Continuous Water Phase Research Articles

Effective Cryopreservation and Recovery of Living Cells Encapsulated in Multiple Emulsions.

Background: The ability to preserve living cells or stem cells is critical for their use in cell therapy, especially for regenerative, reproductive, and transfusion medicine. This article addresses the low survival rates of cells and their loss of function during traditional freezing and banking (cells in a liquid medium with cryoprotectants). Aim: In this article, we developed multiple emulsions (water-in-oil-in-water type) for the effective encapsulation and cryopreservation of cells. In multiple emulsions, the oil drops, acting as a protective membrane, contain even smaller water droplets with encapsulated living cells, dispersed in the continuous water phase. Materials and Methods: The multiple emulsions with HEK293 cells encapsulated in the internal alginate droplets were successfully prepared in a Couette-Taylor flow biocontactor. The cryoprotectants (sucrose/dimethyl sulfoxide-DMSO) were located within the internal or external or both water phases of the emulsions. Encapsulated and non-encapsulated cells were frozen to -80°C (cooling rate: -1°C/min) and then transferred to liquid nitrogen (-196°C) for 24 hours. The standard rapid warming procedure was applied to thaw samples. Cell proliferation and viability were measured by using the AlamarBlue™ assay after recovery of cells. Results: The results showed that the viability of cells encapsulated in the internal droplets of multiple emulsions, and then cryopreserved, was significantly higher, up to 27.9%, than that observed for cells conventionally cryopreserved (non-encapsulated cells in water). Moreover, the effective cell-loaded multiple emulsions-based banking method allowed DMSO-toxic cryoprotectant-to be eliminated from the cryopreservation system. Conclusion: The proposed approach of the cryoprotection of cells encapsulated in multiple emulsions could minimize cell damage, degradation, and their loss during freezing-thawing processes.

Nanostructure and poroviscoelasticity in cell wall materials from onion, carrot and apple: Roles of pectin

The hierarchical organisation of polysaccharides in primary plant cell walls is responsible for their unique mechanical properties, and in turn for the textural and rheological properties of plant-based foods and ingredients. It is expected that at the nano scale, the mechanical properties of cell wall materials arise from a combination of structural deformation of the polysaccharide networks and hydraulic properties of the continuous water phase, as has been shown for other cellulose-based composites. Pectin plays a key role in the load bearing properties of (bacterial) cellulose-pectin composites due to its contribution to both hydration structure and the dynamics of water movement. To investigate whether these features are also important in plant cell wall materials we have used a set of advanced characterisation techniques to elucidate cell wall structural features at different length scales (X-ray diffraction and small angle X-ray and neutron scattering) in cell walls from two dicotyledons (apple and carrot) and a non-commelinid monocotyledon (onion). The strength of isolated cell walls was measured under compression and fitted to a poroviscoelastic mechanical model, demonstrating that the mechanical properties of the isolated cell wall materials are directly linked to both polysaccharide networks and fluid flow through the networks. Our results show how pectin polysaccharides influence the viscoelastic behaviour of these materials and contribute to the texture of plant-derived food systems.

Effect of residence time and energy dissipation on drop size distribution for the dispersion of oil in water using KMS and SMX+ static mixer

The Planar Laser Induced Fluorescence technique was used to determine the drop size distribution of oil dispersed in water at the inlet and outlet of two static mixer geometries (KMS and Sulzer_SMX+) equipped with either 6 or 12 elements. A mineral oil (Lytol®), three times more viscous than the water continuous phase, was used as the dispersed phase. The oil flow rate was kept constant through all experiments forcing the drop detachment from the secondary inlet. The L–L system was very dilute (˜0.05–0.0007% v/v O/W) to avoid coalescence phenomena. The flowrate of the continuous phase (water) was altered giving values of Reynolds number from 2000 to 12,000, covering high transitional and turbulent flow regimes. Increasing the flow rate of the continuous phase, the detached oil drops from the secondary inlet decreased in size as expected. However, same drops after flowing a length of 0.4m of an empty pipe reached a constant size. To investigate a wider range of energy dissipation and residence time, the presence of static mixers has been investigated. Pressure drops, hence energy consumed, were measured to compare the different set ups and drop size distributions. The results show that by increasing the flow rate, the drop size decreased up to a critical point, beyond which oil droplet size reduction became inefficient. The collected data were then used to derive a methodology to identify the optimal flow conditions and choice of static mixer device to achieve best drop size reduction with less energy per unit mass.

