The authors gratefully acknowledge insight and assistance from W. Cook, S. J .S. Rubin, J. Zehner, C. Barraugh, C. Fukushima, M. Mulligan, M. Keckley, and A. Bosshardt, and financial support from The Rose Hills Foundation and The Johnson Summer Student Research Grant.&#160; The authors also acknowledge preliminary work on viscosity as a means of tracking silicone polymerization by the students of Advanced Laboratory in Chemistry (Fall 2017).

1. PDMS Filaments
<ol>
	<li>Furnace and extrusion assembly
	<ol>
		<li>Attach 1.59 mm inner-diameter high temperature silicone rubber tubing to house air supply through a metering valve (see Figure 1). Connect the other end of the tubing to an extrusion adaptor consisting of a sheath around a 1.08 mm radius opening, which will produce a steady downward airflow around the filament (e.g., a custom machined brass sheath at an airflow of approximately 1.4 L/min; see Supplemental Figure 1 for specifications). 
		NOTE: Preferably produce filaments in a reduced air-flow environment with a fire extinguisher nearby.</li>
		<li>Cover the surface below a cylindrical ceramic tube furnace (e.g., 17 mm inner diameter, 107.7 mm length) with foil to capture any excess PDMS.</li>
		<li>Mount the extrusion adaptor above the vertical tube furnace, centering the opening to the furnace and leveling the furnace so the filament will pass through.</li>
		<li>Connect the extruder to the extrusion adaptor via high temperature silicone rubber semi-clear tubing.</li>
		<li>Heat the furnace until the inner temperature is approximately 250 &#176;C as measured by an infrared thermometer, using a variable transformer to regulate temperature.</li>
		<li>Move the furnace out from under the extrusion adaptor so that the extrusion adapter does not heat up prior to filament production.</li>
	</ol>
	</li>
	<li>Partially pre-curing PDMS
	<ol>
		<li>Preheat a disposable sample tube to 65.0 &#176;C in a viscometer with temperature control. Use an appropriate viscometer and spindle, such that one can measure viscosities in the range of 200-10000 mPa&#183;s.</li>
		<li>Thoroughly mix 18.0 g of PDMS base with 1.8 g of its curing agent in a weigh boat and place the mixture in a room temperature (RT) vacuum desiccator for 15 min or until no bubbles remain. Vent the desiccator periodically to pop the bubbles near the surface. 
		NOTE: The following timing assumes use of the PDMS base and curing agent specified in the Table of Materials.</li>
		<li>Pour 17.7 g of the mixture into the preheated sample tube on the countertop (some is lost to adhesion to the weigh boat). Re-insert the sample tube into the viscometer.</li>
		<li>Take viscosity measurements once per minute, keeping the viscometer spinning slowly (5 rpm).</li>
		<li>When the viscosity reaches 4000 mPa&#183;s, remove the sample tube with pliers and immediately pour into the room temperature extruder. Produce filaments in a time window that starts approximately 4.5 min from heat removal and lasts for a subsequent 4 min.</li>
	</ol>
	</li>
	<li>Extruding PDMS to form filaments
	<ol>
		<li>During the delay time, ensure the furnace is at 250 &#176;C using an infrared thermometer.</li>
		<li>Approximately 4 min after removal of the sample tube from the viscometer, move the furnace back underneath the extrusion adapter and align the inner needle of the extrusion adapter with the tube furnace using a heat-safe glove.</li>
		<li>Periodically twist the screw on the extruder, allowing a steady stream of PDMS to drip through the furnace. 
		NOTE: If droplets form instead of filaments, wait 30 s for further RT curing and try again. Constant twisting pushes the PDMS through the furnace too quickly. Generally, small flare-ups can be handled by turning off the furnace and using a non-conductive stick to dislodge any built up PDMS from the furnace. 
		CAUTION: If PDMS drips onto the walls or top of the furnace, there is the possibility of a flare-up.</li>
		<li>Once the PDMS stream begins to thin, twist the extruder an additional half-revolution. Each trial has about 16 revolutions using the given extruder.</li>
		<li>Gather the filaments on wooden sticks beneath the furnace after each twist and lay them across wooden racks to finish curing for approximately 12 h.</li>
	</ol>
	</li>
</ol>
2. Patterning Surfaces of PDMS Filaments with Computer-controlled Corona Discharge
<ol>
	<li>Arduino-controlled filament-positioning and corona discharge control system: assemble the open-source Arduino microprocessor-controlled stepper motor that pulls the filament under a corona discharge device per the wiring diagram in the Supplemental Materials. Upload the custom Arduino code software in the supplemental materials to the system.</li>
	<li>Patterning filament surface with the device
	<ol>
		<li>Enter desired pattern into code (&#8220;Pattern&#8221; array) and upload it to the Arduino via USB.</li>
		<li>Wash a cured filament with 1% sodium dodecyl sulfate and rinse with excessive pure water. Dry the filament with air.</li>
		<li>Place filament on an electrically non-conducting slab with a cut-out (e.g., laser-cut acrylic, see Supplemental Figure 3A) that allows the filament to be suspended in air. Use double-sided tape to secure the ends of the filament to the slab.</li>
		<li>Place the slab in a ventilated corona discharge box in between acrylic tracks and ensure that it is level. Place an immobile metal slab under the acrylic, aligning the filament along the edge of the metal slab.</li>
		<li>Place the corona discharge electrode (e.g., a spring electrode tip) approximately 3 mm above the filament and plug the corona discharger into the Arduino-controlled outlet.</li>
		<li>Tie a non-conductive line to the circular cut-out on the acrylic slab. Adhere the other end of the line to the Arduino-controlled stepper motor (see Supplemental Figure 3BC).</li>
		<li>Press the button in the Arduino circuit to begin patterning with the programmed code. Corona discharge is a produced by a low current 4.5 MHz electric field with an output voltage of 10-40 kV that modifies the surface of the PDMS to render it hydrophilic. 
		CAUTION: The current is low, but the device produces ozone and UV radiation in air. Preferably use it in a fume hood, behind a vented acrylic shield.</li>
	</ol>
	</li>
</ol>

