Name: multiscale structures aggregated by imprinted nanofibers for functional surfaces
Uploaded: 2018-09-11T14:45:00
Description: Watch this Scientific Journal Video about Multiscale Structures Aggregated by Imprinted Nanofibers for Functional Surfaces at JoVE.com

This material is based on work supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (NRF-2017R1A2B4008053) and the Ministry of Trade, Industry and Energy (MOTIE, Korea) under Industrial Technology Innovation Program No. 10052802 and the Korea Institute for the Advancement of Technology (KIAT) through the Encouragement Program for The Industries of Economic Cooperation Region (N0002310).

1. Fabrication of Nano-Micro Multiscale Structure Surface Using an AAO Filter (Figure 1)
<ol>
	<li>Purchase an AAO filter with a pore size, height, and diameter of 200 nm, 60 &#181;m, and 25 mm, respectively.</li>
	<li>1.2. Clean the surface of the Polyethylene terephthalate (PET) film having a thickness of 100 &#956;m to use acetone with 99.8% and isopropyl alcohol (IPA) with 99.9% for 5 min, and completely dry for 3 min using an air gun.</li>
	<li>Place the PET film on a flat surface wit...

<ol>
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H., Hwang, J., Lee, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Replication+of+cicada+wing's+nano-patterns+by+hot+embossing+and+UV+nanoimprinting.">Replication of cicada wing's nano-patterns by hot embossing and UV nanoimprinting.</a> Nanotechnology. 20, 385303 (2009).</li><li>Han, K. S., Shin, J. H., Yoon, W. Y., Lee, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enhanced+performance+of+solar+cells+with+anti-reflection+layer+fabricated+by+nano-imprint+lithography.">Enhanced performance of solar cells with anti-reflection layer fabricated by nano-imprint lithography.</a> Solar Energy Materials and Solar Cells. 95, 288-291 (2011).</li><li>Choo, S., Choi, H. J., Lee, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Replication+of+rose-petal+surface+structure+using+UV-nanoimprint+lithography.">Replication of rose-petal surface structure using UV-nanoimprint lithography.</a> Materials Letters. 121, 170-173 (2014).</li><li>Yu, Z., Chou, S. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Triangular+profile+imprint+molds+in+nanograting+fabrication.">Triangular profile imprint molds in nanograting fabrication.</a> Nano Letters. 4, 341-344 (2004).</li><li>Hirai, Y., Harara, S., Isaka, S., Kobayashi, M., Tanaka, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nano-Imprint+lithography+using+replicated+mold+by+Ni+electroforming.">Nano-Imprint lithography using replicated mold by Ni electroforming.</a> Japanese Journal of Applied Physics. 41, 4186 (2002).</li><li>Kim, J. H., Cho, Y. T., Jung, Y. 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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=Nanoporous+alumina+as+templates+for+multifunctional+applications.">Nanoporous alumina as templates for multifunctional applications.</a> Applied Physics Reviews. 1, 031102 (2014).</li><li>Hong, S. H., Bae, B. J., Lee, H., Jeong, J. 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The key step in fabrication of the self-aggregated nanofiber assembly is to ensure that the brittle AAO filter does not break when applying the resin with the rubber rollers. In fact, it should be ensured that the AAO filter does not break at any point before the etching step. Because the AAO filter is 25 mm in diameter, the size of the substrate is approximately 30 x 30 mm.
The self-aggregated nanofiber assembly allows us to provide various functional surfaces through the proper surface treat...

