid interface chemistry, addressing the demand for robust emulsion systems across various applications. An innovative nanoparticle, synthesized from a cyclodextrin metal-organic framework encapsulated with a composite of resveratrol and soy isolate protein (RCS), was employed to fortify a high internal phase emulsion. The emulsion's three-dimensional printing capabilities, alongside the encapsulated delivery efficacy for β-carotene, were thoroughly examined. Cyclodextrin metal-organic frameworks (CD-MOFs), facilitated by cellulose nanofibrils, were synthesized to yield particles at the nanoscale, maintaining a remarkable 97.67 % cellular viability at an elevated concentration of 1000 μg/ml. The RCS nanoparticles demonstrated thermal stability and antioxidant capacities surpassing those of CD-MOF. The integration of soybean isolate protein augmented both the hydrophobicity (from 21.95 ± 0.64° to 59.15 ± 0.78°) and the interfacial tension (from 14.36 ± 0.46 mN/m to 5.34 ± 0.81 mN/m) of the CD-MOF encapsulated with resveratrol, thereby enhancing the RCS nanoparticles' adsorption at the oil-water interface with greater stability. The durability of the RCS-stabilized high internal phase emulsions was contingent upon the RCS concentration. Emulsions stabilized with 5 wt%-RCS exhibited optimal physical and chemical robustness, demonstrating superior performance in emulsion 3D printing and β-carotene encapsulation delivery. This investigation furnishes a novel perspective on the amalgamation of food customization and precision nutrition.

Low gelatin concentration assisted cellulose nanocrystals stabilized high internal phase emulsion: The key role of interaction

Low concentrations of gelatin (0.02-0.20 wt%) were applied to regulate the surface and interface properties of CNC (0.50 wt%) by forming CNC/G complexes. As gelatin concentration increased from 0 to 0.20 wt%, the potential value of CNC/G gradually changed from -44.50 to -17.93 mV. Additionally, various gelatin concentrations led to micromorphology changes of CNC/G complexes, with the formation of particle interconnection at gelatin concentration of 0.10 wt%, followed by network structure and enhanced aggregation at gelatin concentration of 0.15 and 0.20 wt% respectively. The water contact angle (25.91°-80.23°) and interface adsorption capacity of CNC/G were improved due to hydrophobic group exposure of gelatin. When gelatin concentration exceeded 0.10 % at a fixed oil phase volume fraction (75 %), a high internal phase emulsion (HIPE) stabilized by CNC/G can be formed with a good storage stability. The rheological and microstructure results of HIPE confirmed that low gelatin concentration can assist CNC to form stable emulsion structure. Especially, the auxiliary stabilization mechanism of various gelatin concentration was different. CNC/G-0.10 % and CNC/G-0.15 % stabilized HIPE mainly depended on the enhanced interface adsorption and network structure, while CNC/G-0.20 % stabilized HIPE mainly relied on enhanced interface adsorption/accumulation due to weak electrostatic repulsion and aggregate granular morphology of CNC/G-0.20 %.

Preparation and Application of High Internal Phase Pickering Emulsion Gels Stabilized by Starch Nanocrystal/Tannic Acid Complex Particles

Herein, the starch nanocrystal/tannic acid (ST) complex particles, which were prepared based on the hydrogen bond between starch nanocrystal (SNC) and tannic acid (TA), were successfully used to stabilize the HIPPE gels. The optimal TA concentration of the ST complex particles resulted in better water dispersibility, surface wettability, and interfacial activity as compared to SNC. The hydrogen bond responsible for the formation of ST complex particles and subsequent stable emulsions was demonstrated by varying the pH and ionic strength of the aqueous phase. Notably, the HIPPE gels stabilized via the ST complex particles can maintain long-term stability for up to three months. The HIPPEs stabilized via the ST complex particles all displayed gel-like features and had smaller droplets and denser droplet networks than the SNC-stabilized HIPPEs. The rheological behavior of HIPPE gels stabilized via the ST complex particles can be readily changed by tuning the mass ratio of SNC and TA as well as pH. Finally, the prepared HIPPE gels used to effectively protect encapsulated β-carotene against high temperatures and ultraviolet radiation and its controllable release at room temperature were demonstrated. It is anticipated that the aforementioned findings will provide new perspectives on the preparation of Pickering emulsion for delivery systems.

