Convective Instabilities of Electrokinetic Flows in a Cross-Shaped Microchannel

2004 ◽  
Author(s):  
Jonathan D. Posner ◽  
Juan G. Santiago
Keyword(s):  
Electric Fields ◽  
Epifluorescence Microscopy ◽  
Bulk Liquid ◽  
Mixing Rate ◽  
Sample Stacking ◽  
Convective Instabilities ◽  
Absolute Flow ◽  
Average Probability ◽  
Electrokinetic Flows ◽  
Indeterminate Sample

Electrokinetic instabilities (EKI) in cross-shaped channels are relevant to injections for field amplified sample stacking, flow intersections in multi-dimensional assay devices, and electrokinetic systems with indeterminate sample chemistry. Electrokinetic instabilities are generated by a coupling of electric fields and ionic conductivity gradients. This coupling results in an electric body force in the bulk liquid that can generate temporal, convective, and absolute flow instabilities. In this work, we perform a parametric experimental study of convective instabilities in cross-shaped microchannels using epifluorescence microscopy and digital imaging. We report coherent flow structures and show that the critical electric field for instability is both a function of center-to-sheath conductivity ratio and applied field ratio. Finally, we quantify the degree of mixing rate of electrokinetically unstable flows with time-average probability density functions of concentration profiles.

Nonlinear Dynamics of Electrokinetic Instabilities

2005 ◽  
Author(s):  
Jonathan D. Posner ◽  
Juan G. Santiago
Keyword(s):  
Electric Fields ◽  
High Speed ◽  
Power Spectra ◽  
Epifluorescence Microscopy ◽  
Bulk Liquid ◽  
Sample Stacking ◽  
Electrokinetic Instability ◽  
Absolute Flow ◽  
Electrokinetic Flows ◽  
Continuous Power

Electrokinetic instabilities are generated by a coupling of electric fields and ionic conductivity gradients. This coupling results in an electric body force in the bulk liquid that can generate temporal, convective, and absolute flow instabilities. In this work, we perform a parametric experimental study of convective instabilities in cross-shaped microchannels using epifluorescence microscopy and high speed digital imaging. We report temporal power spectra and spatiotemporal maps as a function of the applied field. The spectral analyses reveal that disturbances induced by electrokinetic instability are purely sinuous at the onset of instability and exhibit higher-order harmonics, frequency bifurcations, and continuous power spectra with increasing electric Rayleigh number. Electrokinetic instabilities (EKI) in cross-shaped channels are relevant to injections for field amplified sample stacking, electrokinetic flows at the intersections in multi-dimensional assay devices, and systems with indeterminate sample chemistry.

Surface confinement induces the formation of solid-like insulating ionic liquid nanostructures

2017 ◽  
Author(s):  
Massimiliano Galluzzi ◽  
Simone Bovio ◽  
Paolo Milani ◽  
Alessandro Podestà
Keyword(s):  
Ionic Liquid ◽  
Electrical Properties ◽  
Electric Fields ◽  
Relative Dielectric Constant ◽  
Ionic Mobility ◽  
Electric Properties ◽  
Bulk Liquid ◽  
Structural Reorganization ◽  
Surface Confinement ◽  
Insulator Layers

We report on the modification of the electric properties of the imidazolium-based [BMIM][NTf2] ionic liquid upon surface confinement in the sub-monolayer regime. Solid-like insulating nanostructures of [BMIM][NTf2] spontaneously form on a variety of insulating substrates, at odd with the liquid and conductive nature of the same substances in the bulk phase. A systematic spatially resolved investigation by atomic force microscopy of the morphological, mechanical and electrical properties of [BMIM][NTf2] nanostructures showed that this liquid substance rearranges into lamellar nanostructures with a high degree of vertical order and enhanced resistance to mechanical compressive stresses and very intense electric fields, denoting a solid-like character. The morphological and structural reorganization has a profound impact on the electric properties of supported [BMIM][NTf2] islands, which behave like insulator layers with a relative dielectric constant between 3 and 5, comparable to those of conventional ionic solids, and significantly smaller than those measured in the bulk ionic liquid. These results suggest that in the solid-like ordered domains confined either at surfaces or inside the pores of the nanoporous electrodes of photo-electrochemical devices, the ionic mobility and the overall electrical properties can be significantly perturbed with respect to the bulk liquid phase, which would likely influence the<br>performance of the devices.<br>

Ab initio spectroscopy of water under electric fields

2019 ◽  
Vol 21 (38) ◽  
pp. 21205-21212 ◽  
Author(s):  
Giuseppe Cassone ◽  
Jiri Sponer ◽  
Sebastiano Trusso ◽  
Franz Saija
Keyword(s):  
Ab Initio ◽  
Raman Spectra ◽  
Electric Fields ◽  
Liquid Water ◽  
High Frequency ◽  
Water Structure ◽  
Ir And Raman Spectra ◽  
Bulk Liquid ◽  
Librational Mode ◽  
Ir And Raman

