Controllable high-performance liquid marble micromixer

Dynamic behavior of floating magnetic liquid marbles under steady and pulse-width-modulated magnetic fields

Liquid marbles show promising potential for digital microfluidic devices due to their lower friction with the platform surface than non-covered droplets. In this study, the manipulation of a biocompatible magnetic liquid marble with a magnetic shell (LMMS) is experimentally studied. The movement of the floating LMMS on the water surface, which is actuated by DC and pulse width modulation (PWM) magnetic fields, is investigated under the influence of various parameters, including the LMMS volume, the initial distance of the LMMS from the magnetic coil tip, the magnetic coil current, the PWM frequency and its duty cycle. The LMMS has a shorter travel time to the magnetic coil tip under a DC magnetic field by increasing the magnetic coil current, decreasing the initial distance and its volume. In the PWM mode, these parameters show similar behavior; moreover, increasing the PWM duty cycle and decreasing the PWM frequency shorten the travel time. It is demonstrated that actuation by a PWM magnetic field with step-by-step movement provides better control over manipulation of the floating magnetic marble. The dynamic behavior of an LMMS is compared to a ferrofluid marble (FM), which is formed using a ferrofluid instead of water as its core. It is observed that the LMMS has a lower velocity than the FM.

Mixing Performance Analysis and Optimal Design of a Novel Passive Baffle Micromixer

Micromixers, as crucial components of microfluidic devices, find widespread applications in the field of biochemistry. Due to the laminar flow in microchannels, mixing is challenging, and it significantly impacts the efficiency of rapid reactions. In this study, numerical simulations of four baffle micromixer structures were carried out at different Reynolds numbers (Re = 0.1, Re = 1, Re = 10, and Re = 100) in order to investigate the flow characteristics and mixing mechanism under different structures and optimize the micromixer by varying the vertical displacement of the baffle, the rotation angle, the horizontal spacing, and the number of baffle, and by taking into account the mixing intensity and pressure drop. The results indicated that the optimal mixing efficiency was achieved when the baffle's vertical displacement was 90 μm, the baffle angle was 60°, the horizontal spacing was 130 μm, and there were 20 sets of baffles. At Re = 0.1, the mixing efficiency reached 99.4%, and, as Re increased, the mixing efficiency showed a trend of, first, decreasing and then increasing. At Re = 100, the mixing efficiency was 97.2%. Through simulation analysis of the mixing process, the structure of the baffle-type micromixer was effectively improved, contributing to enhanced fluid mixing efficiency and reaction speed.

Biocompatible Hydrogel-Based Liquid Marbles with Magnetosomes

Liquid marbles are widely known for their potential biomedical applications, especially due to their versatility and ease of preparation. In the present work, we prepared liquid marbles with various cores composed of water, agar-based hydrogels, magnetic fluids, or non-aqueous substances. As a coating material, we used biocompatible particles of plant origin, such as turmeric grains and Lycopodium pollen. Additionally, we provided marbles with magnetic properties by incorporating either magnetosomes or iron oxide nanoparticles as a powder or by injecting another magnetic fluid. Structures obtained in this way were stable and susceptible to manipulation by an external magnetic field. The properties of the magnetic components of our marbles were verified using electron paramagnetic resonance (EPR) spectroscopy and vibrating sample magnetometry (VSM). Our approach to encapsulation of active substances such as antibiotics within a protective hydrogel core opens up new perspectives for the delivery of hydrophobic payloads to the inherently hydrophilic biological environment. Additionally, hydrogel marbles enriched with magnetic materials showed promise as biocompatible heating agents under alternating magnetic fields. A significant innovation of our research was also the fabrication of composite structures in which the gel-like core was surrounded without mixing by a magnetic fluid covered on the outside by the particle shell. Our liquid marbles, especially those with a hydrogel core and magnetic content, due to the ease of preparation and favorable properties, have great potential for biomedical use. The fact that we were able to simultaneously produce, functionalize (by filling with predefined cargo), and manipulate (by means of an external magnetic field) several marbles also seems to be important from an application point of view.

Liquid marbles: review of recent progress in physical properties, formation techniques, and lab-in-a-marble applications in microreactors and biosensors

Liquid marbles (LMs) are nonsticking droplets whose surfaces are covered with low-wettability particles. Owing to their high mobility, shape reconfigurability, and widely accessible liquid/particle possibilities, the research on LMs has flourished since 2001. Their physical properties, fabrication mechanisms, and functionalisation capabilities indicate their potential for various applications. This review summarises the fundamental properties of LMs, the recent advances (mainly works published in 2020-2023) in the concept of LMs, physical properties, formation methods, LM-templated material design, and biochemical applications. Finally, the potential development and variations of LMs are discussed.

Universality of Scaling Laws Governing Contact and Spreading Time Spans of Bouncing Liquid Marbles and its Physical Origin

The impact of liquid marbles coated with a diversity of hydrophobic powders with various solid substrates, including hydrophobic, hydrophilic, and superhydrophobic ones, was investigated. The contact time of the bouncing marbles was studied. Universal scaling behavior of the contact time tc as a function of the Weber number (We) was established; the scaling law tc = tc(We) was independent of the kind of powder and the type of solid substrate. The total contact time consists of spreading time and retraction time. It is weakly dependent on We and this is true for all kinds of studied powders and substrates. This observation hints to the surface tension/inertia spring model governing the impact. By contrast, the spreading time ts scales as [Formula: see text], n = 0.28 - 0.30 ± 0.002. We relate the origin of this scaling law to the viscous dissipation occurring within the spreading marbles. The retraction time tr grows weakly with the Weber number. The scaling law was changed at threshold values of We ≅ 15-20. It is reasonable to explain this change with the breaking of the Leidenfrost regime of spreading under high values of We.

Dynamic Liquid-Liquid Interface: Applying a Spinning Interfacial Microreactor to Actively Converge Biphasic Reactants for the Enhanced Interfacial Reaction

A liquid-liquid interfacial reaction combines reactants with large polarity disparity to achieve greener and more efficient chemistry that is otherwise challenging in traditional single-phase systems. However, current interfacial approaches suffer from the need for a large amount of solvent/reactant/emulsifier and poor reaction performance arising from intrinsic thermodynamic constraints. Herein, we achieve an efficient interfacial reaction by creating a magnetic-responsive, microscale liquid-liquid interface and exploit its dynamic spinning motion to generate vortex-like hydrodynamic flows that rapidly converge biphasic reactants to the point-of-reaction. Notably, the spinning of this functional interface at 800 rpm boosts the reaction efficiency and its apparent equilibrium constant by > 500-fold and 10⁵-fold, respectively, higher than conventional methods that utilize bulk and/or non-dynamic liquid interfaces, even with external mechanical stirring. By driving reaction equilibrium toward favorable product formation, our unique design offers enormous opportunities to realize efficient multiphasic reactions crucial for diverse applications in chemical synthesis, environmental remediation, and even molecular recycling.