Name: generation and control of electrohydrodynamic flows in aqueous electrolyte solutions
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The authors have no acknowledgments.

1. EHD Flow Induced by Rectified Ion Transport
<ol>
	<li>Development of a flow channel device to rectify ion transport pathways
	<ol>
		<li>Make a PTFE mold of the reservoir:
		<ol>
			<li>Cut a 13 x 30 x 10 mm3 mold from a polytetrafluoroethylene (PTFE) block using a milling machine (see Figure 2). Alternatively, purchase a custom-made product.</li>
			<li>Adhere acrylic plates of 15 x 18 x 1 mm3 at both ends of the PTFE mold with a plastic adhesive,...

<ol>
	<li>Stuetzer, O. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ion+drag+pressure+generation.">Ion drag pressure generation.</a> Journal of Applied Physics. 30, 984-994 (1959).</li><li>Stuetzer, O. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ion+drag+pumps.">Ion drag pumps.</a> Journal of Applied Physics. 31, 136-146 (1960).</li><li>Melcher, J. R., Taylor, G. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrohydrodynamics:+A+review+of+the+role+of+interfacial+shear+stresses.">Electrohydrodynamics: A review of the role of interfacial shear stresses.</a> Annual Review of Fluid Mechanics. 1, 111-146 (1969).</li><li>Saville, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrohydrodynamics:+The+Taylor-Melcher+leaky+dielectric+model.">Electrohydrodynamics: The Taylor-Melcher leaky dielectric model.</a> Annual Review of Fluid Mechanics. 29, 27-64 (1997).</li><li>Stein, D., Kruithof, M., Dekker, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface-charge-governed+ion+transport+in+nanofluidic+channels.">Surface-charge-governed ion transport in nanofluidic channels.</a> Physical Review Letters. 93, 035901 (2004).</li><li>Dekker, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Solid-state+nanopores.">Solid-state nanopores.</a> Nature Nanotechnology. 2, 209-215 (2007).</li><li>Schoch, R. 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A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electric+field+modulation+of+the+membrane+potential+in+solid-state+ion+channels.">Electric field modulation of the membrane potential in solid-state ion channels.</a> Nano Letters. 12, 6441-6447 (2012).</li><li>Yasui, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=DNA+manipulation+and+separation+in+sublithographic-scale+nanowire+array.">DNA manipulation and separation in sublithographic-scale nanowire array.</a> ACS Nano. 7, 3029-3035 (2013).</li><li>Ren, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Particle+rotational+trapping+on+a+floating+electrode+by+rotating+induced-charge+electroosmosis.">Particle rotational trapping on a floating electrode by rotating induced-charge electroosmosis.</a> Biomicrofluidics. 10, 054103 (2016).</li><li>Ren, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flexible+particle+&#64258;ow-focusing+in+microchannel+driven+by+droplet-directed+induced-charge+electroosmosis.">Flexible particle &#64258;ow-focusing in microchannel driven by droplet-directed induced-charge electroosmosis.</a> ELECTROPHORESIS. 39, 597-607 (2018).</li><li>Qian, W., Doi, K., Uehara, S., Morita, K., Kawano, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Theoretical+study+of+the+transpore+velocity+control+of+single-stranded+DNA.">Theoretical study of the transpore velocity control of single-stranded DNA.</a> International Journal of Molecular Sciences. 15, 13817-13832 (2014).</li><li>Qian, W., Doi, K., Kawano, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+polymer+length+and+salt+concentration+on+the+transport+of+ssDNA+in+nanofluidic+channels.">Effect of polymer length and salt concentration on the transport of ssDNA in nanofluidic channels.</a> Biophysical Journal. 112, 838-849 (2017).</li><li>Liu, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+universal+design+of+field-effect-tunable+microfluidic+ion+diode+based+on+a+gating+cation-exchange+nanoporous+membrane.">A universal design of field-effect-tunable microfluidic ion diode based on a gating cation-exchange nanoporous membrane.</a> Physics of Fluids. 29, 112001 (2017).</li><li>Liu, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Control+of+two-phase+flow+in+microfluidics+using+out-of-phase+electroconvective+streaming.">Control of two-phase flow in microfluidics using out-of-phase electroconvective streaming.</a> Physics of Fluids. 29, 112002 (2017).</li><li>Osman, O. O., Shintaku, H., Kawano, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+micro-vibrating+flow+pumps+using+MEMS+technologies.">Development of micro-vibrating flow pumps using MEMS technologies.</a> Microfluidics and Nanofluidics. 13, 703-713 (2012).</li><li>Osman, O. O., Shirai, A., Kawano, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+numerical+study+on+the+performance+of+micro-vibrating+flow+pumps+using+the+immersed+boundary+method.">A numerical study on the performance of micro-vibrating flow pumps using the immersed boundary method.</a> Microfluidics and Nanofluidics. 19, 595-608 (2015).</li><li>Daiguji, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ion+transport+in+nanofluidic+channels.">Ion transport in nanofluidic channels.</a> Chemical Society Reviews Home. 39, 901-911 (2010).</li><li>Ristenpart, W. D., Aksay, I. A., Saville, D. 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B., Hann, J., Renaud, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+the+surface+charge+on+ion+transport+through+nanoslits.">Effect of the surface charge on ion transport through nanoslits.</a> Physics of Fluids. 17, 100604 (2005).</li><li>Ross, D., Johnson, T. J., Locascio, L. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Imaging+of+electroosmotic+flow+in+plastic+microchannels.">Imaging of electroosmotic flow in plastic microchannels.</a> Analytical Chemistry. 73, 2509-2515 (2001).</li><li>Hsieh, S. -. S., Lin, H. -. C., Lin, C. -. 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K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+insulating+walls+on+the+structure+of+electrodynamic+flows+in+a+channel.">Effect of insulating walls on the structure of electrodynamic flows in a channel.</a> Technical Physics. 57, 1181-1187 (2012).</li><li>Yano, A., Doi, K., Kawano, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Observation+of+electrohydrodynamic+flow+through+a+pore+in+ion-exchange+membrane.">Observation of electrohydrodynamic flow through a pore in ion-exchange membrane.</a> International Journal of Chemical Engineering and Applications. 6, 254-257 (2015).</li><li>Doi, K., Yano, A., Kawano, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrohydrodynamic+flow+through+a+1+mm2+cross-section+pore+placed+in+an+ion-exchange+membrane.">Electrohydrodynamic flow through a 1 mm2 cross-section pore placed in an ion-exchange membrane.</a> The Journal of Physical Chemistry B. 119, 228-237 (2015).</li><li>Yano, A., Shirai, H., Imoto, M., Doi, K., Kawano, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Concentration+dependence+of+cation-induced+electrohydrodynamic+flow+passing+through+an+anion+exchange+membrane.">Concentration dependence of cation-induced electrohydrodynamic flow passing through an anion exchange membrane.</a> Japanese Journal of Applied Physics. 56, 097201 (2017).</li><li>Nagura, R., Doi, K., Kawano, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterisation+of+microparticle+transport+driven+by+ionic+current+conditions+in+electrically+polarized+aqueous+solutions.">Characterisation of microparticle transport driven by ionic current conditions in electrically polarized aqueous solutions.</a> Micro &amp; Nano Letters. 12, 526-531 (2017).</li><li>Doi, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nonequilibrium+ionic+response+of+biased+mechanically+controllable+break+junction+(MCBJ)+electrodes.">Nonequilibrium ionic response of biased mechanically controllable break junction (MCBJ) electrodes.</a> The Journal of Physical Chemistry C. 118, 3758-3765 (2014).</li></ol>

