Emulsion Interface Research Articles

Amphiphilic Self-Assembly of Nanocrystals at Emulsion Interface Renders Fast and Scalable Quasi-Nanosheet Formation.

Scalable assembly of nanocrystals (NCs) into two-dimensional (2D) nanosheets has aroused great interest, yet it remains under-explored. This is because current 2D assembly methods rely mainly on the use of solid- or liquid-air interfaces, which are inherently difficult for upscaling and thus lack practicability. Here, with a microemulsion-based amphiphilic assembly technique, we achieve a fast and scalable preparation of free-standing nanosheets comprising few-layer, tightly packed NCs, namely, quasi-nanosheets (quasi-NSs). Acetic acid, acting as both solvent and surface-treatment agent, is used to render the initially hydrophobic NCs amphiphilic, while simultaneously inducing the interfacial instability right after the assembly of NCs at the emulsion interface to afford quasi-NSs. This amphiphilic assembly method is applicable to a variety of NCs, and multicomponent quasi-NSs are also attainable upon coassembly of different types of NCs. In addition, the structural advantages of quasi-NSs in catalysis are showcased by using NiFe2O4 quasi-NSs as electrocatalysts for the oxygen evolution reaction. This work opens a new route for the scalable construction of 2D NC sheets with designated components and functions.

Engineered reversible adhesive biofoams for accelerated dermal wound healing: Intriguing multi-covalent phenylboronic acid/cis-diol interaction

Development of wound dressings that not only have multiple advantages including good biocompatibility, barrier properties, adhesive properties, but also exhibit anti-bacterial, anti-infection, and promote cell adhesion, accelerated wound healing process, remains challenging in the skin tissue engineering. In this work, a noninvasive adhesive biofoam with interconnectivity structure and antibacterial property was first-time designed through solid surfactant stabilized high internal phase emulsion (HIPE) template, where bacteriostatic Zn-CuO@GO nanosheets dynamic assemble with 4-vinylphenylboronic acid at the oil/water interface as cooperative emulsifier. Taking advantage of the cooperative assembly of the PBA/Zn-CuO@GO, the biofoams display microfibrousity and interconnectivity to facilitate material-cellular interaction as well nutrient exchange, and can effectively inhibit the growth of E. coli and S. aureus. Meanwhile, phenylboronic acid functional groups not only endow biofoam reversible adhesive property though dynamic phenylboronic acid/cis-diol interaction, but also facilitate the rearrangement of Zn-CuO@GO nanosheets in more uniform way at emulsion interface. Taken together, the biofoams can strongly adhere to the wound bed reducing the risk of infection and accelerate earlier tissue regeneration, which exhibit great potential in bioengineering application.

Pickering Emulsions Stabilized by Lignin/Chitosan Nanoparticles for Biphasic Enzyme Catalysis.

In this study, we construct a green and high-performance platform using Pickering emulsions for biphasic catalysis. The oil-in-water Pickering emulsions stabilized by the lignin/chitosan nanoparticles (Lig/Chi NPs) have great stability and alkali resistance, showing pH-responsive reversible emulsification and demulsification which can be recycled at least three times. The Pickering emulsion also has fluorescence and wide availability to different oil-to-water volume ratios, types of oil, storage times, temperatures, and ion concentrations. When this system is applied to the lipase-catalyzed reaction for the hydrolysis of p-nitrophenol palmitate, it will provide stable and large oil-water reaction interface areas, and the negatively charged lipase will enrich at the emulsion interface by electrostatic adsorption of the positively charged Lig/Chi NPs to achieve immobilization (lipase-Lig/Chi NPs). The reaction conversion rate can reach nearly 100% in 30 min, which is nearly three times higher than that of the conventional two-phase system. Moreover, the lipases in Pickering emulsion stabilized by Lig/Chi NPs exhibit great recyclability because of the protection of Lig/Chi NPs.

Enhancement of dewatering from oily sludge by addition of alcohols as cosolvents with dimethyl ether

The oil industry produces a large amount of oily sludge (OS) annually, posing a severe environmental hazard. Conventional OS treatments are limited in industrial applications owing to the high moisture content of OS. This study investigates the extraction of water from OS using alcohols as cosolvents with dimethyl ether (DME). Furthermore, the effects of the type and dosage of the cosolvent on the dehydration rate and chemical profile of the solid product were evaluated. Results revealed that the addition of alcohols significantly enhanced dewatering from OS using DME; the maximum dewatering rate exceeded 95%, which was equivalent to saving more than half the amount of DME. The cosolvents facilitated the dissolution of resins and certain asphaltenes on the water-in-oil (W/O) emulsion interface layer, breaking the structure of the W/O emulsion and converting the mixture into an easily separated solid–liquid two-phase substance. This could reduce the amount of DME needed during the dewatering process. The thermal properties of the solid products did not change significantly, which is advantageous for their subsequent processing and utilization.