<ol>
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M., Gangopadhyay, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Studies+on+surface+wettability+of+poly+(dimethyl)+siloxane+(PDMS)+and+glass+under+oxygen-plasma+treatment+and+correlation+with+bond+strength.">Studies on surface wettability of poly (dimethyl) siloxane (PDMS) and glass under oxygen-plasma treatment and correlation with bond strength.</a> Journal of Microelectromechanical Systems. 14 (3), 590-597 (2005).</li><li>Efimenko, K., Wallace, W. E., Genzer, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface+modification+of+Sylgard-184+poly+(dimethyl+siloxane)+networks+by+ultraviolet+and+ultraviolet/ozone+treatment.">Surface modification of Sylgard-184 poly (dimethyl siloxane) networks by ultraviolet and ultraviolet/ozone treatment.</a> Journal of Colloid and Interface Science. 254 (2), 306-315 (2002).</li><li>Johnston, I. D., McCluskey, D. K., Tan, C., Tracey, M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanical+characterization+of+bulk+Sylgard+184+for+microfluidics+and+microengineering.">Mechanical characterization of bulk Sylgard 184 for microfluidics and microengineering.</a> Journal of Micromechanics and Microengineering. 24 (3), 035017 (2014).</li><li>Xue, R., Behera, P., Xu, J., Viapiano, M. S., Lannutti, J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Polydimethylsiloxane+core&#8211;polycaprolactone+shell+nanofibers+as+biocompatible,+real-time+oxygen+sensors.">Polydimethylsiloxane core&#8211;polycaprolactone shell nanofibers as biocompatible, real-time oxygen sensors.</a> Sensors and Actuators B: Chemical. 192, 697-707 (2014).</li><li>Kiessling, R., 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=Gravity-Drawn+Silicone+Filaments:+Production,+Characterization,+and+Wormlike+Chain+Dynamics.">Gravity-Drawn Silicone Filaments: Production, Characterization, and Wormlike Chain Dynamics.</a> ACS Applied Materials &amp; Interfaces. 9 (46), 39916-39920 (2017).</li><li>Roca-Cusachs, P., 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=Stability+of+microfabricated+high+aspect+ratio+structures+in+poly+(dimethylsiloxane).">Stability of microfabricated high aspect ratio structures in poly (dimethylsiloxane).</a> Langmuir. 21 (12), 5542-5548 (2005).</li><li>Yang, D., 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=Electrospinning+of+poly+(dimethylsiloxane)/poly+(methyl+methacrylate)+nanofibrous+membrane:+Fabrication+and+application+in+protein+microarrays.">Electrospinning of poly (dimethylsiloxane)/poly (methyl methacrylate) nanofibrous membrane: Fabrication and application in protein microarrays.</a> Biomacromolecules. 10 (12), 3335-3340 (2009).</li><li>Niu, H., Wang, H., Zhou, H., Lin, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrafine+PDMS+fibers:+preparation+from+in+situ+curing-electrospinning+and+mechanical+characterization.">Ultrafine PDMS fibers: preparation from in situ curing-electrospinning and mechanical characterization.</a> Rsc Advances. 4 (23), 11782-11787 (2014).</li><li>Ramakrishna, S., 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=Electrospun+nanofibers:+solving+global+issues.">Electrospun nanofibers: solving global issues.</a> Materials Today. 9 (3), 40-50 (2006).</li><li>Blyler, L. 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W., Bateman, D., Hauber, S., Wehbring, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> GNU Octave version 4.2.2 manual: a high-level interactive language for numerical computations. , (2018).</li><li>Ziabicki, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Fundamentals of fibre formation: the science of fibre spinning and drawing. , (1976).</li><li>Haji, K., Zhu, Y., Otsubo, M., Honda, 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+modification+of+silicone+rubber+after+corona+exposure.">Surface modification of silicone rubber after corona exposure.</a> Plasma Processes and Polymers. 4 (S1), S1080 (2007).</li></ol>

The authors have nothing to disclose.

