Interface Of Emulsion Droplets Research Articles

Polymer-Grafted, Gold Nanoparticle-Based Nano-Capsules as Reversible Colorimetric Tensile Strain Sensors.

Colloidal colorimetric microsensors enable the in-situ detection of mechanical strains within materials. Enhancing the sensitivity of these sensors to small scale deformation while enabling reversibility of the sensing capability would expand their utility in applications including biosensing and chemical sensing. In this study,weintroduce the synthesis of colloidal colorimetric nano-sensors using a simple and readily scalable fabrication method. Colloidal nano sensors are prepared by emulsion-templated assembly of polymer-grafted gold nanoparticles (AuNP). To direct the adsorption of AuNP to the oil-water interface of emulsion droplets, AuNP (≈11nm) are functionalized with thiol-terminated polystyrene (PS, Mn =11k). These PS-grafted gold nanoparticles are suspended in toluene and subsequently emulsified to form droplets with a diameter of ≈30µm. By evaporating the solvent of the oil-inwater emulsion, weform nanocapsules (AuNC) (diameter < 1µm) decorated by PS-grafted AuNP. To test mechanical sensing, the AuNC are embedded in an elastomer matrix. The addition of a plasticizer reduces the glass transition temperature of the PS brushes, and in turn imparts reversible deformability to the AuNC. The plasmonic peak of the AuNC shifts towards lower wavelengths upon application of uniaxial tensile tension, indicating increased inter-nanoparticle distance, and reverts back as the tension is released.

Water-in-water Pickering emulsion stabilized by cellulose nanocrystals as space-confined encapsulating systems: From establishment to stability

The development of new water-in-water (W/W) emulsion systems and the improvement of the long-term stability of emulsions could create opportunities for studying interfacial bionic systems and microencapsulation applications. In this study, the new W/W emulsion systems were constructed from hydroxypropyl methylcellulose (HPMC) and maltodextrin (MD). The effects of cellulose nanocrystals (CNC) and environmental factors (ionic strength and pH) on the stability of W/W Pickering emulsions were investigated. The stabilizing effect was observed at contents of CNC as low as 0.025 wt%. The W/W Pickering emulsion showed no phase separation within 30 days when the CNC concentration was above 0.025 wt%, indicating that the emulsions were stable during the observation period. The stability of W/W Pickering emulsions was driven by the electrostatic repulsion provided by the CNC adsorbed at the droplet interface, which decreased with increasing NaCl concentration. This was attributed to the charge-shielding effect of NaCl weakening the electrostatic repulsion of the CNCs at the emulsion droplet interface. Lactobacillus helveticus cells were encapsulated in the W/W Pickering emulsion. These results revealed that the developed W/W Pickering emulsions have potential applications in protecting the activity of probiotic bacteria and investigating the behavior of cells in restricted spaces.

Water-in-water emulsions stabilized by self-assembled chitosan colloidal particles

Dextran (Dex) and poly(ethylene glycol) (PEG)-based aqueous emulsions were stabilized using the self-assembled chitosan colloidal particles (CS CPs). Besides, the effects of pH, CS CPs concentration, polymer concentration, volume ratio of PEG solution to Dex solution, temperature, homogenizing speed and homogenizing time on the property of the W/W emulsions were investigated, respectively. In order to enhance the stability of the PEG-Dex emulsion, sodium tripolyphosphate was used to cross-link the CS CPs at the interface of emulsion droplets, which resulted in the stability duration for >1 year. Finally, the CS CPs were used as a support to immobilize urease and bovine serum albumin and a stabilizer to prepare W/W emulsion, which were then adopted as a catalysis system and as a spinning solution to fabricate drug-loaded nanofiber. This strategy potentially provides a new opportunity to encapsulate the active molecules at the water-water interface, and enrich the types of usable active molecules in the encapsulation in the W/W emulsions.

Porous boronate imprinted microsphere prepared based on new RAFT functioned cellulose nanocrystalline with multiple H-bonding at the emulsion droplet interface for highly specific separation of Naringin