Flow Regimes in Two-Phase Hexane/Water Semibatch Vertical Taylor Vortex Flow

Optical-based experiments were carried out using the immiscible pair of liquids hexane and water in a vertically oriented Taylor–Couette reactor operated in a semibatch mode. The dispersed droplet phase (hexane) was continually fed and removed from the reactor in a closed loop setup. The continuous water phase did not enter or exit the annular gap. Four distinct flow patterns were observed including (1) a pseudo-homogenous dispersion, (2) a weakly banded regime, (3) a horizontally banded dispersion, and (4) a helical flow regime. These flow patterns can be organized into a two-dimensional regime map using the azimuthal and axial Reynolds numbers as axes. In addition, the dispersed phase holdup was found to increase monotonically with both the azimuthal and axial Reynolds numbers. The experimental observations can be explained in the context of a competition between the buoyancy-driven axial flow of hexane droplets and the wall-driven vortex flow of the continuous water phase.

Effect of synthesized lysine-grafted silica nanoparticle on surfactant stabilized O/W emulsion stability: Application in enhanced oil recovery

Abstract In enhanced oil recovery processes surfactants and nanoparticles are being widely used mainly due to their properties to reduce the interfacial tension between crude oil and aqueous phase. This results in a stable film of emulsion between these two immiscible fluids in case of surfactants and nanoparticles can form a solid layer at the droplet's interface and stand as a resistant stabilizer under harsh reservoir conditions. This research manifests whether the combination of surfactants and Lysine grafted silica nanoparticle (LGS) can provide a more stable emulsion. Oil in water and water in oil emulsions that are stabilized with different surface coating nanoparticles of uniform size have been developed. LGS was synthesized and characterized with FTIR, FESEM, EDX and TGA for proper understanding. Phase behavior study has been done with respect to salinity and synthesized nanoparticle concentration at high temperature. Prepared emulsions were also characterized by IFT, Micro-emulsion images and rheology. Results showed that synthesized surfactant from jatropha oil with a water continuous phase could give a stable emulsion. More emulsion stability was achieved by adding LGS to surfactant synthesized from jatropha oil. Sandpack flooding results were also found to be in line with the results and showed a greater recovery in the presence of LGS with an additional recovery of 24.6% which was much better the surfactant itself. Results showed that lysine grafted silica Nano-particle in combination with surfactant can be a potential candidate for EOR recovery in comparison to conventional flooding applied in the reservoirs.

Stabilization of oil-in-water emulsions with graphene oxide and cobalt oxide nanosheets and preparation of armored polymer particles

Pickering emulsions are emulsions stabilized by particles instead of small molecules or polymers, and commonly consist of oil droplets dispersed into a continuous water phase with particles lying at the fluid-fluid interface. New particle surfactants are important for tuning the composition and properties of assemblies and enabling advanced applications, such as energy harvesting and management. Although most particle surfactants are spherical, graphene oxide (GO) nanosheets and clay platelets have garnered recent attention as 2D (i.e., planar) particle surfactants. Herein, we report the preparation of Pickering emulsions stabilized by a composite of GO nanosheets and cobalt oxide (CoOx) nanosheets, and illustrate the impact of GO:CoOx ratio, oil identity, and flocculating agent (i.e., salts) on emulsion formation and stability. Distinct effects were noted for salt concentration and identity, as well as GO: CoOx ratio. We further illustrate the applicability of these GO-CoOx-stabilized emulsions in dispersion polymerization, preparing polystyrene particles armored with both nanosheets. This work provides a method for facilitating oil-in-water emulsions with composite particle surfactants that are stable for at least a week and offers the foundation for using the fluid-fluid interface to architect structures of dissimilar materials.

