Experimental study on dynamic interfacial tension with mixture of SDS-PEG as surfactants in a coflowing microfluidic device

Multiphase displacement manipulated by micro/nanoparticle suspensions in porous media via microfluidic experiments: From interface science to multiphase flow patterns

Multiphase displacement in porous media can be adjusted by micro/nanoparticle suspensions, which is widespread in many scientific and industrial contexts. Direct visualization of suspension flow dynamics and corresponding multiphase patterns is crucial to understanding displacement mechanisms and eventually optimizing these processes in geological, biological, chemical, and other engineering systems. However, suspension flow inside the opaque realistic porous media makes direct observation challenging. The advances in microfluidic experiments have provided us with alternative methods to observe suspension influence on the interface and multiphase flow behaviors at high temporal and spatial resolutions. Macroscale processes are controlled by microscale interfacial behaviors, which are affected by multiple physical factors, such as particle adsorption, capillarity, and hydrodynamics. These properties exerted on the suspension flow in porous media may lead to interesting interfacial phenomena and new displacement consequences. As an underpinning science, understanding and controlling the suspension transport process from interface to flow patterns in porous media is critical for a lower operating cost to improve resource production while reducing harmful emissions and other environmental impacts. This review summarizes the basic properties of different micro/nanoparticle suspensions and the state-of-the-art microfluidic techniques for displacement research activities in porous media. Various suspension transport behaviors and displacement mechanisms explored by microfluidic experiments are comprehensively reviewed. This review is expected to boost both experimental and theoretical understanding of suspension transport and interfacial interaction processes in porous media. It also brings forward the challenges and opportunities for future research in controlling complex fluid flow in porous media for diverse applications.

Comparison of surfactant mass transfer with drop formation times from dynamic interfacial tension measurements in microchannels

Dynamic interfacial tension was studied experimentally during drop formation in a flow-focusing microchannel. A low viscosity silicone oil (4.6 mPa s) was the continuous phase and a mixture of 48% w/w water and 52% w/w glycerol was the dispersed phase. An anionic (sodium dodecylsulfate, SDS), a cationic (dodecyltrimethylammonium bromide, DTAB) and a non-ionic (Triton™ X-100, TX100) surfactant were added in the dispersed phase, at concentrations below and above the critical micelle concentration (CMC). For SDS and DTAB the drop size against continuous phase flowrate curves initially decreased with surfactant concentration and then collapsed to a single curve at concentrations above CMC. For TX100 the curves only collapsed at surfactant concentrations 8.6 times the CMC. From the collapsed curves a correlation of drop size with capillary number was derived, which was used to calculate the dynamic interfacial tension at times as low as 3 ms. The comparison of the surfactant mass transport and adsorption times to the interface against the drop formation times indicated that surfactant adsorption also contributes to the time required to reach equilibrium interfacial tension. Criteria were proposed for drop formation times to ensure that equilibrium interfacial tension has been reached and does not affect the drop formation.

Multiphase Microfluidics: Fundamentals, Fabrication, and Functions

Multiphase microfluidics enables an alternative approach with many possibilities in studying, analyzing, and manufacturing functional materials due to its numerous benefits over macroscale methods, such as its ultimate controllability, stability, heat and mass transfer capacity, etc. In addition to its immense potential in biomedical applications, multiphase microfluidics also offers new opportunities in various industrial practices including extraction, catalysis loading, and fabrication of ultralight materials. Herein, aiming to give preliminary guidance for researchers from different backgrounds, a comprehensive overview of the formation mechanism, fabrication methods, and emerging applications of multiphase microfluidics using different systems is provided. Finally, major challenges facing the field are illustrated while discussing potential prospects for future work.

Numerical Study of Surfactant Dynamics during Emulsification in a T-Junction Microchannel

Microchannel emulsification requires large amounts of surfactant to prevent coalescence and improve emulsions lifetime. However, most numerical studies have considered surfactant-free mixtures as models for droplet formation in microchannels, without taking into account the distribution of surfactant on the droplet surface. In this paper, we investigate the effects of nonuniform surfactant coverage on the microfluidic flow pattern using an extended lattice-Boltzmann model. This numerical study, supported by micro-particle image velocimetry experiments, reveals the likelihood of uneven distribution of surfactant during the droplet formation and the appearance of a stagnant cap. The Marangoni effect affects the droplet breakup by increasing the shear rate. According to our results, surfactant-free and surfactant-rich droplet formation processes are qualitatively different, such that both the capillary number and the Damköhler number should be considered when modeling the droplet generation in microfluidic devices. The limitations of traditional volume and pressure estimation methods for determining the dynamic interfacial tension are also discussed on the basis of the simulation results.

Investigation of dynamic surface tension in gas–liquid absorption using a microflow interfacial tensiometer

Dynamic surface tension in gas–liquid absorption is studied using a microflow device.

Mass-Transfer-Controlled Dynamic Interfacial Tension in Microfluidic Emulsification Processes

Varied interfacial tension caused by the unsaturated adsorption of surfactants on dripping droplet surfaces is experimentally studied. The mass transfer and adsorption of surfactants, as well as the generation of fresh interfaces, are considered the main factors dominating the surfactant adsorption ratio on droplet surfaces. The diffusion and convective mass transfer of the surfactants are first distinguished by comparing the adsorption depth and the mass flux boundary layer thickness. A characterized mass transfer time is then calculated by introducing an effective diffusion coefficient. A time ratio is furthermore defined by dividing the droplet generation time by the characteristic mass transfer time, t/tm, in order to compare the rates of surfactant mass transfer and droplet generation. Different control mechanisms for different surfactants are analyzed based on the range of t/t(m), and a criterion time ratio using a simplified characteristic mass transfer time, t(m)*, is finally proposed for predicting the appearance of dynamic interfacial tension.