Synergistic stabilization of high internal phase Pickering emulsions by peanut isolate proteins and cellulose nanocrystals for β-carotene encapsulation

In this study, high internal phase Pickering emulsions (HIPPEs) were stabilized by the complexes of peanut protein isolate (PPI) and cellulose nanocrystals (CNCs) for encapsulation β-carotene to retard its degradation during processing and storage. CNCs were prepared by H2SO4 hydrolysis (HCNCs), APS oxidation (ACNCs) and TEMPO oxidation (TCNCs), exhibiting needle-like or rod-like structures with nanoscale size and uniformly distributed around the spherical PPI particle, which enhanced the emulsifying capability of PPI. Results of optical micrographs and droplet size measurement showed that Pickering emulsions stabilized by PPI/ACNCs complexes exhibited the most excellent stability after 30 days of storage, which indicated that ACNCs had the most obvious effect to improve emulsifying capability of PPI. HIPPEs encapsulated β-carotene (βc-HIPPEs) were stabilized by PPI/ACNCs complexes and showed excellent inverted storage stability. Moreover, βc-HIPPEs exhibited typical shear thinning behavior investigated by rheological properties analysis. During thermal treatment, ultraviolet radiation and oxidation, the retentions of β-carotene encapsulated in HIPPEs were improved significantly. This research holds promise in expanding Pickering emulsions stabilized by proteins-polysaccharide particles to delivery systems for hydrophobic bioactive compounds.

Delivery systems designed to enhance stability and suitability of lipophilic bioactive compounds in food processing: A review

Lipophilic compounds, such as flavors, fat-soluble vitamins, and hydrophobic nutrients possess vital properties including antioxidant effects, functional attributes, and nutritional value that can improve human health. However, their susceptibility to environmental factors including heat, pH changes, and ionic strength encountered during food processing poses significant challenges. To address these issues, diverse bioactive delivery systems have been developed. This review explores delivery systems designed to optimize the stability and suitability of lipophilic bioactive compounds in food processing. Extensive literature analysis reveals that tailoring delivery systems with various biopolymers can protect bioactives through steric hindrance and formation of thick interfacial layers on the emulsion surfaces. Thus, the access of oxygen, prooxidants, and free radicals at the emulsion interface could be inhibited, resulting in enhanced processing suitability of bioactives as well as chemical stability under diverse environmental conditions. The insights presented in this review hold immense value for the food and beverage industries.

Analysis of instability of starch-based Pickering emulsion under acidic condition of pH < 4 and improvement of emulsion stability

Starch-based Pickering emulsions exhibit high interfacial stability in a certain range of mild pH environments. On the contrary, many studies have reported that when the pH value is <4, it often leads to different degrees of emulsion instability. In this paper, the microscopic state of starch granules in the emulsion and its effect on the stability of the emulsion were observed and analyzed by atomic force microscope (AFM) in tapping mode. At the same time, Pickering emulsions in acidic environment were prepared by using the gel properties of methyl cellulose (MC) in synergy with esterified high amylose maize starch (M-HAMS) granules. The results show that in the emulsion with pH 3, the excessive H + ion inhibits the swelling of M-HAMS granules and prevents it from forming a stable gel structure, which is the main cause of emulsion instability. The polarity of MC with water contact angle (WCA) of 81.8° is similar to that of M-HAMS granules with WCA of 80.1°, and a uniform and ordered micro-nanostructure is formed in the aqueous phase. The prepared acidic (pH 3-4) emulsion has good stability during the observation period of 30 days.

A review of high internal phase Pickering emulsions: Stabilization, rheology, and 3D printing application

High internal phase Pickering emulsion (HIPPE) is renowned for its exceptionally high-volume fraction of internal phase, leading to flocculated yet deformed emulsion droplets and unique rheological behaviors such as shear-thinning property, viscoelasticity, and thixotropic recovery. Alongside the inherent features of regular emulsion systems, such as large interfacial area and well-mixture of two immiscible liquids, the HIPPEs have been emerging as building blocks to construct three-dimensional (3D) scaffolds with customized structures and programmable functions using an extrusion-based 3D printing technique, making 3D-printed HIPPE-based scaffolds attract widespread interest from various fields such as food science, biotechnology, environmental science, and energy transfer. Herein, the recent advances in preparing suitable HIPPEs as 3D printing inks for various applied fields are reviewed. This work begins with the stabilization mechanism of HIPPEs, followed by introducing the origin of their distinctive rheological behaviors and strategies to adjust the rheological behaviors to prepare more eligible HIPPEs as printing inks. Then, the compatibility between extrusion-based 3D printing and HIPPEs as building blocks was discussed, followed by a summary of the potential applications using 3D-printed HIPPE-based scaffolds. Finally, limitations and future perspectives on preparing HIPPE-based materials using extrusion-based 3D printing were presented.

