Emulsion Interface Research Articles

Pickering emulsions immobilized within hydrogel matrix with enhanced resistance against harsh processing conditions and sequential digestion

Protein particles stabilized Pickering emulsions are unstable under harsh processing conditions and vulnerable to premature lipid phase release during gastric digestion. The objective of this study is to encapsulate kafirin nanoparticles-stabilized Pickering emulsions (KPE) within hydrogel matrix to develop orally administrated Pickering emulsions with enhanced storage and sequential release properties. By premixing KPE and sodium alginate with different volume ratios, emulsion hydrogels (EGs) with various emulsion fractions were immobilized within the calcium ions crosslinked sodium alginate hydrogel matrix thereafter. Ultra small-angle x-ray scattering (USAXS)/small-angle x-ray scattering (SAXS) analyses suggested that encapsulation of KPE resulted in shrinkage in hydrogel network mesh size, and the emulsion interface evolved from smooth to course one as volume ratio of sodium alginate to KPE increased. When incubated under alkaline (i.e., pH = 8.5) or high-temperature (i.e., 60 °C) conditions which were previously reported to cause severe structural collapse for KPE, the coalescence and lipid phase release in EGs were largely inhibited. EGs were also found to be less subjective to stimulated gastric digestion, while the collapse of EGs and thus the release of lipid phase took place in simulated intestinal fluid. The volume fraction of alginate in EGs did not affect the ultimate free fatty acid (FFA) release extent, but it had a negative correlation with the bioaccessibility of lipophilic nutraceutical. This study highlights the potential of designing hydrogel carrier for the oral administration of Pickering emulsion with ease of preparation, improved processing stability and controlled digestion profile.

Isolating Reactions at the Picoliter Scale: Parallel Control of Reaction Kinetics at the Liquid–Liquid Interface

AbstractMiniaturized liquid–liquid interfacial reactors offer enhanced surface area and rapid confinement of compounds of opposite solubility, yet they are unable to provide in situ reaction monitoring at a molecular level at the interface. A picoreactor operative at the liquid–liquid interface is described, comprising plasmonic colloidosomes containing Ag octahedra strategically assembled at the water‐in‐decane emulsion interface. The plasmonic colloidosomes isolate ultrasmall amounts of solutions (<200 pL), allowing parallel monitoring of multiple reactions simultaneously. Using the surface‐enhanced Raman spectroscopy (SERS) technique, in situ monitoring of the interfacial protonation of dimethyl yellow (p‐dimethylaminoazobenzene (DY)) is performed, revealing an apparent rate constant of 0.09 min−1 for the first‐order reaction. The presence of isomeric products with similar physical properties is resolved, which would otherwise be indiscernible by other analytical methods.

Isolating Reactions at the Picoliter Scale: Parallel Control of Reaction Kinetics at the Liquid-Liquid Interface.

Miniaturized liquid-liquid interfacial reactors offer enhanced surface area and rapid confinement of compounds of opposite solubility, yet they are unable to provide in situ reaction monitoring at a molecular level at the interface. A picoreactor operative at the liquid-liquid interface is described, comprising plasmonic colloidosomes containing Ag octahedra strategically assembled at the water-in-decane emulsion interface. The plasmonic colloidosomes isolate ultrasmall amounts of solutions (<200 pL), allowing parallel monitoring of multiple reactions simultaneously. Using the surface-enhanced Raman spectroscopy (SERS) technique, in situ monitoring of the interfacial protonation of dimethyl yellow (p-dimethylaminoazobenzene (DY)) is performed, revealing an apparent rate constant of 0.09 min(-1) for the first-order reaction. The presence of isomeric products with similar physical properties is resolved, which would otherwise be indiscernible by other analytical methods.