The purpose of this study was to separate cations and anions in aqueous solutions in terms of spatial distributions and transport numbers. Using an anion-exchange membrane, the transport of anions and cations could be rectified in the membrane and in a flow channel that penetrates the membrane, respectively. Alternatively, a cation-exchange membrane that separated high and low concentration solutions worked to generate electrically polarized solutions after a considerable waiting time. As a result, rectified ionic curren...

Recently, liquid flow control techniques have attracted much attention because of interest in the applications of micro- and nanofluidic devices1,2,3,4,5,6,7,8,9,10,11,12,13,14,15. In polar solutions, such as aqueous solutions and ionic liquids, ions and electrically charged particles usually bring about electrical charges in liquid flows. The transport of such polarized particles provides an expansion of various applications, such as single-molecule manipulation6,10,11,13,14,15,16,17, ion diode devices12,18, and liquid flow control19,20,21,22. EHD flow has been an applicable phenomenon for liquid flow control systems since Stuetzer1,2 invented the ion drag pump. Melcher and Taylor3 published an important article in which the theoretical framework of EHD flow was well reviewed and some outstanding experiments were also demonstrated. Saville4 and his coworkers23,24 contributed to the following expansion of EHD technologies in liquids. However, there were some limitations to inducing liquid flows driven by electric forces, because tens of kV have to be applied in liquids to inject electrical charges in non-polar solutions, such as oils, to polarize them1,2,3. This is a disadvantage for aqueous solutions because the water electrolysis that is induced by an electric potential higher than 1.23 V changes the characteristics of solutions and makes the solutions unstable.
In micro- and nanofluidic channels, surface charges of channel walls cause the concentration of counterions that effectively induce electroosmotic flows (EOFs) under externally applied electric fields25,26,27,28,29. Using EOFs, some liquid pumping techniques have been applied in aqueous solutions, reducing the electric voltages30,31,32. On the other hand, EOFs are limited to being generated in micro- and nanospaces in which surface areas become more dominant than liquid volumes. Furthermore, depending on the transport of highly concentrated ions very near the wall surfaces, such as in electric double layers, the slip boundary only causes the liquid flow, which may not be sufficient to make pressure gradients7,8,22,26,27. Fine tuning, such as to channel dimensions and salt concentrations, is required for the applications of EOF. In contrast, EHD flows driven by body forces seem to be available to transport masses and energies if the application voltages can be reduced to avoid degrading solvents. Recently, some researchers have suggested applications of EHD flows with low voltages33,34,35,36. Although these technologies have not yet been implemented, the frontiers are expected to expand.
In previous studies, we also conducted experimental and theoretical work on EHD flows in aqueous solutions37,38,39,40. It was supposed that the rectification of ion transport pathways was effective to generate electrically charged solutions that cause electric body forces under electric fields. By using an ion-exchange membrane and a flow channel crossing the membrane, we were able to rectify ionic currents. When applying an anion-exchange membrane, cations concentrated in the flow channel dragged the solvents and developed an EHD flow37,38,39. A difference in the mobility of ion species was an important factor when separating the cationic and anionic currents. Ion-exchange membranes effectively worked to modulate the mobility due to the ion selectivity. Ion transport phenomena were also investigated from the viewpoint of ionic current density influenced by applied electric fields41. These studies have been fruitful for developing manipulation techniques for single molecules, namely, micro- and nanoparticles, whose motions are strongly affected by thermal fluctuations11,16,17. EOFs and EHD flows are expected to expand the variety of precise flow control methods as well as pressure gradients.
In this study, we demonstrate two methods to drive EHD flows in aqueous solutions. First, an NaOH solution is used for a working fluid to drive an EHD flow37,38,39. An anion-exchange membrane separates the liquid into two parts. A polydimethylsiloxane (PDMS) flow channel with a cross-section of 1 x 1 mm and a length of 3 mm penetrates the membrane. By applying an electric potential of 2.2 V, the electrophoretic transport of Na+, H+, and OH&#8722; ions is induced along the electric fields. An anion-exchange membrane and a flow channel effectively work to separate the ion transport pathways, where anions dominantly pass through the membrane and cations concentrate in the flow channel, although both species usually move in opposite directions, maintaining the electroneutrality. Thus, such a condition does not cause a driving force for liquid flows. This structure is crucial to generating an EHD flow whose flow speed reaches on the order of 1 mm/s in the channel because highly concentrated cations accelerated by external electric fields drag solvent molecules. EHD flows are observed and recorded by using a microscope and a high-speed camera as shown in Figure 1. Second, a concentration difference between two liquid phases separated by an ion-exchange membrane causes an electrically polarized condition to be generated crossing an ion-exchange membrane40. In this study, we find the importance of a considerable waiting time to equilibrate ion distributions and a corresponding electric potential, which cause preferable conditions to apply to a body force in a liquid. Crossing the ion-exchange membrane, a weakly polarized condition is achieved. In such a condition, an externally applied electric field induces directional ion transport that generates a body force in a liquid, and as a result, the momentum transfer from the ions to the solvent develops an EHD flow.
