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Ranabir Dey

Bio: Ranabir Dey is an academic researcher from MESA+ Institute for Nanotechnology. The author has contributed to research in topics: Electrowetting & Contact angle. The author has an hindex of 17, co-authored 39 publications receiving 646 citations. Previous affiliations of Ranabir Dey include University of Twente & Max Planck Society.

Papers
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Journal ArticleDOI
TL;DR: In this article, the heat transfer characteristics associated with thermally fully developed combined electromagnetohydrodynamic flows through narrow flow conduits, considering electrokinetics effects, for the constant wall heat flux condition were analyzed.

113 citations

Journal ArticleDOI
TL;DR: The underlying electrokinetic phenomenon results in enhanced liquid transport through the paper-fibre matrix, which exhibits significant active electrical controllability and improved repeatability.
Abstract: We demonstrate the occurrence of electrokinetic phenomenon in paper substrates, by developing a simple “paper-and-pencil” device. The underlying electrokinetic phenomenon results in enhanced liquid transport through the paper-fibre matrix, which exhibits significant active electrical controllability and improved repeatability. These bear far-ranging consequences towards opening up a new paradigm of fluidics over small scales.

68 citations

Journal ArticleDOI
TL;DR: In this article, closed form solutions for the Nusselt number were obtained for hydrodynamically and thermally fully developed combined electroosmotic and pressure-driven flows in narrow confinements for the constant wall heat flux boundary condition.
Abstract: In the present paper, closed form solutions for the Nusselt number are obtained for hydrodynamically and thermally fully developed combined electroosmotic and pressure-driven flows in narrow confinements for the constant wall heat flux boundary condition. Overcoming the constraints of the standard models that are valid only within thin electrical double layer (EDL) limits, the effects of thick electric double layers are accounted for as a distinctive feature of this model. Along with Joule heating, viscous dissipation effects, which are particularly important for ultrathin channel dimensions (typically conforming to the cases of thick EDLs), are taken into account. The results are presented in terms of appropriate nondimensional parameters depicting the relative EDL thickness with respect to the channel height, as well as relative strengths of Joule heating and viscous dissipation effects.

67 citations

Journal ArticleDOI
TL;DR: In this article, the authors report bimodal motility in autophoretic droplet swimmers, driven by characteristic interfacial flow patterns for each propulsive mode, and demonstrate a dynamical transition from quasiballistic to bimanual chaotic propulsion by controlling the viscosity of the environment.
Abstract: Artificial model swimmers offer a platform to explore the physical principles enabling biological complexity, for example, multigait motility: a strategy employed by many biomicroswimmers to explore and react to changes in their environment. Here, we report bimodal motility in autophoretic droplet swimmers, driven by characteristic interfacial flow patterns for each propulsive mode. We demonstrate a dynamical transition from quasiballistic to bimodal chaotic propulsion by controlling the viscosity of the environment. To elucidate the physical mechanism of this transition, we simultaneously visualize hydrodynamic and chemical fields and interpret these observations by quantitative comparison to established advection-diffusion models. We show that, with increasing viscosity, higher hydrodynamic modes become excitable and the droplet recurrently switches between two dominant modes due to interactions with the self-generated chemical gradients. This type of self-interaction promotes self-avoiding walks mimicking examples of efficient spatial exploration strategies observed in nature.

50 citations

Journal ArticleDOI
TL;DR: In this paper, a frugal, printing-based fabrication methodology for paper channels is presented, in which the normal ink-jet cartridge ink is used to create the barriers for the paper channels, without involving any additional complex materials or intermediary ink modification steps.
Abstract: We demonstrate here a frugal, printing-based fabrication methodology for paper channels, in an effort towards developing an inexpensive micromixing device. The proposed fabrication methodology utilizes the normal ink-jet cartridge ink to create the barriers for the paper channels, without involving any additional complex materials or intermediary ink modification steps. We show through experimental observations, and pertinent scaling analysis, that the electrokinetic effects, along with the capillary and viscous forces, play a significant role in enhancing the liquid transport rate through such a paper channel under an applied electrical potential, in comparison with that observed due to natural imbibition. Thereafter, we delineate the modality of active electrical control of mixing of two liquids in such a printed ‘zigzag’ ‘paper-and-pencil’ device, by exploiting the interplay between the electrohydrodynamic flows stemming from the electrokinetic phenomena and the specific channel geometry. The electrokinetically mediated flow of the liquid samples through the ‘zigzag’ paper channel can be judiciously controlled to either appreciably enhance the mixing characteristics or artificially maintain the segregation of the liquid streams by overriding the inherent wicking action-driven mixing within the paper matrix. Hence, the present endeavour will usher in a new generation of paper microfluidic platforms for micromixing, with enhanced production feasibility, controllability, functioning efficiency, and multiplexing capability.