CO2-Switchable colloids

The development and design of CO2-switchable colloidal particles is described. A presentation of the principles of CO2 switching, especially as they apply to colloids, is followed by recent progress in the preparation of several types of colloidal particles (polymer nanoparticles, metal-organic frameworks (MOFs), quantum dots, graphene, cellulose nanocrystals, carbon nanotubes) for various applications (Pickering stabilizers, catalysts, latexes), and our perspective on future opportunities.

Lignin nanoparticles as co-stabilizers and modifiers of nanocellulose-based Pickering emulsions and foams

Nanocellulose is very hydrophilic, preventing interactions with the oil phase in Pickering emulsions. This limitation is herein addressed by incorporating lignin nanoparticles (LNPs) as co-stabilizers of nanocellulose-based Pickering emulsions. LNP addition decreases the oil droplet size and slows creaming at pH 5 and 8 and with increasing LNP content. Emulsification at pH 3 and LNP cationization lead to droplet flocculation and rapid creaming. LNP application for emulsification, prior or simultaneously with nanocellulose, favors stability given the improved interactions with the oil phase. The Pickering emulsions can be freeze-dried, enabling the recovery of a solid macroporous foam that can act as adsorbent for pharmaceutical pollutants. Overall, the properties of nanocellulose-based Pickering emulsions and foams can be tailored by LNP addition. This strategy offers a unique, green approach to stabilize biphasic systems using bio-based nanomaterials without tedious and costly modification procedures.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10570-023-05399-y.

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.

Tartary Buckwheat Bran: A Review of Its Chemical Composition, Processing Methods and Food Uses

Tartary buckwheat (Fagopyrum tataricum Gaertn.) containing large amounts of functional compounds with antioxidant activity, such as rutin, has attracted substantial research attention due to its industrial applications. Particularly, the functional compounds in Tartary buckwheat bran, an unexploited byproduct of the buckwheat flour milling process, are more concentrated than those in Tartary buckwheat flour. Thus, Tartary buckwheat bran is deemed to be a potential material for making functional foods. However, a review that comprehensively summarizes the research on Tartary buckwheat bran is lacking. Therefore, we highlighted current studies on the chemical composition of Tartary buckwheat bran. Moreover, the processing method and food uses of Tartary buckwheat bran are also discussed.

Surface engineering on cholesteric cellulose nanocrystals films inducing emulsification, organic pollutants detection and separation

Nowadays, organic pollutants have been major concerns in many fields. Production of functional materials based on renewable and sustainable resources for organic pollutants detection and removal was of much interest. Herein, multi-functional nanocomposite films based on cellulose nanocrystals (CNCs) with high optical haze, organic pollutant detection and emulsion separation capabilities, have been successfully fabricated based on hydrophobically-modified CNCs suspensions by 2-dodecen-1-succinic anhydride (DDSA) followed by radical polymerization with tridecafluorooctyl (TFMA). The suspensions displayed satisfying oil-in-water emulsion stabilization capabilities and the vacuum-dried films showed birefringence, high transparency, and optical haze (~85 %), due to the ordered arrangements of cellulose nanocrystals. The organic pollutant can be detected through the iridescent colors disappearing by Polarizing Optical Microscope observation. In addition of improved mechanical strength for application (27 MPa) and high contact angle of 131.6°, the hydrophobic films performed as high separation efficiency as >90 % of emulsion, due to the successfully grafting of hydrophobic molecules on the surface of CNCs. Thus, the surface modification for CNCs provide a facile approach of emulsification, pollutants detection and separation properties, which would widen the application potentials of renewable cellulosic resources in fields of environmental protection, engineering control and petroleum industry.

