Microfluidics and Nanofluidics最新文献

Permeability estimation is crucial for providing fundamental information isrequired to establish production and injection rates. Several experimental and numerical approaches have been developed to evaluate the permeability of rock reservoirs at large scales (core-, reservoir-, and field- scales). However, the evaluation of the permeability at the micro-scale has remained a challenge due to the small length scale, variety and complexity of the porous structure of the microfluidic devices. Increasing usage of microfluidic devices in the petroleum field to visualize the pore events and evaluate enhanced oil recovery (EOR) techniques necessitates characterization of permeability at the pore scale. Herein, by the combination of an integrated microfluidic set-up and the analogous electrical circuit, we upgraded the conventional methods to provide an accurate, reproducible, and practical on-chip approach to the real-time absolute permeability of pore networks. Based on the designed fluidic set-up, a sequential flow rate stepping scheme was optimized and used to estimate the permeability of the porous networks after thoroughly saturating them with a fluorescein solution that was driven to the system by a pressure controller. The permeability of the micromodels was obtained by applying Darcy’s law for laminar flow after estimating the differential pressure across the whole system and the pore networks by measuring the equivalent flow resistances of the fluidic circuit. The method is highly accurate, sensitive, and effectively predicts the absolute permeability of the micromodels. The use of a pressure controller and pressure sensors affords the potential of parallelization of the microfluidic set-up and delivers high throughput compared to the previous proposed techniques. The validation of the approach was based on its independence of the porous medium geology and by providing convergent results between the experimental and computed permeability in the microfluidic devices. Moreover, this approach will help in delivering qualitative and quantitative data to understand capillary phenomena and dominant mechanisms of different chemical EOR processes at the pore scale.

Plant-parasitic root-knot nematodes (RKNs) cause significant damage to plant crops by inhibiting nutrient absorption in host plants through infection. Chemotaxis is an important factor in controlling RKNs behavior as well as in understanding the mechanisms of parasitic behavior of RKNs on plants. Thus, studies on RKN chemotaxis are important for developing more environmentally friendly strategies to manage RKN infestations instead of current control methods using environmentally harmful pesticides. To better understand the chemotactic behavior of RKNs, we developed an easy-to-use microfluidic device consisting of two-layer polydimethylsiloxane (PDMS) microchannel chips and a porous hydrophilic polycarbonate membrane. The porous membrane acts both as a filter in introducing agarose gel containing nematodes to the observation chamber and as a diffuser to generate chemical concentration gradients in chemotaxis assays. We demonstrated the chemical concentration gradient was formed within 5 min in the gel-filled chamber using fluorescence substance. Using this device, we analyzed the correlation between nematode activity (chemotactic behavior and mobility) and the concentration gradients of several chemicals including KNO₃, cadaverine, and putrescine (1, 10 and 100 mM). Finally, we confirmed the repellent effect of KNO₃ and the attractive effect of cadaverine and putrescine on the RKN, Meloidogyne incognita, which was cultured on tomatoes, within 10 min after injecting the chemicals and quantitatively identified the correlation between nematode activity and chemical environmental conditions.

Flowable slurry electrodes play important roles in a few promising technologies for energy and water systems including electrochemical flow capacitors (EFCs) and capacitive deionization. The electrochemical performance of slurry electrodes depends on the hydrodynamic behavior of the porous particles in the slurry that serve as individual capacitors, whose dynamic interactions with the stationary electrodes and between each other are essential for spreading charges to the bulk of the slurry. So far, it has been difficult to directly observe the slurry flow and particle interactions because of the opacity of the activated carbon, a typical particle material in slurries. We previously reported a microfluidic electrochemical flow capacitor (µ-EFC), which is made of transparent materials and allows for simultaneous electrochemical characterization and optical observation of slurry electrodes under continuous flow conditions. However, the placement of the stationary Indium Tin Oxide (ITO) electrodes at the top and bottom of the µ-EFC renders it challenging to directly observe the particle dynamics in the boundary layer of the ITO electrode. Here we report on inclusion of three-dimensional (3D) gold electrodes in the µ-EFC channels, which allows for better visualization of the particle behavior in the boundary layer of stationary electrodes. The results show unique particle behaviors as they flow along and interact with the 3D electrodes of different lengths, which have important implications to the electrochemical performance of slurry electrodes.