Experimental and numerical study of oil drop motion within an ESP impeller

The Electrical Submersible Pump (ESP) is a multistage centrifugal pump used in the petroleum industry as an artificial lift method. The ESP usually works with the presence of two-phase liquid-liquid flows that constitute dispersions and emulsions, causing performance losses and operational problems. This research aims to investigate the behavior and evaluate the dynamics of individual oil drops in an oil-in-water dispersion within an ESP impeller. The study adopts experimental and numerical approaches. Initially, experiments were performed using an experimental facility with a high-speed camera and an ESP prototype working at 600 rpm and 900 rpm, for water flows around the Best Efficiency Point (BEP) and with the injection of oil drops at a low flow rate. The acquired images were processed, and a drop sample was tracked, enabling the analysis of the size, shape, path, velocity, and acceleration of the oil drops. Numerical simulations were executed in ANSYS® software to define relevant parameters related to water and oil drops, such as velocities, accelerations, forces, turbulent dissipation, and residence time. The images reveal a unique flow pattern of dispersed drops in a continuous water phase. The oil drops' diameters vary from tenths of a millimeter to around 3 mm. The drops' trajectories can be classified into three different regions within the impeller channels. The drops’ velocities stay in the order of 1 m/s, while accelerations can reach hundreds of m/s2. The velocity profiles show that the oil drops tend to decelerate during their trajectory, while the acceleration profiles suggest peaks at the channel inlet and outlet. High intense turbulence is present in the impeller entrance zone. The evaluation of the residence time and the particle Reynolds number suggest that smaller oil drops follow the water streamlines, while larger oil drops tend to be affected by external forces. The main forces that govern the oil drop motion are the drag, the pressure gradient, and the virtual mass forces. The force from the pressure gradient is tenfold greater than the force from the drag. The virtual mass effect is significant only in the impeller inlet. In general, in this research, numerical results show a satisfactory agreement with the experimental data.

An Experimental Study of Emulsion Phase Behavior and Viscosity for Athabasca Bitumen/Diethylamine/Brine Mixtures

Summary Water is the most dominant component in steam-based oil-recovery methods, such as steam-assisted gravity drainage (SAGD). The central question that motivated this research is whether in-situ bitumen transport in SAGD can be substantially enhanced by generating oil-in-water emulsion, in which the water-continuous phase acts as an effective bitumen carrier. As part of the initial stage of the research project, the main objective of this paper is to present the ability of organic alkali to form oil-in-water emulsions that are substantially less viscous than the original bitumen. Diethylamine (DEA) was used as the organic alkali in this research. Experimental studies were conducted for emulsion phase behavior and viscosity for mixtures of Athabasca bitumen, DEA, and sodium chloride (NaCl) brine. Experimental variables included brine salinity, alkali concentration, water/oil ratio (WOR), temperature, and sample-aging time. The phase-behavior study indicated that conditions conducive to oil-in-water emulsions are low alkali concentrations at salinities less than 1,000 ppm. For example, a single phase of oil-in-water emulsion was observed for 0.5, 1.0, 2.0, and 5.0 wt% DEA with WOR of 7:3 with no NaCl. The emulsion for 0.5 wt% DEA, 1,000 ppm NaCl, and WOR of 7:3 was a single-phase oil-in-water emulsion at temperatures up to 403 K at 35 bar. At lower temperatures, 323 and 298 K, flocculation of emulsions in these samples resulted in the separation between the bitumen-rich and water-rich oil-in-water emulsions. However, essentially all bitumen content was measured from the bitumen-rich oil-in-water emulsion. The oil contents in these emulsions were more than 70 vol% at 298 K and 57 vol% at 323 K. Viscosities of these oil-in-water emulsions ranged between 85 and 115 cp at 1.0 seconds–1 and between 31 and 34 cp at 10.0 seconds–1, at 323 K. At 298 K, they ranged between 105 and 250 cp at 1.0 seconds–1 and between 48 and 74 cp at 10.0 seconds–1. Results in this research show that, compared with the original bitumen, bitumen-rich oil-in-water emulsions were less viscous by three to four orders of magnitude at 298 K, and less viscous by two orders of magnitude at 323 K.

