Colloidal TiO2 nanoparticles with near-neutral wettability: An efficient Pickering emulsifier

Physicochemical properties and antibacterial property of pickering emulsion stabilized by smart Janus nanospheres

In this study, responsive Janus nanospheres were prepared by grafting LMA and DMAEMA monomers on both sides of SiO2 nanospheres using the Pickering emulsion stencil method and RAFT polymerization. The successful synthesis was verified through infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA), scanning electron microscopy (SEM) characterizations. Subsequently, Pickering emulsion was formulated using Janus nanospheres as emulsifiers. The particle size of the emulsion droplets was systematically investigated by manipulating factors such as pH, nanosphere dosage, water to oil ratio, and oil phase polarity. Notably, the Pickering emulsion exhibited responsive properties to pH, temperature, and CO2. Furthermore, Janus nanospheres exhibited excellent emulsification property for real oil phases, including canola oil, kerosene, gasoline, and diesel oil. Building upon this, a smart antibacterial Pickering emulsion was developed using Janus nanospheres, and its inhibition rate against E. coli could reach 100% within 4 h, which would be beneficial for its application in the food field.

Highly Hydrophilic TiO2 Nanoparticles as Stabilizers of Pickering Emulsions with Photosensitive Lipophilic Compounds: Synthesis and Application

Pickering emulsions are a very promising system for encapsulating and photoprotecting active ingredients. The highest photoprotection efficiency can be achieved when bare TiO2 nanoparticles are used as stabilizers. However, the main problem when using highly hydrophilic TiO2 nanoparticles is their inability to adsorb at the oil-water interface. Here, we developed emulsions stabilized by bare, highly hydrophilic TiO2 nanoparticles for the encapsulation and photoprotection of active lipophilic compounds. Emulsion stabilization occurs due to the formation of hydrogen bonds between hydroxyl groups on the particle surface and the carbonyl groups of the oil molecules. The stability and rheological properties of emulsions are explained by the properties of the initial hydrosols. The resulting Pickering emulsions demonstrated effective UV protection of α-lipoic acid. Our results pave the way for the formulation of Pickering emulsions with a widely used cosmetic oil and show for the first time the possibility of photoprotection of a lipophilic active substance using unmodified TiO2 nanoparticles.

Tung oil-based waterborne UV-curable coatings via cellulose nanofibril stabilized Pickering emulsions for self-healing and anticorrosion application

In this study, waterborne UV-curable coatings with self-healing properties based on transesterification were prepared using renewable biomass resources for anti-corrosion application. Tung oil (TO)-based oligomer (TMHT) was synthesized through Diels-Alder reaction of TO with maleic anhydride, subsequent ring opening reaction with hydroxyethyl acrylate (HEA), and final neutralize reaction with triethylamine. A series of waterborne UV-curable coatings were prepared from cellulose nanofibrils (CNF) stabilized TMHT-based Pickering emulsions after drying and UV light-curing processes. It is suggested that CNF significantly improved the storage stability of Pickering emulsions. The obtained waterborne UV-curable coatings with CNF of 1-3 wt% exhibited remarking coating and mechanical performance (pencil hardness up to 5 H, adhesion up to 2 grade, flexibility of 2 mm, tensile strength up to 11.6 MPa, etc.), great transmittance (82.3 %-80.8 %) and great corrosion resistance (|Z|0.01Hz up to 5.4 × 106 Ω·cm2). Because of the presence of the dynamic ester bonds in TMHT, the coatings exhibited excellent self-healing performance (78.05 %-56.34 %) at 150 °C without catalyst and external force. More importantly, the |Z|0.01Hz of the self-healing coating was higher than that of the scratched coating, indicating that the self-healing performance could extend the service life of the coating in corrosion resistant application.