Solid lipid nanoparticles and nanostructured lipid carriers of dual functionality at emulsion interfaces. Part I: Pickering stabilisation functionality

Solid lipid nanoparticles and nanostructured lipid carriers are two types of lipid nanoparticulate systems, that have been primarily studied for their capability to function as active carriers, and only more recently utilised in Pickering emulsion stabilisation. Unveiling the factors that impact upon the lipid particle characteristics related to their Pickering functionality could enable the development of a liquid formulation with tailored microstructure and potentially the capacity to display a two-fold performance. In part I, this work investigates how certain formulation characteristics, namely solid-to-liquid lipid mass ratio and presence of unadsorbed surfactant in the aqueous carrier phase, affect the structural properties of the lipid particles, and in turn how these influence their Pickering stabilisation capacity. The effect of the formulation parameters was assessed in terms of the wettability and physicochemical properties of the lipid particles, including particle size, crystallinity and interfacial behaviour. Lipid particles fabricated with higher liquid lipid content (70% w/w) were shown to be more hydrophilic and have lower surfactant decoration at their surface compared to particles containing lower or no liquid lipid in their crystalline matrix. The emulsion stabilisation ability through a Pickering mechanism was confirmed for all types of lipid particles using polarised microscopy. Increasing liquid lipid content and removal of excess surfactant did not compromise the particle stabilisation capacity, though emulsion droplets of larger sizes were initially acquired in the latter case. The particle-stabilised emulsions maintained their physical integrity, with particles retaining close association with the emulsion interface over a storage period of 12 weeks.

The Influence of Newly Synthesized Demulsifiers on the Interfacial Rheological Properties of a Naturally Occurring Water/Oil Emulsion.

This research aimed to synthesize new polymeric nonionic demulsifiers (DA, DB, and DC) to break 50% of naturally occurring water/oil emulsions. The prepared demulsifiers were synthesized in only two stages utilizing simple techniques. 1H and 13CNMR, MS, and FTIR spectroscopies were performed to validate the chemical composition of the synthesized demulsifiers. The relative solubility number (RSN) and partition coefficient (Kp) were determined for the three demulsifiers. The interfacial tension (IFT) and dehydration ratios of DA, DB, DC, and their triblock copolymers were investigated. Also, interfacial rheological properties for the three demulsifiers were measured. The findings demonstrate that DB possesses a higher RSN value than DA and DC owing to its hydrophilicity. DC exhibited the lowest IFT value compared to DA, DB, and their corresponding triblock copolymers. DB and DC are more effective in demulsifying than DA and triblock copolymers. DC achieved a 100% dehydration ratio at a low dosage of 75 ppm after 120 min. DC’s remarkable performance can be attributed to its aromatic core, molecular weight, and high interfacial activity. According to the rheological data, a higher dehydrating ratio is attained when the demulsifier has a great capacity to lower the viscoelasticity of the W/O emulsion interface. The maximum decrease in G′ and G″ values was attained by DC. The mechanism of DC’s demulsifying interaction on a naturally occurring W/O emulsion was elucidated.

Controlling adsorption density of polymer-stabilised metal nanoparticles at the oil–water interface

Emulsion droplets offer an alternative to solid supports as templates for the deposition of metallic nanoparticles. An emulsion interface provides the opportunity to exploit both sides of the nanoparticles and to utilise the liquid core as a microreactor in addition to forming a scaffold for encapsulation. However, despite the extensive literature studying a very broad range of factors influencing the characteristics of particle-stabilised (Pickering) emulsions, most reports focus on particles of diameters >100 nm and a very small proportions consider particles of diameters <10 nm. For catalytic purposes of course, the latter species are of utmost interest. Here, we report the synthesis of poly(vinyl pyrrolidone) (PVP) stabilised platinum nanoparticles, where the platinum core ranges between 3 and 5 nm in diameter and their subsequent use as emulsifiers for the oil–water interface where they form a densely packed layer. The nanoparticle density at the interface is quantified by both measuring the remaining concentration of nanoparticles in the aqueous phase after adsorption and also directly at the oil–water interface via cryo-TEM. The effect of electrolyte concentration and of addition of excess PVP in the bulk aqueous nanoparticle dispersion prior to emulsification on the resulting nanoparticle density at the oil–water interface is also determined.

