Name: fabrication and design of wood-based high-performance composites
Uploaded: 2019-11-09T14:00:00
Duration: 8 min 8 s
Description: Watch this Scientific Journal Video about Fabrication and Design of Wood-Based High-Performance Composites at JoVE.com

The authors thank Silvan Gantenbein for the 3D printing of porous molds.

1. Delignification of wood veneers
NOTE: This delignification protocol is based on our previous works, published by Frey et al. 20186 and Segmehl et al. 201813.
<ol>
	<li>Mount a stainless-steel sample holder in a crystallizing dish or in a beaker and place a magnetic stir bar below the sample holder. Stack wood veneers on top of the holder and separate them by metal meshes or metal mesh stripes (Figure 2A). Here, we use radial cut spruce veneers with a thickness of 1.5 mm. Wood species and type (tangential, radial, rotary cut veneer) as well as the thickness of veneers can be varied.</li>
	<li>Prepare a 1:1 volume mixture of hydrogen peroxide (30 wt%) and glacial acetic acid and pour the mixture into the crystallizing dish until the veneers are fully covered. Use glass dishes (e.g. Petri dish) to keep the veneers in the solution. Soak samples in the solution at room temperature (RT) overnight while stirring at 150 rpm.</li>
	<li>Heat the solution to 80 &#730;C and run the reaction for 6 h for full delignification. Adjust the delignification time depending on the sample thickness.</li>
	<li>After delignification, pour the delignification solution into an empty beaker and let it cool down before disposal. Gently rinse the delignified veneers multiple times with deionized water. Then, continue washing the veneers without stirring by filling the crystallizing dish (beaker) with deionized water. Replace the water twice a day until a pH value of the washing water of above 5 is reached (Figure 2B).</li>
	<li>Handle wet delignified wood veneers with care, as the cellulose scaffold is rather fragile. Use a metal mesh as support for transportation and draping (Figure 4).</li>
</ol>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/60327/60327fig2a.jpg" /> 
Figure 2: Delignification setup. (A) Crystallizing dish with metal mesh sample holder and wood veneers stacked on top of the sample holder. Metal mesh stripes separate the individual veneers from each other. (B) Delignfied veneers covered by water during the washing process. <a href="https://www.jove.com/files/ftp_upload/60327/60327fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
2. Storage and &#34;cellulose prepreg&#34; production
<ol>
	<li>Consider processing the wet delignified wood samples within 2-3 weeks. Alternatively, preserve the material for long-term storage in ethanol (EtOH) or dry the sheets between metal meshes.</li>
	<li>Store the dry, flat cellulose sheets (&#34;cellulose prepregs&#34;) below 65% relative humidity (RH). Rewet the sheets in water prior to further shaping and processing.</li>
</ol>
3. Densification and forming of delignified wood in closed molds
<ol>
	<li>Use closed molds made out of an open-porous material (e.g. ceramic molds, porous 3D printed polymer molds) to enable water removal and sufficient drying. Pore sizes should be below 2 mm, especially towards the surface, to obtain a smooth surface of the final composite part.</li>
	<li>Condition the delignified wood at desired RH. For curvature radii in the cm range or plane structures, use samples that are conditioned at 95% RH at 20 &#730;C. For smaller curvature radii, drape the veneer in water-saturated state, pre-dry the draped material in an open mold at 95% RH, or pre-dry the material in an oven (65 &#730;C) for 5-30 min (the time is depends on the sample thickness). Curvature considerations are made in relation to veneer thickness (here 1.5 mm).</li>
	<li>Densify the material in the closed mold either by using screw clamps or in a press. Readjust the pressure if needed to compensate for shrinkage. The drying process can be speed up by placing the mold into an oven at 65 &#730;C or by increasing the temperature of the press. 