Effect of Shear and Water Cut on Phase Inversion and Droplet Size Distribution in Oil–Water Flow

Oil–water dispersed flow occurs commonly in the petroleum industry during the production and transportation of crudes. Phase inversion occurs when the dispersed phase grows into the continuous phase and the continuous phase becomes the dispersed phase caused by changes in the composition, interfacial properties, and other factors. Production equipment, such as pumps and chokes, generates shear in oil–water mixture flow, which has a strong effect on phase inversion phenomena. The objective of this paper is to investigate the effects of shear intensity and water cut (WC) on the phase inversion region and also the droplet size distribution. A state-of-the-art closed-loop two phase (oil–water) flow facility including a multipass gear pump and a differential dielectric sensor (DDS) is used to identify the phase inversion region. Also, the facility utilizes an in-line droplet size analyzer (a high speed camera), to record real-time videos of oil–water emulsion to determine the droplet size distribution. The experimental data for phase inversion confirm that as shear intensity increases, the phase inversion occurs at relatively higher dispersed phase fractions. Also the data show that oil-in-water emulsion requires larger dispersed phase volumetric fraction for phase inversion as compared with that of water-in-oil emulsion under the same shear intensity conditions. Experiments for droplet size distribution confirm that larger droplets are obtained for the water continuous phase, and increasing the dispersed phase volume fraction leads to the creation of larger droplets.

Ionic Liquid-Containing Pickering Emulsions Stabilized by Graphene Oxide-Based Surfactants.

Emulsions stabilized by particles (i.e., Pickering emulsions) are complementary to those stabilized by small molecules or polymers and most commonly consist of oil droplets dispersed in a continuous water phase, with particles assembled at the fluid-fluid interface. New particle surfactants and different fluid-fluid interfaces are critical for developing next-generation systems for a number of advanced applications. Herein we report the preparation of IL-containing emulsions stabilized by graphene oxide (GO)-based nanoparticles using the IL [Bmim][PF6]: GO nanosheets stabilize IL-in-water emulsions, and alkylated GO nanosheets (C18-GO) stabilize IL-in-oil emulsions. The impact of particle concentration, fluid-fluid ratio, and addition of acid or base on emulsion formation and stability is studied, with distinct effects for the water and oil systems observed. We then illustrate the broad applicability of GO-based particle surfactants by preparing emulsions with different ILs and preparing inverted emulsions (water-in-IL and oil-in-IL emulsions). The latter systems were accessed by tuning the polarity of GO nanosheets by functionalization with a perfluorinated alkyl chain such that they were dispersible in IL. This work provides insight into the preparation of different IL-containing emulsions and lays a foundation for the architecture of dissimilar materials into composite systems.

Fluid Dynamics of Microgel-Covered Drops Reveal Impact on Interfacial Conditions.

Microgels are deformable polymer-networks with conspicuous properties. Their surface- activity associated with their switchability makes their application in liquid-liquid systems, such as extraction processes, particularly promising. For their application as switchable stabilizers at the interface, a detailed understanding of their impact on process relevant phenomena, such as the sedimentation behavior, is necessary. So far, the focus of research has been on microscopic-scale properties, whereby the propagation to macroscopic effects has rarely been quantified. In this study, single microgel-covered n-butyl acetate drops rising in a quiescent continuous water phase are investigated experimentally. The dependency of the microgel properties, in terms of size and cross-linking density, on the fluid dynamics are addressed. The impact of microgels is studied in detail by sedimentation velocity, drop deformation and the resulting drag coefficient. The deformation of drops is related to shape conserving interfacial properties such as the interfacial tension. Counter to our expectations, microgel-covered drops deform less than the drops of the pure system although microgels reduce the interfacial tension. Moreover, the sedimentation velocity is of special interest, since it reveals the mobility of the interface and friction conditions at the interface. Our results demonstrate the correlation between microgel properties at the interface on a microscopic scale and the macroscopic behavior of microgel-covered drops.