Sedimentation is the settling of solid particles in a liquid medium driven by gravity. This phenomenon poses significant challenges in experimental lab-on-chip (LOC) applications, as they often involve a biological sample to be loaded inside a syringe for prolonged periods (e.g. 3D bioprinting, microfluidic cytometers). Mitigating solutions such as mechanical agitators or buffer adjustments exist, but increase the complexity and cost of the setup. In this work, we developed a model of particle sedimentation inside a horizontal syringe, which highlights the importance of several parameters: syringe radius, particle terminal velocity in the buffer, syringe outlet position, and flow-rate. The model provides a simple way to estimate the concentration half-life (({t}_{1/2})), i.e. the time required for the concentration to halve, which is useful during the experiment design process. The model was initially tested numerically and then validated experimentally. Additionally, the applicability of the model to predict sedimentation of biological particles was experimentally demonstrated. Lastly, the model was used to develop guidelines for the design of setups with minimized sedimentation.

Insulator-based dielectrophoresis (iDEP) technology manipulates particles by creating a non-uniform electric field using insulating microchannel structures. It offers advantages such as high operability and electrode-free fabrication. However, the fluid driving and construction of non-uniform electric fields based on iDEP currently mainly relied on direct current (DC), which can easily lead to water electrolysis and the generation of a large amount of Joule heat. In this study, we used two metal tubes as electrodes to apply the AC and inlet/outlet to provide stable liquid flow based on the syringe pump, ensuring stable flow and achieving the focusing of particles and blood cells. Through numerical simulation, a ratchet structure with semicircular tooth surfaces was selected. This structure provides a more uniform distribution of high-field strength regions and can withstand higher flow rates. Subsequently, experiments were conducted to determine the focusing characteristics of particles under different conditions within this chip. Cell focusing throughout improved by nearly 3 times of magnitude compared to that of similar iDEP focusing techniques. Finally, the visualization experiment realized the defined morphology focusing of blood cells, and the optimal focusing ratio reached 7.27, and the focusing characteristics of blood cells were studied. This study is expected to promote the application of dielectrophoresis technology in clinical, biological and other aspects.

Capillary imbibition in periodically constricted tubes (PCTs) plays a critical role in multiple natural and technological processes, where the control of autonomous flows is intrinsically linked to the geometric architecture of the imbibition space. Here we present analytical expressions for the effective radius ((r_{eff})) of PCTs with different wave shapes and analyze how geometric parameters influence the infiltration dynamics. Our analysis reveals that (r_{eff}) is strongly dependent on the ratio of maximum to minimum radii ((alpha)) and, for stepped geometries, on the relative segment length proportion ((gamma)). Increasing (alpha) enhances (r_{eff}) up to a critical value, beyond which a strong reduction is observed: for (alpha >>) 2, approximately, the infiltration velocity progressively decreases. This counterintuitive behavior arises from the interplay between hydrodynamic resistance and capillary driving forces. We evaluated the effect on different geometries, achieving different (r_{eff}) that can be analytically predicted by closed-form expressions. The model was also validated against previously reported experimental data. These findings underline the potential of geometric design to optimize capillary-driven flows, providing a framework for tailoring PCTs to specific applications in microfluidics, porous media, and related fields.

Recycling of thermosetting material with low energy is still a significant challenge due to their stable and strong chemical bonds existed. In this work, we proposed a super-pressure microchannel liquid collision approach that combined microchannel with super-pressure driving and liquid collision to explore the physical and chemical change of crosslinked polyethylene (XLPE), by which the large bond breaking energy can be obtained and imposed on XLPE particles. Here, a super-pressure microchannel liquid collision generator (SP-MLCG) with 300 MPa input pressure and ~600 m/s output speed was designed to obtain the promising collision energy that calculated from the required energies of breaking the crosslinked bonds in XLPE. The particle size, the surface morphology, the molecular weight, the thermal stability, and the melting properties were evaluated step-by-step by optical image, SEM, GPC, TG, and DSC. By using the SP-MCLG, the size of XLPE particles decreased to ~50 μm. Meanwhile, SP-MLCG can lead to the decrease in the proportion of chains with high molecular weight, and in turn produce the reduction of thermal stable, glass transition temperature and melting temperature of XLPE particles. Especially, melt enthalpy can decrease from −89.65 to −64.14 J·g⁻¹. Hence, our proposed technique might be regarded as a promising method that is able to achieve the recycling and reuse of XLPE due to the considerable transformation of its physical and chemical properties.