	NOTE: A relatively low pressure in the range of a few MPa is sufficient to densify wet delignified wood. The final thickness can be controlled by using spacers with the targeted thickness between the mold surfaces rather than by controlling the pressure.</li>
	<li>After full drying, demold the composite part and reuse the mold for a new run.</li>
</ol>
4. Vacuum shaping and densification of delignified wood in open molds
<ol>
	<li>Use a porous open mold as described in 3.1. Alternatively, use non-porous molds with a porous layer (e.g. mesh, textile, breather) on top of the mold or on top of the delignified wood to enable drying (Figure 3A).</li>
	<li>Use a textile layer (e.g. peel-ply) to protect the mold from contamination. Drape a water-saturated delignified veneer on top of the textile (Figure 3B) and cover it with a second textile layer and flow mesh. 
	NOTE: To obtain a smooth surface finish, we recommend using porous closed-mold processing. For this, replace the flow mesh with the porous top part of the mold. However, if surface patterning with e.g. a mesh is desired, the open-mold process is a good alternative.</li>
	<li>Place the mold on top of a stainless-steel plate, apply sealing tape and vacuum tubing, and wrap the mold (open or closed) with a vacuum bag. Use flow mesh to enable water flow to the vacuum tubing. Optionally, place additional mesh layers below the mold to enhance the drying process and to avoid local vacuum pressure drops, especially for bigger parts (Figure 3C).</li>
	<li>Apply a vacuum for drying and simultaneous densification of the composite. For accelerated drying, place the setup into an oven at elevated temperature (e.g. 65 &#730;C). 
	NOTE: Make sure to use cold traps to avoid water entering the vacuum pump. We here use an oil pump in a pressure range of 10-2 bar. However, it is also possible to use a membrane pump but trade-offs regarding densification degree might need to be taken into account.</li>
	<li>After drying, demold the dry composite and reuse the mold and vacuum setup for a new composite part (Figure 3D).</li>
</ol>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/60327/60327fig3a.jpg" /> 
Figure 3: Schematic illustration of the open-mold process. (A) Porous mold with smaller pores towards the surface. (B) Delignified wood draped on top of the porous mold (grey) and optional textile layer for mold protection (green). (C) Textile, flow mesh and vacuum bag placed on top of delignified wood. Pressure is applied through the vacuum bag and leads to densification and drying of the material. (D) Final composite after demolding. <a href="https://www.jove.com/files/ftp_upload/60327/60327fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
5. Manufacturing of laminated composite parts
<ol>
	<li>Manufacture thick multi-layer composite parts by lay-up techniques and choose the fiber orientation angle of the layers (e.g. [0&#730;], [0&#730;/90&#730;], [0&#730;/-45&#730;/90&#730;/+45&#730;]S) as in traditional composite manufacturing. 
	NOTE: The number of layers can be chosen depending on the targeted thickness of the final part. However, the vacuum time strongly depends on the size and thickness of the part and ranges from 2 h (single layer, 1.5 mm thick) up to 2 days for an 8-ply part.</li>
	<li>Increase bonding between delignified wood layers by applying adhesive between layers during the draping process. Use a water based adhesive (e.g. starch) which allows combined drying and curing of the adhesive. 
	NOTE: We apply 0.04 g/cm2 of a 16.5 wt% starch solution between the layers. However, other water-based glues could be used alternatively.</li>
	<li>Demold the composite part and machine finish by hand or with standard wood tooling (Figure 6E,F).</li>
</ol>
6. Re-use and recycling of composite parts
<ol>
	<li>Place delignified non-glued wood composites in water until the part regains formability. Then, either reshape the material to obtain a new product (see Frey et al. 20197) or reduce it to small pieces.</li>
	<li>Reuse the small pieces of delignified wood to create new products inspired by standard pulp techniques (e.g. pulp molding) and finally let the material biodegrade after end of life.</li>
</ol>