Investigation of the Mechanism of SiO2 Particle and Capsule Formation at the Oil-Water Interface of Dye-Stabilized Emulsions.

In a previous contribution we described the formation of silica nanostructures in dye-stabilized nanoemulsions from tetraethyl orthosilicate droplets in water. Depending on the type of dye, either capsules (crystal violet, CV) or nanoparticles (congo red, CR) are formed. The thorough study of the sol-gel process uses a combination of time- and/or temperature-resolved small-angle X-ray scattering, transmission electron microscopy, and 1H NMR spectroscopy to elucidate the detailed kinetics and mechanism of structure formation. In both cases, small nuclei of 1.5-2 nm are formed, followed by either a fast cluster-cluster (CV) or a much slower monomer-cluster aggregation (CR). The former leads to a cross-linked network and finally to patchy capsules, while the latter leads to individual nanoparticles (SNPs). From an Avrami plot it can be deduced that the SNPs are formed by an interface-controlled one-dimensional growth process. The mechanisms are based on the different local environments at the oil-water interface, which is either slightly acidic (CV) or fairly basic (CR). The kinetics differ by a factor between 3 and 20 and are presumably caused by the different mobility of the catalyzing species H+ or OH-.

Capturing the Evolution of the Oil-in-Water Emulsion Interface by Correlative Imaging

Capturing the Evolution of the Oil-in-Water Emulsion Interface by Correlative Imaging

In-silico zein/tannic acid colloidal nanoparticles and their activity at oil and water interface of Pickering emulsion using molecular dynamics simulation

• Colloidal nanoparticle of α-zein/tannic acid prepared by antisolvent precipitation. • Acceleration distributed linoleic acid molecules of oil droplet. • Oil phase of biphasic system tended to the surface of colloidal nanoparticles. • The van der Waals interactions occurred between nanoparticles and oil phase. The computational method was used to explain the activity of zein-based colloidal nanoparticles at interface between water and oil phases. The α-zein/tannic acid colloidal nanoparticles (ZTPs) were made using three steps including dissolving α-zein (Z19) in aqueous ethanol (ZE), α-zein/tannic acid interactions and antisolvent precipitation. The ZTP showed decreased R g and SASA as expected as well as hydrogen bonds between zein and tannic acids. Moreover, the acceleration, to simulate ultrasonication, indicated the breaking up and recoalescence after applying on the oil droplet. Subsequently, after the combination of ZTPs and acceleration at interface between oil and water phases, results confirmed the capability of the ZTPs to surround the oil phase, the increased density of oil molecules around the hydrophobic surface of ZTPs and more van der Waals interactions. These findings explain the activity of ZTPs at the interface between oil and water from molecular view.

Raspberry-Shaped Microgels Assembled at the Oil–Water Interface by Heterocoagulation of Complementary Microgels

Raspberry-shaped particles have attracted increasing interest due to their tunable surface morphologies and physicochemical properties. A variety of covalent and noncovalent strategies have been developed for the fabrication of raspberry-shaped particles. However, most of these strategies are complex or require precise control of solution conditions. In this work, we develop a direct approach for the fabrication of noncovalent raspberry-shaped microgels. Our strategy works through the electrostatically driven heterocoagulation of binary microgels with complementary functional groups at the oil-water interface. By introducing hexanoic acid (HA) into the oil phase, stable inverse water-in-oil (w/o) Pickering emulsions could be stabilized solely by HA-swollen microgels or self-assembled raspberry-shaped microgels. Furthermore, the formation mechanism and the interfacial properties of interfaces laden with raspberry-shaped microgels were investigated. The results indicate that HA can effectively improve the hydrophobicity and interfacial activity of microgels. In addition, raspberry-shaped microgels achieve high coverage on the droplet surface, resulting in the elastic interface and excellent stability of emulsions. We envision that these results will not only fill a knowledge gap in the field of soft matter interfacial self-assembly, but also will shed light on the rational design of raspberry-shaped soft colloids and the on-demand control of interfacial rheology. In addition, we expect that our results will contribute to wider applications of microgel-stabilized emulsions, including cascade catalysis, microreactor, and in vivo drug delivery.

