Thermosensitive pickering emulsion stabilized by poly(N-isopropylacrylamide)-carrying particles

Photo-responsive Pickering emulsions triggered by in-situ pH modulation using a photoacid generator

HYPOTHESIS

Pickering emulsions that respond to changes in pH by the addition of acid or alkali have been extensively studied, but the development of photo-responsive Pickering emulsions has been more challenging. This study attempts to demonstrate a novel approach to achieve photo-responsiveness in Pickering emulsions by incorporating a photoacid generator (PAG) into the oil phase. Upon UV irradiation, the PAG is expected to release protons (H+), which can then regulate the pH of the emulsion system and control its stability.

EXPERIMENTS

Amphiphilic colloidal particles obtained by modifying silica particles with poly (2-(dimethylamino)ethyl methacrylate) (SiO2-PDMAEMA) are used to stabilize the Pickering emulsions. The protonation and deprotonation of the SiO2-PDMAEMA particles at different pH values allow for the tuning of emulsion stability. By introducing the PAG into the stable Pickering emulsion system and applying UV irradiation to trigger the in-situ release of H+, the pH of the emulsion is systematically decreased, and the corresponding changes in emulsion stability are investigated.

FINDINGS

The results show that UV irradiation alone cannot induce emulsion instability. However, when PAG is added to the oil phase, the Pickering emulsions exhibit a significant decrease in pH under UV irradiation, ultimately leading to emulsion destabilization and phase separation. At a UV intensity of 20 mW/cm2 for 2 min, the H+ release from the PAG significantly lower the emulsion's pH, causing the SiO2-PDMAEMA particles to detach from the oil-water interface and resulting in emulsion instability. Higher concentrations of SiO2-PDMAEMA particles in the emulsion require more PAG to induce instability, as confirm by confocal laser scanning microscopy (CLSM) image. This study presents a versatile approach to develop photo-responsive Pickering emulsions which can have potential applications in areas such as drug delivery, cosmetics, and responsive materials.

CO2/N2 Triggered Aqueous Recyclable Surfactants for Biphasic Catalytic Reactions in the Pickering Emulsions

The utilization of Pickering emulsions in interfacial catalysis offers a promising environmental platform for biphasic reactions. However, complicated surface coating or chemical grafting methods are always required to prepare the surface-active catalysts for the Pickering emulsions, since most of them are commercially unavailable. Here, we report CO2-switchable Pickering emulsions for biphasic reactions, in which Pd@Al2O3 nanoparticles are in situ modified by a CO2/N2 responsive surfactant. Compared with the chemical grafted methods, the in situ formed Pickering interfacial catalysts avoid complex chemical modification. Furthermore, efficient demulsification and separation of the oil phase and the products without surfactant contaminations can be achieved by CO2 trigger. The Pickering interfacial catalysis system can also be reformed after the aqueous phase containing the catalyst nanoparticles, and the surfactant is recycled and reused. The strategy is universal for nitrobenzene reductions and alcohol oxidations, providing a convenient and green method for the preparation of Pickering catalysts with commercially available nanoparticles, efficient emulsion separation, and recovery of the catalyst nanoparticles and emulsifiers in various two-phase organic reactions.

Amphiphilic Nanogels as Versatile Stabilizers for Pickering Emulsions

Pickering emulsions (PEs) are stabilized by particles at the water/oil interface and exhibit superior long-term stability compared to emulsions with molecular surfactants. Among colloidal stabilizers, nano/microgels facilitate emulsification and can introduce stimuli responsiveness. While increasing their hydrophobicity is connected to phase inversion from oil-in-water (O/W) to water-in-oil (W/O) emulsions, a predictive model to relate this phase inversion to the molecular structure of the nano/microgel network remains missing. Addressing this challenge, we developed a library of amphiphilic nanogels (ANGs) that enable adjusting their hydrophobicity while maintaining similar colloidal structures. This enabled us to systematically investigate the influence of network hydrophobicity on emulsion stabilization. We found that W/O emulsions are preferred with increasing ANG hydrophobicity, oil polarity, and oil/water ratio. For nonpolar oils, increasing emulsification temperature enabled the formation of W/O PEs that are metastable at room temperature. We connected this behavior to interfacial ANG adsorption kinetics and quantified ANG deformation and swelling in both phases via atomic force microscopy. Importantly, we developed a quantitative method to predict phase inversion by the difference in Flory-Huggins parameters between ANGs with water and oil (χwater - χoil). Overall, this study provides crucial structure-property relations to assist the design of nano/microgels for advanced PEs.

Soft and Deformable Thermoresponsive Hollow Rod-Shaped Microgels

Depending on their aspect ratio, rod-shaped particles exhibit a much richer 2D and 3D phase behavior than their spherical counterparts, with additional nematic and smectic phases accompanied by defined orientational ordering. While the phase diagram of colloidal hard rods is extensively explored, little is known about the influence of softness in such systems, partly due to the absence of appropriate model systems. Additionally, investigating higher volume fractions for long rods is usually complicated because non-equilibrium dynamical arrest is likely to precede the formation of more defined states. This has motivated us to develop micrometric rod-like microgels with limited sedimentation that can respond to temperature and reversibly reorganize into defined phases via annealing and seeding procedures. A detailed procedure is presented for synthesizing rod-shaped hollow poly(N-isopropylacrylamide) microgels using micrometric silica rods as sacrificial templates. Their morphological characterization is conducted through a combination of microscopy and light scattering techniques, evidencing the unconstrained swelling of rod-shaped hollow microgels compared to core-shell microgel rods. Different aspects of their assembly in dispersion and at interfaces are further tested to illustrate the opportunities and challenges offered by such systems that combine softness, anisotropy, and thermoresponsivity.