Synthesis of surface-active N-heterocyclic carbene ligand and its Pd-catalyzed aqueous Mizoroki–Heck reaction

A surface-active N-heterocyclic carbene (NHC) ligand with an octaethylene glycol monomethyl ether and n-dodecyl chain was synthesized. The NHC and its Pd complex behaved as a general surfactant, and hydrophobic oily substrates such as iodobenzene and styrene were emulsified in water, resulting in the acceleration of the Mizoroki–Heck reaction under heterogeneous conditions. Our results demonstrated that the reactive emulsion interface rendered by the surface-active NHC is effective for the aqueous Mizoroki–Heck reaction.

Polyphenol Oxidase Containing Sidestreams as Emulsifiers of Rumen Bypass Linseed Oil Emulsions: Interfacial Characterization and Efficacy of Protection against in Vitro Ruminal Biohydrogenation.

The low transfer in ruminants of dietary polyunsaturated fatty acids to the milk or peripheral tissues is largely due to ruminal biohydrogenation. Lipids emulsified by a polyphenol oxidase (PPO) rich protein extract of red clover were shown before to be protected against this breakdown after cross-linking with 4-methylcatechol. Protein extracts of 13 other vegetal resources were tested. Surprisingly, the effectiveness to protect emulsified lipids against in vitro ruminal biohydrogenation largely depended on the origin of the extract and its protein concentration but was not related to PPO activity. Moreover, PPO isoforms in vegetal sources, effectively protecting emulsified lipids, were diverse and their presence at the emulsion interface did not seem essential. Potato tuber peels were identified as an interesting biological source of emulsifying proteins and PPO, particularly since protein extracts of industrial potato sidestreams proved to be suitable for the current application.

Fabrication of Hydrophilic and Hydrophobic Sites on Polypropylene Nonwoven for Oil Spill Cleanup: Two Dilemmas Affecting Oil Sorption.

This article mainly deals with the following dilemmas, which affect oil sorption and sorbent preparation: (1) hydrophobization could facilitate oil sorption but has adverse impacts on emulsion sorption; (2) micropores of conventional oil sorbent do not exhibit effective emulsion sorption. To solve the above contradictions, hydrophilic and hydrophobic sites were fabricated onto polypropylene (PP) nonwoven through electron beam radiation and subsequent ring-opening reaction. Further, a similar structure without a hydrophilic site was constructed as comparison to verify the dilemmas. An oil sorption and emulsion adsorption experiment revealed that the PP nonwoven with specific hydrophilic and hydrophobic sites is more suitable for oil cleanup. The hydrophobic site preserved its hydrophobicity and sorption capacity, and the hydrophilic site on PP surface effectively increased the affinity between the hydrophilic interface of emulsion and sorbent. The overlapped and intertwined structures could provide spaces large enough to accommodate oil and emulsion. In addition, the oil and emulsion sorption behaviors were systematically analyzed. The PP nonwoven fabricated in this study may find practical application in the cleanup of oil spills and the removal of organic pollutants from water surfaces.

Influence of interfacial and bulk properties of cellulose ethers on lipolysis of oil-in-water emulsions

Cellulose ethers are usually used as secondary emulsifiers. Different types of commercial hydroxypropylmethylcellulose (HPMC) have been used here as the main emulsifier of oil-in-water emulsions to probe their impact on the lipid digestibility under simulated intestinal conditions. The droplet size distribution and ζ-potential of the emulsions subjected to in-vitro lipolysis have been compared with that of control samples (non-digested). The lipolysis has been quantified over time by means of the pH-stat method. The displacement of HPMC from the oil–water interface by bile salts has been assessed by interfacial tension technique. Results show that HPMC delays the lipid digestion of emulsions regardless of the Mw and methoxyl content. The destabilisation of emulsions under intestinal conditions as well as the resistance of HPMC to be displaced from the emulsion interface by bile salts may contribute to this feature. This provides new insights into the mechanisms whereby dietary fibre reduces fat absorption.