Ultrahigh efficient emulsification with drag-reducing liquid gating interfacial behavior

Emulsification is a crucial technique for mixing immiscible liquids into droplets in numerous areas ranging from food to medicine to chemical synthesis. Commercial emulsification methods are promising for high production, but suffer from high energy input. Here, we report a very simple and scalable emulsification method that employs the drag-reducing liquid gating structure to create a smooth liquid-liquid interface for the reduction of resistance and tunable generation of droplets with good uniformity. Theoretical modeling and experimental results demonstrate that our method exhibits ultrahigh efficiency, which can reach up to more than 4 orders of magnitude greater energy-saving compared to commercial methods. For temperature-sensitive biological components, such as enzymes, proteins, and bacteria, it can offer a comfortable environment to avoid exposure to high temperatures during emulsifying, and the interface also enables the suppression of fouling. This unique drag-reducing liquid gating interfacial emulsification mechanism promotes the efficiency of droplet generation and provides fresh insight into the innovation of emulsifications that can be applied in many fields, including the food industry, the daily chemical industry, biomedicine, material fabrication, the petrochemical industry, and beyond.

Tannic acid enhanced the emulsion stability, rheology and interface characteristics of Clanis Bilineata Tingtauica Mell protein stabilised oil‐in‐water emulsion

SummaryClanis Bilineata Tingtauica Mell Protein (CBTMP) was one of the new natural insect protein resources. However, due to its strong surface hydrophobicity and poor emulsion stability, its application has greatly been limited. In this study, Pickering emulsions were prepared by CBTMP–Tannic acid (CBTMP–TA) particles and soybean oil (φ = 50%). The presence of TA significantly increased the zeta‐potential (from −23.5 ± 0.73 to −29.23 ± 0.58 mV) and three‐phase contact angle (from 129.9 ± 4.53° to 87.27 ± 3.20°) of complex, especially the concentration of TA was 0.4 mm. Besides, the stability of emulsions was significantly improved according to the results of the droplet size and static multiple light scattering. Furthermore, rheological properties including viscosity, thixotropy and creep recovery were significantly enhanced, which indicated the formation of a more stable network structure. Interfacial behaviour (Interfacial tension, interfacial film viscoelasticity and diffusion rate) of emulsions was significantly changed, forming a more stable interfacial layer as TA content increased. The CBTMP–TA complex was adsorbed at the interface and the adsorption rate was also mainly affected by the content of TA. The study indicated CBTMP–TA compositions to enhance stability, rheological behaviours and interfacial characteristics, and demonstrated the potential applications of insect protein resources in food emulsion systems.

Effect of solid dispersants on the formation of hydrates in W/O emulsion systems: Micron and nanoscale

Aiming at the problem of natural gas hydrate blockage in oil and gas pipelines. The key to rationally inhibiting the formation of hydrates in pipelines is to find the factors that lead to the rapid coalescence of hydrates. We studied the effect of 0.2 wt% graphite particles and Fe2O3 particles (20 nm and 1 μm) as solid dispersants on hydrate formation in a W/O emulsion system at 275.15 K and 7 MPa. The results showed that 0.2 wt% solid dispersants could be adsorbed on the interface of Pickering emulsion to inhibit the binding of particles. In addition, solid dispersants improve the mass and heat transfer capacity of the reaction system and increase the final gas consumption. The 20 nm Fe2O3 particle reaction system had the largest gas consumption and the highest reaction rate. A three-dimensional network mechanism was proposed to explain the rapid formation of hydrate particles from the perspective of kinetics. Our experimental results and suggested mechanisms provided a reference for the promotion or inhibition of hydrate growth.

Ethanol-tolerant pickering emulsion stabilized by gliadin nanoparticles

In this paper, ethanol-tolerant Pickering emulsion was prepared using gliadin nanoparticles (NPs) based on pH adjustment coupled heat treatment. The effects of gliadin NPs concentration on ethanol-tolerant Pickering emulsions in terms of emulsion size, microstructure, and rheology were investigated. The results indicated that gliadin NPs exhibited an elliptical appearance. At pH 7, the particle size was 600.04 ± 4.80 nm, and the polydispersity coefficient was 0.18 ± 0.29. Fluorescence spectra showed that this method destroyed the tertiary structure of the protein and initiated the self-assembly of gliadin. With the increase of particle concentration, the size of the Pickering emulsion decreased, and the emulsion gradually became gelatinized. The increase of particle concentration made the oil-water interface in emulsion more robust. This study showed that the preparation of gliadin NPs based on pH regulation coupled heat treatment could stabilized the emulsion in the presence of ethanol. The structural and functional properties of Pickering emulsion could be regulated by the concentration of particle stabilizers, thus providing a theoretical basis for constructing structured and functionalized Pickering emulsions.

Self-Assembly of Polystyrene-b-poly(2-vinylpyridine)/Chloroauric Acid at the Liquid/Liquid Interface.