Development and characterization of cranberry pomace extract incorporated and vitamin E fortified edible films as an edible separation sheet for fruit leather

The separation sheets for fruit leather are traditionally made of plastic film or wax paper, which not only leads to environmental issues but also is inconvenience to consumers. This study evaluated edible fruit leather separation sheets using food polymers, including hydroxypropyl methyl cellulose (HPMC) and incorporation of cranberry pomace water extract (CPE) for providing natural fruit pigment, flavor, and phenolics. HPMCCPE film was then further improved by incorporating hydrophobic compound (oleic acid, OA) and vitamin E (VE) via cellulose nanocrystal (CNC) Pickering emulsion (CNCP) for enhancing film hydrophobicity and nutritional benefit, respectively. The CNCP-HPMCCPE film exhibited reduced water vapor permeability (∼0.033 g mm/m2 d Pa) compared to HPMCCPE film (∼0.59 g mm/m2 d Pa) and had the least change in mass and moisture content when wrapping fruit leather for up to 2 weeks of ambient storage. The fruit leather wrapped by CNCP-HPMCCPE film showed lower weight change than those by films without CNCP due to low mass transfer between film and fruit leather. CNCP resulted in controlled release of VE into a food simulating solvent (ethanol). The developed colorful and edible fruit leather separation sheet satisfied the increased market demands on sustainable food packaging. PRACTICAL APPLICATION: Colorful and flavorful edible films made of edible polymers, fruit pomace water extract, and emulsified hydrophobic compounds with vitamin E were created. The films have the satisfactory performance to replace the conventional fruit leather separation sheet made of plastic or wax paper. The edible films can be eaten with packaged fruit leather for not only reducing packaging waste but also providing convenience and nutritional benefit to consumers. These functional edible films may also be utilized to package other food products for promoting packaging sustainability and nutritional benefit.

Temperature sensitive nanogel-stabilized pickering emulsion of fluoroalkane for ultrasound guiding vascular embolization therapy

Various X-ray imaging technologies like computed tomography (CT) and digital subtraction angiography (DSA) are widely used in transcatheter arterial embolization (TAE) therapy for treating hepatocellular cancer (HCC) patients. Although they display high-contrast imaging, they have a few disadvantages, such as complex operation and exposure to ionizing radiation. Thus, ultrasound (US) imaging plays an important role in medical diagnosis because of its advantages, like simple and fast operation, no ionizing radiation exposure, and accurate real-time imaging. Subsequently, Poly N-isopropylacrylamide-co-2,2,3,4,4,4-Hexafluorobutyl methacrylate (PNF) nanogels were synthesized for stabilizing TGFPE, the Pickering emulsions of 2H, 3H-decafluoropentane (HDFP). These emulsions displayed dual abilities of thermosensitive sol-gel transition and long-term US imaging in vitro. Thus, it was concluded that these emulsions could achieve vascular embolization and long-term US imaging in vivo as per the TAE animal model results. The emulsion droplets' flow and accumulation were visualized under the US imaging guidance. In summary, the Pickering emulsions have the potential to be used as US-guided embolization material for mediating TAE surgeries.

Interactions between interfaces dictate stimuli-responsive emulsion behaviour

Stimuli-responsive emulsions offer a dual advantage, combining long-term storage with controlled release triggered by external cues such as pH or temperature changes. This study establishes that thermo-responsive emulsion behaviour is primarily determined by interactions between, rather than within, interfaces. Consequently, the stability of these emulsions is intricately tied to the nature of the stabilizing microgel particles - whether they are more polymeric or colloidal, and the morphology they assume at the liquid interface. The colloidal properties of the microgels provide the foundation for the long-term stability of Pickering emulsions. However, limited deformability can lead to non-responsive emulsions. Conversely, the polymeric properties of the microgels enable them to spread and flatten at the liquid interface, enabling stimuli-responsive behaviour. Furthermore, microgels shared between two emulsion droplets in flocculated emulsions facilitate stimuli-responsiveness, regardless of their internal architecture. This underscores the pivotal role of microgel morphology and the forces they exert on liquid interfaces in the control and design of stimuli-responsive emulsions and interfaces.

Dual (pH and thermal) stimuli-responsive Pickering emulsion stabilized by chitosan-carrageenan composite microgels

Formulation of water-in-oil (W/O) Pickering emulsion (PE) for food applications has been largely restricted by the limited choices of food-grade Pickering emulsifiers. In this study, composite microgels made of chitosan and carrageenan were explored as a dual (pH and thermal) stimuli-responsive Pickering emulsifier for the stabilization of W/O PE. The chitosan-carrageenan (CS-CRG) composite microgels not only exhibited pH- and thermo-responsiveness, but also displayed enhanced lipophilicity as compared to the discrete polymers. The stability of the CS-CRG-stabilized W/O PE system (CS-CRG PE) was governed by CS:CRG mass ratio and oil fractions used. The CS-CRG PE remained stable at acidic pH and at temperatures below 40 °C. The instability of CS-CRG composite microgels at alkaline pH and at temperatures above 40 °C rendered the demulsification of CS-CRG PE. This stimuli-responsive W/O PE could unlock new opportunities for the development of stimuli-responsive W/O PE using food-grade materials.

Effect of chemicals on the phase and viscosity behavior of water in oil emulsions

Due to population growth, the need for energy, especially fossil fuels, is increased every year. Since the costs of exploring new reservoirs and drilling new wells are very high, most reservoirs have passed their first and second periods of life, and it is necessary to use EOR methods. Water-based enhanced oil recovery (EOR) methods are one of the popular methods in this field. In this method, due to the possibility of emulsion formation is high, and by creating a stable emulsion, viscosity and mobility improved. In this study, the parameters affecting the stability and viscosity of the emulsion have been investigated step by step. In the first step, 50% (v/v) of water has been selected as the best water cut. The type of salt and its best concentration was evaluated in the second step by measuring the average droplets size. The third step investigated the effect of SiO2 nanoparticles and surfactant (span80) on emulsion stability and viscosity. According to the results, the best amount of water cut was 50% due to the maximum viscosity. In salts the yield was as follows: MgCl2 > CaCl2 > MgSO4 > Na2SO4 > NaCl. The best yield was related to MgCl2 at a concentration of 10,000 ppm. Finally, it was shown that the synergy of nanoparticles and surfactants resulted in higher stability and viscosity than in the case where each was used alone. It should be noted that the optimal concentration of nanoparticles is equal to 0.1% (w/w), and the optimal concentration of surfactant is equal to 200 ppm. In general, a stable state was obtained in 50% water-cut with MgCl2 salt at a concentration of 10,000 ppm and in the presence of SiO2 nanoparticles at a concentration of 0.1% and span 80 surfactants at a concentration of 200 ppm. The results obtained from this study provide important insights for optimal selection of the water-based EOR operation parameters. Viscosity showed a similar trend with stability and droplet size. As the average particle size decreased (or stability increased), the emulsion viscosity increased.