The basis of this method is manipulating the material properties of curing PDMS so they are suitable for gravity drawing. Gravity drawing droplets into stable filaments is governed by three dimensionless parameters16. They relate the droplet&#8217;s inertia relative to gravity (Froude), surface-tension (Weber), and viscosity (Reynolds). The critical step of crosslinking the PDMS until it experimentally evidences stable extension per our method most dramatically alters its Reynolds number, reducing it by more than an order of magnitude, from 0.83 to 0.07. In contrast, the next largest change in one of the other dimensionless parameters is the Weber number, which merely doubles. This supports the use of viscosity as a sensitive proxy for tracking PDMS spinnability.
A critical improvement over our earlier filament production method is that the viscosity profile during the protocol is used to determine experimental working times. To determine limitations of the technique, we pre-cured a batch of PDMS per the protocol, removed it from heat, and took viscosity measurements at room temperature as the PDMS continued cross-linking. The resulting viscosity profile (Figure 4) suggests that the window for spinnability is extended dramatically by removing the PDMS from the 65 &#176;C heated viscometer. Our protocol involves removal of the PDMS prior to entering the spinnability window, then allowing of the sample to continue crosslinking for about 4.5 min as it cools to room temperature. Subsequently, the experimenter has approximately 4 min to draw it before the ongoing crosslinking renders the PDMS no longer drawable.
The method as shown readily produces filaments with diameters on the order of 100 s of &#181;m and lengths on the order of 0.5 m. The filament length is limited by accessible space beneath the extrusion and tube furnace. A reasonable modification of the technique would be to install it in a longer chimney to produce longer filaments. A modification that we have not yet explored is mechanically pulling the filaments instead of relying on a gravity drop, which may yield thinner filaments.
A critical step to hydrophobically patterning the filament is exposure to corona discharge in ambient conditions. This introduces some ambiguity, as the shape/intensity of the discharge is affected by ambient conditions and local conductivity. It can be tuned by placing grounded conductors under the filament as well as adjusting the voltage of the corona device (10-40 kV). The mechanism of the corona surface-modification is likely electron energy transfer lysing the PDMS side chains and backbone. To break these bonds, electrons would need less energy than the average energy required to produce a dielectric-barrier discharge17. Thus, an observable discharge that envelops the filament is likely to produce the surface modification and can be readily tested via water droplet contact angle measurements.
This method enables relatively facile production of silicone PDMS filaments and subsequent complex hydrophobic patterning. The initial aim is to produce a model foldamer system in which hydrophobic patterns can be designed to produce observable filament folding pathways and folded structures. This testbed may provide generalizable design rules for engineering folding pathways. These filaments may also have material applications as part of hydrophobic or chemically reactive weaves via solvent swelling, or in the use of reactive compounds suspended in the gas-permeable PDMS.

Polydimethylsiloxane (PDMS) silicone is a broadly used material with many manufacturing and research applications. It is heat and water resistant, electrically insulating, hydrophobic, gas permeable, food-safe, biocompatible, and flexible with an almost ideal Poisson ratio. Additionally, it can readily serve as a host for various functional molecules, added either before or after curing1,2. Its surface is readily modifiable by UVO, oxygen plasma, or Corona discharge to switch its hydrophobicity and induce short-term self-adhesion3,4,5. In particular, it has also been used in microfluidics6.
Filaments of PDMS are particularly useful in producing high surface-area silicone weaves, silicone fiber sensors7, and silicone-based additive manufacturing materials (3D printing). In our labs, we use hydrophobically patterned filaments of PDMS as a platform to study folding. The team studies the filament&#8217;s conformational statistics in an aqueous environment via an athermal acoustic excitation and imaging system previously reported8.