Investigations on the relationship between interfacial and single droplet experiments to describe instability mechanisms in double emulsions

Due to their multicomponent structure, water-in-oil-in-water (WOW) double emulsions are of great interest for the encapsulation of hydrophilic substances. Although promising applications are reported, few double emulsion products are available on the market because their stabilization is still challenging. To stabilize all internal interfaces, at least two interfacial active substances (IAS), a lipophilic and a hydrophilic one, have to be added. These IAS can interact with each other at the interfaces and thus might impair the double emulsion stability. Especially the impact of these interactions on the loss of inner water droplets due to coalescence with the outer water phase is largely unknown.In this study, we investigated if interfacial tension measurements can be related to the loss of inner water caused by coalescence. We determined the outer oil in water interfacial tension of a double emulsion, when a hydrophilic or a lipophilic IAS is used individually as well as in combination. Furthermore, the coalescence process between a water droplet encapsulated in oil and an adjacent continuous water phase was observed in single droplet experiments.As model system polyvinyl-alcohol (PVOH) was used as hydrophilic and polyglycerol-polyricinoleate (PGPR) was used as lipophilic IAS. For the sole use of PVOH, the behavior of the coalescence process can be related to the interfacial tension, which was changed by varying the PVOH type. It could be shown that the lower the interfacial tension is, the longer is the time until the coalescence process takes place. In addition, the duration of the coalescence process itself increases by decreasing the interfacial tension for the system under study.In case of the combined use of PVOH and PGPR, the observations differ in dependency on the PVOH type. In case of PVOH with a low hydrophobicity, the simultaneous presence of PGPR caused only a minor change of the coalescence behavior compared to the sole use of PVOH. In case of a PVOH type with higher hydrophobicity, the coalescence behavior changed clearly by the presence of PGPR. However, no correlation to the interfacial tension was found.

Carbon Capsules of Ionic Liquid for Enhanced Performance of Electrochemical Double-Layer Capacitors.

Ion accessibility, large surface area, and complete wetting of a carbonaceous electrode by the electrolyte are crucial for high-performance electrochemical double-layer capacitors. Herein, we report a facile and scalable method to prepare electrode-electrolyte hybrid materials, where an ionic liquid (IL) electrolyte is encapsulated within a shell of reduced graphene oxide (rGO) nanosheets as the active electrode material (called rGO-IL capsules). These structures were templated using a Pickering emulsion consisting of a dispersed phase of 1-methyl-3-butylimidazolium hexafluorophosphate ([bmim][PF6]) and a continuous water phase; graphene oxide nanosheets were used as the surfactant, and interfacial polymerization yielded polyurea that bound the nanosheets together to form the capsule shell. This method prevents the aggregation and restacking of GO nanosheets and allows wetting of the materials by IL. The chemical composition, thermal properties, morphology, and electrochemical behavior of these new hybrid architectures are fully characterized. Specific capacitances of 80 F g-1 at 18 °C and 127 F g-1 at 60 °C were achieved at a scan rate of 10 mV s-1 for symmetric coin cells of rGO-IL capsules. These architected materials have higher capacitance at low temperature (18 °C) across many scan rates (10-500 mV s-1) compared with analogous cells with the porous carbon YP-50. These results demonstrate a distinct and important methodology to enhance the performance of electrochemical double-layer capacitors by incorporating electrolyte and carbon material together during synthesis.

Preparation of highly interconnected hydrophilic polymers from emulsion templates with improved mechanical properties

Highly interconnected hydrophilic polymers were prepared through the polymerisation of (paraffin-oil)-in-water emulsion templates using internal phases below 74 vol%. These were stabilised by Tween 85 and contained acrylamide and N,N/-methylene bisacrylamide, as monomers, in the continuous water phase. The emulsification energy was increased, resulting in increased contact between emulsion droplets, allowing open cellular and highly interconnected structures to be achieved. This was coupled with a reduction in the internal phase volume allowing the obtainment of highly interconnected materials with excellent mechanical properties under compression, producing a Young’s modulus of 490 ± 90 MPa for a material with 36 ± 3% porosity. It was also found that the morphology of these materials could be altered through variations in the internal phase volume, the surfactant level and the emulsification energy. These porous polymers also possessed quite different behaviours in different solvent environments suggesting applications in controlled release or as rigid absorbents.