Nanoscale textured structures such as nanoparticles, nanotubes, and nanofibers have attracted attention in the scientific community, as they demonstrate unique characteristics in various applications including electrical, biomedical, optical, and surface engineering1,2,3,4,5,6,7,8. In particular, nanofibers are widely used in stretchable and transparent electrodes9, wearable sensors10,11, interconnections12,13, and nano-optics applications14. Among the various methods of fabricating nanoscale structures, such as sol-gel methods, self-assembly, lithography, and replication15,16,17,18,19,20, direct replication using a template is currently considered a promising method because it is simple, cost-effective, and applicable to various curable materials21,22,23,24,25,26.
Owing to its multiscale structure having a large number of nano-scale pores and micro-scale height, AAO is widely used as the template for fabrication of nanofibers and nanotubes with a high aspect ratio27,28,29,30. However, because of the surface tension at such a high aspect ratio, nanofibers tend to easily aggregate31,32,33. Existing research has proved that nanofibers having an aspect ratio greater than 15:1 do not stand upright but instead aggregate, whereas those having a ratio less than 5:1 are individually isolated without aggregation33,34. Capillary force and surface tension play an important role upon the removal of alumina using an etchant, which is one of the processes during nanofiber fabrication. When aspect ratio increases, surface tension among nanofibers tends to pull them closer to one another, causing aggregation. Several studies have focused on methods to prevent such aggregation35, which is particularly observed in polymer and metallic nanofibers. Among these, hydration of the nanofiber surface may reduce the agglomeration because when a liquid occupies the spaces between nanofibers, surface tension decreases. Further, the freeze-drying method may also reduce aggregation by decreasing surface tension between nanofibers. However, despite various efforts, the straightening of nanofibers with a high aspect ratio remains a challenge.
To this end, we report a unique method for fabricating multiscale structures of tangled nanofiber by exploiting the aggregation phenomenon in a positive manner. Here, the nanofiber structure is imprinted using an AAO filter and polyurethane-acrylate (PUA)-type resins with a viscosity of 257.4 cP. After UV nano imprint lithography (UV-NIL) is performed, the mold is etched with a&#160;NaOH solution. To characterize the proposed multiscale structures, we investigate the pattern behaviors of the sample with aggregated nanofibers and the surface wettability after proper surface treatments such as coating with a self-assembled monolayer and UV ozone treatment. Furthermore, we propose that the multiscale porous surface can be converted simply to a slippery surface using a lubricant-infused process.

<table>
	<tbody>
		<tr>
			<td>MINS 511RM</td>
			<td>Minuta Tech</td>
			<td></td>
			<td>UV curable resin</td>
		</tr>
		<tr>
			<td>Octadecyltrichlorosilane (OTS)</td>
			<td>Aldrich</td>
			<td></td>
			<td>Surface treatment</td>
		</tr>
		<tr>
			<td>Sodium oxidanide</td>
			<td>SAMCHUN</td>
			<td></td>
			<td>Etching solution</td>
		</tr>
		<tr>
			<td>Anopore Inoganic Membranes</td>
			<td>Whatman</td>
			<td></td>
			<td>25mm/0.2&#181;m</td>
		</tr>
		<tr>
			<td>MT-UV-A 47</td>
			<td>Meiji Techno</td>
			<td></td>
			<td>UV curing equipment</td>
		</tr>
		<tr>
			<td>UVC-30</td>
			<td>Jaesung Engineering</td>
			<td></td>
			<td>UVO treatment equipment</td>
		</tr>
		<tr>
			<td>Smart Drop Plus</td>
			<td>FEMTOFAB</td>
			<td></td>
			<td>Contact angle measurement</td>
		</tr>
		<tr>
			<td>Fluorinert FC-70</td>
			<td>3M</td>
			<td></td>
			<td>liquid mixture of completely fluorinated aliphatic compounds</td>
		</tr>
		<tr>
			<td>Polyethylene terephthalate film</td>
			<td>Sunchem</td>
			<td></td>
			<td>Substrate</td>
		</tr>
		<tr>
			<td>Acetone (99.8%)</td>
			<td>Daejung</td>
			<td></td>
			<td>Cleaning solution</td>
		</tr>
		<tr>
			<td>Isopropyl alcohol (99.9%)</td>
			<td>Daejung</td>
			<td></td>
			<td>Cleaning solution</td>
		</tr>
		<tr>
			<td>Rubber roller</td>
			<td>Hwahong</td>
			<td></td>
			<td>For application of resin</td>
		</tr>
		<tr>
			<td>Corning Stirring Hot Plates</td>
			<td>Corning</td>
			<td></td>
			<td>Hot plate equipment (5&#34; x 7&#34;)</td>
		</tr>
	</tbody>
</table>

multiscale structures aggregated by imprinted nanofibers for functional surfaces

Multiscale surface structures have attracted increasing interest owing to several potential applications in surface devices. However, an existing challenge in the field is the fabrication of hybrid micro-nano structures using a facile, cost-effective, and high-throughput method. To overcome these challenges, this paper proposes a protocol to fabricate multiscale structures using only an imprint process with an anodic aluminum oxide (AAO) filter and an evaporative self-aggregation process of nanofibers. Unlike previous attempts that have aimed to straighten nanofibers, we demonstrate a unique fabrication method for multiscale aggregated nanofibers with high aspect ratios. Furthermore, the surface morphology and wettability of these structures on various liquids were investigated to facilitate their use in multifunctional surfaces.