Forming high aspect-ratio filaments from PDMS via traditional form-casting is challenging. Filaments have large surface area-to-volume ratios, which complicates release from the molds9. Researchers have had success sheathing PDMS with carrier polymers for continuous electrospinning into nanoscale filaments10,11,12, though the resulting filaments are not pure PDMS.
The predominant manufacturing method to produce macroscale filaments out of other materials involves drawing out a viscous liquid from a reservoir through a pore. Typically, the viscous liquid is a thermoplastic or glass that is fluid at high temperatures in the reservoir and cools into an (often amorphous) solid filament as it is drawn out through a chimney. This process is sometimes called melt spinning, and it is incompatible with PDMS because PDMS does not exhibit long-range fluidity at melting. Block co-polymers of silicone and alpha-methyl styrene have been shown to produce filaments via melt spinning, but again, the resulting filaments are not pure PDMS13.
The method we outline here is akin to melt-spinning, except the relative temperature of the reservoir and chimney are switched. The PDMS is fluid in a room temperature reservoir, as it has not yet completed cross-linking. The viscosity of the PDMS varies as the silicone oil crosslinks with a curing agent, a process that can be thermally accelerated. Before placing it in the reservoir, we heat the curing PDMS until it reaches a viscosity suitable for long gravity-drips, then cure it post-drip via a hot tube furnace in the chimney. The approach is somewhat comparable to &#8220;dry-spinning&#8221;, in which polymers are dissolved in volatile solvents that evaporate during drawing.
To our knowledge, the only reported method of producing long filaments of pure PDMS is our previous publication8 . The method introduced here is a significant improvement upon the original approach, with the intent of minimizing the art of the process. Most notably, by measuring the viscosity during the pre-curing stage and timing cool-down periods, we are able to report an experimentally accessible window of filament spinnability. We also introduce a means of producing repeatable, localized surface modifications on the filament via an Arduino-controlled corona patterning system, enabling longitudinal hydrophobic patterning along the filament.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>2 part PDMS Silicone</td>
			<td>Dow Corning Sylgard 184</td>
			<td>4019862</td>
			<td></td>
		</tr>
		<tr>
			<td>Thermosel</td>
			<td>Brookfield</td>
			<td>HT-110 115, HT-115A DP</td>
			<td></td>
		</tr>
		<tr>
			<td>viscometer</td>
			<td>Brookfield</td>
			<td>RVT115</td>
			<td></td>
		</tr>
		<tr>
			<td>Disposible sample chamber</td>
			<td>Brookfield</td>
			<td>HT-2DB-100</td>
			<td></td>
		</tr>
		<tr>
			<td>Disposible spindle</td>
			<td>Brookfield</td>
			<td>SC4-27D-100, SC4-DSY</td>
			<td></td>
		</tr>
		<tr>
			<td>Extruder</td>
			<td>Makin&#39;s</td>
			<td>35055</td>
			<td></td>
		</tr>
		<tr>
			<td>High-temperature silicone tubing</td>
			<td>McMaster-Carr</td>
			<td>51135K16</td>
			<td></td>
		</tr>
		<tr>
			<td>Cylindrical Tube heater (Ceramic)</td>
			<td></td>
			<td></td>
			<td>Ours is a custom: 17.0 mm inner diameter, 38.7 mm outer diameter, 107.7 mm length, 150 Ohm. Companies include Watlow and Omega. Critical design considerations: smaller inner diameters will require better furnace-filament alignment, longer tubes should also be sufficient.</td>
		</tr>
		<tr>
			<td>Variable Transformer for heater</td>
			<td>Variac</td>
			<td>3PN1010</td>
			<td></td>
		</tr>
		<tr>
			<td>Metering valve</td>
			<td>Swagelok</td>
			<td>SS-2MA1</td>
			<td></td>
		</tr>
		<tr>
			<td>Corona Discharge Device</td>
			<td>Electro-Technic</td>
			<td>BD20A</td>
			<td></td>
		</tr>
		<tr>
			<td>Arduino Kit</td>
			<td>Elegoo</td>
			<td>EL-KIT-003</td>
			<td></td>
		</tr>
		<tr>
			<td>Nylon Fishing Line</td>
			<td>EoongSng</td>
			<td>B075DYVC3F</td>
			<td></td>
		</tr>
		<tr>
			<td>Pasta Drying Rack</td>
			<td>Norpro</td>
			<td>B00004UE7U</td>
			<td></td>
		</tr>
		<tr>
			<td>Infrared thermometer</td>
			<td>Nubee</td>
			<td>81175535214</td>
			<td></td>
		</tr>
		<tr>
			<td>Flatbed scanner</td>
			<td>Canon</td>
			<td>CanoScan 9000F MKII</td>
			<td></td>
		</tr>
	</tbody>
</table>