For porous molecular imprinted polymers (MIPs), introduction of special functional groups and integration porous structure support will endow the MIPs with tunable surface properties and specific affinity performance. Herein, by combination of RAFT molecular imprinting, Pickering emulsion, and boronate affinity methods, a new kind of porous imprinted microspheres (BA-HPMIPs) using the low pKa value of APBA (1-allylpyridinium-3-boronic acid, pKa = 7.4) as functional monomer was prepared for specific molecular recognition and separation of NRG. Meanwhile, the novel RAFT functioned surfactants with dual amide multiple H-bonds were designed as stabilized particles was used to promote sustainability, which further confer them multifunctionality and/or by polymerizing the Pickering emulsion itself. Equilibrium adsorption was reached rapidly within 360 min, and the maximum equilibrium binding capacities of BA-HPMIPs were found to be 118.32 µmol g−1 for NRG. Furthermore, they had a stronger selectivity towards NRG than other competitive target (i.e rutin, catechol, ARS, o-nitrophenol). Moreover, BA-HPMIPs have shown outstanding reusability of 8.63 % loss in enrichment performance after five times repeatedly. As a proof of this concept, a commercially avaliable NRG with purity could be effectively extracted and concentrated to 96.75 % purity. These results demonstrated that, a new kind of porous imprinted microsphere with abundant porous structure and boronic acid recognizing sites has great potential for separation and purification of industrial samples under neutral conditions.

Study of Surfactant‐Induced Deformations at the Interface of Emulsion Droplets by Digital Image Analysis of Droplet Projections

AbstractEmulsion droplets do not always have smooth surfaces. Under certain conditions, the formation of surface‐active species at oil–water interfaces leads to interfacial instabilities that cause a spontaneous increase in the droplet surface area, which results in fascinating droplet morphologies. The specific system presented in this study consists of stearic acid encapsulated in an oil droplet and the quaternary ammonium surfactant cetyltrimethylammonium bromide in the aqueous phase. This system is studied by examining the deformation of single emulsion droplets hanging on a capillary tip. By using digital image analysis, the relative perimeters and fractal dimensions from the droplet outlines are calculated and the influences of several process parameters on their temporal development are studied. It is demonstrated that the surfactant concentration, pH value, salt addition, alcohol addition, and viscosity have a considerable impact on the droplet morphology and possible causes for this behavior are discussed. Through this study, important insights are gained into the deformation mechanism and kinetics that can potentially guide the future preparation of particles with special surface morphologies.

Role of Surface Energy of Nanoparticle Stabilizers in the Synthesis of Microspheres via Pickering Emulsion Polymerization.

Polymer microspheres are important for a variety of applications, such as ion exchange chromatography, catalyst supports, absorbents, etc. Synthesis of large microspheres can be challenging, because they cannot be obtained easily via classic emulsion polymerization, but rather by more complex methods. Here, we present a facile method for obtaining polymer microspheres, beyond 50 μm, via Pickering emulsion polymerization. The method consists in creating oil-in-water (o/w) Pickering emulsion/suspension from vinyl bearing monomers, immiscible with water, whereas silica nanoparticles (NPs), bearing glycidyl functionalities, have a stabilizing role by adsorbing at the monomer/water interface of emulsion droplets. The emulsion is polymerized under UV light, and polymer microspheres decorated with NPs are obtained. We discovered that the contact angle of the NPs with the polymer microsphere is the key parameter for tuning the size and the quality of the obtained microspheres. The contact angle depends on the NPs’ interfacial energy and its polar and dispersive contributions, which we determine with a newly developed NanoTraPPED method. By varying the NPs’ surface functionality, we demonstrate that when their interfacial energy with water decreases, their energy of adhesion to water increases, causing the curvature of the polymer/water interface to decrease, resulting in increasingly larger polymer microspheres.

NanoTraPPED-A New Method for Determining the Surface Energy of Nanoparticles via Pickering Emulsion Polymerization.

Surface energy with its polar and disperse components describes the physicochemical state of nanoparticles’ (NPs) surfaces, and can be a valuable parameter for predicting their bulk behavior in powders. Here, we introduce a new method, namely, Nanoparticles Trapped on Polymerized Pickering Emulsion Droplets (NanoTraPPED), for measuring the surface energy of a series of silica NPs bearing various surface functional groups. The method consists in creating Pickering emulsions from vinyl bearing monomers, immiscible with water, whereas NPs of interest have a stabilizing role, and in the process, become trapped at the monomer/water interface of emulsion droplets. The Pickering emulsion is polymerized, and polymer microspheres (colloidosomes) decorated with NPs are obtained. NanoTraPPED relies on measuring contact angles from the immersion depth of nanoparticles at the interface of various polymer colloidosomes with the electron microscope. The contact angle values are used as input for the Owens-Wendt-Rabel-Kaelble (OWRK) model, to quantitatively determine the total surface energy with water γNP/water, air γNP, and the corresponding polar and dispersive interaction components of NPs carrying -NH2, -SH, -OH, -CN and -C8 surface functional groups, ranking these according to their polarity. Our findings were confirmed independently by calculating the interfacial desorption energies of NPs from contact angles.