We demonstrated a fast and simple method for the fabrication of multiscale nano-micro hybrid structures using an AAO filter as an imprinting mold. The entire process took 30 min (Figure 4). It was noted that after undergoing the etching process using NaOH, the resultant surface exhibited an opaque color similar to the original AAO filter, owing to the aggregated nanofiber assembly caused by surface tension. Further, the results of the EDX analysis confirmed t...

Watch this Scientific Journal Video about Multiscale Structures Aggregated by Imprinted Nanofibers for Functional Surfaces at JoVE.com

Multiscale Structures Aggregated by Imprinted Nanofibers for Functional Surfaces

Presented is an easy method to fabricate nano-micro multiscale structures, for functional surfaces, by aggregating nanofibers fabricated using an anodic aluminum oxide filter.

Multiscale surface structures have attracted increasing interest owing to several potential applications in surface devices. However, an existing ...

This method can help answer key questions in the engineer to surface field in understanding functional surface for tubular morphology and wettability. The main advantage of our approach is that it allows faster fabrication of multiscale nanomicro structures by using only an imprint process with an anodic aluminum oxide filter and a self-aggregation of nano fibers. After imprinting, the replicated surface patterns initially exhibited superhydrophilicity.We can change the surface availability of the imprinted structures by using UV origin treatment and self-assembled monolayer coating. Obtain an anodic aluminum oxide, or AAO, filter with a pore size of 200 nanometers, height of 60 microns, and diameter of 25 milliliters. Clean the surface with polyethylene terephthalate, or PET film, with 99.8%acetone for five minutes, followed by 99.9.isopropyl alcohol for five minutes. Completely dry the film for three minutes using an air gun. Next, place the PET film on a flat surface without contaminants.Add a 0.1 milliliter drop of UV curable polyurethane acrylate type resin with a viscosity of 257.4 CPS on the surface. Place the AAO filter on the resin and press uniformly using a rubber roller with a diameter of 32 millimeters. The spread of the resin is visually confirmed.The roller must be repeated and carefully pushed when pressing. The AAO filter is brittle and may break if excessive force is applied. After rolling, expose the specimen made with the PET and AAO filter to UV light with a wavelength of 365 nanometers for 30 seconds to cure the resin.Then, immerse the cured specimen in 100 milliliters of two molar sodium hydroxide solution for 10 minutes to dissolve the filter. The SEM images show the surface and cross section of the structure. Clean the specimen with deionized water.Then, completely dry it for three minutes using an air gun. Use energy dispersive x-ray analysis to confirm that sodium and aluminum are not detected and are completely etched. To perform the UV ozone treatment, first clean the specimen with nanomicro multiscale structures using isopropyl alcohol for five minutes and then deionized water for five minutes.Dry the washed the specimen using an air gun for three minutes. Irradiate the specimen using UV rays for 60 minutes using UV ozone equipment with an intensity of 25 milliwatts per square centimeter. For OTS self-assembly, place the hot place inside the glovebox, and maintain a nitrogen environment for the vapor deposition process.For filming purposes we will demonstrate the procedure in mock outside a glovebox. Place a beaker on the hot plate and add two milliliters of OTS solution to the beaker using a pipette. Cover the beaker with the glass or plate face on, with the specimen facing downward into the beaker.Process for 60 minutes at 100 degrees Celsius before removing the specimen from the glovebox. To fabricate the functional surface by injecting lubricants, deposit approximately 0.2 milliliters per square centimeter of perfluorocarbon liquid on the OTS coated self-aggregated nanofiber assembly. Observe the wetting process of the perfluorocarbon using an optical microscope at five to 20 times magnification.Finally, remove the excess perfluorocarbon liquid by placing the sample in a vertical position for a few hours. Multiscale nanomicro hybrid structures obtained by the imprint process and evaporation derived self-aggregation are shown here. It is difficult to measure the contact angle because of the superhydrophilicity of the fabricated surface.Interestingly, after UV ozone treatment with sufficient time, the surface morphology and the surface wettability change from superhydrophilicity to hydrophobicity, with a contact angle of 126.8 degrees. Further more, the contact angle can be increased to 133.6 degrees by an additional coating of the self-assembled monolayer. After its development, this technique paved the way for researchers in the field of engineered surface to explore the surface functionality and morphology change with the self-assembly phenomenon and proper surface treatment.Though this method can provide insight into the modification of the surface morphology and wettability, it can also be applied to other applications such as tissue via scalpel, environmental filters, catalyst disruptor, or with diffused optics, because of its larger scale porous structures.

