Name: scalable stamp printing and fabrication of hemiwicking surfaces
Uploaded: 2018-12-18T13:00:00
Description: Watch this Scientific Journal Video about Scalable Stamp Printing and Fabrication of Hemiwicking Surfaces at JoVE.com

This material is based on research partially sponsored by the United States Office of Naval Research under Grant No. N00014-15-1-2481 and the National Science Foundation under Grant No. 1653396. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of U.S. Office of Naval Research, the National Science Foundation, or the United States Government.

1. Create the Patterning Map
<ol>
	<li>Using a graphics editor, create the desired pattern for the hemiwicking structures represented as a bitmap image. 
	NOTE: Some of the wicking design parameters (i.e., angle gradient, depth gradient) can be made to be dependent on the grayscale values assigned to each pixel. These grayscale values are then edited in order to modify the desired parameter.</li>
	<li>Save the bitmap as a portable network graphic (.png) and place the file in a readily available folder.</l...

<ol>
	<li>Plawsky, J. L., 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=Nano-+and+Micro-structures+for+Thin+Film+Evaporation+-+A+Review.">Nano- and Micro-structures for Thin Film Evaporation - A Review.</a> Nanoscale and Microscale Thermophysical Engineering. 18, 251-269 (2014).</li><li>Derjaguin, B. V., Churaev, N. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+the+question+of+determining+the+concept+of+disjoining+pressure+and+its+role+in+the+equilibrium+and+flow+of+thin+films.">On the question of determining the concept of disjoining pressure and its role in the equilibrium and flow of thin films.</a> Journal of Colloid and Interface Science. 66, 389 (1978).</li><li>Ma, H. B., Cheng, P., Borgmeyer, B., Wang, Y. X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluid+flow+and+heat+transfer+in+the+evaporating+thin+film+region.">Fluid flow and heat transfer in the evaporating thin film region.</a> Microfluidics and Nanofluidics. 4 (3), 237-243 (2008).</li><li>Hohmann, C., Stephan, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microscale+temperature+measurement+at+an+evaporating+liquid+meniscus.">Microscale temperature measurement at an evaporating liquid meniscus.</a> Experimental Thermal and Fluid Science. 26 (2-4), 157-162 (2002).</li><li>Potask, M., Wayner, P. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaporation+from+a+two-dimensional+extended+meniscus.">Evaporation from a two-dimensional extended meniscus.</a> International Journal of Heat Mass Transfer. 15 (10), 1851-1863 (1972).</li><li>Panchamgam, S. S., Plawsky, J. L., Wayner, P. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microscale+heat+transfer+in+an+evaporating+moving+extended+meniscus.">Microscale heat transfer in an evaporating moving extended meniscus.</a> Experimental Thermal and Fluid Science. 30 (8), 745-754 (2006).</li><li>Arends, A. A., Germain, T. M., Owens, J. F., Putnam, S. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simultaneous+Reflectometry+and+Interferometry+for+Measuring+Thin-film+Thickness+and+Curvature.">Simultaneous Reflectometry and Interferometry for Measuring Thin-film Thickness and Curvature.</a> Review of Scientific Instruments. 89 (5), (2018).</li><li>Zhu, Y., Antao, D. S., Lu, Z., Somasundaram, S., Zhang, T., Wang, E. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prediction+and+characterization+of+dry+out+heat+flux+in+micropillar+wick+structures.">Prediction and characterization of dry out heat flux in micropillar wick structures.</a> Langmuir. 32 (7), 1920-1927 (2016).</li><li>Kim, J., Moon, M. W., Kim, H. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamics+of+hemiwicking.">Dynamics of hemiwicking.</a> Journal of Fluid Mechanics. 800, 57-71 (2016).</li><li>Ding, C., Soni, G., Bozorgi, P., Meinhart, C. D., MacDonald, N. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wicking+Study+of+Nanostructured+Titania+Surfaces+for+Flat+Heat+Pipes.">Wicking Study of Nanostructured Titania Surfaces for Flat Heat Pipes.</a> Nanotech Conference &amp; Expo. , (2009).</li><li>Chen, R., Lu, M. C., Srinivasan, V., Wang, Z., Cho, H. H., Majumdar, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanowires+for+Enhanced+Boiling+Heat+Transfer.">Nanowires for Enhanced Boiling Heat Transfer.</a> Nano Letters. 9 (2), 548-553 (2009).</li><li>Kim, B. S., Choi, G., Shim, D., Kim, K. M., Cho, H. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface+roughening+for+hemi-wicking+and+its+impact+on+convective+boiling+heat+transfer.">Surface roughening for hemi-wicking and its impact on convective boiling heat transfer.</a> International Journal of Heat and Mass Transfer. 102, 1100-1107 (2016).</li><li>Mikkelsen, M. B., 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=Controlled+deposition+of+sol-gel+sensor+material+using+hemiwicking.">Controlled deposition of sol-gel sensor material using hemiwicking.</a> Journal of Micromechanics and Microengineering. 21 (11), (2011).</li><li>Haatainen, T., Ahopelto, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pattern+Transfer+using+Step&amp;Stamp+Imprint+Lithography.">Pattern Transfer using Step&amp;Stamp Imprint Lithography.</a> Physica Scripta. 67 (4), 357-360 (2003).</li><li>Chou, S. Y., Krauss, P. R., Renstrom, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanoimprint+lithography.">Nanoimprint lithography.</a> Journal of vacuum Science &amp; Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena. 14 (6), 4129 (1996).</li><li>Pozzato, A., 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=Superhydrophobic+surfaces+fabricated+by+nanoprint+lithography.">Superhydrophobic surfaces fabricated by nanoprint lithography.</a> Microelectronic Engineering. 83 (4-9), 884-888 (2006).</li><li>Nair, R. P., Zou, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface-nano-texturing+by+aluminum-induced+crystallization+of+amorphous+silicon.">Surface-nano-texturing by aluminum-induced crystallization of amorphous silicon.</a> Surface and Coatings Technology. 203 (5-7), 675-679 (2008).</li><li>Ashby, P. D., Lieber, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultra-sensitive+Imaging+and+Interfacial+Analysis+of+Patterned+Hydrophilic+SAM+Surfaces+Using+Energy+Dissipation+Chemical+Force+Microscopy.">Ultra-sensitive Imaging and Interfacial Analysis of Patterned Hydrophilic SAM Surfaces Using Energy Dissipation Chemical Force Microscopy.</a> Journal of the American Chemical Society. 127 (18), 6814-6818 (2005).</li></ol>