Interfacial Instability as Shaping Mechanism for Polystyrene Particles with Tunable Surface Texture

AbstractSurfactant‐driven interfacial instability of emulsion droplets has recently emerged as a means for shaping polymeric particles with controllable surface texture. This paper presents a suspension polymerization‐based method to produce surface‐textured polystyrene particles by inducing an instability at the interface of prepolymerized emulsion droplets followed by rapid cooling. The interaction of two surface‐active components, i.e., arachidic acid and cetyltrimethylammonium bromide (CTAB) at the phase boundary triggers the interfacial deformation at a specific point in time. Rapid cooling freezes the deformed emulsion droplets in a nonequilibrium state. Viscosity is proposed as the key parameter influencing the particle morphology, which can be controlled by easily adjustable factors such as initiator concentration, temperature, time, and cooling rate. Contact angle hysteresis measurements of particle thin layers spread on a flat substrate reveal a strong influence of the particle surface texture on the wetting behavior. The presented particle synthesis method requires no specialized equipment and has a high potential for upscaling, making it promising for various applications including hydrophobic coatings, catalyst supports, separation technology, tissue engineering, or drug delivery.

Drug localization and its effect on the physical stability of poloxamer 188-stabilized colloidal lipid emulsions

Colloidal lipid emulsions are a promising formulation option for poorly water-soluble drugs. Due to their complex composition, they provide different sites for the localization of drugs. Drug molecules can be situated in the lipid matrix, in the aqueous phase with its structures formed by an excess of emulsifier or at the droplet interface. The interface and the mechanism of stabilization is mainly characterized by the emulsifier. In this study, the main focus was on the influence of drug localization on the stability of emulsions sterically stabilized with poloxamer188. In addition to 5% of this non-ionic emulsifier, the emulsions contained 10% soybean oil. The localization of the drugs fenofibrate, curcumin, betamethasone valerate, cinnarizine, dibucaine and flufenamic acid within the emulsion system at a physiological pH of 7.4 as well as their influence on emulsion stability were examined. The results indicated that the stability of poloxamer 188-stabilized emulsions can be influenced in a positive or negative way by the localization of drug molecules in the interface of emulsion droplets. Applying cinnarizine as model substance at pH 5, 7.4 and 10, no pronounced change in the localization was detected as a result of alterations in the charge of the drug.

Pickering emulsion-embedded hierarchical solid-liquid hydrogel spheres for static and flow photocatalysis

Pickering emulsion-based photocatalysis is considered to be a promising system due to its large active surface area and water/oil spatial separation capability for enrichment of substrates and products. In this work, a novel hierarchical structure composed of calcium alginate gel sphere wrapped ionic liquid-in-water Pickering emulsion with TiO2 in the water phase, which are stabilized by graphene oxide, is prepared via a facile one-step emulsion gelation method. Such subtle combination of Pickering emulsion, hydrogel and TiO2 with a multi-stage solid-liquid assemblage structure shows enhanced degradation activity of 2-naphthol into small molecular alkanes under simulated solar irradiation. The photodegradation activity is attributed to the ionic liquid as adsorption medium for 2-naphthol, and the high-efficient charge separation at graphene oxide/TiO2 interface superior to that of pure TiO2. More importantly, the as-prepared millimeter-sized assembled gel spheres can be directly used as the column filler to construct continuous flow photocatalytic system, maintaining the promising performance in removing pollutants from water with ~100% remove ability of 2-naphthol on stream. A charge transfer mechanism of the photocatalyst is proposed, i.e. photogenerated charges are separated in TiO2/graphene oxide p-n heterostructure at the interface of Pickering emulsion droplets.

Immobilization of Gold‐on‐Carbon Catalysts Onto Perfluorocarbon Emulsion Droplets to Promote Oxygen Delivery in Aqueous Phase D‐Glucose Oxidation

AbstractThe catalytic activity of metal nanoparticles (NPs) supported on porous supports can be controlled by various factors, such as NPs size, shape, or dispersivity, as well as their interaction with the support or the properties of the support material itself. However, these intrinsic properties are not solely responsible for the catalytic behavior of the overall reaction system, as the local environment and surface coverage of the catalyst with reactants, products, intermediates and other invloved species often play a crucial role in catalytic processes as well. Their contribution can be particularly critical in liquid‐phase reactions with gaseous reactants that often suffer from low solubiltiy. One example is D‐glucose oxidation with molecular oxygen over gold nanoparticles supported on porous carbons. The possibility to promote oxygen delivery in such aqueous phase oxidation reactions via the immobilization of heterogenous catalysts onto the interface of perfluorocarbon emulsion droplets is reported here. Gold‐on‐carbon catalyst particles can stabilize perfluorocarbon droplets in the aqueous phase and the local concentration of the oxidant in the surroundings of the gold nanoparticles accelerates the rate‐limiting step of the reaction. Consequently, the reaction rate of a system with the optimal volume fraction of fluorocarbon is higher than a reference emulsion system without fluorocarbon, and the effect is observed even without additional oxygen supply.