Development and evaluation of antisense shRNA-encoding plasmid loaded solid lipid nanoparticles against 5-α reductase activity

In this study, we aimed to develop and evaluate an effective system for nucleic acid delivery. For this purpose, shRNA-encoding plasmid against 5-α reductase (p5α-Red) activity was selected as a model. In order to achieve the delivery of p5α-Red and to obtain lower cytotoxicity, higher transfection and silencing efficiency, we developed solid lipid nanoparticles (SLNs) as a delivery vector by the melt-emulsification process. As a first step, microemulsions were prepared by using Compritol ATO 888 as internal oil phase; Tween 80 as a surfactant (S); ethanol as co-surfactant (CoS) and ultra-pure water as the continuous water phase. Then, obtained o/w microemulsion was dispersed in cold ultra-pure distilled water (0-4 °C) to form SLNs. The formulated nanoparticles were electrostatically bound to p5α-Red to form SLN:p5α-Red vectors. The SLN:p5α-Red vectors have particle sizes of 62.65 nm, and zeta potential values of 12.9 mV. DNase I protection analysis showed that developed formulation is able to protect the p5α-Red from degradation. The permeation study revealed that SLN:p5α-Red vectors are able to pass the cellulose membrane and 80.2% of the SLN:p5α-Red vectors were dialyzed after 6 h. According to cytotoxicity test results, no significant cytotoxicity was observed on DU-145 cells in the concentration range of 0.3–0.6 μg/well. Furthermore, in vitro gene silencing experiment demonstrated that SLN:p5α-Red vector effectively reduced 5α-Red enzyme level 48 h after administration in DU-145 cell line. Considering the role of 5-α reductase in related diseases such as benign prostatic hyperplasia, androgenic alopecia and prostate cancer, the developed SLN:p5α-Red vector system may have promises in future therapy.

Preparation of Microcapsules Containing Camellia Oil with Heterocoagulation between Chitosan and Oleic Acid

It was tried to microencapsulate camellia oil using heterocoagulation between fatty acid dissolved in camellia oil and chitosan dissolved in the continuous water phase. Oleic acid as a fatty acid was dissolved in camellia oil in order to certainly form the microcapsule shell made from oleic acid and chitosan. The microcapsules were observed with optical microscope and characterized about the diameters, ζ-potential, FTIR analysis and adhesion feature on human hair. Microcapsules with the mean diameter in the range from ca. 1.5 μm to 4.5 μm could be prepared with the preparation method presented in this study. The oil droplets of camellia oil charged negatively to be -54.6 mV and the microcapsules charged positively to be 59.6 mV. The microcapsules adhered well on the negatively charged human hair and were kept stably before and after drying at room temperature for 24 h and blowing.

Numerical assessment of two phase flow modeling using plunging jet configurations

This paper presents unsteady numerical simulation of air entrainment by water plunging jet using Volume of fluid model coupled to PLIC algorithm for phase interface reconstruction and Euler–Euler model considering continuous water phase and dispersed air phase.Plunging jet simulations aim to find out the ability of each model to reproduce air entrainment phenomenon. The investigation tackled the air plume depth, air entrainment rate and velocity profiles. Further simulations were performed to highlight the influence of the free jet length on the entrainment rate and plume development below the free surface.The results show good agreement with the available experimental data particularly velocity profiles in both radial and axial directions, plume shape and development along transient intervals. The initial impact is well reproduced referring to literature and bubbles penetration depth is comparable to the empirical correlations.It is noticed that further improvements are required for interfacial forces modeling in volume of fluid model to ensure good control of bubbles migration in the plume region.Entrainment rate discrepancies in Euler–Euler model are related to the lack of information about interface location due to averaging process; hence, an appropriate interface detection function is needed.

