Size Of Aqueous Droplets Research Articles

Water/Oil Emulsions with Controlled Droplet Sizes for In Vitro Selection Experiments.

In the early history of life, RNA might have had many catalytic functions as ribozymes that do not exist today. To explore this possibility, catalytically active RNAs can be identified by in vitro selection experiments. Some of these experiments are best performed in nanodroplets to prevent diffusion between individual RNA sequences. In order to explore the suitability for the large-scale in emulsio selection of water-in-oil emulsions made by passing a mixture of mineral oil, the emulsifier ABIL-EM90, and a few percent of an aqueous phase through a microfluidizer, we used dynamic light scattering to characterize the size of aqueous droplets dispersed throughout the oil. We found that seven or more passes through the microfluidizer at 8000 psi with close to half molar inorganic salts and 10% polyethylene glycol produced droplets with sizes below 100 nm that were ideal for our purposes. We also identified conditions that would produce larger or smaller droplets, and we demonstrate that the emulsions are stable over weeks and months, which is desirable for different types of in vitro selection experiments.

Electropermanent magnet-driven droplet size modulation for two-phase ferromicrofluidics

A new ferrofluidic droplet generator is demonstrated using an electropermanent magnet to change the viscosity of the ferrofluid oil phase in a flow-focusing junction, which enables control of the aqueous droplet size. Electropermanent magnets are capable of fast switching (< 100 $$\upmu$$ s) and have magnetic field strengths comparable to those of permanent magnets. When switched on, the magnetoviscous effect increases the viscosity of the ferrofluid, thus increasing the channel’s fluidic resistance, slowing the flow rate of the oil-based phase and changing the droplet diameter. We have demonstrated on-demand droplet size modulation as large as 44% at speeds fast enough to modulate the size of a single droplet in a stream. Due to compliance in the supply tubing and Polydimethylsiloxane (PDMS) microfluidic channels, the change in droplet size relaxes with a time scale of seconds. An application of droplet size modulation was demonstrated by integrating a passive size-based magnetic droplet sorting stage.

Slug flow hydrodynamics of immiscible fluids within a rectangular microchannel towards size-controllable fabrication of dextran-based cryogel beads

Cryogel beads are novel adsorbents with potential applications in biotechnology, environmental and tissue engineering. However, the controllable preparation of cryogel beads with expected small and uniform diameters is a challenging work. The micro-flow-focusing method combining with the cryo-polymerization has been suggested as a new approach for the fabrication of cryogel beads. In order to form the uniform droplet, the slug flow is generated in the microchannel, so the slug flow hydrodynamics are crucial and fundamental for this process. In the present work, the dextran-methacrylate (Dex-MA-PEGDA) solution and ethyl acetate containing surfactant of Span 80 were used as the aqueous phase and the water-immiscible, respectively. The fabrication of dextran-based cryogel beads and the slug flow hydrodynamics in a rectangular microchannel were investigated experimentally. The flow regime map was proposed and the typical regime boundaries were measured and correlated, and the formation mechanisms of slugs were also discussed. The regime boundaries were correlated by Weber number and Capillary number, i.e., Weo = 58.16Caw0.92 for the boundary between the annular and the slug flow, and Weo = 4.12Caw0.09 for the slug and the bubbly flow, respectively. Several crucial parameters of the droplets generated by the slug flow, i.e., the aqueous slug length, the aqueous slug velocity and the aqueous droplet size, were measured and correlated. The Dex-MA-PEGDA cryogel beads were prepared successfully under different conditions and their diameters were correlated to the sizes of the droplets. Eventually, the uniform size distributions and supermacroporous microstructures of dextran-based cryogel beads were demonstrated.