As mentioned above, the present devices succeed in drastically decreasing the applied voltage difference to a few volts, and thus this method is can be used for aqueous solutions, although the conventional electrical charge injection methods required tens of kV and are limited to an application to non-aqueous solutions.

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		<tr height="42">
			<td height="42" style="height:42px;width:283px;">Sylgard 184</td>
			<td style="width:279px;">Dow Corning Corp.</td>
			<td style="width:187px;">3097366-0516, 3097358-1004</td>
			<td style="width:167px;">PDMS</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Acetone</td>
			<td style="width:279px;">Wako Pure Chemical Industries, Ltd.</td>
			<td style="width:187px;">012-00343</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Ethanol</td>
			<td style="width:279px;">Wako Pure Chemical Industries, Ltd.</td>
			<td style="width:187px;">054-00461</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">0.1 mol/L Sodium Hydroxide Solution</td>
			<td style="width:279px;">Wako Pure Chemical Industries, Ltd.</td>
			<td style="width:187px;">196-02195</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Pottasium Chloride</td>
			<td style="width:279px;">Wako Pure Chemical Industries, Ltd.</td>
			<td style="width:187px;">163-03545</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Tris-EDTA buffer 100x concentrate</td>
			<td style="width:279px;">Sigma-Aldrich Co. LLC.</td>
			<td style="width:187px;">T9285-10014L</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">2.93 &#956;m polystyrene particle</td>
			<td style="width:279px;">Merck KGaA</td>
			<td style="width:187px;">L300 Rouge</td>
			<td>Tracer particle</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">1.01 &#956;m polystyrene particle</td>
			<td style="width:279px;">Merck KGaA</td>
			<td style="width:187px;">K100(23716)</td>
			<td>Tracer particle</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Anion exchange membrane</td>
			<td style="width:279px;">ASTOM Corp.</td>
			<td style="width:187px;">Neosepta AHA</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Gold (Au)</td>
			<td style="width:279px;">Furuuchi Chemical Corp.</td>
			<td style="width:187px;">AUT-13301X</td>
			<td>Sputtering target metal</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Titanium</td>
			<td style="width:279px;">Furuuchi Chemical Corp.</td>
			<td style="width:187px;">TIT-72301X</td>
			<td>Sputtering target metal</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Chromium</td>
			<td style="width:279px;">Furuuchi Chemical Corp.</td>
			<td style="width:187px;">CRT-24301X</td>
			<td>Sputtering target metal</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Hight-speed CMOS camera</td>
			<td style="width:279px;">Keyence Corp.</td>
			<td style="width:187px;">VW-600M</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Microscope</td>
			<td style="width:279px;">Keyence Corp.</td>
			<td style="width:187px;">VW-9000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Data logger</td>
			<td style="width:279px;">Keyence Corp.</td>
			<td style="width:187px;">NR-500, NR-HA08</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Laser displacement meter</td>
			<td style="width:279px;">Keyence Corp.</td>
			<td style="width:187px;">LK-G5000, LK-H008W</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">PIV and PTV software</td>
			<td style="width:279px;">DITECT Co. Ltd.</td>
			<td style="width:187px;">Flownizer 2D</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Potentiostat</td>
			<td style="width:279px;">AMTEK Inc.&#160;</td>
			<td style="width:187px;">VersaSTAT4</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Inverted microscope</td>
			<td style="width:279px;">Olympus Corp.</td>
			<td style="width:187px;">IX73</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">High-speed CMOS camera</td>
			<td style="width:279px;">Andor Technology Ltd.</td>
			<td style="width:187px;">Zyla 5.5 sCMOS</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Function generator</td>
			<td style="width:279px;">NF Corp.&#160;</td>
			<td style="width:187px;">WF1945B</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Function generator</td>
			<td style="width:279px;">NF Corp.&#160;</td>
			<td style="width:187px;">WF1973</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Ultrasonic cleaner</td>
			<td style="width:279px;">AS ONE Corp.</td>
			<td style="width:187px;">AS22GTU</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Rotary pump</td>
			<td style="width:279px;">ULVAC, Inc.</td>
			<td style="width:187px;">G-100S</td>
			<td>Degas liquid PDMS</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Rotary pump</td>
			<td style="width:279px;">ULVAC, Inc.</td>
			<td style="width:187px;">GLD-201A</td>
			<td>Sputtering&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">Molecular diffusion pump</td>
			<td style="width:279px;">ULVAC, Inc.</td>
			<td style="width:187px;">VPC-400</td>
			<td>Sputtering</td>
		</tr>
	</tbody>
</table>

