Published: December 18th, 2018
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. 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.
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 referenc....
1. Create the Patterning Map
Figure 1 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 .......
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.......
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.....
|The communication interface between the camera and the control switch for the laser.
|A controller to use for the laser that activates the laser based on the voltage sent by the DAQ.
|A flea camera used for imaging the drill bit on the plastic mold.
|Flea Imaging Camera
|A flea camera used for obtaining the side images of the pillars.
|200 Steps/rev, 12V-350mA Stepper Motor (x2)
|The stepper motors are used to control the depth and angle of the end mill.
|10x Infinity Corrected Long Working Distance Objective
|The objective used to get the image of the side of the pillars.
|15x Infinite Conjugate, UV Coated, ReflX Objective
|The objective used to get the image of the top of the pillars.
|72002 0.002D X 0.006 LOC Carbide SQ 2FL Miniature End Mill
|The drill bit that was used to create holes in the plastic mold.
|DC Power Delivery at 1 kW
|Used to power the deposition sputterer.
|Turbo-V 70LP Nacro Torr Pump
|Turbo Pump used to reduce pressure inside deposition chamber.
|2000mw, 405nm High-Power Blue Light Focus Laser
|Sample Heating Laser
|5.875" I.D. Dessicator w/ 0.25" Tube Connections
|SYLGARD 184 Silicone Elastomer, 0.5kg Kit
|The PDMS Kit used to make the base.
|Diaphragm Air Compressor / Vacuum Pump
|Dessicator Vacuum Pump
|Motorized Linear Stages (2x)
|The stepper motors used to control the sample plate in the x- and y- direction.
|2" Diameter Unmounted Poistive Achromatic Doublets, AR Coated: 400-700 nm
|The achromat was ued in order to obtain the images of the side of the pillars.
|Flea 3 Mono Camera, 2448 X 2048 Pixels
|A flea camera used for imiaging the top of the pillars.
|Digital Vacuum Transducer
|Thyrcont Vacuum Instruments
|Used for monitoring pressure inside deposition chamber.
|Pressurized Argon Tank Resovoir
|Gas used in deposition process.
|1-D Translation Stage
|A translation stage used to move the camera to focus on the end mill.
|Cylindrical Laser Mount (x2)
|The laser mount was used to move the camera to focus on the end mill.
|Benchtop Chiller with Centrifugal Pump, 120V, 60Hz
|A chiller used for the deposition assembly.
|Alcatel Adixen 2010SD XP, Explosion Proof Motor, Rotary Vane Vacuum Pump, 1-Phase
|Ideal Vacuum Products
|A vacuum pump used for the deposition assembly.
|Fan, 105 CFM, 115 V (x2)
|A fan used for cooling certain aspects of the deposition assembly.
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