Real-time measurements to characterize dynamics of emulsion interface during simulated intestinal digestion

Efficient delivery of bioactives remains a critical challenge due to their limited bioavailability and solubility. While many encapsulation systems are designed to modulate the digestion and release of bioactives within the human gastrointestinal tract, there is limited understanding of how engineered structures influence the delivery of bioactives. The objective of this study was to develop a real-time quantitative method to measure structural changes in emulsion interface during simulated intestinal digestion and to correlate these changes with the release of free fatty acids (FFAs). Fluorescence resonant energy transfer (FRET) was used for rapid in-situ measurement of the structural changes in emulsion interface during simulated intestinal digestion. By using FRET, changes in the intermolecular spacing between the two different fluorescent probes labeled emulsifier were characterized. Changes in FRET measurements were compared with the release of FFAs. The results showed that bile salts and pancreatic lipase interacted immediately with the emulsion droplets and disrupted the emulsion interface as evidenced by reduction in FRET efficacy compared to the control. Similarly, a significant amount of FFAs was released during digestion. Moreover, addition of a second layer of polymers at emulsion interface decreased the extent of interface disruption by bile salts and pancreatic lipase and impacted the amount or rate of FFA release during digestion. These results were consistent with the lower donor/acceptor ratio of the labeled probes from the FRET result. Overall, this study provides a novel approach to analyze the dynamics of emulsion interface during digestion and their relationship with the release of FFAs.

Multi-responsive hybrid Janus nanoparticles: Surface functionalization through solvent physisorption

In this work, we present a simple methodology to produce multi-responsive Janus nanoparticles using a Pickering emulsion-based approach. In order to use these nanoparticles (NPs) as emulsion stabilizers, tetrahydrofuran was physisorbed on the surface of freshly synthesized Fe3O4@SiO2 NPs, which reduced their inherent hydrophilic character and permitted to create a close packed arrangement of particles at the emulsion interface. This situation allowed selective functionalization of the surface of the nanoparticles exposed to the water phase with a vinyl derivate molecule, which permitted to initiate the sequential polymerization of pNIPAM and poly(vinylimidazole). Thus, we obtained Janus nanoparticles that responded to changes in the temperature and the pH of the media as well as to external magnetic fields. The presented method does not require the surface modification of the original nanoparticles with surfactants or the use of fused silica and provides an easy way to create Janus particles in the nanoscale range.

Microencapsulation of Ascorbic Acid for Cosmetic by Utilizing Self-assembly of Phase Separated Polymer.

Micrometer-sized polymer particles encapsulated ascorbic acid (vitamin C; VC) were successfully prepared by the three types of the self-assembling method, those are, phase separation and self-assembly of added polymer at the oil-water interface in emulsion, microsuspension polymerization utilizing the self-assembling of phase separated polymer (SaPSeP) method, and their hybrid method. In the stability study at 50°C for 2 months, the three kinds of capsule particles exhibited effective protection of VC from the interaction with other components in cosmetic consisting of water-in-oil (W/O) emulsion. The encapsulated VC was easily released from the capsule particles by an excess of water. These encapsulation methods will be useful for the stabilization of water-soluble substances in cosmetic consisting of W/O emulsion.

Emulsion droplets as a dynamic interface for the direct and large-scale synthesis of ultrathin free-standing mesoporous silica films as well as 2D polymeric and carbon nanomaterials.

The efficient synthesis of free-standing mesostructured two-dimensional (2D) nanofilms with high-yield as well as good control of composite, mesophase structure, orientation of the pore channel and thickness represents a big challenge. In this work, it was serendipitously found that microemulsion droplets of tetraethylorthosilicate (TEOS) could serve as a novel dynamic interface for continuous growth of nanofilms. Based on this finding, a general, efficient strategy for the direct and large-scale synthesis of free-standing mesoporous silica films (FSMSFs) was developed. Remarkably, with the careful control of the synthesis conditions, the FSMSFs with high-yield as well as good control of composite, mesophase structure, orientation of the pore channel and thickness could be efficiently achievable. More importantly, by using polymerizable surfactants the preorganized monomers in the nanochannels of the resultant silica films could be further converted into 2D polymers and carbon nanomaterials as well as metal particle-decorated forms, as exemplified by using pyrrole-terminated surfactants, demonstrating a powerful method to create 2D inorganic, organic or hybrid functional nanomaterials.