generation and control of electrohydrodynamic flows in aqueous electrolyte solutions

To drive electrohydrodynamic (EHD) flows in aqueous solutions, the separation of cation and anion transport pathways is essential because a directed electric body force has to be induced by ionic motions in liquid. On the other hand, positive and negative charges attract each other, and electroneutrality is maintained everywhere in equilibrium conditions. Furthermore, an increase in an applied voltage has to be suppressed to avoid water electrolysis, which causes the solutions to become unstable. Usually, EHD flows can be induced in non-aqueous solutions by applying extremely high voltages, such as tens of kV, to inject electrical charges. In this study, two methods are introduced to generate EHD flows induced by electrical charge separations in aqueous solutions, where two liquid phases are separated by an ion-exchange membrane. Due to a difference in the ionic mobility in the membrane, ion concentration polarization is induced between both sides of the membrane. In this study, we demonstrate two methods. (i) The relaxation of ion concentration gradients occurs via a flow channel that penetrates an ion-exchange membrane, where the transport of the slower species in the membrane selectively becomes dominant in the flow channel. This is a driving force to generate an EHD flow in the liquid. (ii) A long waiting time for the diffusion of ions passing through the ion-exchange membrane enables the generation of an ion-dragged flow by externally applying an electric field. Ions concentrated in a flow channel of a 1 x 1 mm2 cross-section determine the direction of the liquid flow, corresponding to the electrophoretic transport pathways. In both methods, the electric voltage difference required for an EHD flow generation is drastically reduced to near 2 V by rectifying the ion transport pathways.

Figure 4 (video figure) presents a representative result of an EHD flow generation, resulting from the rectification of ion transport pathways and highly concentrated cations that induced a liquid flow in the channel, according to step 1 of the protocol. Figure 5 shows a result of the PIV analysis, where 20 data points near the center of the channel (y = z = 0 mm) were averaged. In the case of the 1 x 10&#8...

Watch this Scientific Journal Video about Generation and Control of Electrohydrodynamic Flows in Aqueous Electrolyte Solutions at JoVE.com

Generation and Control of Electrohydrodynamic Flows in Aqueous Electrolyte Solutions

The rectification of ion transport pathways is an effective method to generate one-directional ion-dragged electrohydrodynamic flows. By setting an ion-exchange membrane in a flow channel, an electrically polarized condition is generated and causes a liquid flow to be driven when an electric field is externally applied.

To drive electrohydrodynamic (EHD) flows in aqueous solutions, the separation of cation and anion transport pathways is essential because a directed ...