Biomass-derived furfural conversion over Ni/CNT catalysts at the interface of water-oil emulsion droplets

Carbon nanotubes-supported Ni catalysts were investigated for the hydrogenation of furfural as a biomass-derived furanic model compound at the liquid-liquid interface of Pickering emulsions in a batch reactor at 200 °C and 2.0 MPa of H2 pressure. The catalysts were characterized by N2 physisorption, He-TPD/MS, NH3-TPD/MS, TEM, CO chemisorption, H2-TPR, contact angle and optical/fluorescent microscopy. It was found that an increase of surface oxygen groups allows for the formation of amphiphilic particles. The amphiphilic 10%Ni/CNTox particles were homogeneous dispersed at the water-oil interface of the emulsion droplets thus enhancing the catalytic activity in furfural conversion.

Protein Recovery from Rapeseed Press Cake: Varietal and Processing Condition Effects on Yield, Emulsifying Capacity and Antioxidant Activity of the Protein Rich Extract.

Protein was recovered from five varieties and a mixed blend of cold-pressed rapeseed press cake by leaching and precipitation in a water-based process, and the protein recovery yield varied from 26–41% depending on variety. Exposure for heat during protein recovery severely reduced the rapeseed proteins’ ability to stabilize the oil–water interface of emulsion droplets. Protein extract from Lyside had the best emulsifying properties of the varieties investigated. Oxidation rate was assessed by the Thiobarbituric Acid Reactive Substances (TBARS) method and rapeseed protein extracts from Epure and Festivo had higher capacity to delay oxidation compared with soy lecithin. There are possibilities to broaden the use of rapeseed whereby recovered rapeseed protein can be used as a plant-based multifunctional ingredient with emulsifying capacity and which has a delaying effect on oxidation.

Dynamic Hybrid Colloidosomes via Electrostatic Interactions for pH-Balanced Low Premature Leakage and Ultrafast Cargo Release.

A trade-off between minimized premature leakage and rapid cargo release on demand is an intractable obstacle faced by smart delivery systems that restrains them from lab to market. To address this dilemma, dynamic hybrid colloidosomes relying on strong yet reversible electrostatic interactions are developed, simply through one-pot cooperative self-assembly of silica nanoparticles and fluorescent carbon dots at the interface of emulsion droplets. Specifically, pH-driven charge reversal of zwitterionic carbon dots leads to immediate electrostatic conversion between the two building blocks from attraction to repulsion. This makes robust locking and instantaneous breakdown of the colloidosomes subtly balanced, thus enabling low off-state leakage (10.5% over 7 days) while ultrafast on-state release (>90% within 5 min) upon an acidic stimulus. We envision that such biocompatible, traceable, and smart colloidosomes will offer unique opportunities for broad applications as on-demand release is desired.

Liquid reconfigurable ferromagnetic materials

Magnetic Materials Ferromagnetic materials show a permanent magnetic dipole, whereas superparamagnetic ones only show magnetic properties under an applied field. Some materials, like ferrofluids, show liquid-like behavior but do not retain their magnetization in the absence of an applied field. Liu et al. show remnant magnetization of otherwise superparamagnetic magnetite nanoparticles at an oil-water interface of emulsion droplets (see the Perspective by Dreyfus). The permanent magnetization could be controlled by coupling and uncoupling the magnetization of individual nanoparticles, making it possible to “write and erase” shapes of the droplets or to elongate them into cylinders. Science , this issue p. [264][1]; see also p. [219][2] [1]: /lookup/doi/10.1126/science.aaw8719 [2]: /lookup/doi/10.1126/science.aax8979

Reconfigurable ferromagnetic liquid droplets.