Pickering emulsions stabilized by oppositely charged colloids: Stability and pattern formation.

A binary mixture of oppositely charged colloids can be used to stabilize water-in-oil or oil-in-water emulsions. A Monte Carlo simulation study to address the effect of charge ratio of colloids on the stability of Pickering emulsions is presented. The colloidal particles at the interface are modeled as aligned dipolar hard spheres, with attractive interaction between unlike-charged and repulsive interaction between like-charged particles. The optimum composition (fraction of positively charged particles) required for the stabilization corresponds to a minimum in the interaction energy per particle. In addition, for each charge ratio, there is a range of compositions where emulsions can be stabilized. The structural arrangement of particles or the pattern formation at the emulsion interface is strongly influenced by the charge ratio. We find well-mixed isotropic, square, and hexagonal arrangements of particles on the emulsion surface for different compositions at a given charge ratio. The distribution of coordination numbers is calculated to characterize structural features. The simulation study is useful for the rational design of Pickering emulsifications wherein oppositely charged colloids are used, and for the control of pattern formation that can be useful for the synthesis of colloidosomes and porous shells derived thereof.

Compatibilization of Immiscible Polymer Blends Using in Situ Formed Janus Nanomicelles by Reactive Blending.

Block or graft copolymers located at polymer-polymer interfaces have been considered as ideal compatibilizers for immiscible polymer blends. Herein, we report a novel compatibilization mechanism using Janus nanomicelles (JNMs) formed in situ at the polymer-polymer interface in immiscible polyvinylidene fluoride (PVDF)/polylactic acid (PLLA) blends. A small amount of a reactive graft copolymer, poly(styrene-co-glycidyl methacrylate)-graft-poly(methyl methacrylate) (P((S-co-GMA)-g-MMA)), is incorporated into the PLLA/PVDF blends by simple melt mixing. The in situ grafting of PLLA chains onto P((S-co-GMA)-g-MMA) during melt mixing leads to the formation of numerous JNMs with a shell structure consisting of PLLA and PMMA hemispheres. These JNMs are located at the PLLA/PVDF interface, where they behave as effective compatibilizers for the immiscible PLLA/PVDF blends. This interfacial micelle compatibilization (IMC) mechanism opens new opportunities to exploit interfacial emulsification using JNMs and should be of great significance in the compatibilization of polymer alloys.

Emulsification at the Liquid/Liquid Interface: Effects of Potential, Electrolytes and Surfactants.

Emulsification of oils at liquid/liquid interfaces is of fundamental importance across a range of applications, including detergency. Adsorption and partitioning of the anionic surface active ions at the interface between two immiscible solutions is known to cause predictable chaos at the transfer potential region of the surfactant. In this work, the phenomenon that leads to the chaotic behaviour shown by sodium dodecylbenzene sulfonate (SDBS) at the water/1,2-dichloroethane interface is applied to commercial surfactants and aqueous/glyceryl trioleate interface. Electrochemical methods, electrocapillary curves, optical microscopy and conductivity measurements demonstrated that at 1.5 mm of SDBS, surfactants are adsorbed at the interface and assemble into micelles, leading to interfacial instability. As the concentration of the anionic surfactant was enhanced to 8 and 13.4 mm, the Marangoni effect and the interfacial emulsification became more prominent. The chaotic behaviour was found to be dependent on the surfactant concentration and the electrolytes present.