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The authors have nothing to disclose.

We present versatile fabrication techniques to obtain high-performance delignified wood-based composites and suggest possible re-use and recycling strategies. Closed-mold processing prerequisites pre-conditioning of the material, as it cannot be processed in water-saturated state. Utilizing a closed-mold process, however, could be the method of choice especially if e.g. there is no vacuum setup available or if a nice (smooth) surface finish on both sides is desired.
Open-mold vacuum processing of delignified wood allows for combining shaping, densification, and drying of water-saturated samples in a simple and scalable approach. The technique is applicable for the production of complex geometries and offers a scalable alternative for closed-mold processes. We have manufactured composites by stacking delignified wood veneers using starch as adhesive between layers. Densification down to one quarter of the initial thickness resulted in a final thickness of 2.5 mm of the 8-layer thick composite part. For obtaining a smoother surface finish in the vacuum process, the use of a closed porous mold could be an appropriate alternative.
For both processing methods, we recommend the use of an adhesive system in between delignified wood layers in order to decrease the risk of delamination. For the given example, we choose starch, as it is a well-known bio-based glue for pulp and paper products, such as paper bags, and is water based. Future works will focus on the fabrication of thicker laminates to resolve current limitations in terms of drying and fiber flow deviations.
In general, vacuum processing of delignified wood has the potential for an easy and fast production of large-scale densified cellulose fiber composites. After addressing the material&#39;s durability issue by applying proper coatings, water-stable adhesive systems or chemical modification, possible industrial applications may include automotive components such as door panels, floors, and dashboards. Our material could replace metals or fiber reinforced composites in order to reduce weight for better fuel efficiency and to improve recyclability.

The development of novel natural fiber (NF) based composites equipped with superior mechanical properties represents one of the main tasks in materials science, as they can be sustainable alternatives for current synthetic systems such as glass fiber composites1,2,3. Besides traditional NF composites (flax, hemp, kenaf, etc)4,5, the densification of wood after partial or complete removal of matrix components has received increasing attention in recent years6,7,8,9,10,11. The top-down fabrication route, based on delignification of bulk wood followed by densification, is conceptually contrary to rather complex bottom-up processes for pulp and slurry based products12. In pulp and slurry based products, the beneficial wood fiber alignment is not retained as fibers are separated in the process. In contrast, structure-retaining delignified wood, which is obtained in a top-down process, transfers the sophisticated architecture with aligned cellulose fibers into the new material. To achieve densification of delignified wood without fiber alignment distortions, new processing routes must be developed.
Direct densification of water-saturated delignified wood samples leads to a limited densification degree, cracks, and fiber alignment distortions due to the wet-sample-inherent free water that creates a counter pressure during densification. Current solutions to avoid structural integrity loss upon densification includes utilization of partially delignified wood followed by high-temperature densification9 or pre-drying of delignified wood prior densification6. Both methods enhance connectivity between neighboring cells, either due to the remaining lignin that acts as glue or free water removal between cells.
In both cases, reduced formability occurs, which limits design applications; the required sample pre-conditioning also leads to longer processing times. Therefore, a fast and scalable process that combines shaping and densification in a single step is necessary.
In this regard, we present here open/closed-mold densification and vacuum processing of delignified wood as methods to combine shaping, densification, and drying in a simple and scalable approach. Figure 1 shows delignified densified wood-composite parts, which were obtained by using the techniques described in this work.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/60327/60327fig1a.jpg" /> 
Figure 1: Examples of delignified densified wood composite parts. (A) Door panel, (B) side mirror, (C) door handle of a car, (D) orthosis, (E) cut open helmet, and (F) tachometer cover of a car. <a href="https://www.jove.com/files/ftp_upload/60327/60327fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Acetic acid</td>
			<td>VWR Chemicals</td>
			<td>20104.312</td>
			<td></td>
		</tr>
		<tr>
			<td>Breather</td>
			<td>Suter Kunststoffe AG</td>
			<td>923.015</td>
			<td></td>
		</tr>
		<tr>
			<td>Flow mesh/bleeder</td>
			<td>Suter Kunststoffe AG</td>
			<td>180.007</td>
			<td></td>
		</tr>
		<tr>
			<td>Gypsum</td>
			<td>Suter Kunststoffe AG</td>
			<td>115.3002</td>
			<td></td>
		</tr>
		<tr>
			<td>Hydrogen peroxide, 30%</td>
			<td>VWR Chemicals</td>
			<td>23622.298</td>
			<td></td>
		</tr>
		<tr>
			<td>Oven</td>
			<td>Binder GmbH</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Press</td>
			<td>Imex Technik AG</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Seal tape</td>
			<td>Suter Kunststoffe AG</td>
			<td>31344</td>
			<td></td>
		</tr>
		<tr>
			<td>Stainless steel mesh</td>
			<td>Drawag AG</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Starch</td>
			<td>Agrana Beteilungs AG</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Textile, peel ply</td>
			<td>Suter Kunststoffe AG</td>
			<td>222.001</td>
			<td></td>
		</tr>
		<tr>
			<td>Vacuum bag</td>
			<td>Suter Kunststoffe AG</td>
			<td>215.15</td>
			<td></td>
		</tr>
		<tr>
			<td>Vacuum bag, elastic</td>
			<td>Suter Kunststoffe AG</td>
			<td>390.1761</td>
			<td>elastic vacuum bag for complex shapes</td>
		</tr>
		<tr>
			<td>Vacuum pump</td>
			<td>Vacuumbrand</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Vacuum tubing</td>
			<td>Suter Kunststoffe AG</td>
			<td>77008.001</td>
			<td></td>
		</tr>
		<tr>
			<td>Wood veneers</td>
			<td>Bollinger AG</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