This method can help answer key questions in the micro and nano fluidic research fields, such as how effectively leakage are transported in narrow spaces. The main advantage of this technique is that cations and anions, whose transport pathways are electrified by using an ion exchange membrane, drive the electrohydrodynamic flow. Demonstrating the procedures be Ayoko Yano an assistant professor of Gunma University, who graduated from our laboratory, and Fumika Nito, a PHD student from our laboratory.First, adhere acrylic plates at both ends of a PTFE mold with a plastic adhesive, which will make slits in the reservoir to settle the bias electrodes. In a 50 milliliter tube, mix a silicone elastomer base in curing agent in a ten to one ratio. Following this, set a liquid PDMS in a vacuum vessel, and de-gas it using a rotary pump.Remove the tube from the vacuum vessel. Then pour the PDMS into a 40 by 50 by 24 millimeter cubed plastic vessel, to mold the outer shape of the reservoir, and place the reservoir mold in it. Bake the whole body of the liquid PDMS on a hot plate at 80 degrees Celsius for about four hours.After the bake, isolate the PDMS reservoir from the PTFE mold in the outer vessel by hand. Then make a slit across the center of the reservoir, using a surgical knife. Using tweezers, set glass plates, previously coated with a gold thin film, at both ends of the reservoir, to serve as the bias electrodes.Next, cut an anion exchange membrane into a 20 by 18 millimeter squared rectangle, using scissors. Then cut a three by five point five millimeter squared rectangle from one edge of the membrane. Now, cut a solidified PDMS block with a square flow channel into a three by six by four point five millimeter cubed piece, using a surgical knife.Make slits along the outer edges, and attach it to the membrane within the rectangular cutout. Following this, set the anion exchange membrane with the PDMS flow channel into the PDMS reservoir, with tweezers. Using a micropipette, fill the reservoir with four milliliters of sodium hydroxide solution.Apply an electric potential of two point two volts, using a DC power source, in forward and backward directions, for two hours each in series, to improve the conductivity of the membrane before observation. Following this, pull the gold electrodes out with tweezers. Then, remover the solution from the reservoir, using a micropipette.Set new gold electrodes in the reservoir with tweezers. Fill the reservoir with four milliliters of sodium hydroxide solution, using a micropipette. At this point, set the frame rate and the exposure time of a high-speed complimentary metal oxide semiconductor camera to 500 frames per second and one millisecond, respectively.Remove any bubbles from the channel, by inserting the tip of a micropipette into the channel end to push or pull them out, before applying an electric potential. Now, externally apply an electric potential of two point two volts to the gold bias electrodes. Simultaneously monitor the electrical responses, using a potentiostat, then record the behavior of the tracer particles on the computer.Form gold bias electrodes with a 26 by 10 millimeter squared surface on the bottom glass plate, according to procedures similar to those previously described. Using radio frequency sputtering, coat the glass surface with chromium exposed to argon plasma for two minutes at 75 watts, and deposit a gold, thin film for five minutes at 75 watts. Using a solder iron, solder a lead line at an edge of the electrodes.From a large silicone rubber sheet, cut out two chambers, each made made of a one by one by one millimeter cubed flow channel placed between two reservoirs, using a surgical knife. Next, cut out a cation exchange membrane to 20 by 30 millimeter squared, using a surgical knife. Ultrasonicate each part in pure water for 15 minutes, by applying 100 watts.Insert the cation exchange membrane between the chambers, using tweezers, then press and seal the stack of the chambers and cation exchange membrane, with glass plates. Using syringes, inject previously prepared Tris-EDTA polystyrene particle and Tris-EDTA potassium chloride solutions into the lower and upper chambers, respectively. Now, set the experimental device on the stage of an inverted microscope.Connect the microscope to the high-speed complimentary metal oxide semiconductor camera to monitor the trajectories of the particle motions, and record the observation data on a computer. Finally, apply an electric potential difference of two volts per six seconds between the two electrodes, by using a function generator as a power source. A representative result of an EHD flow generation, resulting from the rectification of ion transport pathways and highly concentrated cations that induced a liquid flow in the channel, is presented here.The PIV analysis, demonstrated that the velocity of the tracer particles quickly increased to a peak value, when an eclectic potential of two point two volts was applied. After that, the velocity decreased and converged to zero. A representative result of the EHD flow generated in an electrically polarized solution, under ionic current conditions, is shown here.The velocity response of the EHD flow was analyzed by tracking the tracer particles, which responded to the electric field when two volts was applied. The particles quickly translocated in the backward direction, and, after a short time response, the flow changed to the forward direction, and the velocity became steady, until the electric potential was turned off. The EHD flow, dragged by sodium ions in the channel, is triggered by the transport of hydroxide ions in an anion exchange membrane.In EHD flow, induced under cationic current conditions, potassium ions penetrate a cation exchange membrane, causing cation dominant conditions, and, as a result, EHD flow is induce along the cationic current. Once mastered, this technique can be done in two hours, if it is performed properly. Note taking into account the time for both the gold electrodes and waiting for the electride solution to stabilize.While attempting this procedure, it is important to remember that incorporation of the electride solutions takes a considerable amount of time. When following this procedure, The electro neutral condition has to be moderated in ionic current conditions to drive the electrohydrodynamic flows. After its development, this technique paved the way for researchers in the field of micro and nano fluidic fanomer, to explore new flow control methods in various types of leakage.After watching this video, you should have a good understanding of how to make electrohydrodynamic flow that are induced by electrified ionic currents. Don't forget that working with high-concentration sodium hydroxide can be extremely hazardous, and precautions, such as wearing safety glasses, gloves and a lab coat should always be taken, while performing this procedure.

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The Preparation of Electrohydrodynamic Bridges from Polar Dielectric Liquids

Horizontal and vertical liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields (8-20 kV/cm) and polar dielectric liquids. These bridges are unique from capillary bridges in that they exhibit extensibility beyond a few millimeters, have complex bi-directional mass transfer patterns, and emit non-Planck infrared radiation. A number of common solvents can form such bridges as well as low conductivity solutions and colloidal suspensions. The macroscopic behavior is governed by electrohydrodynamics and provides a means of studying fluid flow phenomena without the presence of rigid walls. Prior to the onset of a liquid bridge several important phenomena can be observed including advancing meniscus height (electrowetting), bulk fluid circulation (the Sumoto effect), and the ejection of charged droplets (electrospray). The interaction between surface, polarization, and displacement forces can be directly examined by varying applied voltage and bridge length. The electric field, assisted by gravity, stabilizes the liquid bridge against Rayleigh-Plateau instabilities. Construction of basic apparatus for both vertical and horizontal orientation along with operational examples, including thermographic images, for three liquids (e.g., water, DMSO, and glycerol) is presented.