Properties of Pickering emulsions stabilized by cellulose nanocrystals extracted from litchi peels

The development of Pickering emulsions which are applicable to the food industry still remains challenges due to the limited availability for biocompatible, edible and natural emulsifiers. The purpose of this study was to extract cellulose nanocrystals from litchi peels (LP-CNCs), and evaluate their emulsifying properties. The results showed that the LP-CNCs were needle-like and they possessed high crystallinity (72.34 %) and aspect ratio. When the concentrations of LP-CNCs were >0.7 wt% or the contents of oil were no >0.5, stable Pickering emulsions were obtained. The microstructures of emulsions confirmed that LP-CNCs formed dense interfacial layers on the surface of oil droplets, which functioned as barriers to prevent aggregation and flocculation among droplets. Rheological results showed that the emulsions exhibited typical shear thinning behavior. The elastic of emulsions was dominant, and their gel strength could be enhanced by regulating the contents of emulsifiers or oil. Additionally, the Pickering emulsions stabilized by LP-CNCs showed extremely high pH, ionic strength, and temperature tolerance. This strategy provides an innovative alternative to tackle the dilemma of preparing highly stable Pickering emulsions using natural particles in food products.

One-step, highly stable Pickering emulsions stabilized by ZnO: tuning emulsion stability by in situ functionalization

HYPOTHESIS

Oxide-stabilized emulsions generally require a surface functionalization step to tune the oxide wettability, often involving hazardous hydrophobizing agents. Here, we propose the in situ functionalization of ZnO in vegetable oils without the addition of any modifier, resulting in the one-step formation of highly stable Pickering emulsions.

EXPERIMENTS

The role of ZnO surface features was studied by modifying the particles' wettability through surface functionalization and by comparing different oil phases. The emulsion stability was assessed through aging tests, multiple hot-and-cold cycles, centrifugation, and addition of multiple electrolytes.

FINDINGS

While the wetting features of the functionalized oxide play a crucial role when the oil phase is methyl octanoate, emulsions based on vegetable oils form also using hydrophilic ZnO. During the emulsification, an in situ functionalization of bare ZnO particles takes place due to the fatty acids present in vegetable oil. These in situ-generated systems lead to stable emulsions showing < 2 μm-diameter oil droplets. The resulting emulsions display excellent stability over time (over seven months) and against temperature variations, mechanical stress and increased ionic strength. Finally, we demonstrate that this approach can be extended to a variety of vegetable oils and oxides with different morphologies.

Improved stability of liposome-stabilized emulsions as coencapsulation delivery system for vitamin B2, vitamin E and β-carotene

To realize the co-encapsulation of multiple nutraceuticals with different solubilities, Pickering emulsions stabilized by freshly-prepared liposome suspension stabilized emulsion (Fre-Lip-Sus-E) and hydrated lyophilized liposome stabilized emulsion (Hyd-Lyo-Lip-E) were prepared, in...

Emulsions stabilized by highly hydrophilic TiO2 nanoparticles via van der Waals attraction

HYPOTHESIS

Highly hydrophilic nanoparticles are generally considered not suitable for stabilizing Pickering emulsions, since they could not be effectively wetted by the oil phase at the water-oil interface. However, highly hydrophilic nanoparticles with good dispersity are possibly absorbed and packed onto the surface of the oil droplets in water via the van der Waals attraction between the nanoparticles and the oil droplets. Hence, a novel "van der Waals emulsion" should be possible to be stabilized by highly hydrophilic nanoparticles.

EXPERIMENTS

Oil-in-water emulsions solely stabilized by pristine TiO₂ nanoparticles (i.e., TiO₂ without any modification or additives) were prepared. The emulsification behavior under varying pH value, oil fraction, particle content and temperature of the emulsion were explored. Composite wax-based beads which encapsulated chemical sunscreen and was coated by TiO₂ nanoparticles, was also fabricated using the obtained emulsion as the templates.