Recent advances in the design and use of Pickering emulsions for wastewater treatment applications

Pickering emulsions have recently emerged as versatile systems capable of targeting many applications of wastewater treatment. The unique properties, which include high emulsion stability, easy preparation, low toxicity, and stimuli-responsiveness, pave the way for advances in common pollutant control processes. This review aims to provide a comprehensive overview on different aspects in the Pickering emulsion design focusing on the key structural relations and their implications in specific applications. The first section is dedicated to the critical parameters governing the Pickering emulsion type, droplet size and stability. Furthermore, a section describing methods for demulsification and particle recovery is included, in which various stimuli have been explored. Finally, the most potent applications of Pickering emulsions such as photocatalytic degradation, adsorption, extraction, and separation of common wastewater pollutants are presented and discussed with a great deal of attention towards the efficacy, current limitations, and future potential. Recognizing the rise of innovative Pickering emulsion solutions is expected to induce profound effects facilitating the technology transfer to industrial processes.

Temperature-Dependent Nanogel for Pesticide Smart Delivery with Improved Foliar Dispersion and Bioactivity for Efficient Control of Multiple Pests

The use of nanomaterials and nanotechnology to construct a smart pesticide delivery system with target-oriented and controlled-release functions is important to increase the effective utilization rate and minimize environmental residue pollution. A temperature-dependent delivery system can modulate the release of pesticide with temperature to improve the efficacy and precision targeting. A series of poly(N-isopropylacrylamide) (PNIPAM)-based nanogels with high deformability and tunable structure were successfully constructed for smart pesticide delivery and effective pest control. A lambda-cyhalothrin (LC)-loaded Pickering emulsion (LC@TNPE) with a stable gel-like network structure was further formed by the temperature-dependent nanogel to encapsule the pesticide. The foliar wettability, photostability, and controlled-release property of LC@TNPE were effectively enhanced compared to the commercial formulation because of the encapsulation and stabilization of nanogel. The release rate of LC positively correlated with temperature changes and thereby adapted to the trend of pest population increase at higher temperature. The LC@TNPE displayed improved control efficacy on multiple target pests including Plutella xylostella, Aphis gossypii, and Pieris rapae compared with the commercial suspension concentrate and microcapsule suspension, and it showed marked efficacy to control Pieris rapae for an extended duration even at a 40% reduced dosage. Furthermore, the safety was evaluated systematically on cells in vitro and with a nontarget organism. Studies confirmed that the system was relatively safe for HepG2 cells and aquatic organism zebrafish. This research provides an insight into creating an efficient and environmentally friendly pesticide nanoformulation for sustainable agriculture production.

Thermosensitive poly(N-isopropylacrylamide)-grafted magnetic-cored dendrimers for benzene uptake

A series of thermosensitive and magneto-responsive dendrimers was synthesized based on magnetic-cored dendrimers (MCD) and carboxylic end-capped poly(N-isopropylacrylamide) (PNIPAM) to obtain PNIPAM-g-MCD. Thermo-response profiles of the PNIPAM-g-MCD from dynamic light scattering within the temperature range of 25-45 °C indicated that the lower critical solution temperature (LCST) of the PNIPAM-g-MCD was 32 °C. The physical size of the PNIPAM-g-MCD decreased as the temperature increased above the LCST. The initial hydrodynamic size of the PNIPAM-g-MCDs at 25 °C was 298.6 nm and reached 226.4 nm at 45 °C upon heating. Adsorption of benzene onto the PNIPAM-g-MCD at 25 °C was assessed, and the results showed that hydrophobic benzene was included within the internal cavities of lipophilic PNIPAM-g-MCD to maintain a thermodynamically stable state. Entrapment effects of the PNIPAM-g-MCD were confirmed at 45 °C, and the removal efficiency of benzene increased considerably to 50% when benzene was adsorbed, and the entrapment process was added. The shrunken PNIPAM terminal groups aggregated and trapped benzenes within the cavities of PNIPAM-g-MCD to prevent escape into the aqueous solution. Un-trapped benzene was removed through coalescence with PNIPAM-g-MCD because hydrophobic interactions prevailed with increasing temperature. PNIPAM-g-MCD were also able to form emulsions below the LCST and disrupted emulsions above the LCST in oil-water emulsions.

Macromolecular Crowding as an Intracellular Stimulus for Responsive Nanomaterials

Stimuli-responsive materials are exploited in biological, materials, and sensing applications. We introduce a new endogenous stimulus, biomacromolecule crowding, which we achieve by leveraging changes in thermoresponsive properties of polymers upon high concentrations of crowding agents. We prepare poly(2-oxazoline) amphiphiles that exhibit lower critical solution temperatures (LCST) in serum above physiological temperature. These amphiphiles stabilize oil-in-water nanoemulsions at temperatures below the LCST but are ineffective surfactants above the LCST, resulting in emulsion fusion. We find that the transformations observed upon heating nanoemulsions above their surfactant's LCST can instead be induced at physiological temperatures through the addition of polymers and protein, rendering thermoresponsive materials "crowding responsive." We demonstrate that the cytosol is a stimulus for nanoemulsions, with droplet fusion occurring upon injection into cells of living zebrafish embryos. This report sets the stage for classes of thermoresponsive materials to respond to macromolecule concentration rather than temperature changes.

Light-responsive Pickering emulsions based on azobenzene-modified particles

Light-responsive particle-stabilised (Pickering) emulsions can in principle be selectively emulsified/demulsified on-demand through the remote application of light. However, despite their wide-ranging potential in applications such as drug delivery and biphasic catalysis, their rational design is extremely challenging and there are very few examples to date. Herein, we investigate a model system based on silica particles functionalised with azobenzene photoswitches to understand the key factors that determine the characteristics of light-responsive Pickering emulsions. The particle hydrophobicity is tuned through judicious variation of the spacer length used to graft the chromophores to the surface, the grafting density, and irradiation to induce trans-cis photoisomerisation. For select emulsions, and for the first time, a reversible transition between emulsified water-in-oil droplets and demulsified water and oil phases is observed with the application of either UV or blue light, which can be repeatedly cycled. A combination of surface energy analysis and optical microscopy is shown to be useful in predicting the stability, and expected light-response, of a given emulsion. Using the observed trends, a set of design rules are presented which will help facilitate the rational design, and therefore, more widespread application of light-responsive Pickering emulsions.