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JoVE Journal

Engineering

Probing and Mapping Electrode Surfaces in Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen 1-7. The performance of SOFCs and the rates of many chemical and energy transformation processes in energy storage and conversion devices in general are limited primarily by charge and mass transfer along electrode surfaces and across interfaces. Unfortunately, the mechanistic understanding of these processes is still lacking, due largely to the difficulty of characterizing these processes under in situ conditions. This knowledge gap is a chief obstacle to SOFC commercialization. The development of tools for probing and mapping surface chemistries relevant to electrode reactions is vital to unraveling the mechanisms of surface processes and to achieving rational design of new electrode materials for more efficient energy storage and conversion2. Among the relatively few in situ surface analysis methods, Raman spectroscopy can be performed even with high temperatures and harsh atmospheres, making it ideal for characterizing chemical processes relevant to SOFC anode performance and degradation8-12. It can also be used alongside electrochemical measurements, potentially allowing direct correlation of electrochemistry to surface chemistry in an operating cell. Proper in situ Raman mapping measurements would be useful for pin-pointing important anode reaction mechanisms because of its sensitivity to the relevant species, including anode performance degradation through carbon deposition8, 10, 13, 14 ("coking") and sulfur poisoning11, 15 and the manner in which surface modifications stave off this degradation16. The current work demonstrates significant progress towards this capability. In addition, the family of scanning probe microscopy (SPM) techniques provides a special approach to interrogate the electrode surface with nanoscale resolution. Besides the surface topography that is routinely collected by AFM and STM, other properties such as local electronic states, ion diffusion coefficient and surface potential can also be investigated17-22. In this work, electrochemical measurements, Raman spectroscopy, and SPM were used in conjunction with a novel test electrode platform that consists of a Ni mesh electrode embedded in an yttria-stabilized zirconia (YSZ) electrolyte. Cell performance testing and impedance spectroscopy under fuel containing H2S was characterized, and Raman mapping was used to further elucidate the nature of sulfur poisoning. In situ Raman monitoring was used to investigate coking behavior. Finally, atomic force microscopy (AFM) and electrostatic force microscopy (EFM) were used to further visualize carbon deposition on the nanoscale. From this research, we desire to produce a more complete picture of the SOFC anode.

We present a unique platform for characterizing electrode surfaces in solid oxide fuel cells (SOFCs) that allows simultaneous performance of multiple characterization techniques (e.g. in situ Raman spectroscopy and scanning probe microscopy alongside electrochemical measurements). Complementary information from these analyses may help to advance toward a more profound understanding of electrode reaction and degradation mechanisms, providing insights into rational design of better materials for SOFCs.

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen ...

Fabrication of Nano-engineered Transparent Conducting Oxides by Pulsed Laser Deposition

Nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas allows the deposition of metal oxides with tunable morphology, structure, density and stoichiometry by a proper control of the plasma plume expansion dynamics. Such versatility can be exploited to produce nanostructured films from compact and dense to nanoporous characterized by a hierarchical assembly of nano-sized clusters. In particular we describe the detailed methodology to fabricate two types of Al-doped ZnO (AZO) films as transparent electrodes in photovoltaic devices: 1) at low O2 pressure, compact films with electrical conductivity and optical transparency close to the state of the art transparent conducting oxides (TCO) can be deposited at room temperature, to be compatible with thermally sensitive materials such as polymers used in organic photovoltaics (OPVs); 2) highly light scattering hierarchical structures resembling a forest of nano-trees are produced at higher pressures. Such structures show high Haze factor (&gt;80%) and may be exploited to enhance the light trapping capability. The method here described for AZO films can be applied to other metal oxides relevant for technological applications such as TiO2, Al2O3, WO3 and Ag4O4.

