Suppression of dendrite growth by cross-flow in microfluidics

Scientific Reports, 2016

It is shown that surface conduction can stabilize electrodeposition in random, charged porous media at high rates, above the diffusion-limited current. After linear sweep voltammetry and impedance spectroscopy, copper electrodeposits are visualized by scanning electron microscopy and energy dispersive spectroscopy in two different porous separators (cellulose nitrate, polyethylene), whose surfaces are modified by layer-by-layer deposition of positive or negative charged polyelectrolytes. Above the limiting current, surface conduction inhibits growth in the positive separators and produces irregular dendrites, while it enhances growth and suppresses dendrites behind a deionization shock in the negative separators, also leading to improved cycle life. The discovery of stable uniform growth in the random media differs from the non-uniform growth observed in parallel nanopores and cannot be explained by classic quasi-steady "leaky membrane" models, which always predict instability and dendritic growth. Instead, the experimental results suggest that transient electro-diffusion in random porous media imparts the stability of a deionization shock to the growing metal interface behind it. Shock electrodeposition could be exploited to enhance the cycle life and recharging rate of metal batteries or to accelerate the fabrication of metal matrix composite coatings.

The Analyst, 2015

Current Nanoscience, 2012

This interdisciplinary view of microfluidics at the interface with life sciences starts with presentation of the advantages and challenges presented by microfluidic devices. The forces important for flow in microchannels are discussed and special emphasis is placed on electrokinetic effects. The laws and principles governing flow in microchannels are compared to those important in macroflow and experimental methods used to measure flow in microchannels are introduced. Because flow in microchannels is laminar, for many applications there is need to enhance mixing and different ways to achieve this are presented herein. Due to the important influence of surface interactions for microfluidics, the materials used to manufacture microchannels are very important in flow control. A separate section discusses glass, silicon-based materials, and newer soft polymers used in microfluidic devices and the connection between their structure and the properties they impart to the flow. The field in which there are already numerous commercially available microfluidic devices is biotechnology. Some applications are discussed in a separate section. Lab-on-a-chip devices, due to their importance, are presented in a separate unit. Future directions of research in this interdisciplinary field are briefly discussed.

Sensors and Actuators B: Chemical, 2011

A flexible strategy for the on-demand control of the particle enrichment and positioning in a microfluidic channel is proposed and demonstrated by the use of a locally controlled floating metal electrode attached to the channel bottom wall. The channel is subjected to an axially acting global DC electric field, but the degree of charge polarization of the floating electrode is governed largely by a local control of the voltage applied to two micron-sized control electrodes (CEs) on either side of the floating electrode (FE). This strategy allows an independent tuning of the electrokinetic phenomena engendered by the floating electrode regardless of the global electric field across the channel, thus making the method for particle manipulation far more versatile and flexible. In contrast to a dielectric microchannel wall possessing a nearly uniform surface charge (or zeta potential), the patterned metal strip (floating electrode) is polarized under electric field resulting in a non-uniform distribution of the induced surface charge with a zero net surface charge, and accordingly induced-charge electro-osmotic (ICEO) flow. The ICEO flow can be regulated by the control electric field through tuning the magnitude and polarity of the voltage applied to the CEs, which in turn affects both the hydrodynamic field as well as the particle motion. By controlling the control electric field, on-demand control of the particle enrichment and its position inside a microfluidic channel has been experimentally demonstrated. Buffalo in 1987. His research interests cover aspects of mechanics and instabilities of soft visco-elastic interfaces; thin films and nano-confined systems; self-organized mesopatterning of polymers, ceramics, hydrogels and carbon; interfacial and colloidal interactions; wetting and adhesion; smart and functional materials: adhesives, catalytic, optical, super-hydrophobic and nano-composites; biosurfaces: surface chemistry of cornea and tear film; cell adhesion; and interfaces in membranes and microfluidics.

ELECTROPHORESIS, 2021

Electrokinetically driven insulator-based microfluidic devices represent an attractive option to manipulate particle suspensions. These devices can filtrate, concentrate, separate, or characterize micro and nanoparticles of interest. Two decades ago, inspired by electrodebased dielectrophoresis, the concept of insulator-based dielectrophoresis (iDEP) was born. In these microfluidic devices, insulating structures (i.e., posts, membranes, obstacles, or constrictions) built within the channel are used to deform the spatial distribution of an externally generated electric field. As a result, particles suspended in solution experience dielectrophoresis (DEP). Since then, it has been assumed that DEP is responsible for particle trapping in these devices, regardless of the type of voltage being applied to generate the electric field-direct current (DC) or alternating current. Recent findings challenge this assumption by demonstrating particle trapping and even particle flow reversal in devices that prevent DEP from occurring (i.e., unobstructed long straight channels stimulated with a DC voltage and featuring a uniform electric field). The theory introduced to explain those unexpected observations was then applied to conventional "DC-iDEP" devices, demonstrating better prediction accuracy than that achieved with the conventional DEP-centered theory. This contribution summarizes contributions made during the last two decades, comparing both theories to explain particle trapping and highlighting challenges to address in the near future.