Horizontal and vertical electrohydrodynamic liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields and polar dielectric liquids. The construction of basic apparatus and operational examples, including thermographic images, for three liquids (e.g., water, DMSO, and glycerol) is presented.

Horizontal and vertical liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields (8-20 kV/cm) and ...

Non-aqueous Electrode Processing and Construction of Lithium-ion Coin Cells

Research into new and improved materials to be utilized in lithium-ion batteries (LIB) necessitates an experimental counterpart to any computational analysis. Testing of lithium-ion batteries in an academic setting has taken on several forms, but at the most basic level lies the coin cell construction. In traditional LIB electrode preparation, a multi-phase slurry composed of active material, binder, and conductive additive is cast out onto a substrate. An electrode disc can then be punched from the dried sheet and used in the construction of a coin cell for electrochemical evaluation. Utilization of the potential of the active material in a battery is critically dependent on the microstructure of the electrode, as an appropriate distribution of the primary components are crucial to ensuring optimal electrical conductivity, porosity, and tortuosity, such that electrochemical and transport interaction is optimized. Processing steps ranging from the combination of dry powder, wet mixing, and drying can all critically affect multi-phase interactions that influence the microstructure formation. Electrochemical probing necessitates the construction of electrodes and coin cells with the utmost care and precision. This paper aims at providing a step-by-step guide of non-aqueous electrode processing and coin cell construction for lithium-ion batteries within an academic setting and with emphasis on deciphering the influence of drying and calendaring.

Non-aqueous electrode processing is central to the construction of coin cells and the evaluation of new electrode chemistries for lithium-ion batteries. A step-by-step guide to the basic practices needed as an electrochemical engineer working with batteries in an academic experimental setting is furnished.

Research into new and improved materials to be utilized in lithium-ion batteries (LIB) necessitates an experimental counterpart to any computational ...

Free-form Light Actuators &#8212; Fabrication and Control of Actuation in Microscopic Scale

Liquid crystalline elastomers (LCEs) are smart materials capable of reversible shape-change in response to external stimuli, and have attracted researchers&#39; attention in many fields. Most of the studies focused on macroscopic LCE structures (films, fibers) and their miniaturization is still in its infancy. Recently developed lithography techniques, e.g., mask exposure and replica molding, only allow for creating 2D structures on LCE thin films. Direct laser writing (DLW) opens access to truly 3D fabrication in the microscopic scale. However, controlling the actuation topology and dynamics at the same length scale remains a challenge.
In this paper we report on a method to control the liquid crystal (LC) molecular alignment in the LCE microstructures of arbitrary three-dimensional shape. This was made possible by a combination of direct laser writing for both the LCE structures as well as for micrograting patterns inducing local LC alignment. Several types of grating patterns were used to introduce different LC alignments, which can be subsequently patterned into the LCE structures. This protocol allows one to obtain LCE microstructures with engineered alignments able to perform multiple opto-mechanical actuation, thus being capable of multiple functionalities. Applications can be foreseen in the fields of tunable photonics, micro-robotics, lab-on-chip technology and others.

Free-form Light Actuators &amp;#8212; Fabrication and Control of Actuation in Microscopic Scale

Here, we fabricate 3D polymeric micro/nano structures in which both the shape and the molecular alignment can be engineered with nanometer scale accuracy by the use of direct laser writing. Light induced deformation of several types of liquid crystalline elastomer microstructures can be controlled in the microscopic scale.

Liquid crystalline elastomers (LCEs) are smart materials capable of reversible shape-change in response to external stimuli, and have attracted ...

Gain-compensation Methodology for a Sinusoidal Scan of a Galvanometer Mirror in Proportional-Integral-Differential Control Using Pre-emphasis Techniques

Galvanometer mirrors are used for optical applications such as target tracking, drawing, and scanning control because of their high speed and accuracy. However, the responsiveness of a galvanometer mirror is limited by its inertia; hence, the gain of a galvanometer mirror is reduced when the control path is steep. In this research, we propose a method to extend the corresponding frequency using a pre-emphasis technique to compensate for the gain reduction of galvanometer mirrors in sine-wave path tracking using proportional-integral-differential (PID) control. The pre-emphasis technique obtains an input value for a desired output value in advance. Applying this method to control the galvanometer mirror, the raw gain of a galvanometer mirror in each frequency and amplitude for sine-wave path tracking using a PID controller was calculated. Where PID control is not effective, maintaining a gain of 0 dB to improve the trajectory tracking accuracy, it is possible to expand the speed range in which a gain of 0 dB can be obtained without tuning the PID control parameters. However, if there is only one frequency, amplification is possible with a single pre-emphasis coefficient. Therefore, a sine wave is suitable for this technique, unlike triangular and sawtooth waves. Hence, we can adopt a pre-emphasis technique to configure the parameters in advance, and we need not prepare additional active control models and hardware. The parameters are updated immediately within the next cycle because of the open loop after the pre-emphasis coefficients are set. In other words, to regard the controller as a black box, we need to know only the input-to-output ratio, and detailed modeling is not required. This simplicity allows our system to be easily embedded in applications. Our method using the pre-emphasis technique for a motion-blur compensation system and the experiment conducted to evaluate the method are explained.