fabrication and design of wood-based high-performance composites

Delignified densified wood is a new promising and sustainable material that possesses the potential to replace synthetic materials, such as glass fiber reinforced composites, due to its excellent mechanical properties. Delignified wood, however, is rather fragile in a wet state, which makes handling and shaping challenging. Here we present two fabrication processes, closed-mold densification and vacuum densification, to produce high-performance cellulose composites based on delignified wood, including an assessment of their advantages and limitations. Further, we suggest strategies for how the composites can be re-used or decomposed at the end-of-life cycle. Closed-mold densification has the advantage that no elaborate lab equipment is needed. Simple screw clamps or a press can be used for densification. We recommend this method for small parts with simple geometries and large radii of curvature. Vacuum densification in an open-mold process is suitable for larger objects and complex geometries, including small radii of curvature. Compared to the closed-mold process, the open-mold vacuum approach only needs the manufacture of a single mold cavity.

Delignification and handling of wood veneers.
Complete delignification leads to a mass reduction of around 40% and a volume reduction of around 20% after drying at 65% RH6. Besides lignin, a fraction of hemicelluloses gets removed too. Removal of these components results in a fragile cellulose material (see Figure 4). Using metal meshes as supports eases handling and draping.
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/60327/60327fig4a.jpg" /> 
Figure 4: Handling of delignified wood in wet state. (A) Fragile delignified wood in its wet state. (B) Handling of the material is eased by using a metal mesh for transportation or (C) for draping the material to a mold. (D) Delignified wood draped on top of a porous 3D-printed mold. <a href="https://www.jove.com/files/ftp_upload/60327/60327fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Densification and forming of delignified wood in closed molds.
Densification of water-saturated delignified wood (Figure 5A-C) is demanding, as free water in the scaffold creates a counter pressure upon densification and allows the material to flow during processing. This causes fiber deviations and cracks in the final material (Figure 5B,C). One possibility to bypass these limitations is to use moist pre-conditioned (95% RH and 20 &#730;C), delignified wood. In this condition, delignified wood is still reasonably shapeable and its densification does not lead to fiber alignment distortions and defects.
Pre-conditioned material, however, is more rigid compared to the water-saturated state, which makes it difficult to obtain small curvature radii without material damage. For small curvature radii, wet draping followed by conditioning in an already shaped state prior densification can be used. However, conditioning is rather time consuming and therefore not recommended for large-scale applications.
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/60327/60327fig5a.jpg" /> 
Figure 5: Closed-mold densification of delignified wood in a wet and moist state. (A) Densification of the water-saturated cellulose material leads to (B,C) cracks and fiber misalignment. (D-F) Densification of moist material, conditioned at 95% RH results in a better preservation of fiber alignment and less defects. <a href="https://www.jove.com/files/ftp_upload/60327/60327fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Vacuum shaping and densification of a laminated part in an open mold.
Exemplarily for vacuum shaping, we manufactured a helmet in a self-made gypsum mold using an open-mold process (Figure 6A,B). As lay-up, we draped 2 layers of hexagon-flakes for surface texturing followed by 4 layers of delignified wood veneer in a [0&#730;/90&#730;] lay-up (Figure 6C). The flakes provide an attractive surface design, whereas the unidimensional (UD) layers add strength and stiffness to the composite. We applied 16.5 wt% starch as adhesive between layers to prevent delamination14.
Vacuum densification (Figure 6D) leads to full drying of the part within 48 h and densification down to a thickness of 3 mm (1/3rd of the initial thickness). After the vacuum processing, the composite part is demolded (Figure 6E) and the edges are trimmed with a cutter (Figure 6F).