Multifunctional Silica-Modified Hybrid Microgels Templated from Inverse Pickering Emulsions

Microgels are regarded as soft colloids with environmental responsiveness. However, the majority of reported microgels are inherently hydrophilic, resulting in aqueous dispersions, and only used in water-based applications. Herein, we reported an efficient method for hybridization of poly(N-isopropylacrylamide) microgel by coating hydrophobic silica nanoparticles on their surface. The resultant hybrid microgel had switchable surface wettability and could be dispersed in both aqueous and oil phases. Meanwhile, the coated hydrophobic silica nanoparticles solved the difficulty in redispersing microgels caused by particle aggregation and film formation during the drying process, providing a significant advantage in dried storage. Furthermore, the introduction of hydrophobic silica nanoparticles endowed the hybrid microgel with a variety of applications, including cargo encapsulation, active release induced by emulsion reversion, and trace water absorption.

Recent Advances on Pickering Emulsions Stabilized by Diverse Edible Particles: Stability Mechanism and Applications

Pickering emulsions, which are stabilized by particles, have gained considerable attention recently because of their extreme stability and functionality. A food-grade particle is preferred by the food or pharmaceutical industries because of their noteworthy natural benefits (renewable resources, ease of preparation, excellent biocompatibility, and unique interfacial properties). Different edible particles are reported by recent publications with distinct shapes resulting from the inherent properties of raw materials and fabrication methods. Furthermore, they possess distinct interfacial properties and functionalities. Therefore, this review provides a comprehensive overview of the recent advances in the stabilization of Pickering emulsions using diverse food-grade particles, as well as their possible applications in the food industry.

Investigation of the Contact Angle and Packing Density of Silica Nanoparticles at a Pickering Emulsion Interface Fixed by UV Polymerization

The contact angle of colloidal particles at an oil-water interface plays a crucial role in determining Pickering emulsion stability and emulsion type, but the contact angle cannot be directly determined using conventional methods. In this work, a Pickering emulsion was prepared with photocurable resin as the internal phase containing silica nanoparticle stabilizers. Particles adsorbed at the oil-water interface were then fixed through UV curing, allowing for the investigation of various parameters that influence the contact angle of colloidal particles at the interface. After curing, the contact angle can then be observed using scanning electron microscopy and subsequently measured. The contact angle of interfacial adsorbed silica nanoparticles gradually decreases as the size increases due to the line tension at the three-phase contact line, but, more importantly, we found that the surface chemistry of the silica nanoparticles plays the most important role in determining the contact angle. The fast fixation of solid nanoparticles at emulsion interfaces facilitates accurate measurements of the partition of particles between oil and water, providing a new method for studying the factors that affect Pickering emulsion stability.

Pickering emulsion droplet-based biomimetic microreactors for continuous flow cascade reactions

A continuous flow cascade of multi-step catalytic reactions is a cutting-edge concept to revolutionize stepwise catalytic synthesis yet is still challenging in practical applications. Herein, a method for practical one-pot cascade catalysis is developed by combining Pickering emulsions with continuous flow. Our method involves co-localization of different catalytically active sub-compartments within droplets of a Pickering emulsion yielding cell-like microreactors, which can be packed in a column reactor for continuous flow cascade catalysis. As exemplified by two chemo-enzymatic cascade reactions for the synthesis of chiral cyanohydrins and chiral ester, 5 − 420 fold enhancement in the catalysis efficiency and as high as 99% enantioselectivity were obtained even over a period of 80 − 240 h. The compartmentalization effect and enriching-reactant properties arising from the biomimetic microreactor are theoretically and experimentally identified as the key factors for boosting the catalysis efficiency and for regulating the kinetics of cascade catalysis.

A continuous flow cascade of multi-step catalytic reactions would provide significant advantages in faster reaction times, waste reduction, and lowered step-count of syntheses, yet this ideal remains challenging in practical applications. Here the authors describe continuous flow cascade catalysis through co-localization of two catalytically active subcompartments within Pickering emulsion droplets.

Fundamental aspects of nanocellulose stabilized Pickering emulsions and foams

Nanocelluloses in recent years have garnered a lot of attention for their use as stabilizers of liquid-liquid and gas-liquid interfaces. Both cellulose nanocrystals (CNCs) and cellulose nanofibers (CNFs) have been used extensively in multiple studies to prepare emulsions and foams. However, there is limited literature available that systematically discusses the mechanisms that affect the ability of nanocelluloses (modified and unmodified) to stabilize different types of interfaces. This review briefly discusses key factors that affect the stability of Pickering emulsions and foams and provides a detailed and systematic analysis of the current state knowledge on factors affecting the stabilization of liquid-liquid and gas-liquid interfaces by nanocelluloses. The review also discusses the effect of nanocellulose surface modifications on mechanisms driving the Pickering stabilization of these interfaces.

Temperature-responsive Pickering high internal phase emulsions for recyclable efficient interfacial biocatalysis

The field of biocatalysis is expanding owing to the increasing demand for efficient low-cost green chemical processes. However, a feasible strategy for achieving product separation, enzyme recovery, and high catalytic efficiency in biocatalysis remains elusive. Herein, we present thermoresponsive Pickering high internal phase emulsions (HIPEs) as controllable scaffolds for efficient biocatalysis; these HIPEs demonstrate a transition between emulsification and demulsification depending on temperature. Ultra-high-surface-area Pickering HIPEs were stabilized by Candida antarctica lipase B immobilized on starch particles modified with butyl glycidyl ether and glycidyl trimethyl ammonium chloride, thus simplifying the separation and reuse processes and significantly improving the catalytic efficiency. In addition, the switching temperature can be precisely tuned by adjusting the degree of substitution of the modified starches to meet the temperature demands of various enzymes. We believe that this system provides a green platform for various interfacial biocatalytic processes of industrial interest.

The thermoresponsive Pickering high internal phase emulsions stabilized by starch particles as controllable scaffolds for efficient biocatalysis, which simplified the separation and reuse processes and significantly improved the catalytic efficiency.

A three-tiered colloidosomal microreactor for continuous flow catalysis

Integrative colloidosomes with hierarchical structure and advanced function may serve as biomimetic microreactors to carry out catalytic reactions by compartmentalizing biological species within semipermeable membranes. Despite of recent progress in colloidosome design, integration of biological and inorganic components into tiered structures to tackle the remaining challenges of biocatalysis is highly demanded. Here, we report a rational design of three-tiered colloidosomes via the Pickering emulsion process. The microreactor consists of crosslinked amphiphilic silica-polymer hybrid nanoparticles as the semipermeable shell, an enzyme-incorporated catalytic sub-layer, and a partially-silicified adsorptive lumen. By leveraging confinement and enrichment effect, we demonstrate the acceleration of lipase-catalyzed ester hydrolysis within the microcompartment of organic-inorganic hybrid colloidosomes. The catalytic colloidosomes are further assembled into a closely packed column for enzymatic reactions in a continuous flow format with enhanced reaction rates. The three-tiered colloidosomes provide a reliable platform to integrate functional building blocks into a biomimetic compartmentalized microreactor with spatially controlled organization and high-performance functions.