Thermoresponsive nanofibers loaded with antimicrobial α-aminophosphonate-o/w emulsion supported by cellulose nanocrystals for smart wound care patches

Long-term topical application of antibiotics on wounds has led to the emergence of drug-resistant bacterial infections. Antibiotic incorporation into the wound dressing requires enormous advancement of the field to ensure that the needed dose is released when the infection arises. This study synthesized a series of antimicrobial α-aminophosphonate derivatives, and the most effective compound was incorporated into thermoresponsive wound dressing patches. Wound dressing mats were fabricated by needleless electrospinning, and the resultant nanofiber mats were coated with a thermoresponsive eicosane/cellulose nanocrystals o/w system loaded with active α-aminophosphonate derivatives. Chemical, physical, thermal, and antimicrobial properties of the wound dressings were characterized wound dressings. Using SEM analysis, Nanofibers spun with 20 % w/v solutions were selected for drug-emulsion loading since they showed lower diameters with higher surface area. Furthermore, the drug-emulsion coating on the electrospun dressings improved the hydrophilicity of the wound dressings, and the thermoresponsive behavior of the mats was proved using differential scanning calorimetry data. Finally, the drug-loaded electrospun meshes were found active against tested microorganisms, and clear inhibition zones were observed. In conclusion, this novel approach of synthesizing a new family of antimicrobial molecules and their incorporation into nanofibers from renewable sources exhibits great potential for smart and innovative dressings.

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.

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.

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.

Correlation between interfacial layer properties and physical stability of food emulsions: current trends, challenges, strategies, and further perspectives

Emulsions are thermodynamically unstable systems that tend to separate into two immiscible phases over time. The interfacial layer formed by the emulsifiers adsorbed at the oil-water interface plays an important role in the emulsion stability. The interfacial layer properties of emulsion droplets have been considered the cutting-in points that influence emulsion stability, a traditional motif of physical chemistry and colloid chemistry of particular significance in relation to the food science and technology sector. Although many attempts have shown that high interfacial viscoelasticity may contribute to long-term emulsion stability, a universal relationship for all cases between the interfacial layer features at the microscopic scale and the bulk physical stability of the emulsion at the macroscopic scale remains to be established. Not only that, but integrating the cognition from different scales of emulsions and establishing a unified single model to fill the gap in awareness between scales also remain challenging. In this review, we present a comprehensive overview of recent progress in the general science of emulsion stability with a peculiar focus on interfacial layer characteristics in relation to the formation and stabilization of food emulsions, where the natural origin and edible safety of emulsifiers and stabilizers are highly requested. This review begins with a general overview of the construction and destruction of interfacial layers in emulsions to highlight the most important physicochemical characteristics of interfacial layers (formation kinetics, surface load, interactions among adsorbed emulsifiers, thickness and structure, and shear and dilatational rheology), and their roles in controlling emulsion stability. Subsequently, the structural effects of a series of typically dietary emulsifiers (small-molecule surfactants,proteins, polysaccharides, protein-polysaccharide complexes, and particles) on oil-water interfaces in food emulsions are emphasized. Finally, the main protocols developed for modifying the structural characteristics of adsorbed emulsifiers at multiple scales and improving the stability of emulsions are highlighted. Overall, this paper aims to comprehensively study the literature findings in the past decade and find out the commonality of multi-scale structures of emulsifiers, so as to deeply understand the common characteristics and emulsification stability behaviour of adsorption emulsifiers with different interfacial layer structures. It is difficult to say that there has been significant progress in the underlying principles and technologies in the general science of emulsion stability over the last decade or two. However, the correlation between interfacial layer properties and physical stability of food emulsions promotes revealing the role of interfacial rheological properties in emulsion stability, providing guidance on controlling the bulk properties by tuning the interfacial layer functionality.

Cellulose-based, flexible polyurethane polyHIPEs with quasi-closed-cell structures and high stability for thermal insulation

Cellulose-based, closed-cell porous materials templated from emulsions are promising for thermal insulation, but their low stability imposed by physical interaction hinders the materials from real applications. Herein, we report the fabrication of cellulose-based, flexible polyurethane polyHIPEs with quasi-closed-cell structures, high stability and flexibility for thermal insulation. The polyHIPEs were prepared from cellulose-stabilized Pickering high internal phase emulsions through interfacial crosslinking using isocyanate. The resulting polyurethane polyHIPEs showed controllable external shapes, quasi-closed-cell structures, high flexibility, low density, and robust compression (without fracture even after compression to 30 % original height). The crosslinking enabled the polyHIPEs to show hydrophobicity, good stability (without breakage and dissolution observed after immersing in NaOH solution at pH 12, HCl solution at pH 1 and hot water at 100 °C, for 24 h) and decreased moisture uptake (below 1 %). The low density and quasi-closed-cell structures endowed the polyHIPEs with high thermal insulation, with thermal conductivity as low as 33.1 mW/(m K). These features make the cellulose-based, closed-cell polyHIPEs as an excellent candidate for thermal insulting.