The maximum layup thickness that could be densified and fully dried with the open-molding approach was an 8-layer layup (8 x 1.5 mm veneer) with an end thickness of this part of 2.5 mm, which corresponds to a densification down to approximately one quarter of the initial thickness of dry delignified wood, taking into account the layer shrinkage upon delignification and drying. To obtain such high densification degrees, a low vacuum in the range of 10-2 bar is needed.
Delignified wood composites that are densified to around one quarter of their initial thickness typically achieve elastic moduli values around 25 GPa and strength values in the range of 150-180 MPa, as shown in our previous work (Table 1)7.

<img alt="Table 1" src="/files/ftp_upload/60327/60327table1.jpg" />
Table 1: Literature values for tensile elastic modulus and tensile strength of densified delignified wood. The vacuum processing results in a densification down to 1/4th of the initial thickness, which corresponds to an FVC of 66%.
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/60327/60327fig6a.jpg" /> 
Figure 6: Manufacturing of a helmet by open-mold processing. (A,B) Molding of the original helmet using a gypsum mold. (C) Draping of two outer layers with hexagon flakes followed by draping the inner 4-layers in a [0/90] layup. (D) Densification and drying of the part by vacuum. (E) Demolding of the dry part and (F) finish using a cutter. <a href="https://www.jove.com/files/ftp_upload/60327/60327fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Utilizing flow meshes typically results in a mesh-imprint in the sample. This can either be considered as a process-inherent design strategy or can be prevented by placing an additional thicker textile layer between delignified wood and flow mesh.
Alternatively, closed molds combined with vacuum processing as described in protocol step 4.2 can be used. Regular patterning can be obtained by placing small pieces of delignified veneers in a defined order, as shown before for our example with the hexagon patterning on the helmet.
Problems that can arise during vacuum processing include warpages in the composite part, which are caused by incomplete drying and the occurrence of cracks (Figure 7). Cracks mainly result in delignified wood that was stored in EtOH prior composite fabrication. Therefore, after EtOH storage, we recommend to carefully soak delignified wood in water before further processing. Additionally, careful draping followed by slight densification by hand to remove some free water reduces the risk of cracking.
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/60327/60327fig7a.jpg" /> 
Figure 7: Possible problems arising in fabrication of complex geometries. (A) Back view and (B) side view of the manufactured helmet. (C,D) Small cracks due to shrinkage of the material during processing. <a href="https://www.jove.com/files/ftp_upload/60327/60327fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Re-use or decomposition of composite parts.
Our cellulose-starch composite is all bio-based and can disintegrate in water. On the one hand, the hydrophilicity of the material is a disadvantage, as it leads to reduced mechanical performance when in contact with water. A simple method to protect the composite from liquid water comprises hydrophobic coatings, as we have shown in Frey et al. 20197. On the other hand, a hydrophilic behavior of the material can also be beneficial when it comes to end-of life use and recycling aspects. The sample can simply be disintegrated in water to smaller pieces and the fibrous slurry can further be used for the production of new fiber-based products as shown in Figure 8. Furthermore, the fibrous material is fully biodegradable, as shown in Figure 9.
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/60327/60327fig8a.jpg" /> 
Figure 8: Re-use of delignified wood fibers. (A-C) Reduction of delignified wood veneers into small pieces by dispersing the material in water. (D-F) Re-use of the fiber slurry for producing the lining of a helmet. (D) Reveting of a silicon mold with fiber slurry. (E) Final lining of the helmet. (F) Lining made out of disintegrated delignified wood inside of the hard shell of the helmet. <a href="https://www.jove.com/files/ftp_upload/60327/60327fig8large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 9" class="xfigimg" src="/files/ftp_upload/60327/60327fig9a.jpg" /> 
Figure 9: Degradation of delignified wood fibers. (A) Petri dish filled with soil. (B) Placing the fiber slurry on top of the soil and (C) filling it with water. (D) Bio-degradation after one day, (E) after eight days, and (F) after 26 days. <a href="https://www.jove.com/files/ftp_upload/60327/60327fig9large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Fabrication and Design of Wood-Based High-Performance Composites at JoVE.com