48 citations


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TL;DR: This two-part series considers steric effects on diffuse charge dynamics (in the absence of electro-osmotic flow) and two simple models for the charging of a thin double layer, which must form a condensed layer of close-packed ions near the surface at high voltage.
Abstract: The classical Poisson-Boltzmann (PB) theory of electrolytes assumes a dilute solution of point charges with mean-field electrostatic forces. Even for very dilute solutions, however, it predicts absurdly large ion concentrations (exceeding close packing) for surface potentials of only a few tenths of a volt, which are often exceeded, e.g. in microfluidic pumps and electrochemical sensors. Since the 1950s, several modifications of the PB equation have been proposed to account for the finite size of ions in equilibrium, but in this two-part series, we consider steric effects on diffuse charge dynamics (in the absence of electro-osmotic flow). In this first part, we review the literature and analyze two simple models for the charging of a thin double layer, which must form a condensed layer of close-packed ions near the surface at high voltage. A surprising prediction is that the differential capacitance typically varies non-monotonically with the applied voltage, and thus so does the response time of an electrolytic system. In PB theory, the capacitance blows up exponentially with voltage, but steric effects actually cause it to decrease above a threshold voltage where ions become crowded near the surface. Other nonlinear effects in PB theory are also strongly suppressed by steric effects: The net salt adsorption by the double layers in response to the applied voltage is greatly reduced, and so is the tangential "surface conduction" in the diffuse layer, to the point that it can often be neglected compared to bulk conduction (small Dukhin number).

603 citations

Journal ArticleDOI
TL;DR: This review introduces the design, fabrication and applications of paper-based SCs, giving a comprehensive coverage of this interesting field.
Abstract: Paper-based supercapacitors (SCs), a novel and interesting group of flexible energy storage devices, are attracting more and more attention from both industry and academia. Cellulose papers with a unique porous bulk structure and rough and absorptive surface properties enable the construction of paper-based SCs with a reasonably good performance at a low price. The inexpensive and environmentally friendly nature of paper as well as simple fabrication techniques make paper-based SCs promising candidates for the future ‘green’ and ‘once-use-and-throw-away’ electronics. This review introduces the design, fabrication and applications of paper-based SCs, giving a comprehensive coverage of this interesting field. Challenges and future perspectives are also discussed.

512 citations

Journal ArticleDOI
TL;DR: An up-to-date overview of both technological and chemical aspects of liquid phase oxidation chemistry in continuous-flow microreactors is given, including the use of oxygen, hydrogen peroxide, ozone and other oxidants in flow.
Abstract: Continuous-flow liquid phase oxidation chemistry in microreactors receives a lot of attention as the reactor provides enhanced heat and mass transfer characteristics, safe use of hazardous oxidants, high interfacial areas, and scale-up potential. In this review, an up-to-date overview of both technological and chemical aspects of liquid phase oxidation chemistry in continuous-flow microreactors is given. A description of mass and heat transfer phenomena is provided and fundamental principles are deduced which can be used to make a judicious choice for a suitable reactor. In addition, the safety aspects of continuous-flow technology are discussed. Next, oxidation chemistry in flow is discussed, including the use of oxygen, hydrogen peroxide, ozone and other oxidants in flow. Finally, the scale-up potential for continuous-flow reactors is described.

402 citations

Journal ArticleDOI
TL;DR: This work focuses on three-Dimensional Electrochemical Detection, which automates the very labor-intensive and therefore time-heavy and expensive process of characterize and characterize the electrochemical activity of the response of the immune system.
Abstract: Applications Yuanyuan Yang,† Eka Noviana,† Michael P. Nguyen,† Brian J. Geiss,‡ David S. Dandy, and Charles S. Henry*,†,§ †Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, United States ‡Department of Microbiology, Immunology, and Pathology, Colorado State University, Fort Collins, Colorado 80523, United States Department of Chemical and Biological Engineering, Colorado State University, Fort Collins, Colorado 80523, United States ■ CONTENTS Fabrication 71 Hydrophobic/Solvent Barrier 72 Deposition 73 Flow and Injection Control 74 Three-Dimensional Devices 75 Incorporating Nonsensing Electrodes 75 Colorimetric Detection 75 Detectors and Readout 75 Reflectance-Based Measurement 75 Transmittance-Based Measurement 77 Instrument-Free Measurement 77 Biomedical Applications 77 Enzymatic Methods 77 Immunoassays 78 Other 79 Environmental Applications 79 Other Applications 80 Electrochemical Detection 80 Electrodes 80 Carbon Electrodes 81 Metallic Electrodes 81 Biological Applications 82 Glucose Sensors 82 Immunosensors 84 Other Examples 84 Environmental Applications 84 Other Technologies 85 Chemiluminescence and Electrochemiluminescence 85 Fluorescence 85 Surface-Enhanced Raman Spectroscopy 85 Separation 86 Preconcentration 86 Conclusions and Future Directions 87 Author Information 87 Corresponding Author 87 ORCID 87 Notes 87 Biographies 87 Acknowledgments 88 References 88

388 citations

Journal ArticleDOI
Yan Zhang1, Lina Zhang1, Kang Cui1, Shenguang Ge1, Xin Cheng1, Mei Yan1, Jinghua Yu1, Hong Liu1 
TL;DR: It is envisioned that more design concepts, working principles, and advanced papermaking techniques will be developed in the near future for the advanced functionalization of paper, paving the way for the mass production and commercial applications of flexible paper-based flexible electronics.
Abstract: Over the past several years, a new surge of interest in paper electronics has arisen due to the numerous merits of simple micro/nanostructured substrates. Herein, the latest advances and principal issues in the design and fabrication of paper-based flexible electronics are highlighted. Following an introduction of the fascinating properties of paper matrixes, the construction of paper substrates from diverse functional materials for flexible electronics and their underlying principles are described. Then, notable progress related to the development of versatile electronic devices is discussed. Finally, future opportunities and the remaining challenges are examined. It is envisioned that more design concepts, working principles, and advanced papermaking techniques will be developed in the near future for the advanced functionalization of paper, paving the way for the mass production and commercial applications of flexible paper-based electronic devices.

278 citations