drawing and hydrophobicity-patterning long polydimethylsiloxane silicone filaments

Polydimethylsiloxane (PDMS) silicone is a versatile polymer that cannot readily be formed into long filaments. Traditional spinning methods fail because PDMS does not exhibit long-range fluidity at melting. We introduce an improved method to produce filaments of PDMS by a stepped temperature profile of the polymer as it cross-links from a fluid to an elastomer. By monitoring its warm-temperature viscosity, we estimate a window of time when its material properties are amendable to drawing into long filaments. The filaments pass through a high-temperature tube oven, curing them sufficiently to be harvested. These filaments are on the order of hundreds of micrometers in diameter and tens of centimeters in length, and even longer and thinner filaments are possible. These filaments retain many of the material properties of bulk PDMS, including switchable hydrophobicity. We demonstrate this capability with an automated corona-discharge patterning method. These patternable PDMS silicone filaments have applications in silicone weavings, gas-permeable sensor components, and model microscale foldamers.

The method (Figure 1) successfully produces filaments of approximately 200 &#181;m in diameter (Figure 2) and of varying lengths on the order of 10 cm. Longer filaments could be produced by raising the drawing apparatus, and average filament diameters can vary between 50-300 &#181;m per run. Filaments are flexible and robust, and their modulus of elasticity is comparable to bulk PDMS8. In this protocol, the working time between pre-curing the PDMS and drawing the filaments is conveniently long enough for transporting the material (Figure 3).
Hydrophobicity patterning via the corona discharge can be verified via droplet contact angles. The contact angle analysis is complicated by the cylindrical shape of the filament; droplets can form either a symmetrical barrel shape or asymmetrical shell shape14. For our filaments, using 1 &#181;L water droplets, these two shapes correspond to corona-treated hydrophilic surfaces and untreated hydrophobic PDMS, respectively (Figure 4).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/58826/58826fig1.jpg" /> 
Figure 1: Schematic of the filament production method. Degassed, cross-linking PDMS is heated at 65 &#176;C until its viscosity reaches 4000 mPa&#183;s. It is then cooled and transferred to an extruder that pushes the material through a downward air-flow-sheathed opening, then through a tube furnace before being harvested as filaments. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58826/58826fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/58826/58826fig2.jpg" /> 
Figure 2: Histogram of filament widths from a demonstration of the method. Widths are per cm of filament over 6 filaments, whose total length was approximately 80 cm. Filaments were scanned by a flatbed scanner and analyzed by custom Octave scripts15. Inset: a representative image of an extended filament next to a ruler.<a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58826/58826fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/58826/58826fig3.jpg" /> 
Figure 3: PDMS viscosity vs. time. Viscosity measurements (at 5 RPM) of degassed PDMS base and curing agent as a function of time, with different temperature profiles. Continuous heating (gray diamonds) is at 65 &#176;C, demonstrating a rapid increase in viscosity. Black data points are at 65 &#176;C, prior to removal to room temperature when viscosity reaches 4000 mPa&#183;s per the method above. Red data points represent the same sample&#39;s viscosity after cooling to 25 &#176;C. Gap shown in the data occurs while the viscometer is being cooled to 25 &#176;C with ice-water flow. Cyan window is time when filament production occurs as per the method. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58826/58826fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/58826/58826fig4.jpg" /> 
Figure 4: Hydrophobically patterned filament. (A) Filament was patterned with an alternating hydrophobicity pattern, every 2 cm, using the Arduino-controlled-Corona method described above, and visualized with 1 &#181;L droplets of water. (B) Droplets adopt either a shell (left) or barrel (right) conformation depending on the filament&#8217;s local hydrophobicity14. Shell contact angles are estimated directly, whereas planar-equivalent contact angles on barrel-droplets are determined by fitting to an analytical solution8. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58826/58826fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Supplemental Figure 1" src="/files/ftp_upload/58826/58826figS1.jpg" /> 
Supplemental Figure 1: Dimensions of extrusion adapter with airflow sheath. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58826/58826figS1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Supplemental Figure 2" src="/files/ftp_upload/58826/58826figS2.jpg" /> 
Supplemental Figure 2: Wiring diagram for Corona patterner. Corona discharge device is plugged into the relayed power source. The filament is loaded on a tray attached by a non-conducting wire to the stepper motor via a spindle (Supplemental Figure 3). The pattern is uploaded onto the Arduino microprocessor on the bottom left. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58826/58826figS2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Supplemental Figure 3" src="/files/ftp_upload/58826/58826figS3.jpg" /> 
Supplemental Figure 3: Schematic of parts for filament patterner. (A) Tray with an opening where the filament is suspended. (B) Spindle for the nonconducting wire connecting the stepper motor to the tray via the 0.8 cm hole. (C) Bottom view of the spindle, showing the adapter to the stepper motor shaft. We fabricated all parts from laser-cut 3.2 mm acrylic, which was glued together when necessary. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58826/58826figS3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Supplemental Figure 4" src="/files/ftp_upload/58826/58826figS4.jpg" /> 
Supplemental Figure 4: Image of the filament patterner. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58826/58826figS4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Drawing and Hydrophobicity-patterning Long Polydimethylsiloxane Silicone Filaments at JoVE.com

Drawing and Hydrophobicity-patterning Long Polydimethylsiloxane Silicone Filaments

Here, we present a protocol to produce long filaments of polydimethylsiloxane (PDMS) silicone by gravity-drawing through a furnace. Filaments are on the order of hundreds of micrometers in diameter and tens of centimeters in length and are hydrophobically patternable via an Arduino-controlled corona discharge system.

Polydimethylsiloxane (PDMS) silicone is a versatile polymer that cannot readily be formed into long filaments. Traditional spinning methods fail because ...

drawing-hydrophobicity-patterning-long-polydimethylsiloxane-silicone

Nanyang Technological University

Research

JoVE Journal

Engineering

8.8K Views.  Claremont McKenna College. Here, we present a protocol to produce long filaments of polydimethylsiloxane (PDMS) silicone by gravity-drawing through a furnace. Filaments are on the order of hundreds of micrometers in diameter and tens of centimeters in length and are hydrophobically patternable via an Arduino-controlled corona discharge system.

Video: Drawing and Hydrophobicity-patterning Long Polydimethylsiloxane Silicone Filaments

Fabricating Metamaterials Using the Fiber Drawing Method

Metamaterials are man-made composite materials, fabricated by assembling components much smaller than the wavelength at which they operate 1. They owe their electromagnetic properties to the structure of their constituents, instead of the atoms that compose them. For example, sub-wavelength metal wires can be arranged to possess an effective electric permittivity that is either positive or negative at a given frequency, in contrast to the metals themselves 2. This unprecedented control over the behaviour of light can potentially lead to a number of novel devices, such as invisibility cloaks 3, negative refractive index materials 4, and lenses that resolve objects below the diffraction limit 5. However, metamaterials operating at optical, mid-infrared and terahertz frequencies are conventionally made using nano- and micro-fabrication techniques that are expensive and produce samples that are at most a few centimetres in size 6-7. Here we present a fabrication method to produce hundreds of meters of metal wire metamaterials in fiber form, which exhibit a terahertz plasmonic response 8. We combine the stack-and-draw technique used to produce microstructured polymer optical fiber 9 with the Taylor-wire process 10, using indium wires inside polymethylmethacrylate (PMMA) tubes. PMMA is chosen because it is an easy to handle, drawable dielectric with suitable optical properties in the terahertz region; indium because it has a melting temperature of 156.6 &deg;C which is appropriate for codrawing with PMMA. We include an indium wire of 1 mm diameter and 99.99% purity in a PMMA tube with 1 mm inner diameter (ID) and 12 mm outside diameter (OD) which is sealed at one end. The tube is evacuated and drawn down to an outer diameter of 1.2 mm. The resulting fiber is then cut into smaller pieces, and stacked into a larger PMMA tube. This stack is sealed at one end and fed into a furnace while being rapidly drawn, reducing the diameter of the structure by a factor of 10, and increasing the length by a factor of 100. Such fibers possess features on the micro- and nano- scale, are inherently flexible, mass-producible, and can be woven to exhibit electromagnetic properties that are not found in nature. They represent a promising platform for a number of novel devices from terahertz to optical frequencies, such as invisible fibers, woven negative refractive index cloths, and super-resolving lenses.