Pickering Emulsions Stabilized by Diblock Copolymer Worms Prepared via Reversible Addition-Fragmentation Chain Transfer Aqueous Dispersion Polymerization: How Does the Stimulus Sensitivity Affect the Rate of Demulsification?

Responsive Pickering emulsions exhibit promising application in industry owing to the integration of the high storage stability with on-demand demulsification. In this study, stimuli-responsive Pickering emulsions stabilized by poly[oligo(ethylene glycol) methyl ether methacrylate]₁₅-b-poly(diacetone acrylamide)₁₂₀ (E₁₅D₁₂₀) worms were indicated, in which E₁₅D₁₂₀ worms were prepared via reversible addition-fragmentation chain transfer-based aqueous dispersion polymerization using thermo-sensitive POEGMA₁₅ as both the stabilizer block and macro-chain transfer agent. The factors influencing the morphologies of copolymers during polymerization-induced self assembly have been investigated. A series of different morphological polymer nanoparticles including spheres, worms, and vesicles could be produced through rational synthesis. E₁₅D₁₂₀ worms demonstrated excellent emulsifying performances and could be used as emulsifiers to form n-dodecane-in-water Pickering emulsions at a low content. The formed n-dodecane-in-water Pickering emulsions revealed a slow demulsification at pH 10 or 70 °C or pH 10/70 °C combinations, and several hours were needed for the demulsification of Pickering emulsions. However, n-dodecane-in-water Pickering emulsions displayed a rapid demulsification (∼10 min) at an elevated temperature, such as 90 °C. The different demulsification rates were attributed to different sensitivities of E₁₅D₁₂₀ worms to external stimuli. Pickering emulsions integrating a rapid responsive demulsification with a slow one would be well satisfactory on different occasions.

Exploring water in oil emulsions simultaneously stabilized by solid hydrophobic silica nanospheres and hydrophilic soft PNIPAM microgel

A general drawback of microgels is that they do not stabilize water-in-oil (w/o) emulsions of non-polar oils. Simultaneous stabilization with solid hydrophobic nanoparticles and soft hydrophilic microgels overcomes this problem. For a fundamental understanding of this synergistic effect the use of well defined particle systems is crucial. Therefore, the present study investigates the stabilization of water droplets in a highly non-polar oil phase using temperature responsive, soft and hydrophilic PNIPAM microgel particles (MGs) and solid and hydrophobic silica nanospheres (SNs) simultaneously. The SNs are about 20 times smaller than the MGs. In a multiscale approach the resulting emulsions are studied from the nanoscale particle properties over microscale droplet sizes to macroscopic observations. The synergy of the particles allows the stabilization of water-in-oil (w/o) emulsions, which was not possible with MGs alone, and offers a larger internal interface than the stabilization with SNs alone. Furthermore, the incorporation of hydrophilic MGs into a hydrophobic particle layer accelerates the emulsions sedimentation speed. Nevertheless, the droplets are still sufficiently protected against coalescence even in the sediment and can be redispersed by gentle shaking. Based on droplet size measurements and cryo-SEM studies we elaborate a model, which explains the found phenomena.

Salt-Resistant Switchable Pickering Emulsions Stabilized by Mesoporous Nanosilica Hydrophobized In Situ by pH-Insensitive Surfactants

Novel oil-in-water (O/W) Pickering emulsions (PEs) were prepared using mesoporous nanosilica in combination with a pH-insensitive cationic surfactant as a stabilizer and show an interesting sensitivity to acids and bases. Adding a suitable amount of NaOH (n_NaOH/n_{cationic surfactant} ≥ 1) led to prompt demulsification within 10 s. Upon further adding HCl solutions (n_HCl/n_NaOH = 1), stable PEs re-formed after homogenization. These emulsions remained stable for over 30 days after 60 cycles, switching from stable to unstable and back to stable states, and showed a high salt tolerance. A mechanism for the switching of the Pickering emulsion (PE) to unstable and back to stable states was derived and involved anionic and neutral forms of hydroxyl groups at the mesopores of the mesoporous silica nanoparticles (MSNPs). This work reveals a switchable PE system involving a pH-insensitive surfactant, in which the species of oils and cationic surfactants can be arbitrarily selected, a feature that greatly expands the applicability of PEs.

Limonene-in-water Pickering emulsion and on-demand separation using thermo-responsive biodegradable nanoparticles

In the last few decades, Pickering emulsions have regained attention due to the possibility of forming stable oil-in-water emulsions with interesting interfacial properties. As an example, the more and more stringent regulations on the products for home and personal care are pushing the market towards the use of biodegradable materials in order to reduce their environmental impact. In this scenario, an appealing opportunity is offered by the use of biodegradable polymeric nanoparticles (NPs) for the stabilization of fragrance oils in water. In this work, modular biodegradable NPs have been synthesized through a combination of ring opening polymerization and reversible addition-fragmentation chain transfer emulsion polymerization and used to produce limonene-in-water Pickering emulsions. This strategy allowed controlling independently the NP size, polymer molecular weight, and hydrophobicity acting on the microstructure of the constituting copolymers. Stable limonene-in-water Pickering emulsions could be obtained, with the size of the oil phase and the wetting by limonene that can be strictly controlled by tuning the NP physico-chemical properties. Finally, the adoption of thermo-responsive polymer chains within the shell of the Pickering emulsifiers enabled the on-demand destabilization of the emulsions and hence the selective dispensing of limonene by simply increasing the temperature.

Effect of cetyltrimethyl-ammonium bromide on the properties of hydroxyapatite nanoparticles stabilized Pickering emulsion and its cured poly(L-lactic acid) materials

Hydroxyapatite (HAp) nanoparticles stabilized Pickering emulsions were prepared by dichloromethane (CH₂ Cl₂ ) dissolved poly(L-lactic acid) (PLLA) as the oil phase and the deionized water with different concentrations of cetyltrimethyl-ammonium bromide (CTAB) as the aqueous phase. Effect of CTAB concentration on emulsions type and stability were studied. The emulsion type underwent a two-phase inversion, and emulsion stability increased first and then decreased with increasing CTAB concentrations. Besides, effect of CTAB concentration on zeta potential, aggregate size, contact angle of HAp nanoparticles and the oil-water interfacial tension were studied. The results indicated that zeta potential value of HAp nanoparticles changed from negative to positive, and the contact angle increased to over 80° initially and then decreased to below 40° rapidly. The distribution of HAp nanoparticles on the surface of emulsion droplets with different concentrations of CTAB (5 and 20 mM) was characterized using laser-induced confocal microscope. It revealed the distribution of HAp nanoparticles changed with different CTAB concentrations. The cured PLLA materials were obtained after the solvent being volatilized using as-received emulsions as templates. Scanning electron microscope images showed both microspheres and porous materials with interconnected pore structure were obtained. In conclusion, the microstructure of microspheres or porous PLLA materials is controllable by adjusting the property of HAp nanoparticles stabilized Pickering emulsions with appropriate amount of CTAB.