Transesterification of oil to biodiesel in a continuous tubular reactor with static mixers: Modelling reaction kinetics, mass transfer, scale-up and optimization considering fatty acid composition

Simulations of the methanolysis of lipids in a mixer-packed bed heterogeneous flow process were performed based on the thermodynamics (equilibrium) as well as mechanism and chemical kinetics of glycerides and fatty acid methyl esters (FAME) containing different combinations of gadoleic (G), linoleic (L), linolenic (Ln), oleic (O), palmitic (P) and stearic (S) acids, bonded as glycerol (alcohol) substituents. Transport phenomena and fluid dynamics were established for emulsion interface films and through axial dispersion coefficients (Péclet number) in a fixed bed for both transient and stationary operation. Alcoholysis was also studied experimentally within a broad range of temperatures, hydrodynamic conditions in terms of volumetric flow rates, phase ratios and base catalyst concentrations. Diffusion resistance proved to be negligible, temperature was proven as a prevalent factor, while steady state was reached only after a few residence times elapsed. Process economics were finally evaluated in terms of cost and price breakdown, allowing methodology extension to other waste oil resources. Sensitivity analysis revealed high LLL triglyceride content in oil having the greatest positive, and OOL negative effect on FAME yield. Process intensification with static mixers was proven feasible upon scaling-up from 5 to 10mm internal diameter with no deterioration in overall process progression.

Diversity of Bioleaching Microorganisms in Interfacial Emulsion of Copper Solvent Extraction

In the bioleaching - solvent extraction - electrowinning practices for copper extraction, the solvent extraction process is used to enrich the copper in the leachate to a high lever to make the sequent electrowinning process possible. O/W type of interfacial emulsion always forms at the interface between organic phase and aqueous phase in the solvent extraction practices. Diversified microorganisms were discovered by microscope growing in the interface emulsion of copper solvent extraction. The diversity of them was analyzed by using 16s rRNA gene sequencing. It was indicated that there exist seven categories of bacteria in the interface emulsion, among which common bioleaching bacteria, such as Leptospirillum sp.,Acidithiobacillus ferrooxidans, Metallibacterium sp., are included. The dominant strains are Leptospirillum sp. E4-L9 and Acidithiobacillus ferrooxidans ATCC 23270, which account up to 40.48 % and 38.1 %, respectively. It was uncovered that bioleaching bacteria can be intercepted by interfacial emulsion of solvent extraction to make their population in the raffinate lower and the efficiency of bioleaching decrease consequently.

A confocal microscopy study of micron-sized poly(N-isopropylacrylamide) microgel particles at the oil–water interface and anisotopic flattening of highly swollen microgel

HypothesisResponsive poly(N-isopropylacrylamide) microgel (PNIPAM microgel) stabilized Pickering emulsions were investigated in this study. A recent theoretical study of other researchers has suggested that large soft particles at the oil/water interface are less deformable than their small counterparts. Therefore, we expected that our micron-sized microgel particles might not significantly deform at the oil/water interface. ExperimentsWe applied confocal laser scanning microscopy (CLSM) to examine the structure of soft PNIPAM-based microgel particles at the decane–water interface in a microgel-stabilized emulsion. Using micron-sized microgel particles with better labelling techniques, we could compensate the weakness in resolution of using CLSM. Seven PNIPAM-based microgel samples with various softness values and morphologies were examined at different pH values. FindingsOur results demonstrate that the deformation of ordinary micron-sized microgel samples was not significant if they were not in the pH-swollen state. Nevertheless, the soft, pH-swollen microgel particles exhibited anisotropic deformation at the decane–water interface. Such flattening was not reported in previous studies. The studies of microgel particles at the oil–water interface with different imaging techniques and their comparison are valuable to help to elucidate the particles’ roles in stabilizing the Pickering emulsions.

Dendritic Amphiphile Mediated One-Pot Preparation of 3D Pt Nanoparticles-Decorated PolyHIPE as a Durable and Well-Recyclable Catalyst.