A method has been introduced to create patterned pillar arrays for hemiwicking structures; this is accomplished by imprinting cavities on a plastic wafer with an engraving apparatus that follows patterning from a bitmap created by the user. A PDMS mixture is then poured, cured and coated with a thin film of aluminum via deposition. The pillar array characteristics can be customized depending on the gray scale value that is assigned in the bitmap following this protocol. This crucial aspect of patterning can crea...

Recently there has been increased interest in being able to both actively and passively control the wetting, evaporation, and mixing of fluids. Uniquely textured hemiwicking surfaces provide a novel solution for cooling techniques because these textured surfaces act as a fluid (and/or heat) pump without the moving parts. This fluid motion is driven by a cascade of capillary action events associated with the dynamic curvature of the liquid thin-film. In general, when a fluid wets a solid surface, a curved liquid thin-film (i.e., liquid meniscus) rapidly forms. The fluid thickness and curvature profile evolve until a free-energy minimum is reached. For reference, this dynamic wetting profile can rapidly decay to tens of nanometers in thickness within a spanning (fluid-wetting) length-scale of only tens of micrometers. Thus, this transitional (liquid-film) region can undergo significant changes in liquid-interface curvature. The transitional (thin-film) region is where nearly all the dynamic physics and chemistry originates. In particular, the transitional (thin-film) region is where maximum (1) evaporation rates, (2) dis-joining pressure gradients, and (3) hydrostatic pressure gradients are found1,2. As a result, curved liquid-films play a vital role in thermal transport, phase separation, fluid instabilities, and the mixing of multi-component fluids. For instance, with respect to heat transfer, the highest wall heat fluxes have been observed in this highly curved, transitional thin-film region3,4,5,6,7.
Recent hemiwicking studies have shown that the geometry (e.g., height, diameter, etc.) and placement of the pillars determine the wetting front profile and velocity of the fluid running through the structures8. As the fluid front is evaporating off the end of the last structure in an array, the fluid front is maintained at a constant distance and curvature, as the evaporated fluid is being replaced by the fluid stored in the wicking structures9. Hemiwicking structures have also been used in heat pipes and on boiling surfaces to analyze and enhance different heat transfer mechanisms.10,11,12.
One method currently used to create wicking structures is thermal imprint lithography13. This method is performed by stamping the desired layout into a resist layer on a silicon mold sample with a thermoplastic polymer stamp, then removing the stamp to maintain the microstructures. Once removed, the sample is put through a reactive ion etching process to remove any of the excess resist layer14,15. This process, however, can be sensitive to the temperature of the fabrication of the wicking structures and includes multiple steps that utilize various coatings to ensure the accuracy of the wicking structures16. It is also the case that lithography techniques are not practical for macro-scale patterning; while they still provide a way to create a pattern of microstructures on a surface, the throughput of this procedure is far less than ideal for large-scale reproduction. Considering large-scale, reproducible texturing, such as spin or dip coating, there is an inherent lack of controllable patterning. These methods create a random array of microstructures on the target surface but can be scaled to cover vastly larger areas than traditional lithography techniques17.
The protocol outlined within this report attempts to combine the strengths of traditional texturing methods while simultaneously eliminating the specific weaknesses of each; it defines a way to fabricate custom hemiwicking structures of various heights, shapes, orientations, and materials on a macro-scale and with potentially high throughput. Various wicking patterns can be quickly created for the purpose of optimization of wicking characteristics, such as directional control of fluid velocity, propagation, and mixing of different fluids. The use of different wicking structures can also provide varying thin-film thickness and curvature profiles, which can be used to systematically study the coupling between heat and mass transfer with different thickness and curvature profiles of the liquid meniscus.