We describe the experimental method to deposit nanostructured oxide thin films by nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas. By using this method Al-doped ZnO (AZO) films, from compact to hierarchically structured as nano-tree forests, can be deposited.

Nanosecond Pulsed  Laser Deposition (PLD) in the presence of a background gas allows the deposition  of metal oxides with tunable morphology, structure, ...

High-speed Particle Image Velocimetry Near Surfaces

Multi-dimensional and transient flows play a key role in many areas of science, engineering, and health sciences but are often not well understood. The complex nature of these flows may be studied using particle image velocimetry (PIV), a laser-based imaging technique for optically accessible flows. Though many forms of PIV exist that extend the technique beyond the original planar two-component velocity measurement capabilities, the basic PIV system consists of a light source (laser), a camera, tracer particles, and analysis algorithms. The imaging and recording parameters, the light source, and the algorithms are adjusted to optimize the recording for the flow of interest and obtain valid velocity data. 
Common PIV investigations measure two-component velocities in a plane at a few frames per second. However, recent developments in instrumentation have facilitated high-frame rate (&gt; 1 kHz) measurements capable of resolving transient flows with high temporal resolution. Therefore, high-frame rate measurements have enabled investigations on the evolution of the structure and dynamics of highly transient flows. These investigations play a critical role in understanding the fundamental physics of complex flows.
A detailed description for performing high-resolution, high-speed planar PIV to study a transient flow near the surface of a flat plate is presented here. Details for adjusting the parameter constraints such as image and recording properties, the laser sheet properties, and processing algorithms to adapt PIV for any flow of interest are included.

A procedure for studying transient flows near boundaries using high-resolution, high-speed particle image velocimetry (PIV) is described here. PIV is a non-intrusive measurement technique applicable to any optically accessible flow by optimizing several parameter constraints such as the image and recording properties, the laser sheet properties, and analysis algorithms.

Multi-dimensional and transient flows play a key role in many areas of science, engineering, and health sciences but are often not well understood. The ...

Monolayer Contact Doping of Silicon Surfaces and Nanowires Using Organophosphorus Compounds

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra shallow and sharp doping profiles at the nanometer scale. In MLCD process the dopant source is a monolayer containing dopant atoms.
In this article a detailed procedure for surface doping of silicon substrate as well as silicon nanowires is demonstrated. Phosphorus dopant source was formed using tetraethyl methylenediphosphonate monolayer on a silicon substrate. This monolayer containing substrate was brought to contact with a pristine intrinsic silicon target substrate and annealed while in contact. Sheet resistance of the target substrate was measured using 4 point probe. Intrinsic silicon nanowires were synthesized by chemical vapor deposition (CVD) process using a vapor-liquid-solid (VLS) mechanism; gold nanoparticles were used as catalyst for nanowire growth. The nanowires were suspended in ethanol by mild sonication. This suspension was used to dropcast the nanowires on silicon substrate with a silicon nitride dielectric top layer. These nanowires were doped with phosphorus in similar manner as used for the intrinsic silicon wafer. Standard photolithography process was used to fabricate metal electrodes for the formation of nanowire based field effect transistor (NW-FET). The electrical properties of a representative nanowire device were measured by a semiconductor device analyzer and a probe station.

A detailed procedure for surface doping of Silicon interfaces is provided. The ultra-shallow surface doping is demonstrated by using phosphorus containing monolayers and rapid annealing process. The method can be used for doping of macroscopic area surfaces as well as nanostructures.

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra ...

Seedless Growth of Bismuth Nanowire Array via Vacuum Thermal Evaporation

Here a seedless and template-free technique is demonstrated to scalably grow bismuth nanowires, through thermal evaporation in high vacuum at RT. Conventionally reserved for the fabrication of metal thin films, thermal evaporation deposits bismuth into an array of vertical single crystalline nanowires over a flat thin film of vanadium held at RT, which is freshly deposited by magnetron sputtering or thermal evaporation. By controlling the temperature of the growth substrate the length and width of the nanowires can be tuned over a wide range. Responsible for this novel technique is a previously unknown nanowire growth mechanism that roots in the mild porosity of the vanadium thin film. Infiltrated into the vanadium pores, the bismuth domains (~ 1 nm) carry excessive surface energy that suppresses their melting point and continuously expels them out of the vanadium matrix to form nanowires. This discovery demonstrates the feasibility of scalable vapor phase synthesis of high purity nanomaterials without using any catalysts.