One-Step Formation of Double Emulsions Stabilized by PNIPAM-based Microgels: The Role of Co-monomer

Microgels have been widely used as particulate emulsifiers to stabilize emulsions due to their multiresponsiveness and deformability. Generally, microgels stabilize oil-in-water (o/w) emulsions, whereas occasionally water-in-oil (w/o) emulsions are reported using oils like n-octanol in which microgels can swell. However, the use of microgels to stabilize double emulsions (DEs) remains scarce. In this work, we report a special poly(N-isopropylacrylamide)- (PNIPAM-) based microgel to obtain water-in-oil-in-water (w/o/w) DEs in one step with the introduction of 1-vinylimidazole (VIM) as comonomer and hydroxy silicone oil as the oily phase. By comparison, when methacrylic acid (MAA) is used, an o/w emulsion will be obtained. The same holds true even when we freeze-dry and redisperse the microgels in the oil. Compared with PNIPAM-co-MAA microgel, PNIPAM-co-VIM microgel achieves a lower interfacial tension (IFT) when dispersed in the aqueous phase. This interfacial affinity of PNIPAM-co-VIM is believed to result from acid-base interaction between VIM and hydroxyl groups of the silicone oil, the same interaction used for preparing silica-vinyl polymer composite particles. Increasing the particle concentrations from 0.05% to 0.9% (w/v), we observe the inversion from w/o to o/w/o and w/o/w emulsions. When the oil fraction is changed from 0.1 to 0.9, the emulsion morphology evolves from o/w and w/o/w to w/o emulsions. At last, we examine the emulsifying ability of PNIPAM-co-VIM microgel with other oils and find that w/o/w emulsions are obtained with edible oils as well. Considering the similarity between microgels and biopolymers, the discovery in this work will help in designing food-grade emulsifiers to form edible DEs.

Microgels self-assembly at liquid/liquid interface as stabilizers of emulsion: Past, present & future

The most recent developments on Pickering emulsions deal with the design of responsive emulsions able to undergo fast destabilization under the effect of an external stimulus. In this scenario, soft colloidal particles like microgels are considered novel class suitable emulsifiers. Microgels particles self-assemblies are highly deformable at interfaces covering higher surfaces than hard particles and their interfacial behavior strongly depends on external-stimuli. Microgels are very diverse owing to the large variety of them from the point of view of possible combinations of stimuli-responsiveness and different microstructures (crosslinking density and distribution). Herein, we illustrate the use of different types of responsive microgels not only from a structural point of view but also even from physical one. For that, the effect of different microgels parameters such as internal structure and charge density on mechanical properties of the interface will be discussed.

Pickering Emulsifiers Based on Block Copolymer Nanoparticles Prepared by Polymerization-Induced Self-Assembly

Block copolymer nanoparticles prepared via polymerization-induced self-assembly (PISA) represent an emerging class of organic Pickering emulsifiers. Such nanoparticles are readily prepared by chain-extending a soluble homopolymer precursor using a carefully selected second monomer that forms an insoluble block in the chosen solvent. As the second block grows, it undergoes phase separation that drives in situ self-assembly to form sterically stabilized nanoparticles. Conducting such PISA syntheses in aqueous solution leads to hydrophilic nanoparticles that enable the formation of oil-in-water emulsions. Alternatively, hydrophobic nanoparticles can be prepared in non-polar media (e.g., n-alkanes), which enables water-in-oil emulsions to be produced. In this review, the specific advantages of using PISA to prepare such bespoke Pickering emulsifiers are highlighted, which include fine control over particle size, copolymer morphology, and surface wettability. This has enabled various fundamental scientific questions regarding Pickering emulsions to be addressed. Moreover, block copolymer nanoparticles can be used to prepare Pickering emulsions over various length scales, with mean droplet diameters ranging from millimeters to less than 200 nm.

Desorption energy of soft particles from a fluid interface

The efficiency of soft particles to stabilize emulsions is examined by measuring their desorption free energy, i.e., the mechanical work required to detach the particle from a fluid interface. Here, we consider rubber-like elastic as well as microgel particles, using coarse-grained molecular dynamics simulations. The energy of desorption is computed for two and three-dimensional configurations by means of the mean thermodynamic integration method. It is shown that the softness affects the particle-interface binding in two opposing directions as compared to rigid particles. On the one hand, a soft particle spreads at the interface and thereby removes a larger unfavorable liquid-liquid contact area compared to rigid particles. On the other hand, softness provides the particle with an additional degree of freedom to get reshaped instead of deforming the interface, resulting in a smaller restoring force during the detachment. It is shown that the first effect prevails so that a soft spherical particle attaches to the fluid interface more strongly than rigid spheres. Finally, we consider microgel particles both in the swollen and in the collapsed state. Surprisingly, we find that the latter has a larger binding energy. All results are rationalised using thermodynamic arguments and thereby offer detailed insights into the desorption energy of soft particles from fluid interfaces.

A microgel-Pickering emulsion route to colloidal molecules with temperature-tunable interaction sites

A simple Pickering emulsion route has been developed for the assembly of temperature-responsive poly(N-isopropylacrylamide) (PNIPAM) microgel particles into colloidal molecules comprising a small number of discrete microgel interaction sites on a central oil emulsion droplet. Here, the surface activity of the microgels serves to drive their assembly through adsorption to growing polydimethylsiloxane (PDMS) emulsion oil droplets of high monodispersity, prepared in situ via ammonia-catalysed hydrolysis and condensation of dimethyldiethoxysilane (DMDES). A dialysis step is employed in order to limit further growth once the target assembly size has been reached, thus yielding narrowly size-distributed, colloidal molecule-like microgel-Pickering emulsion oil droplets with well-defined microgel interaction sites. The temperature-responsiveness of the PNIPAM interaction sites will allow for the directional interactions to be tuned in a facile manner with temperature, all the way from soft repulsive to short-range attractive as the their volume phase transition temperature (VPTT) is crossed. Finally, the microgel-Pickering emulsion approach is extended to a mixture of PNIPAM and poly(N-isopropylmethacrylamide) (PNIPMAM) microgels that differ with respect to their VPTT, this in order to prepare patchy colloidal molecules where the directional interactions will be more readily resolved.