IR and Raman spectra of bulk liquid water under intense electric fields reveal the contraction of both spectra and the onset of a novel high-frequency librational mode band. Moreover, the water structure evolves toward “ice-like” arrangements.

scholarly journals Dynamics of Field Amplified Sample Stacking

2001 ◽  
Author(s):  
Rajiv Bharadwaj ◽  
Juan G. Santiago
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Concentration Field ◽  
Initial Step ◽  
Step Function ◽  
Buffer Concentration ◽  
Sample Stacking ◽  
Sample Concentration ◽  
Concentration Enhancement ◽  
Channel Configuration

Abstract We present an analysis and an experimental study of field amplified sample stacking. The analysis consists of a one dimensional, unsteady electromigration model of the concentration fields in sample stacking. The model predicts that the sample concentration develops as a non-linear concentration wave with a peak concentration increasing with time that reaches a maximum value determined by ratio of electric fields in the sample and the buffer region. The experimental work is a preliminary study of the effects of electroosmotic flow on sample stacking for a single fluid-fluid interface within a glass microchannel. Using a simple cross-channel configuration a high-gradient initial step-function in the buffer concentration field was established which causes an unsteady sample concentration process. The experimental results qualitatively confirm the wave-like profile of the stacked analyte predicted by the analytical model. Experiments also provide evidence of internal pressure generation due to mis-matched electroosmotic velocities during stacking. The effect of electric field strength and sample-to-background buffer concentration ratio, γ, are also presented. Stacked sample concentration at γ = 4 is found to initially increase with increasing electric field but saturates at higher electric fields. Stacking rates at higher γ ratios indicate that concentration enhancement is quickly limited by dispersion due to internally generated pressure gradients.

Novel Application of Microfluidic Channels in Studying Cell Migration and Reorientation in Response to Direct Current Electric Fields

2002 ◽  
Author(s):  
P. Grace Chao ◽  
Elsa Angelini ◽  
Zhongliang Tang ◽  
Winston Chang ◽  
J. Chloe¨ Bulinski ◽  
...  
Keyword(s):  
Cell Migration ◽  
Electric Fields ◽  
Cell Shape ◽  
Cell Types ◽  
Microfluidic System ◽  
Epifluorescence Microscopy ◽  
Microfluidic Channels ◽  
Embryonic Cells ◽  
Dimethyl Siloxane ◽  
Underlying Mechanisms

Electric fields have been shown to induce cell migration (galvanotaxis) and cell shape changes (galvanotropism) in many cell types, such as neural crest cells, embryonic cells, and chondrocytes [1–3]. In this study, a novel microfluidic system was developed to study individual cellular responses to applied electric fields. These microfabricated channels are made from commercially available poly-dimethyl-siloxane (PDMS). This gas permeable, tough, and transparent polymer provides a sterile tissue culture environment and permits visualization of cells using epifluorescence microscopy. In conjunction with the device, a custom computer program was written to quantify the migratory behavior of cells by analyzing changes in position and cell shape. The flexibility of the channel geometry allows for a wider range of chamber resistance and applied currents (achieving a particular field strength) that may permit further study into the underlying mechanisms of electric field directed cell migration and orientation.

Lubrication theory for electro-osmotic flow in a non-uniform electrolyte

2007 ◽  
Vol 576 ◽  
pp. 139-172 ◽  
Author(s):  
T. L. SOUNART ◽  
J. C. BAYGENTS
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Numerical Solutions ◽  
Fluid Velocity ◽  
Lubrication Theory ◽  
Debye Screening Length ◽  
Sample Stacking ◽  
Osmotic Flow ◽  
Analytic Expressions ◽  
Electro Osmotic Flow

A lubrication theory has been developed for the electro-osmotic flow of non-uniform buffers in narrow rectilinear channels. The analysis applies to systems in which the transverse dimensions of the channel are large compared with the Debye screening length of the electrolyte. In contrast with related theories of electrokinetic lubrication, here the streamwise variations of the velocity field stem from, and are nonlinearly coupled to, spatiotemporal variations in the electrolyte composition. Spatially non-uniform buffers are commonly employed in electrophoretic separation and transport schemes, including iso-electric focusing (IEF), isotachophoresis (ITP), field-amplified sample stacking (FASS), and high-ionic-strength electro-osmotic pumping. The fluid dynamics of these systems is controlled by a complex nonlinear coupling to the ion transport, driven by an applied electric field. Electrical conductivity gradients, attendent to the buffer non-uniformities, result in a variable electro-osmotic slip velocity and, in electric fields approaching 1 kV cm−1, Maxwell stresses drive the electrohydrodynamic circulation. Explicit semi-analytic expressions are derived for the fluid velocity, stream function, and electric field. The resulting approximations are found to be in good agreement with full numerical solutions for a prototype buffer, over a range of conditions typical of microfluidic systems. The approximations greatly simplify the computational analysis, reduce computation times by a factor 4–5, and, for the first time, provide general insight on the dominant fluid physics of two-dimensional electrically driven transport.