Metamaterials at terahertz frequencies offer unique opportunities, but are challenging to fabricate in bulk. We adapt the fabrication procedure for microstructured polymer optical fibers to inexpensively fabricate metamaterials potentially on an industrial scale. We produce polymethylmethacrylate fibers containing ~10 &mu;m diameter indium wires separated by ~100 &mu;m, which exhibit a terahertz plasmonic response.

Metamaterials are man-made composite materials, fabricated by assembling components much smaller than the wavelength at which they operate 1. They owe ...

Fabrication And Characterization Of Photonic Crystal Slow Light Waveguides And Cavities

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view and for its considerable potential for practical applications. Slow light photonic crystal waveguides, in particular, have played a major part and have been successfully employed for delaying optical signals1-4 and the enhancement of both linear5-7 and nonlinear devices.8-11
Photonic crystal cavities achieve similar effects to that of slow light waveguides, but over a reduced band-width. These cavities offer high Q-factor/volume ratio, for the realization of optically12 and electrically13 pumped ultra-low threshold lasers and the enhancement of nonlinear effects.14-16 Furthermore, passive filters17 and modulators18-19 have been demonstrated, exhibiting ultra-narrow line-width, high free-spectral range and record values of low energy consumption.
To attain these exciting results, a robust repeatable fabrication protocol must be developed. In this paper we take an in-depth look at our fabrication protocol which employs electron-beam lithography for the definition of photonic crystal patterns and uses wet and dry etching techniques. Our optimised fabrication recipe results in photonic crystals that do not suffer from vertical asymmetry and exhibit very good edge-wall roughness. We discuss the results of varying the etching parameters and the detrimental effects that they can have on a device, leading to a diagnostic route that can be taken to identify and eliminate similar issues.
The key to evaluating slow light waveguides is the passive characterization of transmission and group index spectra. Various methods have been reported, most notably resolving the Fabry-Perot fringes of the transmission spectrum20-21 and interferometric techniques.22-25 Here, we describe a direct, broadband measurement technique combining spectral interferometry with Fourier transform analysis.26 Our method stands out for its simplicity and power, as we can characterise a bare photonic crystal with access waveguides, without need for on-chip interference components, and the setup only consists of a Mach-Zehnder interferometer, with no need for moving parts and delay scans.
When characterising photonic crystal cavities, techniques involving internal sources21 or external waveguides directly coupled to the cavity27 impact on the performance of the cavity itself, thereby distorting the measurement. Here, we describe a novel and non-intrusive technique that makes use of a cross-polarised probe beam and is known as resonant scattering (RS), where the probe is coupled out-of plane into the cavity through an objective. The technique was first demonstrated by McCutcheon et al.28 and further developed by Galli et al.29

Use of photonic crystal slow light waveguides and cavities has been widely adopted by the photonics community in many differing applications. Therefore fabrication and characterization of these devices are of great interest. This paper outlines our fabrication technique and two optical characterization methods, namely: interferometric (waveguides) and resonant scattering (cavities).

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view ...

Synthesis and Microdiffraction at Extreme Pressures and Temperatures

High pressure compounds and polymorphs are investigated for a broad range of purposes such as determine structures and processes of deep planetary interiors, design materials with novel properties, understand the mechanical behavior of materials exposed to very high stresses as in explosions or impacts. Synthesis and structural analysis of materials at extreme conditions of pressure and temperature entails remarkable technical challenges. In the laser heated diamond anvil cell (LH-DAC), very high pressure is generated between the tips of two opposing diamond anvils forced against each other; focused infrared laser beams, shined through the diamonds, allow to reach very high temperatures on samples absorbing the laser radiation. When the LH-DAC is installed in a synchrotron beamline that provides extremely brilliant x-ray radiation, the structure of materials under extreme conditions can be probed in situ. LH-DAC samples, although very small, can show highly variable grain size, phase and chemical composition. In order to obtain the high resolution structural analysis and the most comprehensive characterization of a sample, we collect diffraction data in 2D grids and combine powder, single crystal and multigrain diffraction techniques. Representative results obtained in the synthesis of a new iron oxide, Fe4O5 1 will be shown.

The laser heated diamond anvil cell combined with synchrotron micro-diffraction techniques allows researchers to explore the nature and properties of new phases of matter at extreme pressure and temperature (PT) conditions. Heterogeneous samples can be characterized in situ under high pressure by 2D mapping and combined powder, single-crystal and multigrain diffraction approaches.

High pressure compounds and polymorphs are investigated for a broad range of purposes such as determine structures and processes of deep planetary ...