Sugar-responsive Pickering emulsions mediated by switching hydrophobicity in microgels

HYPOTHESIS

Pickering emulsions stabilized by soft and responsive microgels can demulsify on demand upon microgel collapse. The concept has been explored with simple model microgels such as poly(N-isopropylacrylamide) (pNIPAM) and their derivatives, but the role of functionalization is largely unexplored.

EXPERIMENTS

Saccharide-responsive phenylboronic-modified microgels are used as Pickering emulsion stabilizers. Emulsion stability and microgel organization at drop surface are studied as a function of saccharide concentration. Better insight into their behavior at interfaces is gained through adsorption kinetics and Langmuir film studies at air-water interface.

FINDINGS

The functionalization of water-swollen microgels by phenylboronic functions imparts some hydrophobicity to the structure, at the origin of additional internal cross-links analogous which rigidify the structure compared to non-functionalized microgels, as proved by their slow adsorption kinetics and poor interfacial compressibility. Upon boronate ester formation with diol groups of the saccharide, the hydrophobic character of the phenylboronic acid decreases, increasing the adsorption kinetics and their interfacial compressibility. Emulsions are stable in the presence of saccharide, given the high deformability of the yet-hydrophilic microgels, and mechanically unstable with less deformable particles in low saccharide concentration. The hydrophobic-hydrophilic switch acts as a trigger to tune the microgel stabilizing properties.

Nitrogen-aeration tuned ultrasonic synthesis of SiO2@PNIPAm nanoparticles and preparation of temperature responsive Pickering emulsion

Ultrasonic synthesis has shown great potential applications in preparing varieties of nanostructured materials. However, fabrication of nanomaterials with tunable structures and desirable properties is still challenging because of the instability and nonuniform distribution of cavitation effect in liquid phase. In this study, a novel aeration tuned ultrasonic synthesis approach is proposed for optimizing the cavitation effect in both time and space scales and fabricating SiO₂@PNIPAm NPs. By alternation of ultrasonication and N₂ aeration, more and more gas bubbles are formed in the reaction liquid, and the collapse of those bubbles is further enhanced by the reactants of solid SiO₂ and intermediate functionalized SiO₂ NPs. As a result, SiO₂@PNIPAm NPs with various grafting ratios are successfully synthesized simply by changing the number of ultrasonic synthesis cycle. The SiO₂@PNIPAm NPs are subsequently used as stabilizer to form Pickering emulsions with different temperature response. This work provides a potential facile sonochemical synthesis method with high efficiency in obtaining inorganic/organic NPs of well determined structures.

Novel amphiphilic cellulose nanocrystals for pH-responsive Pickering emulsions

Development of a green, recyclable emulsifier for pH-responsive Pickering emulsion would be of great importance to many industries. To this end, a novel emulsifier, benzyl-polyethyleneimine modified cellulose nanocrystals (Ben-PEI-CNCs), was developed via the periodate oxidation of cellulose nanocrystals and reductive amination. Ben-PEI-CNCs possess pH-responsive amphiphilicity due to the existence of hydrophilic amino and hydrophobic benzyl groups. The Pickering emulsions stabilized by Ben-PEI-CNC2 and Ben-PEI-CNC18 are very responsive to pH changes, and adjusting the pH from 3 to 7 effectively triggers oil-water separation and emulsification. Additionally, cyclic testing establishes the robustness of this process. Overall, this study demonstrates that Ben-PEI-CNCs can promote the transition from a stable emulsion to an unstable emulsion by adjusting the pH, allowing the recovery of oil and the recycling of the emulsifier.

Surface Grafting Polyphosphoesters on Cellulose Nanocrystals To Improve the Emulsification Efficacy

Particle-stabilized emulsion systems have been developed to address the problematic properties of conventional surfactants. However, the nature and properties of the fine particles used in such systems remain a critical issue for stability enhancement. Herein, we describe a thermoswitchable oil-in-water (O/W) particle-stabilized emulsion that exhibits improved stability due to the addition of cellulose nanocrystals (CNCs) modified with poly[2-isopropoxy-2-oxo-1,3,2-dioxaphospholane] (PIPP), which exhibits relatively good biocompatibility and biodegradability. Various parameters, such as surface activity, concentration of particles, polarity of solvents, and temperatures, on the formation of emulsions with CNCs grafted with PIPP (CNC-g-PIPP) were investigated. Results showed that the surface activity of CNC-g-PIPP was significantly improved compared with the unmodified material. Heptane-in-water particle-stabilized emulsions with CNC-g-PIPP were stably formed, and the effect of temperature on the stability of the emulsions was characterized. CNC-g-PIPP exhibited function as an effective particulate emulsifier at 4 °C because of the strong adsorption at the oil-water interface. However, the emulsions rapidly disintegrated at 45 °C, which is above the low critical solution temperature of PIPP on CNC, as the hydrophobized CNC-g-PIPP desorbed from the oil-water interface. Based on these findings, a thermally induced reversible emulsification/demulsification was presented. The resulting switchable particle-stabilized emulsion based on CNC-g-PIPP shows promise for the ability to control the stability of an emulsion in response to temperature, which is attractive for use in biological applications.

Polymer Brush Graft-Modified Starch-Based Nanoparticles as Pickering Emulsifiers

We study biosourced core-shell particles with a starch-based core and thermo-responsive polymer brush shell using surface-initiated single-electron transfer living radical polymerization (SI-SET-LRP) as a Pickering stabilizer. The shell endows the Pickering stabilizer with reversible emulsification/demulsification of oil and water properties. The initiator attached to the starch-based nanosphere (Br-SNP) core particle was first fabricated using the precipitation method. Subsequently, dense poly( N-isopropylacrylamide) (PNIPAM) brush graft-modified starch-based nanoparticles (SNP- g-PNIPAM) were obtained via the SI-SET-LRP process. Interfacial properties of the resultant particles were analyzed by interfacial tensiometer measurements, as were the effects of the grafted polymer chain length and temperature on the interfacial activity. Pickering emulsion was obtained using SNP- g-PNIPAM particles as the stabilizer. The effect of the concentration of the Pickering stabilizer on the size of emulsion droplets was analyzed. The emulsification/demulsification process of the Pickering emulsion can be reversed and easily repeated by changing the temperature.