Immiscible liquid–liquid slug flow characteristics in the generation of aqueous drops within a rectangular microchannel for preparation of poly(2-hydroxyethylmethacrylate) cryogel beads

The microchannel liquid-flow focusing and cryo-polymerization is an efficient method for the preparation of cryogel beads with a narrow diameter distribution. In order to prepare cryogel beads with expected diameters, it is necessary to get insights in the liquid–liquid immiscible flow characteristics of the flow-focusing fluid and the monomer solution in microchannels. In this work, the slug flow behaviors of two immiscible liquids regarding the preparation of poly(2-hydroxyethylmethacrylate) (pHEMA) cryogel beads in a rectangular cross-junction microchannel were investigated experimentally by the high-speed imaging method. Correlations of the immiscible liquid–liquid slug flow parameters like the aqueous slug velocity and length, the aqueous slug nose and tail lengths, the water-immiscible slug length as well as the aqueous droplet size were obtained. The pHEMA cryogel beads were prepared under certain flow conditions and the bead sizes were measured by laser particle size analyzer. The obtained correlations were then employed to estimate the bead sizes and compared with those obtained experimentally. The results showed that the present correlations gave reasonable estimations of the mean bead diameters at various conditions and thus, could be useful and helpful in the preparation of cryogel beads with expected size distributions in rectangular microchannels.

Dextran-encapsulated barium sulfate nanoparticles prepared for aqueous dispersion as an X-ray contrast agent

Barium sulfate (BaSO4) nanoparticles (\100 nm) are of interest to provide improved performance over microscale BaSO4 particles, which are currently used clinically as an X-ray contrast agent or radiopacifier, and to further enable passive or targeted delivery of BaSO4 contrast agents. The stability of BaSO4 nanoparticle dispersions in aqueous media is critical for these uses but has received little attention. Therefore, the objective of this study was to prepare and characterize a BaSO4 nanoparticle con- trast agent with colloidal stability in aqueous media. Monodisperse BaSO4 nanoparticles, *13 nm in diameter, were synthesized using water-in-oil nano- emulsions wherein the aqueous droplet size limited particle growth and the surfactant layer provided a barrier against aggregation. The as-synthesized nano- particles were readily redispersed in organic solvents but agglomerated when redispersed in aqueous media due to exhibiting a low, nearly isoelectric zeta potential at neutral pH. Therefore, the as-synthesized BaSO4 nanoparticles were subsequently encapsulated by crosslinked dextran within the nanoemulsion droplets in order to provide both steric and electro- static stabilization upon breaking the nanoemulsion. Dextran encapsulation increased the particle diameter to *40 nm, but enabled BaSO4 nanoparticles to be readily redispersed in water and maintain colloidal stability for more than a month. The X-ray attenuation of dispersed dextran-encapsulated BaSO4 nanoparti- cles was not different from that measured for either a commercial microscale BaSO4 suspension or a solu- tion of barium ions prepared in water at an equal mass concentration of barium, but was significantly greater than the attenuation exhibited by soft tissues. Thus, dextran-encapsulated BaSO4 nanoparticles appear to be suitable for passive or targeted delivery as an X-ray contrast agent.

Kinetic stability and rheology of wax-stabilized water-in-oil emulsions at different water cuts

The impact of continuous phase wax solidification on the isothermal rheological properties of water-in-oil (W/O) emulsions at different water cuts (10–50wt%) was investigated. Rotational viscometry, oscillatory rheology and creep compliance and recovery were performed on emulsions aged up to 28days. Higher water cuts yielded emulsions with a higher bulk viscosity and storage modulus (G′) but lower maximum creep compliance (Jmax) values. The development of a more pronounced continuous phase wax crystal network with age led to a corresponding increase in emulsion bulk viscosity and G′ as well as a decrease in Jmax. Supporting results for these findings were acquired with light microscopy, solid wax content, and aqueous droplet size analysis. This study established that both water cut and continuous phase wax solidification play a significant role in W/O emulsion rheology, though this greatly depends on the age of the emulsion. Such findings may be used to better understand and tailor emulsion properties in fields such as the petrochemical, cosmetics, food and pharmaceutical industries.