Micromachines, 2017

We present a total of 19 articles in this special issue of Micromachines entitled, "Insights and Advancements in Microfluidics." Among the 19 articles, two perspectives, eight reviews, and nine research articles were solicited from leading researchers, pioneers, and emerging investigators. The topics covered in this issue ranges from biology, chemistry, and physics to the intersection of engineering, optics, and material sciences. As editors for this issue, we are both gratified and extremely thankful for the overwhelming responses and contributions from our fellow colleagues within the field of microfluidics. The special issue is themed to provide both insights and advancements in microfluidics. This well-timed issue touches on a field which has evolved tremendously in the last few decades. Professor Yanyi Huang from Peking University of China provided his unique insight and perspective on digital polymerase chain reaction (PCR) [1]. In his article, an informative guide was provided on the proper designing rules of digital PCR at the micro-scale. Professor Guoqing Hu from the Chinese Academy of Sciences, Beijing, China, provided his astute insights and perspective on particle manipulation based on hydrodynamic effect [2]. His article summarizes both the progress and fundamental mechanisms in particle manipulation using elasto-inertial microfluidics. In the eight reviews articles, different branches and sub-branches of microfluidics were presented and comprehensively reviewed. These include microfluidic sensing, liquid handling, optofluidics, the use of microfluidics in cytotoxicity, Janus micro-motors, single-cell impedance cytometry, droplets, and polymer microfluidics. We were extremely fortunate to receive contributions from both Professor Dongqing Li and Professor Nam-Trung Nguyen. Both are leading pioneers and extraordinary visionary leaders in the field of microfluidics. Professor Li et al. [3] reviewed the basic theories in both microfluidic and nanofluidic resistive pulse sensing (RPS). His article focuses on the latest developments in the last six years. Future research direction and challenges in this area are also outlined in the review. Professor Nguyen et al. [4] discussed the recent advances and future perspective on microfluidic liquid handling. The first part of the review covers two main and opposing applications of liquid handling in continuous-flow microfluidics: mixing and separation. The second part focuses on various digital microfluidic strategies based on both droplets and liquid marbles. The applications of the emerging field of liquid-marble-based digital microfluidics are also highlighted in the article. Song et al. [5] provided an overview on the recent development of optofluidics. They discussed the critical challenges that hamper the transformation of optofluidic technologies from lab-based procedures to practical usages and commercialization. Priest et al. [6] reviewed the different microfluidic chips that can used for toxicity screening. Li et al. [7] discussed the self-propulsion of a platinum-silica (Pt-SiO 2) spherical Janus micro-motor (JM). Their paper reviews

Journal of Crystal Growth, 2015

Design, fabrication and testing of an apparatus for in-situ investigation of free dendritic growth under an applied electric field,

Journal of The Electrochemical Society, 2021

This work deals with the formation of dendritic structures by electrodeposition of Cu2+ and Ag+ without supporting electrolyte in Hele-Shaw cells. The transition between the two main patterns, ramified branches and dendrites, is specifically addressed at the scale of branch microstructure using careful SEM observations. Ramified branches, composed only of grain assemblies, are obtained at low current densities because of a re-nucleation process induced by space charge dynamics (Fleury, Nature, 1997). For current densities higher than a given threshold, ramified branches are also formed by re-nucleation but another growth mode, the dendritic growth, is also observed while, at the macro-scale, the pattern remains fractal and isotropic. This shows that 1) pattern transition originates from a morphological transition at microstructure scale and 2) the re-nucleation process enables a freedom in local growth direction allowing the pattern to be fractal at the macro-scale. The onset of the...

Cell electrofusion in microfluidic devices attracted great attention in recent years due to its widespread applications potential in cell-based studies. In these microfluidic devices, many manipulation methods, such as chemical conjugation, electric field induced dielectrophoresis, and microfluidic controlling based on microstructure, are used to improve the pairing precision of cells, especially heterogeneous cells. High-strength electric field can produce minipores on cell membrane and induce cell fusion. It can be generated by a constricting electric field with microstructures or two microelectrodes. In comparison with the traditional electrofusion or other cell-fusion methods, microfluidic cell-electrofusion method has many advantages such as precise manipulation, high efficiency in cell pairing and fusion, higher cell viability, lower sample contamination and smaller Joule heating effect. In this article, the development of various microfluidic cell-electrofusion methods is reviewed. Some important parameters affecting the cell electrofusion are discussed in detail. Techniques that can be integrated on microfluidic devices for high-efficiency cell electrofusion, such as on-chip cell separation and culture, are also discussed comprehensively.

CORROSION, 1990

As part of an investigation of electrochemical failure mechanisms occurring in electronic devices, factors affecting the formation and growth rate of dendrites on a model microelectronic device substrate have been examined. Experiments have been performed by immersing the devices in selected electrolytes and using a potentiostat to apply a constant cathodic potential or a constant potential bias. The effects of electrolyte composition and cathodic overpotential on dendrite formation and growth rate in HCl electrolytes have been delineated. Dendrites were observed at lower pH, but none were observed when the pH > 5.0, due to the formation of insoluble copper corrosion products such as Cu20. Several features of the growth of dendrites in 0.1 M HCl electrolytes were observed to be similar to previous investigations: a minimum cathodic potential (approximately-0.450 V vs a saturated calomel electrode [SCE]) was required for the appearance and propagation of copper dendrites; at constant cathodic overpotential, the growth rate of dendrites was found to have a linear dependence on copper ion concentration; and the induction time prior to the detection of dendrites decreased as the cathodic overpotential increased. Although, experimentally measured dendrite growth rates were found to be up to three orders of magnitude smaller than theoretical predictions based on a maximum growth velocity model of dendrite growth, the model is stijl useful for predicting the functional dependence of velocity on a variety of electrochemical parameters. Suggestions for the development of an alternate, more accurate model are provided.