<table>
	<tbody>
		<tr>
			<td>NI-DAQ 9403</td>
			<td>National Instruments</td>
			<td>370466AE-01</td>
			<td>The communication interface between the camera and the control switch for the laser.</td>
		</tr>
		<tr>
			<td>Control Switch</td>
			<td>Crouzet</td>
			<td>GN84134750</td>
			<td>A controller to use for the laser that activates the laser based on the voltage sent by the DAQ.</td>
		</tr>
		<tr>
			<td>Flea Camera</td>
			<td>FLIR</td>
			<td>FL3-U3-120S3C-C</td>
			<td>A flea camera used for imaging the drill bit on the plastic mold.&#160;</td>
		</tr>
		<tr>
			<td>Flea Imaging Camera</td>
			<td>Point Grey</td>
			<td>FL3-U3-20E4M-C</td>
			<td>A flea camera used for obtaining the side images of the pillars.</td>
		</tr>
		<tr>
			<td>200 Steps/rev, 12V-350mA Stepper Motor (x2)</td>
			<td>AdaFruit</td>
			<td>324</td>
			<td>The stepper motors are used to control the depth and angle of the end mill.&#160;</td>
		</tr>
		<tr>
			<td>10x Infinity Corrected Long Working Distance Objective</td>
			<td>Mitutoyo&#160;</td>
			<td>#46-144</td>
			<td>The objective used to get the image of the side of the pillars.</td>
		</tr>
		<tr>
			<td>15x Infinite Conjugate, UV Coated, ReflX Objective</td>
			<td>TechSpec</td>
			<td>#58-417</td>
			<td>The objective used to get the image of the top of the pillars.&#160;</td>
		</tr>
		<tr>
			<td>72002 0.002D X 0.006 LOC Carbide SQ 2FL Miniature End Mill</td>
			<td>Harvey Tools</td>
			<td>72002</td>
			<td>The drill bit that was used to create holes in the plastic mold.&#160;</td>
		</tr>
		<tr>
			<td>DC Power Delivery at 1 kW</td>
			<td>Advanced Energy</td>
			<td>MDX-1K</td>
			<td>Used to power the deposition sputterer.&#160;</td>
		</tr>
		<tr>
			<td>Turbo-V 70LP Nacro Torr Pump</td>
			<td>Varian</td>
			<td>9699336</td>
			<td>Turbo Pump used to reduce pressure inside deposition chamber.</td>
		</tr>
		<tr>
			<td>2000mw, 405nm High-Power Blue Light Focus Laser</td>
			<td>WDLasers</td>
			<td>KREE</td>
			<td>Sample Heating Laser</td>
		</tr>
		<tr>
			<td>5.875&#34; I.D. Dessicator w/ 0.25&#34; Tube Connections</td>
			<td>McMaster-Carr</td>
			<td>2204K5</td>
			<td>PDMS Dessicator</td>
		</tr>
		<tr>
			<td>SYLGARD 184 Silicone Elastomer, 0.5kg Kit</td>
			<td>Dow-Corning</td>
			<td>4019862</td>
			<td>The PDMS Kit used to make the base.</td>
		</tr>
		<tr>
			<td>Diaphragm Air Compressor / Vacuum Pump</td>
			<td>Gast</td>
			<td>DOL-701-AA</td>
			<td>Dessicator Vacuum Pump</td>
		</tr>
		<tr>
			<td>Motorized Linear Stages (2x)</td>
			<td>Standa</td>
			<td>8MT175</td>
			<td>The stepper motors used to control the sample plate in the x- and y- direction.&#160;</td>
		</tr>
		<tr>
			<td>2&#34; Diameter Unmounted Poistive Achromatic Doublets, AR Coated: 400-700 nm</td>
			<td>ThorLabs</td>
			<td>AC508-150-A</td>
			<td>The achromat was ued in order to obtain the images of the side of the pillars.&#160;</td>
		</tr>
		<tr>
			<td>Flea 3 Mono&#160; Camera, 2448 X 2048 Pixels</td>
			<td>Point Grey</td>
			<td>FL3-GE-50S5M-C</td>
			<td>A flea camera used for imiaging the top of the pillars.</td>
		</tr>
		<tr>
			<td>Digital Vacuum Transducer</td>
			<td>Thyrcont Vacuum Instruments</td>
			<td>4940-CF-212734</td>
			<td>Used for monitoring pressure inside deposition chamber.</td>
		</tr>
		<tr>
			<td>Pressurized Argon Tank Resovoir</td>
			<td>Airgas</td>
			<td>AR RP300</td>
			<td>Gas used in deposition process.</td>
		</tr>
		<tr>
			<td>1-D Translation Stage</td>
			<td>Newport Corporation</td>
			<td>TSX-1D</td>
			<td>A translation stage used to move the camera to focus on the end mill.&#160;</td>
		</tr>
		<tr>
			<td>Cylindrical Laser Mount (x2)</td>
			<td>Newport Corporation</td>
			<td>ULM-TILT-M</td>
			<td>The laser mount was used to move the camera to focus on the end mill.</td>
		</tr>
		<tr>
			<td>Benchtop Chiller with Centrifugal Pump, 120V, 60Hz</td>
			<td>Polyscience</td>
			<td>LS51MX1A110C</td>
			<td>A chiller used for the deposition assembly.</td>
		</tr>
		<tr>
			<td>Alcatel Adixen 2010SD XP, Explosion Proof Motor, Rotary Vane Vacuum Pump, 1-Phase</td>
			<td>Ideal Vacuum Products</td>
			<td>210SDMLAM-XP</td>
			<td>A vacuum pump used for the deposition assembly.&#160;</td>
		</tr>
		<tr>
			<td>Fan, 105 CFM, 115 V (x2)</td>
			<td>Comair Rotron</td>
			<td>MU2A1</td>
			<td>A fan used for cooling certain aspects of the deposition assembly.</td>
		</tr>
	</tbody>
</table>