Fabrication and Design of Wood-Based High-Performance Composites

Delignified densified wood represents a new promising lightweight, high-performance and bio-based material with great potential to partially substitute natural fiber reinforced- or glass fiber reinforced composites in the future. We here present two versatile fabrication routes and demonstrate the possibility to create complex composite parts.

Delignified densified wood is a new promising and sustainable material that possesses the potential to replace synthetic materials, such as glass fiber ...

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Design, Fabrication, and Experimental Characterization of Plasmonic Photoconductive Terahertz Emitters

In this video article we present a detailed demonstration of a highly efficient method for generating terahertz waves. Our technique is based on photoconduction, which has been one of the most commonly used techniques for terahertz generation 1-8. Terahertz generation in a photoconductive emitter is achieved by pumping an ultrafast photoconductor with a pulsed or heterodyned laser illumination. The induced photocurrent, which follows the envelope of the pump laser, is routed to a terahertz radiating antenna connected to the photoconductor contact electrodes to generate terahertz radiation. Although the quantum efficiency of a photoconductive emitter can theoretically reach 100%, the relatively long transport path lengths of photo-generated carriers to the contact electrodes of conventional photoconductors have severely limited their quantum efficiency. Additionally, the carrier screening effect and thermal breakdown strictly limit the maximum output power of conventional photoconductive terahertz sources. To address the quantum efficiency limitations of conventional photoconductive terahertz emitters, we have developed a new photoconductive emitter concept which incorporates a plasmonic contact electrode configuration to offer high quantum-efficiency and ultrafast operation simultaneously. By using nano-scale plasmonic contact electrodes, we significantly reduce the average photo-generated carrier transport path to photoconductor contact electrodes compared to conventional photoconductors 9. Our method also allows increasing photoconductor active area without a considerable increase in the capacitive loading to the antenna, boosting the maximum terahertz radiation power by preventing the carrier screening effect and thermal breakdown at high optical pump powers. By incorporating plasmonic contact electrodes, we demonstrate enhancing the optical-to-terahertz power conversion efficiency of a conventional photoconductive terahertz emitter by a factor of 50 10.

We describe methods for the design, fabrication, and experimental characterization of plasmonic photoconductive emitters, which offer two orders of magnitude higher terahertz power levels compared to conventional photoconductive emitters.

In this video article we present a detailed demonstration of a highly efficient method for generating terahertz waves. Our technique is based on ...