Factors affecting protein release behavior from surfactant–protein complexes under physiological conditions

Protein release behavior from its complex with edible surfactants was investigated under physiological conditions using hen egg lysozyme and Aspergillus niger glucose oxidase as model proteins. It revealed that protein release rates could be controlled by hydrophobicity of surfactants and the molar ratio of proteins to surfactants in the preparation of the complexes. Evaluation of functional integrity of a protein on the basis of specific activity of an enzyme released from the complex suggested that lower hydrophobicity of surfactants led to higher retention of catalytic activity. In addition, it was found that protein release rates from the complexes were correlated with the aqueous droplet size of water-in-oil emulsions in the preparation of the complexes. The results suggest the potential of surfactant–protein complexes in pharmaceutical formulations for mucosal delivery of therapeutic proteins.

Steric Repulsion between Internal Aqueous Droplets and the External Aqueous Phase in Double Emulsions

A theoretical model for analyzing the steric repulsion energy between internal aqueous droplets and the external aqueous phase in double emulsions, which results from the steric interaction between the surfactant molecules adsorbed at the two interfaces, has been established. The steric interaction is dependent on the separation distance between the internal aqueous droplets and the external aqueous phase, the thicknesses of the two adsorbed surfactant layers, and the size of the internal aqueous droplets and the oil globules, all of which determine the extent of the compression of the adsorbed surfactant molecules. The thickness of each of the two surfactant layers have the same effect on the steric repulsion, and stronger steric interaction can be achieved with thicker adsorbed layers, which can effectively prevent coalescence between the internal aqueous droplets and the external aqueous phase. Increasing the internal aqueous droplet size can produce stronger steric repulsion; however, larger oil globules will weaken the steric repulsion, indicating that a more stable double-emulsion system can be achieved by preparing the system with smaller oil globules and larger internal aqueous droplets.

Water in soybean oil microemulsions as medium for electrochemical measurements

Microemulsions of water in soybean oil (w/o ME) were prepared with sodium dodecyl sulfate (SDS) as surfactant and amyl or isoamyl alcohol, as co-surfactants. Microemulsions containing 40.0% oil, 43.2% alcohol, 10.8% SDS and 6.0% water in weight, in the ratio 1:4 [SDS]:[alcohol] showed the highest thermodynamic stability. The aqueous droplet size and its diffusion coefficient Dw/o in the ME were determined through dynamic light scattering (DLS). Voltammetric measurements in the ME at a Pt disk ultramicroelectrode (ume) evidenced the oxidation of both water and ferrocene (Fc), and the reduction of oleic acid. The Dw/o values calculated from the limiting current being lower than the ones obtained from DLS indicate that water oxidation probably requires diffusion towards the electrode of both the droplets and the water molecules from inside the droplets. The results show that electroanalytical determinations can be carried out in w/o ME.

Unsteady-State Absorption of Co 2 Into W/O Type Emulsion with Aqueous Amine Liquid Droplets

Unsteady-state absorption of CO 2 into W/O type emulsion was studied by both experimental measurements and prediction from mathematical modeling. Absorption experiments were carried out using a stirred vessel with a flat gas-liquid interface under 0.101 MPa and 25°C. Continuous phase was benzene, which has larger solubility than water. Dispersed phase was an aqueous solution of MEA, DEA, TEA, and AMP. The effects of reactant concentration, size of aqueous droplets, volume fraction of continuous phase, and stirring speed on the absorption rate of CO 2 were investigated. In the mathematical model, the mechanism of CO 2 absorption into the continuous phase through a gas-liquid interface was described on the basis of the penetration model, while the subsequent absorption/reaction in dispersed droplets was modeled on the basis of the film model.

CO2 absorption into w/o emulsion with aqueous amine liquid droplets

Rates of CO2 absorption into aqueous droplets of monoethanolamine (MEA), diethanolamine (DEA), and triethanolamine (TEA) in water-in-oil (w/o) emulsion were measured in a flat-stirred vessel at 25°C. The effects of reactant concentration, size of aqueous droplets, volume fraction of continuous phase, and stirring speed on the absorption rate of CO2 were investigated. The absorption mechanism of CO2 into the continuous benzene phase through a gas–liquid interface was described on the basis of the penetration model, while the subsequent absorption/reaction in the dispersed aqueous droplets was modeled by the film model.