The self-assembly of polystyrene-block-poly(2-vinylpyridine) at the liquid/liquid interface has been systematically investigated to develop a series of primary morphologies of the aggregates. The block copolymers self-assembled into large areas of nanodot arrays, parallel nanostrands, layered films, parallel nanobelts, honeycomb monolayers, and foams by reacting with chloroauric acid, depending on the molecular structure of the block copolymers and the amount of chloroauric acid. The formation of the first four ordered structures resulted from interfacial adsorption and self-assembly, and nucleation and epitaxial growth. The latter two structures were attributed to the water hole templating effect and spontaneous interfacial emulsification, respectively. This work provides insight into the self-assembly behavior of block copolymers at the interface and provides a facile approach for fabricating functional structures.

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.

Crystal substrate inhibition during microbial transformation of phytosterols in Pickering emulsions.

Water-oil interface of bacterial cell-stabilized Pickering emulsions is an exceptional habitat for microbial assimilation of both hydrophobic nutrients solubilized in oil phase and hydrophilic ones solubilized in water phase. Crystal substrate inhibition, i.e., decreasing phytosterol degradation with the increase loading of crystal phytosterols, is always observed during microbial transformation of phytosterols into steroid synthons in Mycolicibacterium sp (China Center of Industrial Culture Collection, CICC 21,097) cell-stabilized Pickering emulsions. In the present work, we confirmed that crystal substrate inhibition was attributed to the interaction between M. neoaurum and phytosterol crystals that led to the detachment of bacterial cells from the oil-water interfaces in bacterial cell-stabilized Pickering emulsions. Under the selected operation condition (25ml BEHP per 40ml water, 60g/L glucose, 25g/L phytosterols), the product androst-4-ene-3, 17-dione (AD) and androsta-1, 4-dien-3, 17-dione (ADD) concentration increased linearly with the progress of microbial transformation and reached almost 6g/L at the 11th day. This is a paradigm for microbial transformation of crystal substrates as well as in the presence of other surface active additives (such as chitosan and nonionic surfactants) in bacterial cell-stabilized Pickering emulsions. KEY POINTS: • Microbial transformation of crystal phytosterols in Pickering emulsions • Crystal substrate inhibition occurring during microbial transformation • Interaction between phytosterol crystals and bacterial cells leading to demulsification.

Protease-induced soy protein isolate (SPI) characteristics and structure evolution on the oil–water interface of emulsion

The evolution of the microstructures and properties of soy protein isolate (SPI) at the oil–water interface under the induction of protease within 0.5 h and 2.0 h were analyzed by macroscopic characterization and structural analysis. There were significant differences in average particle size, zeta potential, microstructure, FT-IR, Raman and endogenous fluorescence of emulsion samples produced by different treatment times. Visual comparison showed the relatively uniform aggregation and distribution of SPI on the interface when induced for 1.0 h and characterized by zeta potential and rheology. Moreover, in FT-IR, Raman and intrinsic fluorescence spectra, it was found that with the induction of 0.5–2.0 h, the content of the β-turn structure was highest at 1.0 h, and strong fluorescence quenching occurred, which indicated that SPI at the interface was hydrolyzed into small peptides, and aggregated at 1.0 h and then hydrolyzed. What is more, no significant change in rheological properties was observed after induction for 1.5 h and 2.0 h. The results indicated that there existed –CO– and –NH binding due to electrostatic interaction and hydrogen bonding at 1.0 h, which caused the recombination of SPI molecules at the interface. The preparation process of SPI emulsion samples and the structural changes of SPI molecules in the oil-water interface under different protease induction times were investigated. • Evolution of structure and properties of SPI at oil–water interface protease treated. • SPI at the oil–water interface undergo aggregation and recombination after 1.0 h. • Longer treatment time reduces the viscosity and viscoelasticity of SPI emulsion. • Electrostatic interaction and hydrogen cause the aggregation and recombination of SPI.

Hierarchical Colloidosomes and Superlattices via Confined Assembly of Polymer-Tethered Inorganic Nanoparticles

Self-assembly of polymer-tethered metal nanoparticle (NP) building blocks is studied via an emulsion interface self-assembly strategy. The results show that the hollow colloidosomes with a highly ordered hexagonal arrangement of metal NP building blocks are obtained. The interparticle distance between the adjacent metal NPs within the hollow colloidosomes can be effectively tuned by adjusting the molecular weight of the polymeric ligands. Interestingly, with an increase in the volume fraction of the internal hexadecane phase, the particular sheet-like superlattices can be formed. Moreover, the prepared colloidosomes can serve as an excellent substrate for the surface-enhanced Raman scattering and have potential application in photothermal therapy. We believe that this study can provide a promising way to fabricate hierarchical ordered metal superstructures, which have potential applications in photothermal therapy, chemical sensors, and biological optical-imaging.