Droplet Transportation through an Orifice on Electrode for Digital Microfluidics Modulations

A digital microfluidic modular interface (chip-to-chip interface) which possesses an electrode with an orifice to vertically transport core–shell droplets is presented. The electrodes were geometrically designed to promote droplet deformation and suspension. The droplets were then applied with an electrical potential for insertion into and passage through the orifice. The concepts were tested with three types of droplets at the volume of 0.75~1.5 μL, which is usually difficult to transfer through an orifice. The integration of electrowetting on dielectric (EWOD) with paper-based microfluidics was demonstrated: the droplet could be transported within 10 s. More importantly, most of the core droplet (~97%) was extracted and passed through with only minimal shell droplets accompanying it.

Effects of Surfactant Volume Fraction on the Antioxidant Efficiency and on The Interfacial Concentrations of Octyl and Tetradecyl p-Coumarates in Corn Oil-in-Water Emulsions

Surfactants have been used for decades in the food industry for the preparation of lipid-based emulsified food stuffs. They play two main roles in the emulsification processes: first they decrease the interfacial tension between the oil and water, facilitating droplet deformation and rupture; second, they reduce droplet coalescence by forming steric barriers. However, addition of surfactants to binary oil-water mixtures also brings up the formation of three-dimensional interfacial layers, surrounding each emulsion droplet, that significantly alter chemical reactivity. This is the case, for instance, in the inhibition reaction between antioxidants and the lipid radicals formed in the course of the spontaneous oxidation reaction of unsaturated lipids, which are commonly employed in the preparation of food-grade emulsions. The rate of the inhibition reaction depends on the effective concentrations of antioxidants, which are mostly controlled by the amount of surfactant employed in the preparation of the emulsion. In this work, we analyze the effects of the surfactant Tween 20 on the oxidative stability and on the effective concentrations of two model antioxidants derived from cinnamic acid, determining their interfacial concentrations in the intact emulsions to avoid disrupting the existing equilibria and biasing results. For this purpose, a recently developed methodology was employed, and experimental results were interpreted on the grounds of a pseudophase kinetic model.

Experimental Investigation of Trapped Oil Mobilization with Ferrofluid

Summary Nanoparticles have great potential to mobilize trapped oil in reservoirs because of their chemical, thermal, and interfacial properties. However, the direct application of magnetic forces on superparamagnetic nanoparticles in reservoir engineering applications has not been extensively investigated. We demonstrate the enhanced oil recovery (EOR) potential of hydrophilic superparamagnetic nanoparticles in oil production by direct observation using microfluidics. We studied the mobilization of oil blobs by a ferrofluid (a suspension of hydrophilic superparamagnetic nanoparticles in water) both in a converging/diverging micromodel channel and in a foot-long pore network micromodel, both with varying depth (so-called 2.5D micromodels). The water-based ferrofluid in all cases was the wetting fluid. Initial ferrofluid flooding experiments in single channels were performed without and then with a static magnetic field. This magnetic field caused oil droplet deformation, dynamic breakup into smaller droplets, and subsequent residual oil saturation reduction. During the flooding, after the magnetic field was applied, significant oil displacement was observed within 2 hours [6 pore volumes injected (PVI)], and 86.2% of the oil that was not mobilized without a magnetic field was mobilized within 64 hours (192 PVI). Then, in experiments in the micromodel and in a Hele-Shaw cell without flooding, we observed self-assembly of oil droplets, indicating the formation of the hydrophilic magnetic nanoparticle microstructures (chains under the magnetic field) and their interaction with the oil blobs. Further ferrofluid flooding experiments were performed in a foot-long micromodel under a rotating magnetic field. The oil saturation was reduced from 44.6 to 33.3% after 17 hours (8.5 PVI) of ferrofluid flooding after the rotating magnetic field was applied. Finally, a discussion of field application of ferrofluid flooding is presented.

Sequential storage and release of microdroplets

Droplet microfluidic methods have opened up the possibility of studying a plethora of phenomena ranging from biological to physical or chemical processes at ultra low volumes and high throughput. A key component of such approaches is the ability to trap droplets for observation, and many device architectures for achieving this objective have been developed. A challenge with such approaches is, however, recovering the droplets following their confinement for applications involving further analysis. Here, we present a device capable of generating, confining and releasing microdroplets in a sequential manner. Through a combination of experimental and computational simulations, we shed light on the key features required for successful droplet storage and retrieval. Moreover, we explore the effect of the flow rate of the continuous phase on droplet release, determining that a critical rate is needed to ensure complete droplet deformation through constrictions holding the droplets in place prior to release. Finally, we find that once released, droplets can be retrieved and collected off chip. The ability to generate, store and sequentially release droplets renders such a device particularly promising for future applications where reactions may not only be monitored on-chip, but droplets can also be retrieved for further analysis, facilitating new exploratory avenues in the fields of analytical chemistry and biology.

Sequential Storage and Release of Microdroplets for On and Off-chip Analysis

Droplet microfluidic methods have opened up the possibility of studying a plethora of phenomena ranging from biological to physical or chemical processes at ultra-low volumes and high throughput. A key component of such approaches is the ability to trap droplets for observation, and many device architectures for achieving this objective have been developed. A challenge with such approaches is, however, recovering the droplets following their confinement for applications involving further analysis. Here, we present a device capable of generating, confining and releasing microdroplets in a sequential manner. Through a combination of experimental and computational simulations, we shed light on the key features required for successful droplet storage and retrieval. Moreover, we explore the effect of the ow rate of the continuous phase on droplet release, determining that a critical rate is needed to ensure complete droplet deformation through constrictions holding the droplets in place prior to release. Finally, we find that once released, droplets can be retrieved and collected off chip. The ability to generate, store and sequentially release droplets renders such a device particularly promising for future applications where reactions may not only be monitored on-chip, but droplets can be retrieved for further analysis, facilitating new exploratory avenues in the fields of analytical chemistry and biology.

Research on the phase transition process of sessile droplet on carbon fiber cold surface

The droplet phase transition process on the cold surface of a T300 carbon fiber substrate was studied by observing the droplet freezing process. Through the construction of visualized experimental device, the change in the droplet phase transition time under different experimental conditions, the progression of the solid-liquid interface during the phase transition process, the droplet deformation rate, and the ratio of growth of the interface height after the phase interface appears were experimentally obtained. The influence of different surface temperatures and different droplet volumes on the phase transition process was investigated. The experimental results show that the phase interface shows an irregular profile during the phase transition of the sessile droplet on the cold surface of the carbon fiber substrate, it presents a wave-shape early and smooth concave-shape later. The influence of droplet volume on the phase transition time is not a simple linear relationship. The height of the solid-liquid phase interface during the droplet phase transition process first grows rapidly, then slowly, and then fast once again. In other words, the growth rate of the phase interface is relatively fast when the phase transition has just occurred and the when the bulged tip is formed. At different cold surface temperatures, the droplet deformation rate with a volume of 10μL is basically the same, which is about 32.4%, within an uncertainty of about 1%. However, the influence of gravity factor is important in determining the droplet deformation rate for different droplet volumes.