Straightforward organization of platinum nanoparticles (PtNPs) onto a macroscopic and robust material is described. PtNPs are in situ produced and stabilized by a dendritic amphiphile, where the latter consists of a hyperbranched polyethylenimine (PEI) as core and poly(styrene-co-2-ethylhexyl acrylate (P(St-EHA)) as shell. The resulting Pt@PEI@P(St-EHA), upon mixing with biphasic water and oil (a mixture of EHA and a dimethacrylate cross-linker in toluene), can self-assemble along the water/oil (W/O) interface and result in a stable emulsion. At W/O = 80/20 (volume ratio), a high internal phase emulsion (HIPE) forms and can be radically transformed into an open-cellular and elastic monolith termed Pt-polyHIPE, with PtNPs decorated on the surface. The Pt-polyHIPE is mechanically robust, and the cross-linking homogeneity by the dimethacrylate is responsible for the strength. The Pt-polyHIPE shows an active catalytic property, as evaluated by reduction of 4-nitrophenol. The material is conveniently and well recyclable, showing no decrease in catalytic activity at least within 20 cycles. Energy-dispersive X-ray spectra and thermogravimetric analysis also support sufficient retaining of the Pt species, where the multivalent and multiligand PEI should be responsible for this property.

Diffusion controlling porphyrin assembled structures

Here we report a mechanistic study on the diversity of assembled structures. We take the assembly of porphyrin molecules as an example to investigate how the diffusion of molecules influences the structure of assemblies. The diffusion is regulated by changing the composition of solvents. Diverse structures of porphyrin particles are assembled at various volume ratios of ethanol in water, including strip-like particles forming at 50%, tubular particles forming at 80% and rod-like particles forming at 95%. The in situ examination on the self-assembly process by confocal microscopy reveals that at the low volume ratio the nucleation initiates at the interface of emulsion followed by the growth of particles in the solvent. The diffusion limitation of molecules in the solvent is remarkable at the low volume ratio of ethanol as a result of high viscosity of the solvent and low solubility to the molecule, which enables the anisotropic growth of particles forming strip-like particles. With the increase of volume ratio of ethanol, the diffusion limitation is attenuated, leading to the thickening of particles and the formation of rod-like products. The thickening under diffusion limitation also causes a preferential growth of outer layer of particles resulting in the formation of hollow structures. The findings in this paper show that the diffusion of molecules plays an important role in shaping structures of assemblies, which was underestimated in previous studies.

Spruce galactoglucomannans in rapeseed oil-in-water emulsions: Efficient stabilization performance and structural partitioning

Food emulsions can be stabilized by various components, and their cost is important for the food industry that is always looking for cheaper alternatives. Consumer demand is leading food companies toward a clean label policy, and natural ingredients are the way to go. Modern forestry biorefineries offer an attractive option; novel plant-based hydrocolloids, such as spruce galactoglucomannans (GGM), are available in large quantities. Here we test their functionality and compare it with that of known food stabilizers. Rapeseed oil-in-water (O/W) emulsions stabilized by GGM and their carboxymethyl derivatives (CMGGM) were characterized in detail in terms of droplet size distribution, surface charge, and polysaccharide composition in the aqueous phase and on the droplet surface. The emulsifying and stabilizing capacities of GGM and CMGGM were compared to those of known stabilizers, namely, corn fiber gum (CFG) and gum arabic (GA), the latter of which is the gold standard in food emulsions. During high-pressure homogenization, GGM and CMGGM enabled the formation of emulsions with an average droplet size (D[3,2]) of about 400 nm and stabilized the droplets against creaming more effectively than GA (D[3,2] = 1.27 μm). The GGM and the CMGGM exhibited natural heterogeneity in their molecular composition and were distributed between the aqueous phase and the droplet interface of emulsions according to their molar mass and the CMGGM pattern of carboxymethyl substitution. This study clearly shows that wood-derived natural emulsifiers, GGM and CMGGM, meet the needs of the food industry.