Formulation and stabilization of high internal phase emulsions: Stabilization by cellulose nanocrystals and gelatinized soluble starch

In this work, high internal phase emulsions (HIPEs) stabilized by naturally derived cellulose nanocrystals (CNC) and gelatinized soluble starch (GSS) were fabricated to stabilize oregano essential oil (OEO) in the absence of surfactant. The physical properties, microstructures, rheological properties, and storage stability of HIPEs were investigated by adjusting CNC contents (0.2, 0.3, 0.4 and 0.5 wt%) and starch concentration (4.5 wt%). The results revealed that CNC-GSS stabilized HIPEs exhibited good storage stability within one month and the smallest droplets size at a CNC concentration of 0.4 wt%. The emulsion volume fractions of 0.2, 0.3, 0.4 and 0.5 wt% CNC-GSS stabilized HIPEs after centrifugation reached 77.58, 82.05, 94.22, and 91.41 %, respectively. The effect of native CNC and GSS were analyzed to understand the stability mechanisms of HIPEs. The results revealed that CNC could be used as an effective stabilizer and emulsifier to fabricate the stable and gel-like HIPEs with tunable microstructure and rheological properties.

Influence of Cellulose Nanofibers on the Behavior of Pickering Emulsions. Part 1. Microscopy and Startup Flow Test

The dispersibility of flexible polymer chains present at the emulsion's interface between the dispersed and continuous phase has obvious effects on rheology and dielectric properties of the whole emulsion. Cellulose nanofiber (CNF)-based Pickering emulsions are good systems to research these properties with respect to their microscopic phase structure, dielectric, and rheological properties by using CNF as a water-dispersible Pickering emulsifier, liquid paraffin as an oil phase, and didodecyldimethylammonium bromide (DDAB) as a cationic auxiliary surfactant. The CNF and DDAB contents were systematically varied while the water-to-paraffin oil ratio was kept constant to discern the influence of the Pickering emulsifiers. Polarized optical microscopic images reveal that the droplets tend to shrink at higher CNF content but grow bigger when increasing the DDAB content, which is proved by fluorescence analysis of the CNF dispersibility with varying DDAB content. The dielectric damping exhibits a minimum, whose value decreases with increasing DDAB and CNF content. Increasing the DDAB content promotes the solubilization of CNF in the aqueous phase, which will increase the overall viscosity and yield points. Similarly, a higher CNF content leads to a higher viscosity and yield point, but at high DDAB contents, the viscosity function exhibits an S-shape at intermediate CNF contents. To evaluate the results further, they were compared with CNF dispersions (without oil phase), which showed a surfactant effect slightly on maximum stress but strongly on yield stress τy, indicating that DDAB can promote the formation of a CNF network rather than the viscosity of the whole system. This paper provides information on how a systematical variation of the composition influences morphology and physico-chemical interactions as detected by broadband dielectric spectroscopy and rheological behavior.

Research Progress of Food-Grade High Internal Phase Pickering Emulsions and Their Application in 3D Printing

High internal phase Pickering emulsion (HIPPE) is a type of emulsion stabilized by solid particles irreversibly adsorbed on an interfacial film, and the volume fraction of the dispersed phase (Φ) is larger than the maximum packing volume fraction (Φ_max). Proteins, polysaccharides, and their composite particles can be used as good particle stabilizers. The contact angle can most intuitively demonstrate the hydrophilicity and hydrophobicity of the particles and also determines the type of emulsions (O/W or W/O type). Particles' three-phase contact angles can be adjusted to about 90° by compounding or modification, which is more conducive to emulsion stability. As a shear thinning pseudoplastic fluid, HIPPE can be extruded smoothly through 3D printer nozzles, and its high storage modulus can support the structure of printed products. There is huge potential for future applications in 3D printing of food. This work reviewed the biomacromolecules that can be used to stabilize food-grade HIPPE, the stabilization mechanism of the emulsions, and the research progress of food 3D printing to provide a reference for the development of advanced food products based on HIPPE.