Research and Development of High-performance Explosives

Developmental testing of high explosives for military applications involves small-scale formulation, safety testing, and finally detonation performance tests to verify theoretical calculations. For newly developed formulations, the process begins with small-scale mixes, thermal testing, and impact and friction sensitivity. Only then do subsequent larger scale formulations proceed to detonation testing, which will be covered in this paper. Recent advances in characterization techniques have led to unparalleled precision in the characterization of early-time evolution of detonations. The new technique of Photonic Doppler Velocimetry (PDV) for the measurement of detonation pressure will be shared and compared with traditional fiber-optic detonation velocity and plate-dent calculation of detonation pressure. In particular, the role of aluminum in explosive formulations will be discussed. Recent developments led to the development of explosive formulations that result in reaction of aluminum very early in the detonation product expansion. This enhanced reaction leads to changes in the detonation velocity and pressure due to reaction of the aluminum with oxygen in the expanding gas products.

Developmental testing of high explosives for military applications involves small-scale formulation, safety testing, and finally detonation performance tests to verify theoretical calculations. This paper will share typical development tests associated with the measurement of detonation velocity and detonation pressure.

Developmental testing of high explosives for military applications involves small-scale formulation, safety testing, and finally detonation performance ...

Ultrasonic Welding of Thermoplastic Composite Coupons for Mechanical Characterization of Welded Joints through Single Lap Shear Testing

This paper presents a novel straightforward method for ultrasonic welding of thermoplastic-composite coupons in optimum processing conditions. The ultrasonic welding process described in this paper is based on three main pillars. Firstly, flat energy directors are used for preferential heat generation at the joining interface during the welding process. A flat energy director is a neat thermoplastic resin film that is placed between the parts to be joined prior to the welding process and heats up preferentially owing to its lower compressive stiffness relative to the composite substrates. Consequently, flat energy directors provide a simple solution that does not require molding of resin protrusions on the surfaces of the composite substrates, as opposed to ultrasonic welding of unreinforced plastics. Secondly, the process data provided by the ultrasonic welder is used to rapidly define the optimum welding parameters for any thermoplastic composite material combination. Thirdly, displacement control is used in the welding process to ensure consistent quality of the welded joints. According to this method, thermoplastic-composite flat coupons are individually welded in a single lap configuration. Mechanical testing of the welded coupons allows determining the apparent lap shear strength of the joints, which is one of the properties most commonly used to quantify the strength of thermoplastic composite welded joints.

A straightforward procedure for ultrasonic welding of thermoplastic composite coupons for basic mechanical testing is described. Key characteristics of this ultrasonic welding process are the use of flat energy directors for simplified process preparation and the use of process data for the fast definition of optimum processing conditions.

This paper presents a novel straightforward method for ultrasonic welding of thermoplastic-composite coupons in optimum processing conditions. The ...

Probing C84-embedded Si Substrate Using Scanning Probe Microscopy and Molecular Dynamics

This paper reports an array-designed C84-embedded Si substrate fabricated using a controlled self-assembly method in an ultra-high vacuum chamber. The characteristics of the C84-embedded Si surface, such as atomic resolution topography, local electronic density of states, band gap energy, field emission properties, nanomechanical stiffness, and surface magnetism, were examined using a variety of surface analysis techniques under ultra, high vacuum (UHV) conditions as well as in an atmospheric system. Experimental results demonstrate the high uniformity of the C84-embedded Si surface fabricated using a controlled self-assembly nanotechnology mechanism, represents an important development in the application of field emission display (FED), optoelectronic device fabrication, MEMS cutting tools, and in efforts to find a suitable replacement for carbide semiconductors. Molecular dynamics (MD) method with semi-empirical potential can be used to study the nanoindentation of C84-embedded Si substrate. A detailed description for performing MD simulation is presented here. Details for a comprehensive study on mechanical analysis of MD simulation such as indentation force, Young&#39;s modulus, surface stiffness, atomic stress, and atomic strain are included. The atomic stress and von-Mises strain distributions of the indentation model can be calculated to monitor deformation mechanism with time evaluation in atomistic level.

Probing C84-embedded Si Substrate Using Scanning Probe Microscopy and Molecular Dynamics

This paper reports the nanomaterial fabrication of a fullerene Si substrate inspected and verified by nanomeasurements and molecular dynamic simulation.