FINDINGS

The emulsions displayed the highest stability near the isoelectric points of the TiO₂ nanoparticles, which was attributed to the van der Waals attraction between TiO₂ nanoparticles and oil droplets. Such mechanism was supported by a theoretical analysis based on calculation of the Hamaker constants and experimental evidences. Therefore, this work presents a simple, general and green method for preparing particle-stabilized emulsions.

Food-Grade Pickering Emulsions: Preparation, Stabilization and Applications

In recent years, Pickering emulsions have emerged as a new method and have attracted much attention in the fields of food sciences. Unlike conventional emulsions, Pickering emulsions are stabilized by solid particles, which can irreversibly adsorb on the oil-water interface to form a dense film to prevent the aggregation of droplets. The research and development of food-grade solid particles are increasingly favored by scientific researchers. Compared with conventional emulsions, Pickering emulsions have many advantages, such as fewer using amounts of emulsifiers, biocompatibility and higher safety, which may offer feasibility to have broad application prospects in a wide range of fields. In this article, we review the preparation methods, stabilization mechanism, degradation of Pickering emulsions. We also summarize its applications in food sciences in recent years and discuss its future prospects and challenges in this work.

Pickering Interfacial Catalysis-Knoevenagel Condensation in Magnesium Oxide-Stabilized Pickering Emulsion

In the present study, a novel catalytic route for the Knoevenagel condensation reaction has been developed by Pickering interfacial catalysis using magnesium oxide (MgO) as both an emulsion stabilizer and a base catalyst. MgO was prepared by the precipitation method using sodium hydroxide or ammonium hydroxide as the precipitating agent and calcined at different temperatures. The calcined samples were characterized by XRD, SEM, TEM, AFM, BET, and DLS techniques. The catalytic application of the emulsions stabilized by MgO was investigated for the Knoevenagel condensation reaction of benzaldehyde and its derivatives with malononitrile. All of the reactions were carried out at an ambient temperature (30 °C) under static conditions without stirring. Both the emulsion-stabilizing ability and the catalytic activity of MgO were found to be affected by the method of preparation, calcination temperature, and the nature of the oil phase. It was observed that the method of preparation varied the texture and morphology of MgO and thus the stability and droplet size of the emulsion formed. This was further reflected in the catalytic activity. The highest yield (87%) of the condensation product was obtained with MgO prepared by precipitation using a strong base (NaOH) and further calcined at 400 °C. The developed catalytic system offers several green chemistry advantages such as reusable solid-base catalyst and use of a single material as both emulsion stabilizer and catalyst. Room-temperature reaction under static conditions is an additional advantage of the developed catalytic system.

PDMS polymerized high internal phase emulsions (polyHIPEs) with closed-cell, aqueous-filled microcavities

Emulsion templates can produce a wide range of unique microstructures via solidification of the continuous phase. Some of these structures result in unique, fluid-filled composites reminiscent of biological tissue when the templating droplets develop into closed-cell structures. However, the state-of-the-art falls short in replicating the mechanical and functional response of biological structures due to stiff, fragile, and bio-incompatible materials while lacking systematic processing parameters. This article describes the synthesis of high internal phase, closed-cell, polydimethylsiloxane (PDMS) elastomeric foams which simultaneously achieve biocompatibility, mechanical robustness, flexibility, and selective permeability. Water-in-oil high internal phase emulsions (HIPEs) stabilized by silica nano-particles (SNPs) provide the microstructural template, resulting in a >74% by volume aqueous phase (up to 82%). To overcome the prohibitive barrier to HIPE formation when using a mechanically-superior, but highly viscous commercial PDMS kit, we produce HIPE templates via centrifugation of low internal phase emulsions (LIPEs, <30% by volume dispersed phase). This oil phase crosslinks into an aqueous-filled (water + glycerol + NaCl) elastomeric composite. The composite's microstructural dependence on viscosity ratio, mixing speed, emulsifier concentration, and centrifugal force are systematically characterized. The resulting microstructured, fluid-filled elastomer composites exhibit mechanically robust and highly flexible behavior due to the excellent properties of the PDMS continuous phase.