Emulsions stabilized by cellulose-based nanoparticles for curcumin encapsulations: In vitro antioxidant properties

To improve the dispersity and antioxidant properties of curcumin, curcumin emulsions covered with cellulose particles (CP) with different structures were successfully prepared, and the structural characteristics, stability, and antioxidant properties of emulsions were investigated. The results showed that the CP obtained by increasing the hydrolysis time had smaller particle size, better water dispersion, and interfacial adsorption capacity. The encapsulation efficiency of curcumin in emulsion stabilized by cellulose particle hydrolyzed for 10 h can reach about 80%. After 9 days, all emulsions showed good stability, and no obvious creamed layer was observed. Compared to cellulose particles hydrolyzed for 2 h (CP2), emulsions stabilized by cellulose particles hydrolyzed for 6 h (CP6) and 10 h (CP10) exhibited better stability and free fatty acid (FFA) release. Meanwhile, the DPPH scavenging activity of curcumin emulsion stabilized by CP significantly increased with increasing the hydrolysis time and was much higher than that of pure emulsion and curcumin/water due to the higher solubility (1,455 times compared with curcumin/water solution) of curcumin, and these results could provide useful data for the stability and encapsulation of curcumin.

pH-Induced reversible conversion between non-Pickering and Pickering high internal phase emulsion

Solid-stabilized high internal phase emulsions have received extensive attention. Many previous studies have confirmed that solid emulsifiers in high internal phase Pickering emulsions (HIPPEs) provide a great interface mechanical barrier. With the development of research, novel solid-stabilized emulsions have emerged. These emulsions are stabilized by the electrostatic repulsion between the surfactants and hydrophilic solid particles. They are distinct from Pickering emulsions in that the solid particles do not exist at the oil-water interface, but are dispersed in the continuous phase, so it is called a non-Pickering emulsion. However, high internal phase non-Pickering emulsions (HIPNPEs) are rarely reported. Herein, HIPNPEs that are synergistically stabilized by anionic surfactants with dynamic covalent bonds and negatively charged nano-SiO₂ particles were prepared. In the presence of dodecylamine, the acidity causes the dynamic covalent bonds to break and the surfactant to be inactivated. Additionally, the long-chain amine is protonated and adsorbed on nano-SiO₂ particles to form a new surfactant for stabilizing HIPPEs. However, alkalinity causes the HIPNPEs to form again. In addition, rheological tests confirmed that the HIPNPEs and HIPPEs had similar rheological behaviors, which were typical gel-like fluids. The emulsion can quickly respond to realize the conversion between the different types of high internal phase emulsion by simple stimulation, which provides a new direction for stimulus-responsive high internal phase emulsions.

Emulsion-based, flexible and recyclable aerogel composites for latent heat storage

Although emulsion-based, phase change material-encapsulated monolithic composites are promising for latent heat storage, their rigidity and non-recyclability imposed by the relatively dense covalent crosslinking hinder the composites from real applications. Herein, we report the fabrication of aerogel composites with flexibility and recyclability from cellulose nanocrystal-stabilized, octadecane-encapsulated Pickering emulsions solidified using physical gelation. The resulting monolithic composites exhibited controllable external shapes, and the introduction of poly(vinyl alcohol) significantly reduced the leakage of the encapsulated octadecane. The aerogel composites showed flexibility at temperature over 30 °C, and robust compressive behavior, without fracture at 70% compressive strain. The composites possessed similar heat storage (melting) temperature and heat release (crystallization) temperature to that of bulk octadecane, high heat capacity (up to 253 J^.g^-1) and high reusability, without obvious deterioration in heat capacity after 100 heating-cooling cycles. Moreover, the aerogel composites exhibited recyclability, simply by dissolving the composites in hot water to form emulsions and then by freeze drying to form aerogel composites. The flexibility and recyclability, together with robust compression, controllable external shapes, high heat capacity and good reusability, make the aerogel composites to be excellent candidates for latent heat storage.