Self-Aeration Modelling Using a Sub-Grid Volume-Of-Fluid Model

Abstract The accurate prediction of self-aerated flow is not always easy to obtain, particularly if the computational performance is the main concern. Two-fluid formulation is suitable to simulate the dispersed air in a continuous water phase (e.g. bubbly flows) in a fine mesh, whereas the interface tracking methods are used for sharp interfaces with two continuous and contiguous phases (e.g. free-surface flows). Several approaches have emerged to combine both methods; however all found a gap in the transition between resolved and unresolved scales of air at the interface. Including a source term that predicts the self-aeration process is viewed as a promising step to overcome such difficulty. In this work, we added to the volume-of-fluid formulation an extra advection-diffusion equation connected to a source of air at the free surface to simulate the dispersed bubble phase. One-way coupling and two-way coupling versions of this model are tested along with sensitivity tests to show the accuracy of the new source term that does not require calibration. The location of the aeration is analysed and investigated. Results are obtained in terms of free-surface flow depths, air–concentration profiles and velocity fields and compared to experimental data acquired in a scaled stepped spillway model with good agreement. The free-surface given by the air-entrainment model is in good agreement in both non-aerated and aerated zone of the spillway.

Investigations on the influence of osmotic active substances on the structure of water in oil emulsions for the application as inner phase in double emulsions

Water in oil in water (WOW) double emulsions have a great potential as encapsulation systems in different industrial sections. Nevertheless, there are only few double emulsion based products available on market. An important limitation, regarding the product launch, is the insufficient stability of these products. Many instability mechanisms have to be taken into account: coalescence between inner water droplets, coalescence between outer oil droplets, coalescence between inner and outer water phase, and diffusion between the dispersed water droplets and the continuous outer water phase. In the present study, we focus on structural changes and stabilization mechanisms of inner water in oil (WO) emulsions. Osmotic active substances (OAS) have to be used in the inner water droplets to limit the diffusion processes between the water phases in double emulsions. We therefore investigated the influence of different OAS on the structural changes in WO emulsions. We focused on three subprocesses influencing the emulsification result: droplet breakup, stabilization directly after breakup and diffusional processes after droplet stabilization. For this, we prepared WO emulsions using sodium chloride, calcium chloride and glucose as OAS and polyglycerine-polyricinoleate as lipophilic emulsifier. The droplet size distribution was determined to evaluate structural changes. Furthermore, we measured interfacial properties and emulsion viscosities to evaluate stabilizing effects. Kinetic stabilization effects were evaluated by applying high pressure homogenization, known as a process with high requirements on the stabilization efficiency. The osmolality of the inner water phases was determined as parameter for the likelihood of diffusional processes. This characteristic value strongly depends on OAS type and concentration. Adsorption kinetics and diffusional processes turned out as the main factors influencing inner emulsion structure.

Mechanism of biosurfactant adsorption to oil/water interfaces from millisecond scale tensiometry measurements.

Many biological molecules are by their nature amphiphilic and have the ability to act as surfactants, stabilizing interfaces between aqueous and immiscible oil phases. In this paper, we explore the adsorption kinetics of surfactin, a naturally occurring cyclic lipopeptide, at hexadecane/water interfaces and compare and contrast its adsorption behaviour with that of synthetic alkyl benzene sulfonate isomers, through direct measurements of changes in interfacial tension upon surfactant adsorption. We access millisecond time resolution in kinetic measurements by making use of droplet microfluidics to probe the interfacial tension of hexadecane droplets dispersed in a continuous water phase through monitoring their deformation when the droplets are exposed to shear flows in a microfluidic channel with regular corrugations. Our results reveal that surfactin rapidly adsorbs to the interface, thus the interfacial tension equilibrates within 300 ms, while the synthetic surfactants used undergo adsorption processes at an approximately one order of magnitude longer timescale. The approach presented may provide opportunities for understanding and modulating the adsorption mechanism of amphiphiles on a variety of interfaces in the context of life sciences and industrial applications.