Solid ferromagnetic materials are rigid in shape and cannot be reconfigured. Ferrofluids, although reconfigurable, are paramagnetic at room temperature and lose their magnetization when the applied magnetic field is removed. Here, we show a reversible paramagnetic-to-ferromagnetic transformation of ferrofluid droplets by the jamming of a monolayer of magnetic nanoparticles assembled at the water-oil interface. These ferromagnetic liquid droplets exhibit a finite coercivity and remanent magnetization. They can be easily reconfigured into different shapes while preserving the magnetic properties of solid ferromagnets with classic north-south dipole interactions. Their translational and rotational motions can be actuated remotely and precisely by an external magnetic field, inspiring studies on active matter, energy-dissipative assemblies, and programmable liquid constructs.

Ultrasensitive Electrochemical Immunoassay Based on Cargo Release from Nanosized PbS Colloidosomes.

Colloidosome is a novel nanostructure composed of millions of colloid particles. In this work, nanosized PbS colloidosomes were initially prepared and applied as nanoprobes for an ultrasensitive immunoassay. The colloidosomes were simply prepared in mild conditions by assembling the elementary approximately 8 nm PbS nanoparticles at the water-in-oil interface of emulsion droplets. To enhance the rigidity and biocompatibility of the colloidosomes, interfacial polymer was introduced by utilizing self-polymerization of dopamine. By treating with dilute nitric acid, a bursting release of lead ions from the colloidosomes occurred and the lead ions can be detected easily by anodic stripping voltammetry. In this way, a colloidosome-based electrochemical immunoassay was developed by using the nanosized PbS colloidosomes as electroactive labels. The proposed method featured a linear calibration range from 10 fg·mL-1 to 100 ng·mL-1 with a low detection limit of 3.4 fg·mL-1 for the detection of human epididymis protein 4. This work introduced a new member for the family of colloidosomes and offered a novel perspective for the rational implementation of various colloidosomes for novel low-abundance cancer biomarkers analysis.

Influence of structural properties of emulsifiers on citral degradation in model emulsions.

The storage stability of compounds encapsulated in emulsions is strongly influenced by the properties of the droplet interfacial membrane. To evaluate the effect of emulsion droplet interface thickness on the degradation of citral, emulsions were prepared using polyoxyethylene alkyl ether-type emulsifiers with hydrophilic and hydrophobic groups of various sizes. Acid cyclization of citral at pH 3 promoted faster degradation than that at pH 7. Ferrous irons accelerated citral degradation in the emulsions at pH 3 but not at pH 7, because they decomposed the products of the acid-catalyzed cyclization of citral through redox reactions rather than direct degradation. Water-soluble radicals dramatically increased the rate of citral degradation, irrespective of pH. Notably, at low pH, the rate of citral degradation by ferrous irons was higher than that by radicals. These findings suggest that the thickness and density of emulsion droplet surfaces are not important factors for inhibiting citral degradation in emulsions.

Lipid hydroperoxide decomposition in model emulsions stabilized with emulsifiers having various sizes of hydrophilic heads.

The vulnerability of oils in emulsions to oxidation depends on the structural and physicochemical properties of oil droplet interface. To evaluate the implications of the interfacial characteristics of emulsion droplets on lipid oxidation, particularly lipid hydroperoxide decomposition, emulsions were prepared using emulsifiers with various lengths of polar groups because the length of hydrophilic heads of emulsifiers could be an important factor in determining the thickness of the droplet surface. The decomposition rate constants of cumene hydroperoxide in emulsions showed that the cumene hydroperoxide in emulsions having a thick emulsion droplet interface was decomposed faster than in emulsions having a loosen one. Our findings also showed that the denseness of the droplet interface affected cumene hydroperoxide decomposition in emulsions. Conclusively, this study suggested that the interfacial thickness and denseness of the emulsion droplets influence oxidative stability of emulsions.

Effects of interfacial composition on the stability of emulsion and encapsulated bioactives after thermal and high pressure processing

The composition of the oil-in-water (O/W) interface of emulsion droplets plays a critical role in their physicochemical stability as well as that of encapsulated bioactives during processing. This study evaluates three emulsifiers, whey protein isolate (WPI), Tween 20 and Ludox HS-30 silica (Pickering), which stabilize O/W emulsions containing either all-trans retinol or curcumin, and determines the physicochemical stability of the emulsion and encapsulated bioactives post processing. In addition to thermal methods, this study utilizes high hydrostatic pressure processing (HPP) (600 MPa for 5 min). Physical stability of emulsions was characterized using particle size and ζ-potential measurements. Recovery of bioactives was determined using UV-vis spectrophotometry. WPI emulsions maintained a constant particle size across all processing parameters compared to other formulations. Tween 20 provided the most protective effect to encapsulated bioactives during processing. HPP had no significant effect on the physicochemical stability for any emulsion and had minimum effect on bioactive recovery.