The Simultaneous Production of Two Distinct Types of Cellulose Nanocrystals

We develop a route to prepare two types of cellulose nanocrystals (CNCs, CNC1 and CNC2) from a unique biomass resource, the fruit shell of Camellia oleifera Abel (SCOA), by integrating sulfuric acid hydrolysis and high-pressure homogenization and examine the effects of hydrolysis time on characteristics of the CNCs during the process. The CNCs exhibit different evolutions in size, morphology, surface charge, and crystallinity with increasing hydrolysis time. While both the CNCs have high crystallinity, CNC1 is of rod-like character with a relatively low aspect ratio, and CNC2 exhibits a hairy appearance with a high aspect ratio. We highlight that controlled acid hydrolysis contributes to the formation of weak spots with an increased susceptibility for homogenizing cellulosic solid residues into hairy CNCs. This is a good step toward tailoring CNC properties in a conventional and scalable approach to maximize their potential applications.

Effect of Oil Phase Transition on the Stability of Pickering Emulsions Stabilized by Cellulose Nanocrystals

Emulsifier design is one of the key strategies in interfacial engineering for emulsion stability. In this study, cellulose nanocrystals (CNCs) were used as an interfacial stabilizer to improve the stability of coconut oil (CO)-in-water emulsions. A Pickering emulsion consisting of CO and water was optimized based on four parameters using the response surface methodology and the central composite design. The droplet coverage remained stable during the crystallization of the oil phase when the temperature was reduced below the melting temperature of CO. Fluorescent-labeled CNCs were used to monitor the partitioning of CNC at the O/W interface during the crystallization of CO. The Generation 6 polyamidoamine (G6 PAMAM) dendrimer covalently grafted on the surface of CNC was used as an intrinsic fluorescent dye. Since it displayed similar properties as the emulsifier, it could be used to monitor the CNC coverage on the oil droplets at various temperatures. The fluorescence micrographs showed that the emission of PAMAM CNCs at the O/W interface remained on both the liquid and solid CO droplets, confirming that oil crystallization did not affect the fluorescent CNC coverage on the oil droplets.

A rheological investigation of oil-in-water Pickering emulsions stabilized by cellulose nanocrystals

HYPOTHESIS

High and medium internal phase Pickering emulsions stabilized with cellulose nanocrystals (CNCs) exhibited very different performance compared to their peers stabilized with a surfactant. In this paper, we ascribed the difference to the formation of hydrogen bonding and van der Waals interactions between the CNC nanoparticles on adjacent oil droplets.

EXPERIMENTS

Rheological properties of CNC-stabilized oil-in-water medium internal phase emulsions (MIPEs, oil content = 65% v/v) and high internal phase emulsions (HIPEs, oil content = 80% v/v) were comprehensively characterized using both oscillatory and rotational tests.

FINDINGS

It was found that in the MIPEs, the van der Waals and hydrogen bonding interactions dominate the emulsion properties, whereas the compact structure of oil droplets plays a more important role in the HIPEs. CNC concentration in the aqueous phase also affects the emulsion properties, especially for the HIPEs, and the results can be correlated to the stabilization mechanisms we previously reported. The information from these tests provides a much-needed guidance for the practical application of CNC-stabilized emulsions.

Pickering Emulsions Stabilized by an Alkyl Chain-Bridged Lignin-Based Polymer without Additives and Organic Solvents

In this article, an alkyl chain-bridged lignin polymer was prepared from our previous study. Then, an ultrafiltration method was used to classify the polymer into three fractions with a narrow molecular weight distribution. These three fractions were used to prepare novel Pickering emulsions without additives and organic solvents. The results show that the Pickering emulsion with fraction-3 of the highest molecular weight shows the best result compared with the other two fractions, and the Pickering emulsion is formed of droplets. The influence of oil-water ratios and fraction-3 dosages on the Pickering emulsions was also investigated in our study. The results show that the diameter of the droplets increases with increasing oil proportion and decreases with increasing lignin-based polymer dose. UV spectroscopy shows that the prepared Pickering emulsions have strong absorption properties from 300 to 800 nm, which will be expected to be applied in cosmetics, especially in sunscreen creams. Finally, the Pickering emulsion was also used to deliver ibuprofen, and the results showed that the embedding rate was as high as 10%. It is suggested that the Pickering emulsion stabilized by lignin-based polymers can be used for drug delivery. This will provide a potential research idea for high-value applications of lignin.