We propose a method to extend the corresponding frequency by using a pre-emphasis technique. This method compensates for the gain reduction of a galvanometer mirror in sine-wave path tracking using proportional-integral-differential control.

Galvanometer mirrors are used for optical applications such as target tracking, drawing, and scanning control because of their high speed and accuracy. ...

In Situ Monitoring of the Accelerated Performance Degradation of Solar Cells and Modules: A Case Study for Cu(In,Ga)Se2 Solar Cells

The levelized cost of electricity (LCOE) of photovoltaic (PV) systems is determined by, among other factors, the PV module reliability. Better prediction of degradation mechanisms and prevention of module field failure can consequently decrease investment risks as well as increase the electricity yield. An improved knowledge level can for these reasons significantly decrease the total costs of PV electricity. 
In order to better understand and minimize the degradation of PV modules, the occurring degradation mechanisms and conditions should be identified. This should preferably happen under combined stresses, since modules in the field are also simultaneously exposed to multiple stress factors. Therefore, two 'Combined Stress test with in situ measurement' setups have been designed and constructed. These setups allow the simultaneous use of humidity, temperature, illumination, and electrical biases as independently controlled stress factors on solar cells and minimodules. The setups also allow real-time monitoring of the electrical properties of these samples. This protocol presents these setups and describes the experimental possibilities. Moreover, results obtained with these setups are also presented: various examples about the influence of both deposition and degradation conditions on the stability of thin film Cu(In,Ga)Se2 (CIGS) as well as Cu2ZnSnSe4 (CZTS) solar cells are described. Results on the temperature dependency of CIGS solar cells are also presented.

In Situ Monitoring of the Accelerated Performance Degradation of Solar Cells and Modules: A Case Study for CuIn,GaSe2 Solar Cells

Two &#39;Combined Stress test with in situ measurement&#39; setups, which allow real-time monitoring of accelerated degradation of solar cells and modules, were designed and constructed. These setups allow the simultaneous use of humidity, temperature, electrical biases, and illumination as independently controlled stress factors. The setups and various experiments executed are presented.

The levelized cost of electricity (LCOE) of photovoltaic (PV) systems is determined by, among other factors, the PV module reliability. Better prediction ...

Study of Siphon Breaker Experiment and Simulation for a Research Reactor

Under the design conditions of a research reactor, the siphon phenomenon induced by pipe rupture can cause continuous outward flow of water. To prevent this outflow, a control device is required. A siphon breaker is a type of safety device that can be utilized to control the loss of coolant water effectively.
To analyze the characteristics of siphon breaking, a real-scale experiment was conducted. From the results of the experiment, it was found that there are several design factors that affect the siphon breaking phenomenon. Therefore, there is a need to develop a theoretical model capable of predicting and analyzing the siphon breaking phenomenon under various design conditions. Using the experimental data, it was possible to formulate a theoretical model that accurately predicts the progress and the result of the siphon breaking phenomenon. The established theoretical model is based on fluid mechanics and incorporates the Chisholm model to analyze two-phase flow. From Bernoulli&#39;s equation, the velocity, quantity, undershooting height, water level, pressure, friction coefficient, and factors related to the two-phase flow could be obtained or calculated. Moreover, to utilize the model established in this study, a siphon breaker analysis and design program was developed. The simulation program operates on the theoretical model basis and returns the result as a graph. The user can confirm the possibility of the siphon breaking by checking the shape of the graph. Furthermore, saving the entire simulation result is possible and it can be used as a resource for analyzing the real siphon breaking system.
In conclusion, the user can confirm the status of the siphon breaking and design the siphon breaker system using the program developed in this study.

The siphon breaking phenomenon was investigated experimentally and a theoretical model was proposed. A simulation program based on the theoretical model was developed and the results of the simulation program were compared with experimental results. It was concluded that the results of the simulation program matched the experimental results well.

Under the design conditions of a research reactor, the siphon phenomenon induced by pipe rupture can cause continuous outward flow of water. To prevent ...

