Emulsion droplet formation in coflowing liquid streams

Array-structured microcapsule fibers for efficient fire extinguishing in confined spaces

Fire incidents in confined spaces pose significant risks to human lives and property. In such scenarios, achieving structural encapsulation and design of fire extinguishing agents is crucial. However, there is still a significant knowledge gap in the rational structural design and understanding of fire extinguishing mechanisms. Herein, we have developed a fire extinguishing material with a hemispherical knotted microfiber structure by microfluidic spinning and achieved directed multiple-fire extinguishing in a confined space. Fire-extinguishing microfibers (FEMFs) are uniformly distributed with perfluorohexanone (PFH)-embedded knots, each of which acts as an independent fire-extinguishing unit. The rational design of fiber microstructure can achieve a variety of dosage ratios of extinguishing agents that activate at a fire extinguishing temperature of 120 °C. Through high-speed imaging and simulation calculations, we found that FEMFs containing only 0.2 g PFH can generate up to 207 directional jets to extinguish fires. Fire-extinguishing patches (FEPs) made from FEMFs have a uniform distribution of the extinguishing agent and exhibit excellent fire extinguishing performance in electrical junction boxes. This new fire extinguishing material is believed to have broad applications in enhancing fire safety within confined spaces.

Structure and in vitro bioactive properties of O/W emulsions generated with fava bean protein hydrolysates

The use of plant-derived proteins in the generation of food products is gaining popularity as an alternative to proteins of animal origin. This study described the emulsifying and bioactive properties of fava bean protein hydrolysates (FBH) generated at low and high degree of hydrolysis (DH), i.e., FBH₈ (low DH: 8.4 ± 0.3) and FBH₂₁₀ (high DH: 15.6 ± 0.7) when adjusted to three different pHs (3.0, 5.0 and 8.0). Overall, FBH₈, had more favourable emulsifying properties compared to the FBH_210. The emulsion generated with FBH₈ at pH 8.0 also had the highest antioxidant activity when measured by the oxygen radical absorbance capacity (ORAC) and ferric reducing antioxidant power (FRAP) assays with values of 1108.6 ± 3.8 and 1159.9 ± 20.5 μmol Trolox Eq·g^-1 emulsion, respectively. The antioxidant activity of the emulsions, in most cases, remained unchanged following in vitro simulated gastrointestinal digestion. Both the FBH₈ and FBH₂₁₀ emulsions following in vitro simulated gastrointestinal digestion were able to inhibit the activities of dipeptidyl peptidase-IV (DPP-IV) and angiotensin converting enzyme (ACE) with ∼45% and 65% inhibition, respectively. These results indicated that hydrolysates from fava bean may find use for the generation of bioactive emulsions.

Simple and reusable off-the-shelf microfluidic devices for the versatile generation of droplets

A novel, facile, and flexible approach for the easy assembly of microfluidic droplet devices using commercially available components is presented. Three different types of devices have been designed and tested, and the experimental results indicated that the devices offer a promising platform for the controllable generation of highly monodisperse droplets with sizes in the micrometer to millimeter diameter ranges. The advantages of the devices include their low cost, portability, reusability, high accuracy, and reliability. Most importantly, the simple and reversible combination of the different components allows the flexible design of versatile devices for fabricating multiple droplets with diverse structures. Therefore, the devices constitute a powerful microplatform that can be used for scientific and industrial applications.

Dynamics of double emulsion break-up in three phase glass capillary microfluidic devices

Pinch-off of a compound jet in 3D glass capillary microfluidic device, which combines co-flowing and countercurrent flow focusing geometries, was investigated using an incompressible three-phase axisymmetric Volume of Fluid-Continuum Surface Force (VOF-CSF) numerical model. The model showed good agreement with the experimental drop generation and was capable of predicting formation of core/shell droplets in dripping, narrowing jetting and widening jetting regimes. In dripping and widening jetting regimes, the presence of a vortex flow around the upstream end of the necking thread facilitates the jet break-up. No vortex flow was observed in narrowing jetting regime and pinch-off occurred due to higher velocity at the downstream end of the coaxial thread compared to that at the upstream end. In all regimes, the inner jet ruptured before the outer jet, preventing a leakage of the inner drop into the outer fluid. The necking region moves at the maximum speed in the narrowing jetting regime, due to the highest level of shear at the outer surface of the thread. However, in widening jetting regime, the neck travels the longest distance downstream before it breaks.

Large ultrathin shelled drops produced via non-confined microfluidics

We present a facile approach for producing large and monodisperse core-shell drops with ultrathin shells using a single-step process. A biphasic compound jet is introduced into a quiescent third (outer) phase that ruptures to form core-shell drops. Ultrathin shelled drops could only be produced within a certain range of surfactant concentrations and flow rates, highlighting the effect of interfacial tension in engulfing the core in a thin shell. An increase in surfactant concentrations initially resulted in drops with thinner shells. However, the drops with thinnest shells were obtained at an optimum surfactant concentration, and a further increase in the surfactant concentrations increased the shell thickness. Highly monodisperse (coefficient of variation smaller than 3 %) core-shell drops with diameter of ∼200 μm-2 mm with shell thickness as small as ∼2 μm were produced. The resulting drops were stable enough to undergo polymerisation and produce ultrathin shelled capsules.

Dynamical formation of lipid bilayer vesicles from lipid-coated droplets across a planar monolayer at an oil/water interface

Recently, the transfer method has been shown to be useful for preparing cell-sized phospholipid bilayer vesicles, within which desired substances at desired concentrations can be encapsulated, with a desired asymmetric lipid composition. Here, we investigated the transfer process of water-in-oil (W/O) droplets coated by phospholipid monolayers across an oil/water interface by both experimental observation and theoretical modeling. Real-time experimental observation of the transfer revealed that the transfer process is characterized by three kinetic regimes: a precontact process (approaching regime), an early fast process (entering regime), and a late slow process (relaxation regime). In addition, bigger droplets require much more time to transfer than smaller droplets. We propose a theoretical model to interpret this kinetic process. Our theoretical model reproduces the essential aspects of the transfer kinetics, including its size-dependence.

Photonic crystal beads from gravity-driven microfluidics

This Letter reports a simple method for the mass production of 3D colloidal photonic crystal beads (PCBs) by using a gravity-driven microfluidic device and online droplet drying method. Compared to traditional methods, the droplet templates of the PCBs are generated by using the ultrastable gravity as the driving force for the microfluidics, thus the PCBs are formed with minimal polydispersity. Moreover, drying of the droplet templates is integrated into the production process, and the nanoparticles in the droplets self-assemble online. Overall, this process results in PCBs with good morphology, low polydispersity, brilliant structural colors, and narrow stop bands. PCBs could be bulk generated by this process for many practical applications, such as multiplex-encoded assays and the construction of novel optical materials.