Stabilization of Pickering Emulsions by Hairy Nanoparticles Bearing Polyanions

Pickering emulsions are increasingly applied in drug delivery, oil-water separation, composite materials preparation, and other fields. However, systematic studies on the stabilization of Pickering emulsions to satisfy the growing application demands in multiple fields with long-term conservation are rare. Compared to conventional solid nanoparticles, polyanion-modified hairy nanoparticles are more stable in practical environments and are investigated in this study. Poly (sodium p-styrenesulfonate) was grafted to a polystyrene (PS) core via a photoemulsion polymerization. A hairy nanoparticle bearing polyanions called poly (sodium p-styrenesulfonate) brush (PS@PSS) was synthesized. The size and uniformity of the Pickering emulsions stabilized by PS@PSS were investigated via a polarizing microscope. The stability of Pickering emulsions were optimized by adjusting critical factors like ultrasonic power and time, standing time, oil phases, salt concentration, and water:oil ratio. Results indicated that the Pickering emulsions could be stabilized by PS@PSS nanoparticles, which showed remarkable and adjustable partial wetting properties. It was found that the optimized conditions were ultrasonic power of 150 W, ultrasonic time of 3 min, salt concentration of 0.1 mM, oil phase of hexadecane, and water:oil ratio of 1:1. The formation and stability of Pickering emulsion are closely related to the hairy poly (sodium p-styrenesulfonate) brush layer on the nanoparticle surface.

Confinement-Induced Alteration of Morphologies of Oil-Water Emulsions

Reversible alteration between different emulsion morphologies like core-shell and Janus is conventionally triggered by altering the interfacial energy between different phases. In contrast, here, we show that the morphology of dispersed droplets can be changed also when the emulsion is sufficiently confined between two parallel plates. In particular, we use three immiscible phases: silicone oil, paraffin oil, and aqueous solution of surface-active agents like agarose, sodium dodecylsulfate, dioctyl sodium sulfosuccinate, and cetyl trimethylammonium bromide to generate oil-in-water emulsions consisting of complex morphologies of the dispersed droplets. In the unconfined state, the core-shell drops appear with paraffin oil at the core and silicone oil at the shell. However, the morphology of oil droplets changes to Janus when the emulsion is confined between two parallel plates. We have shown that the meniscus of the continuous phase that forms between the parallel plates alters the pressure field in the emulsion and the total energy of the system, which trigger such morphological transition.

Synthesis, Characterization, and Pickering Emulsifier Performance of Anisotropic Cross-Linked Block Copolymer Worms: Effect of Aspect Ratio on Emulsion Stability in the Presence of Surfactant

Reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization is used to prepare epoxy-functional PGMA-P(HPMA- stat-GlyMA) diblock copolymer worms, where GMA, HPMA, and GlyMA denote glycerol monomethacrylate, 2-hydroxypropyl methacrylate, and glycidyl methacrylate, respectively. The epoxy groups on the GlyMA residues were ring-opened using 3-aminopropyltriethoxysilane (APTES) in order to cross-link the worm cores via a series of hydrolysis-condensation reactions. Importantly, the worm aspect ratio can be adjusted depending on the precise conditions selected for covalent stabilization. Relatively long cross-linked worms are obtained by reaction with APTES at 20 °C, whereas much shorter worms with essentially the same copolymer composition are formed by cooling the linear worms from 20 to 4 °C prior to APTES addition. Small-angle X-ray scattering (SAXS) studies confirmed that the mean aspect ratio for the long worms is approximately eight times greater than that for the short worms. Aqueous electrophoresis studies indicated that both types of cross-linked worms acquired weak cationic surface charge at low pH as a result of protonation of APTES-derived secondary amine groups within the nanoparticle cores. These cross-linked worms were evaluated as emulsifiers for the stabilization of n-dodecane-in-water emulsions via high-shear homogenization at 20 °C and pH 8. Increasing the copolymer concentration led to a reduction in mean droplet diameter, indicating that APTES cross-linking was sufficient to allow the nanoparticles to adsorb intact at the oil/water interface and hence produce genuine Pickering emulsions, rather than undergo in situ dissociation to form surface-active diblock copolymer chains. In surfactant challenge studies, the relatively long worms required a thirty-fold higher concentration of a nonionic surfactant (Tween 80) to be displaced from the n-dodecane-water interface compared to the short worms. This suggests that the former nanoparticles are much more strongly adsorbed than the latter, indicating that significantly greater Pickering emulsion stability can be achieved by using highly anisotropic worms. In contrast, colloidosomes prepared by reacting the hydroxyl-functional adsorbed worms with an oil-soluble polymeric diisocyanate remained intact when exposed to high concentrations of Tween 80.

Shape-Anisotropic Colloids at Interfaces

Research in the 1980s demonstrated the formation of monolayers of particles achieved by interfacial particle trapping as a model system for investigating colloids in two dimensions. Since then, microscopy visualization of two-dimensional particle monolayers and quantification of the microstructure have led to significant fundamental understanding of a number of phenomena such as crystallization, freezing and melting transitions, dislocation dynamics, aggregation kinetics, and others. On the application front, particles at curved interfaces, as often the case in particle-stabilized emulsions and foams, have received considerable attention in the last few decades. The growing interest in the search for novel particles and new strategies to effect emulsion stabilization stems from their application in several disciplines. Moreover, particle-stabilized Pickering emulsions and foams can also be used to derive a number of advanced functional materials. Compared to several accounts of research on spherical colloids at fluid-fluid interfaces, investigations of the behavior of shape-anisotropic particles at interfaces, albeit receiving considerable attention in recent years, are still in a nascent stage. The objective of this feature article is to highlight our recent work in this area. In particular, the adsorption of shape-anisotropic particles to interfaces, wetting behavior, interfacial self-assembly, the response of nonspherical-particle-coated interfaces to compression and shear, and their ability to stabilize emulsions are discussed.

Hydrophobized nanocomposite hydrogel microspheres as particulate stabilizers for water-in-oil emulsions

Hydrophobized nanocomposite microgels can serve as particulate emulsifiers for water-in-oil (W/O) emulsions with different types of oils, including non-polar oils, which usually do not form W/O emulsions with conventional microgels.