Droplet microfluidics, a subset of microfluidics, focuses on the controlled generation, manipulation, and transport of micro- to femto-scale droplets. In the last three decades, this technology has become essential in high-throughput applications across biological and chemical analyses, enabling advances in areas such as cell encapsulation, drug screening, digital PCR, and protein crystallization along with applications in chemical mixing, chemical kinetics and chromatography. This review systematically classifies droplet generation methods into classical and contemporary techniques to discuss the technological evolution in droplet generation practice, and further subdivision into passive and active methods based on their operational principles. The paper further discusses about centrifugal microfluidic platform and its applications. Furthermore, the review briefly discusses recent trends in closed-loop feedback based droplet generation methods. By comparing the strengths, limitations, and applications of these techniques, this review provides information on the selection of droplet generation methods for specific applications and highlights potential directions for future research and technological development.

The convection analysis of nanofluid flow under the effect of Marangoni convection, provides important insights into thermal control and fluid dynamics. This phenomenon is critical in many applications, including electronic cooling, heat exchangers, solar thermal collectors, and enhancement in oil recovery by improving fluid flow and promoting controlled crystallization during material processing. Inspired by applications mentioned above, the present research focuses on the couple stress nanofluid flow across a stretching surface while accounting the Marangoni convection, magnetic field, nanoparticles shape factors and thermal radiations. Blood based nanofluid, with the considerations of nanoparticles (gold(Au) and iron-oxide(Fe₂O₃)) is supposed for the present research. Boundary layer assumptions and conservation laws are utilized to model a governing mathematical system for the assumed problem. The emerging partial differential equations (PDEs) of the supposed problem is transformed to the ordinary differential equations (ODEs) by utilizing the appropriate similarity transformations. The numerical outcomes are generated in MATLAB using the bvp4c (approach is designed to solve boundary value problems) solver. Results indicates that the increasing estimates of Marangoni number leads the enhancement in the velocity profile and temperature shows a declining trend in the considered scenarios. It is also observed that the velocity-distribution diminishes for the increasing values of magnetic parameter. The temperature profile of the studied nanofluid is decreasing when the Prandtl number and couple stress parameter increases. The effects of the emerging dimensionless parameters on skin friction and Nusselt number are also revealed in the tabulated form. Research may substantially improve the design of nanofluid-based systems, drug delivery techniques, renewable energy technologies, materials engineering, and electronic cooling systems.

Experimental research on microfluidic devices requires adequate control over surface parameters like wettability. Plasma has already been proven to be a promising tool for the control and alteration of the wettability of solid surfaces, yet its propagation in microfluidic devices and treatment stability remains challenging. Our idea is to produce and propagate an atmospheric pressure helium plasma directly into closed micrometer-size glass channels for in situ wettability treatment. This approach enables better control over the treatment parameters compared to conventional treatments in low-pressure chamber-type plasma reactors. With a homemade kHz dielectric barrier discharge-like setup, we successfully propagated plasma through a (4,hbox {cm}) long rectangular microchannel of uniform depth ((100,upmu hbox {m})) and variable width (250–500 (,upmu hbox {m})). Results obtained by in situ contact angle measurement on images indicate uniform wettability treatment with increased hydrophilic properties after only 1 min of treatment. The wettability achieved on a glass with our setup offers stability for up to 70 days depending on the plasma treatment and storage parameters. Contact angle results are further supported with X-ray photoelectron spectroscopy (XPS) surface analysis which revealed that the two effective mechanisms for wettability alteration are cleaning and surface functionalization.