Surface confinement induces the formation of solid - like insulating ionic liquid nanostructures

2018 ◽  
Author(s):  
Massimiliano Galluzzi ◽  
Simone Bovio ◽  
Paolo Milani ◽  
Alessandro Podestà
Keyword(s):  
Ionic Liquid ◽  
Electrical Properties ◽  
Electric Fields ◽  
Relative Dielectric Constant ◽  
Ionic Mobility ◽  
Electric Properties ◽  
Bulk Liquid ◽  
Structural Reorganization ◽  
Surface Confinement ◽  
Insulator Layers

We report on the modification of the electric properties of the imidazolium-based [BMIM][NTf2] ionic liquid upon surface confinement in the sub-monolayer regime. Solid-like insulating nanostructures of [BMIM][NTf2] spontaneously form on a variety of insulating substrates, at odd with the liquid and conductive nature of the same substances in the bulk phase. A systematic spatially-resolved investigation by atomic force microscopy of the morphological, mechanical and electrical properties of [BMIM][NTf2] nanostructures showed that this liquid substance rearranges into lamellar nanostructures with a high degree of vertical order and enhanced resistance to mechanical compressive stresses and very intense electric fields, denoting a solid-like character. The morphological and structural reorganization has a profound impact on the electric properties of supported [BMIM][NTf2] islands, which behave like insulator layers with a relative dielectric constant between 3 and 5, comparable to those of conventional ionic solids, and significantly smaller than those measured in the bulk ionic liquid. These results suggest that in the solid-like ordered domains confined either at surfaces or inside the pores of the nanoporous electrodes of photo-electrochemical devices, the ionic mobility and the overall electrical properties can be significantly perturbed with respect to the bulk liquid phase, which would likely influence the performance of the devices. <br><br>Published on J. Phys. Chem. C, 2018, 122 (14), pp 7934–7944. DOI: 10.1021/acs.jpcc.7b12600. <br>

scholarly journals Surface confinement induces the formation of solid - like insulating ionic liquid nanostructures

2018 ◽  
Author(s):  
Massimiliano Galluzzi ◽  
Simone Bovio ◽  
Paolo Milani ◽  
Alessandro Podestà
Keyword(s):  
Ionic Liquid ◽  
Electrical Properties ◽  
Electric Fields ◽  
Relative Dielectric Constant ◽  
Ionic Mobility ◽  
Electric Properties ◽  
Bulk Liquid ◽  
Structural Reorganization ◽  
Surface Confinement ◽  
Insulator Layers

We report on the modification of the electric properties of the imidazolium-based [BMIM][NTf2] ionic liquid upon surface confinement in the sub-monolayer regime. Solid-like insulating nanostructures of [BMIM][NTf2] spontaneously form on a variety of insulating substrates, at odd with the liquid and conductive nature of the same substances in the bulk phase. A systematic spatially-resolved investigation by atomic force microscopy of the morphological, mechanical and electrical properties of [BMIM][NTf2] nanostructures showed that this liquid substance rearranges into lamellar nanostructures with a high degree of vertical order and enhanced resistance to mechanical compressive stresses and very intense electric fields, denoting a solid-like character. The morphological and structural reorganization has a profound impact on the electric properties of supported [BMIM][NTf2] islands, which behave like insulator layers with a relative dielectric constant between 3 and 5, comparable to those of conventional ionic solids, and significantly smaller than those measured in the bulk ionic liquid. These results suggest that in the solid-like ordered domains confined either at surfaces or inside the pores of the nanoporous electrodes of photo-electrochemical devices, the ionic mobility and the overall electrical properties can be significantly perturbed with respect to the bulk liquid phase, which would likely influence the performance of the devices.<br>

Electrokinetic Dispersion in Field Amplified Sample Stacking

2018 ◽  
Author(s):  
Kaushlendra Dubey ◽  
Amit Gupta ◽  
Supreet Singh Bahga
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Body Force ◽  
Vital Role ◽  
Scaling Analysis ◽  
Unstable Flow ◽  
Sample Stacking ◽  
Concentration Enhancement ◽  
High Electric Fields ◽  
Conductivity Gradient

In this work, we performed an experimental study of electrohydrodynamic effects on the dispersion of sample ions in field amplified sample stacking (FASS). A typical FASS experiment involves a streamwise electrical conductivity gradient collinear to the applied electric field to enhance the sample stacking. Earlier studies on FASS have focused on how the conductivity gradient sets a non-uniform electro-osmotic flow which causes the dispersion. However, the coupling of the electric field with conductivity gradient leads to a destabilizing electric body force and generates unstable flow. This work demonstrates that generated body force influences the dynamics of FASS. We present a scaling analysis to show that at high fields, electrohydrodynamic effects play a vital role in sample dispersion. To justify our scaling arguments, we performed experiments at varied electric fields which shows that at high electric fields maximum concentration enhancement is lowered significantly. To ensure the EHD effects on the dynamics of FASS, we have also performed experiments with suppressed EOF conditions.

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