A protocol for seedless and high yield growth of bismuth nanowire arrays through vacuum thermal evaporation technique is presented.

Here a seedless and template-free technique is demonstrated to scalably grow bismuth nanowires, through thermal evaporation in high vacuum at RT. ...

Evanescent Field Based Photoacoustics: Optical Property Evaluation at Surfaces

Here, we present a protocol to estimate material and surface optical properties using the photoacoustic effect combined with total internal reflection. Optical property evaluation of thin films and the surfaces of bulk materials is an important step in understanding new optical material systems and their applications. The method presented can estimate thickness, refractive index, and use absorptive properties of materials for detection. This metrology system uses evanescent field-based photoacoustics (EFPA), a field of research based upon the interaction of an evanescent field with the photoacoustic effect. This interaction and its resulting family of techniques allow the technique to probe optical properties within a few hundred nanometers of the sample surface. This optical near field allows for the highly accurate estimation of material properties on the same scale as the field itself such as refractive index and film thickness. With the use of EFPA and its sub techniques such as total internal reflection photoacoustic spectroscopy (TIRPAS) and optical tunneling photoacoustic spectroscopy (OTPAS), it is possible to evaluate a material at the nanoscale in a consolidated instrument without the need for many instruments and experiments that may be cost prohibitive.

Here we present a protocol to estimate material and surface optical properties using the photoacoustic effect combined with total internal reflection. This technique evanescent field-based photoacoustics can be used to create a photoacoustic metrology system to estimate materials&#39; thicknesses, bulk and thin film refractive indices, and explore their optical properties.

Here, we present a protocol to estimate material and surface optical properties using the photoacoustic effect combined with total internal reflection. ...

Strain Sensing Based on Multiscale Composite Materials Reinforced with Graphene Nanoplatelets

The electrical response of NH2-functionalized graphene nanoplatelets composite materials under strain was studied. Two different manufacturing methods are proposed to create the electrical network in this work: (a) the incorporation of the nanoplatelets into the epoxy matrix and (b) the coating of the glass fabric with a sizing filled with the same nanoplatelets. Both types of multiscale composite materials, with an in-plane electrical conductivity of ~10-3 S/m, showed an exponential growth of the electrical resistance as the strain increases due to distancing between adjacent functionalized graphene nanoplatelets and contact loss between overlying ones. The sensitivity of the materials analyzed during this research, using the described procedures, has been shown to be higher than commercially available strain gauges. The proposed procedures for self-sensing of the structural composite material would facilitate the structural health monitoring of components in difficult to access emplacements such as offshore wind power farms. Although the sensitivity of the multiscale composite materials was considerably higher than the sensitivity of metallic foils used as strain gauges, the value reached with NH2 functionalized graphene nanoplatelets coated fabrics was nearly an order of magnitude superior. This result elucidated their potential to be used as smart fabrics to monitor human movements such as bending of fingers or knees. By using the proposed method, the smart fabric could immediately detect the bending and recover instantly. This fact permits precise monitoring of the time of bending as well as the degree of bending.

The integration of conductive nanoparticles, such as graphene nanoplatelets, into glass fiber composite materials creates an intrinsic electrical network susceptible to strain. Here, different methods to obtain strain sensors based on the addition of graphene nanoplatelets into the epoxy matrix or as a coating on glass fabrics are proposed.

The electrical response of NH2-functionalized graphene nanoplatelets composite materials under strain was studied. Two different manufacturing methods are ...

Pool-Boiling Heat-Transfer Enhancement on Cylindrical Surfaces with Hybrid Wettable Patterns

In this study, pool-boiling heat-transfer experiments were performed to investigate the effect of the number of interlines and the orientation of the hybrid wettable pattern. Hybrid wettable patterns were produced by coating superhydrophilic SiO2 on a masked, hydrophobic, cylindrical copper surface. Using de-ionized (DI) water as the working fluid, pool-boiling heat-transfer studies were conducted on the different surface-treated copper cylinders of a 25-mm diameter and a 40-mm length. The experimental results showed that the number of interlines and the orientation of the hybrid wettable pattern influenced the wall superheat and the HTC. By increasing the number of interlines, the HTC was enhanced when compared to the plain surface. Images obtained from the charge-coupled device (CCD) camera indicated that more bubbles formed on the interlines as compared to other parts. The hybrid wettable pattern with the lowermost section being hydrophobic gave the best heat-transfer coefficient (HTC). The experimental results indicated that the bubble dynamics of the surface is an important factor that determines the nucleate boiling.