scalable stamp printing and fabrication of hemiwicking surfaces

Hemiwicking is a process where a fluid wets a patterned surface beyond its normal wetting length due to a combination of capillary action and imbibition. This wetting phenomenon is important in many technical fields ranging from physiology to aerospace engineering. Currently, several different techniques exist for fabricating hemiwicking structures. These conventional methods, however, are often time consuming and are difficult to scale-up for large areas or are difficult to customize for specific, nonhomogeneous patterning geometries. The presented protocol provides researchers with a simple, scalable, and cost-effective method for fabricating micro-patterned hemiwicking surfaces. The method fabricates wicking structures through the use of stamp printing, polydimethylsiloxane (PDMS) molding, and thin-film surface coatings. The protocol is demonstrated for hemiwicking with ethanol on PDMS micropillar arrays coated with a 70 nm thick aluminum thin-film.

Figure 1&#160;provides a schematic of how the stamping mechanism would create the mold for the wicking structures on a plastic mold. To investigate the quality of the stamping apparatus in manufacturing wicking films, two different pillar arrays were created to analyze the quality of the pillars for future wicking experiments. Aspects of the apparatus investigated were the accuracy of the height of the pillars (with and without a depth gradient), the quality ...

Watch this Scientific Journal Video about Scalable Stamp Printing and Fabrication of Hemiwicking Surfaces at JoVE.com

Scalable Stamp Printing and Fabrication of Hemiwicking Surfaces

A simple protocol is provided for the fabrication of hemiwicking structures of varying sizes, shapes, and materials. The protocol uses a combination of physical stamping, PDMS molding, and thin-film surface modifications via common materials deposition techniques.

Hemiwicking is a process where a fluid wets a patterned surface beyond its normal wetting length due to a combination of capillary action and imbibition. ...

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