Measurement and Analysis of Atomic Hydrogen and Diatomic Molecular AlO, C2, CN, and TiO Spectra Following Laser-induced Optical Breakdown

In this work, we present time-resolved measurements of atomic and diatomic spectra following laser-induced optical breakdown. A typical LIBS arrangement is used. Here we operate a Nd:YAG laser at a frequency of 10 Hz at the fundamental wavelength of 1,064 nm. The 14 nsec pulses with anenergy of 190 mJ/pulse are focused to a 50 &#181;m spot size to generate a plasma from optical breakdown or laser ablation in air. The microplasma is imaged onto the entrance slit of a 0.6 m spectrometer, and spectra are recorded using an 1,800 grooves/mm grating an intensified linear diode array and optical multichannel analyzer (OMA) or an ICCD. Of interest are Stark-broadened atomic lines of the hydrogen Balmer series to infer electron density. We also elaborate on temperature measurements from diatomic emission spectra of aluminum monoxide (AlO), carbon (C2), cyanogen (CN), and titanium monoxide (TiO).
The experimental procedures include wavelength and sensitivity calibrations. Analysis of the recorded molecular spectra is accomplished by the fitting of data with tabulated line strengths. Furthermore, Monte-Carlo type simulations are performed to estimate the error margins. Time-resolved measurements are essential for the transient plasma commonly encountered in LIBS.

Measurement and Analysis of Atomic Hydrogen and Diatomic Molecular AlO, C2, CN, and TiO Spectra Following Laser-induced Optical Breakdown

Time-resolved atomic and diatomic molecular species are measured using LIBS. The spectra are collected at various time delays following the generation of optical breakdown plasma with Nd:YAG laser radiation&#160;and are analyzed to infer electron density and temperature.

In this work, we present time-resolved measurements of atomic and diatomic spectra following laser-induced optical breakdown. A typical LIBS arrangement ...

Fabrication Process of Silicone-based Dielectric Elastomer Actuators

This contribution demonstrates the fabrication process of dielectric elastomer transducers (DETs). DETs are stretchable capacitors consisting of an elastomeric dielectric membrane sandwiched between two compliant electrodes. The large actuation strains of these transducers when used as actuators (over 300% area strain) and their soft and compliant nature has been exploited for a wide range of applications, including electrically tunable optics, haptic feedback devices, wave-energy harvesting, deformable cell-culture devices, compliant grippers, and propulsion of a bio-inspired fish-like airship. In most cases, DETs are made with a commercial proprietary acrylic elastomer and with hand-applied electrodes of carbon powder or carbon grease. This combination leads to non-reproducible and slow actuators exhibiting viscoelastic creep and a short lifetime. We present here a complete process flow for the reproducible fabrication of DETs based on thin elastomeric silicone films, including casting of thin silicone membranes, membrane release and prestretching, patterning of robust compliant electrodes, assembly and testing. The membranes are cast on flexible polyethylene terephthalate (PET) substrates coated with a water-soluble sacrificial layer for ease of release. The electrodes consist of carbon black particles dispersed into a silicone matrix and patterned using a stamping technique, which leads to precisely-defined compliant electrodes that present a high adhesion to the dielectric membrane on which they are applied.

This manuscript shows the fabrication process for the manufacture of dielectric elastomer soft actuators based on silicone membranes. The three key stages of production are presented in detail: blade casting of thin silicone membranes; pad printing of compliant electrodes; and the assembly of all the components.

This contribution demonstrates the fabrication process of dielectric elastomer transducers (DETs). DETs are stretchable capacitors consisting of an ...

Reaction Kinetics and Combustion Dynamics of I4O9 and Aluminum Mixtures

Tetraiodine nonoxide (I4O9) has been synthesized using a dry approach that combines elemental oxygen and iodine without the introduction of hydrated species. The synthesis approach inhibits the topochemical effect promoting rapid hydration when exposed to the relative humidity of ambient air. This stable, amorphous, nano-particle material was analyzed using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) and showed an exothermic energy release at low temperature (i.e., 180 &#176;C) for the transformation of I4O9 into I2O5. This additional exothermic energy release contributes to an increase in overall reactivity of I4O9 when dry mixed with nano-aluminum (Al) powder, resulting in a minimum of 150% increase in flame speed compared to Al + I2O5. This study shows that as an oxidizer, I4O9 has more reactive potential than other forms of iodine(V) oxide when combined with Al, especially if I4O9 can be passivated to inhibit absorption of water from its surrounding environment.

Reaction Kinetics and Combustion Dynamics of I4O9 and Aluminum Mixtures

A protocol for measuring flame speeds of a reactive mixture composed of tetraiodine nonoxide (I4O9) and aluminum (Al) is presented. A method for resolving reaction kinetics using differential scanning calorimetry (DSC) is also presented. It was found that I4O9 is 150% more reactive than other iodine(V) oxides.

Tetraiodine nonoxide (I4O9) has been synthesized using a dry approach that combines elemental oxygen and iodine without the introduction of hydrated ...