Pool-boiling heat-transfer experiments were carried out to observe the effects of hybrid wettable patterns on the heat-transfer coefficient (HTC). The parameters of investigation are the number of interlines and the pattern orientation of the modified wettable surface.

In this study, pool-boiling heat-transfer experiments were performed to investigate the effect of the number of interlines and the orientation of the ...

Preparation of Liquid Crystal Networks for Macroscopic Oscillatory Motion Induced by Light

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous light irradiation. The photo-excitation of dopants that can quickly dissipate light into heat, coupled with anisotropic thermal expansion and self-shadowing of the film, gives rise to the self-sustained deformation. The oscillations observed are influenced by the dimensions and the modulus of the film, and by the directionality and intensity of the light. The system developed offers applications in energy conversion and harvesting for soft-robotics and automated systems.
The general method described here consists of creating free-standing liquid crystalline films and characterizing the mechanical and thermal effects observed. The molecular alignment is achieved using alignment layers (rubbed polyimide), commonly used in the display manufacturing industry. To obtain actuators with large deformation, the mesogens are aligned and polymerized in a splay/bend configuration, i.e., with the director of the liquid crystals (LCs) going gradually from planar to homeotropic through the film thickness. Upon irradiation, the mechanical and thermal oscillations obtained are monitored with a high-speed camera. The results are further quantified by image analysis using an image processing program.

The goal of the protocol is to create liquid crystalline polymer films that can mechanically oscillate under continuous light irradiation. We describe in great detail the conception of free-standing films, from the liquid crystal alignment method to the photo-actuation. The experimental protocol applied to prepare this material is broadly applicable.

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous ...

Fabricating Reactive Surfaces with Brush-like and Crosslinked Films of Azlactone-Functionalized Block Co-Polymers

In this paper, fabrication methods that generate novel surfaces using the azlactone-based block co-polymer, poly (glycidyl methacrylate)-block-poly (vinyl dimethyl azlactone) (PGMA-b-PVDMA), are presented. Due to the high reactivity of azlactone groups towards amine, thiol, and hydroxyl groups, PGMA-b-PVDMA surfaces can be modified with secondary molecules to create chemically or biologically functionalized interfaces for a variety of applications. Previous reports of patterned PGMA-b-PVDMA interfaces have used traditional top-down patterning techniques that generate non-uniform films and poorly controlled background chemistries. Here, we describe customized patterning techniques that enable precise deposition of highly uniform PGMA-b-PVDMA films in backgrounds that are chemically inert or that have biomolecule-repellent properties. Importantly, these methods are designed to deposit PGMA-b-PVDMA films in a manner that completely preserves azlactone functionality through each processing step. Patterned films show well-controlled thicknesses that correspond to polymer brushes (~90 nm) or to highly crosslinked structures (~1-10 &#956;m). Brush patterns are generated using either the parylene lift-off or interface directed assembly methods described and are useful for precise modulation of overall chemical surface reactivity by adjusting either the PGMA-b-PVDMA pattern density or the length of the VDMA block. In contrast, the thick, crosslinked PGMA-b-PVDMA patterns are obtained using a customized micro-contact printing technique and offer the benefit of higher loading or capture of secondary material due to higher surface area to volume ratios. Detailed experimental steps, critical film characterizations, and trouble-shooting guides for each fabrication method are discussed.

Surface fabrication methods for patterned deposition of nanometer thick brushes or micron thick, crosslinked films of an azlactone block co-polymer are reported. Critical experimental steps, representative results, and limitations of each method are discussed. These methods are useful for creating functional interfaces with tailored physical features and tunable surface reactivity.

In this paper, fabrication methods that generate novel surfaces using the azlactone-based block co-polymer, poly (glycidyl methacrylate)-block-poly (vinyl ...