Simultaneous Multi-surface Anodizations and Stair-like Reverse Biases Detachment of Anodic Aluminum Oxides in Sulfuric and Oxalic Acid Electrolyte

After reporting on the two-step anodization, nanoporous anodic aluminum oxides (AAOs) have been widely utilized in the versatile fields of fundamental sciences and industrial applications owing to their periodic arrangement of nanopores with relatively high aspect ratio. However, the techniques reported so far, which could be only valid for mono-surface anodization, show critical disadvantages, i.e., time-consuming as well as complicated procedures, requiring toxic chemicals, and wasting valuable natural resources. In this paper, we demonstrate a facile, efficient, and environmentally clean method to fabricate nanoporous AAOs in sulfuric and oxalic acid electrolytes, which can overcome the limitations that result from conventional AAO fabricating methods. First, plural AAOs are produced at one time through simultaneous multi-surfaces anodization (SMSA), indicating mass-producibility of the AAOs with comparable qualities. Second, those AAOs can be separated from the aluminum (Al) substrate by applying stair-like reverse biases (SRBs) in the same electrolyte used for the SMSAs, implying simplicity and green technological characteristics. Finally, a unit sequence consisting of the SMSAs sequentially combined with SRBs-based detachment can be applied repeatedly to the same Al substrate, which reinforces the advantages of this strategy and also guarantees the efficient usage of natural resources.

A protocol for fabricating nanoporous anodic aluminum oxides via simultaneous multi-surfaces anodization followed by stair-like reverse biases detachments is presented. It can be applied repeatedly to the same aluminum substrate, exhibiting a facile, high-yield, and environmentally clean strategy.

After reporting on the two-step anodization, nanoporous anodic aluminum oxides (AAOs) have been widely utilized in the versatile fields of fundamental ...

Electric-field Control of Electronic States in WS2 Nanodevices by Electrolyte Gating

A method of carrier number control by electrolyte gating is demonstrated. We have obtained WS2 thin flakes with atomically flat surface via scotch tape method or individual WS2 nanotubes by dispersing the suspension of WS2 nanotubes. The selected samples have been fabricated into devices by the use of the electron beam lithography and electrolyte is put on the devices. We have characterized the electronic properties of the devices under applying the gate voltage. In the small gate voltage region, ions in the electrolyte are accumulated on the surface of the samples which leads to the large electric potential drop and resultant electrostatic carrier doping at the interface. Ambipolar transfer curve has been observed in this electrostatic doping region. When the gate voltage is further increased, we met another drastic increase of source-drain current which implies that ions are intercalated into layers of WS2 and electrochemical carrier doping is realized. In such electrochemical doping region, superconductivity has been observed. The focused technique provides a powerful strategy for achieving the electric-filed-induced quantum phase transition.

Electric-field Control of Electronic States in WS2 Nanodevices by Electrolyte Gating

Here, we present a protocol to control the carrier number in solids by using the electrolyte.

A method of carrier number control by electrolyte gating is demonstrated. We have obtained WS2 thin flakes with atomically flat surface via scotch tape ...

Generation and Coherent Control of Pulsed Quantum Frequency Combs

We present a method for the generation and coherent manipulation of pulsed quantum frequency combs. Until now, methods of preparing high-dimensional states on-chip in a practical way have remained elusive due to the increasing complexity of the quantum circuitry needed to prepare and process such states. Here, we outline how high-dimensional, frequency-bin entangled, two-photon states can be generated at a stable, high generation rate by using a nested-cavity, actively mode-locked excitation of a nonlinear micro-cavity. This technique is used to produce pulsed quantum frequency combs. Moreover, we present how the quantum states can be coherently manipulated using standard telecommunications components such as programmable filters and electro-optic modulators. In particular, we show in detail how to accomplish state characterization measurements such as density matrix reconstruction, coincidence detection, and single photon spectrum determination. The presented methods form an accessible, reconfigurable, and scalable foundation for complex high-dimensional state preparation and manipulation protocols in the frequency domain.

A protocol is presented for the practical generation and coherent manipulation of high-dimensional frequency-bin entangled photon states using integrated micro-cavities and standard telecommunications components, respectively.

We present a method for the generation and coherent manipulation of pulsed quantum frequency combs. Until now, methods of preparing high-dimensional ...

UV-Vis Spectroscopic Characterization of Nanomaterials in Aqueous Media

The physicochemical characterization of nanomaterials (NMs) is often an analytical challenge, due to their small size (at least one dimension in the nanoscale, i.e. 1&#8211;100 nm), dynamic nature, and diverse properties. At the same time, reliable and repeatable characterization is paramount to ensure safety and quality in the manufacturing of NM-bearing products. There are several methods available to monitor and achieve reliable measurement of nanoscale-related properties, one example of which is Ultraviolet-Visible Spectroscopy (UV-Vis). This is a well-established, simple, and inexpensive technique that provides non-invasive and fast real-time screening evaluation of NM size, concentration, and aggregation state. Such features make UV-Vis an ideal methodology to assess the proficiency testing schemes (PTS) of a validated standard operating procedure (SOP) intended to evaluate the performance and reproducibility of a characterization method. In this paper, the PTS of six partner laboratories from the H2020 project ACEnano were assessed through an interlaboratory comparison (ILC). Standard gold (Au) colloid suspensions of different sizes (ranging 5&#8211;100 nm) were characterized by UV-Vis at the different institutions to develop an implementable and robust protocol for NM size characterization.

This study presents the benchmarking results for an interlaboratory comparison (ILC) designed to test the standard operating procedure (SOP) developed for gold (Au) colloid dispersions characterized by ultraviolet-visible Spectroscopy (UV-Vis), amongst six partners from the H2020 ACEnano project for sample preparation, measurement, and analysis of the results.

The physicochemical characterization of nanomaterials (NMs) is often an analytical challenge, due to their small size (at least one dimension in the ...