Design and Evaluation of Smart Glasses for Food Intake and Physical Activity Classification

This study presents a series of protocols of designing and manufacturing a glasses-type wearable device that detects the patterns of temporalis muscle activities during food intake and other physical activities. We fabricated a 3D-printed frame of the glasses and a load cell-integrated printed circuit board (PCB) module inserted in both hinges of the frame. The module was used to acquire the force signals, and transmit them wirelessly. These procedures provide the system with higher mobility, which can be evaluated in practical wearing conditions such as walking and waggling. A performance of the classification is also evaluated by distinguishing the patterns of food intake from those physical activities. A series of algorithms were used to preprocess the signals, generate feature vectors, and recognize the patterns of several featured activities (chewing and winking), and other physical activities (sedentary rest, talking, and walking). The results showed that the average F1 score of the classification among the featured activities was 91.4%. We believe this approach can be potentially useful for automatic and objective monitoring of ingestive behaviors with higher accuracy as practical means to treat ingestive problems.

This study presents a protocol of designing and manufacturing a glasses-type wearable device that detects the patterns of food intake and other featured physical activities using load cells inserted in both hinges of the glasses.

This study presents a series of protocols of designing and manufacturing a glasses-type wearable device that detects the patterns of temporalis muscle ...

Determination of the Excitation and Coupling Rates Between Light Emitters and Surface Plasmon Polaritons

We have developed a unique method to measure the excitation and coupling rates between the light emitters and surface plasmon polaritons (SPPs) arising from metallic periodic arrays without involving time-resolved techniques. We have formulated the rates by quantities that can be measured by simple optical measurements. The instrumentation based on angle- and polarization-resolved reflectivity and photoluminescence spectroscopy will be described in detail here. Our approach is intriguing due to its simplicity, which requires routine optics and several mechanical stages, and thus is highly affordable to most of the research laboratories.

This protocol describes the instrumentation for determining the excitation and coupling rates between light emitters and Bloch-like surface plasmon polaritons arising from periodic arrays.

We have developed a unique method to measure the excitation and coupling rates between the light emitters and surface plasmon polaritons (SPPs) arising ...

One-Step Approach to Fabricating Polydimethylsiloxane Microfluidic Channels of Different Geometric Sections by Sequential Wet Etching Processes

Polydimethylsiloxane (PDMS) materials are substantially exploited to fabricate microfluidic devices by using soft lithography replica molding techniques. Customized channel layout designs are necessary for specific functions and integrated performance of microfluidic devices in numerous biomedical and chemical applications (e.g., cell culture, biosensing, chemical synthesis, and liquid handling). Owing to the nature of molding approaches using silicon wafers with photoresist layers patterned by photolithography as master molds, the microfluidic channels commonly have regular cross sections of rectangular shapes with identical heights. Typically, channels with multiple heights or different geometric sections are designed to possess particular functions and to perform in various microfluidic applications (e.g., hydrophoresis is used for sorting particles and in continuous flows for separating blood cells6,7,8,9). Therefore, a great deal of effort has been made in constructing channels with various sections through multiple-step approaches like photolithography using several photoresist layers and assembly of different PDMS thin sheets. Nevertheless, such multiple-step approaches usually involve tedious procedures and extensive instrumentation. Furthermore, the fabricated devices may not perform consistently and the resulted experimental data may be unpredictable. Here, a one-step approach is developed for the straightforward fabrication of microfluidic channels with different geometric cross sections through PDMS sequential wet etching processes, that introduces etchant into channels of planned single-layer layouts embedded in PDMS materials. Compared to the existing methods for manufacturing PDMS microfluidic channels with different geometries, the developed one-step approach can significantly simplify the process to fabricate channels with non-rectangular sections or various heights. Consequently, the technique is a way of constructing complex microfluidic channels, which provides a fabrication solution for the advancement of innovative microfluidic systems.

Several methods are available for the fabrication of channels of non-rectangular sections embedded in polydimethylsiloxane microfluidic devices. Most of them involve multistep manufacturing and extensive alignment. In this paper, a one-step approach is reported for fabricating microfluidic channels of different geometric cross sections by polydimethylsiloxane sequential wet etching.

Polydimethylsiloxane (PDMS) materials are substantially exploited to fabricate microfluidic devices by using soft lithography replica molding techniques. ...

Synchrotron X-ray Microdiffraction and Fluorescence Imaging of Mineral and Rock Samples

In this report, we describe a detailed procedure for acquiring and processing&#160;x-ray microfluorescence (&#956;XRF), and Laue and powder microdiffraction two-dimensional (2D) maps at beamline 12.3.2 of the Advanced Light Source (ALS), Lawrence Berkeley National Laboratory. Measurements can be performed on any sample that is less than 10 cm x 10 cm x 5 cm, with a flat exposed surface. The experimental geometry is calibrated using standard materials (elemental standards for XRF, and crystalline samples such as Si, quartz, or Al2O3 for diffraction). Samples are aligned to the focal point of the x-ray microbeam, and raster scans are performed, where each pixel of a map corresponds to one measurement, e.g., one XRF spectrum or one diffraction pattern. The data are then processed using the in-house developed software XMAS, which outputs text files, where each row corresponds to a pixel position. Representative data from moissanite and an olive snail shell are presented to demonstrate data quality, collection, and analysis strategies.

We describe a beamline setup meant to carry out rapid two-dimensional x-ray fluorescence and x-ray microdiffraction mapping of single crystal or powder samples using either Laue (polychromatic radiation) or powder (monochromatic radiation) diffraction. The resulting maps give information about strain, orientation, phase distribution, and plastic deformation.