This paper reports an array-designed C84-embedded Si substrate fabricated using a controlled self-assembly method in an ultra-high vacuum chamber. The ...

A High Performance Impedance-based Platform for Evaporation Rate Detection

This paper describes the method of a novel impedance-based platform for the detection of the evaporation rate. The model compound hyaluronic acid was employed here for demonstration purposes. Multiple evaporation tests on the model compound as a humectant with various concentrations in solutions were conducted for comparison purposes. A conventional weight loss approach is known as the most straightforward, but time-consuming, measurement technique for evaporation rate detection. Yet, a clear disadvantage is that a large volume of sample is required and multiple sample tests cannot be conducted at the same time. For the first time in literature, an electrical impedance sensing chip is successfully applied to a real-time evaporation investigation in a time sharing, continuous and automatic manner. Moreover, as little as 0.5 ml of test samples is required in this impedance-based apparatus, and a large impedance variation is demonstrated among various dilute solutions. The proposed high-sensitivity and fast-response impedance sensing system is found to outperform a conventional weight loss approach in terms of evaporation rate detection.

This paper presents an impedance-based apparatus for evaporation rate detection of solutions. It offers clear advantages over a conventional weight loss approach: a fast response, high-sensitivity detection, a small sample requirement, multiple sample measurements, and easy disassembly for cleaning and reuse purposes.

This paper describes the method of a novel impedance-based platform for the detection of the evaporation rate. The model compound hyaluronic acid was ...

Nanostructured Ag-zeolite Composites as Luminescence-based Humidity Sensors

Small silver clusters confined inside zeolite matrices have recently emerged as a novel type of highly luminescent materials. Their emission has high external quantum efficiencies (EQE) and spans the whole visible spectrum. It has been recently reported that the UV excited luminescence of partially Li-exchanged sodium Linde type A zeolites [LTA(Na)] containing luminescent silver clusters can be controlled by adjusting the water content of the zeolite. These samples showed a dynamic change in their emission color from blue to green and yellow upon an increase of the hydration level of the zeolite, showing the great potential that these materials can have as luminescence-based humidity sensors at the macro and micro scale. Here, we describe the detailed procedure to fabricate a humidity sensor prototype using silver-exchanged zeolite composites. The sensor is produced by suspending the luminescent Ag-zeolites in an aqueous solution of polyethylenimine (PEI) to subsequently deposit a film of the material onto a quartz plate. The coated plate is subjected to several hydration/dehydration cycles to show the functionality of the sensing film.

A protocol for the synthesis of moisture-responsive luminescent Ag-zeolite composites is described in this report.

Small silver clusters confined inside zeolite matrices have recently emerged as a novel type of highly luminescent materials. Their emission has high ...

Scalable Solution-processed Fabrication Strategy for High-performance, Flexible, Transparent Electrodes with Embedded Metal Mesh

Here, the authors report the embedded metal-mesh transparent electrode (EMTE), a new transparent electrode (TE) with a metal mesh completely embedded in a polymer film. This paper also presents a low-cost, vacuum-free fabrication method for this novel TE; the approach combines lithography, electroplating, and imprint transfer (LEIT) processing. The embedded nature of the EMTEs offers many advantages, such as high surface smoothness, which is essential for organic electronic device production; superior mechanical stability during bending; favorable resistance to chemicals and moisture; and strong adhesion with plastic film. LEIT fabrication features an electroplating process for vacuum-free metal deposition and is favorable for industrial mass production. Furthermore, LEIT allows for the fabrication of metal mesh with a high aspect ratio (i.e., thickness to linewidth), significantly enhancing its electrical conductance without adversely losing optical transmittance. We demonstrate several prototypes of flexible EMTEs, with sheet resistances lower than 1 &#937;/sq and transmittances greater than 90%, resulting in very high figures of merit (FoM) &#8211; up to 1.5 x 104 &#8211; which are amongst the best values in the published literature.

This protocol describes a solution-based fabrication strategy for high-performance, flexible, transparent electrodes with fully-embedded, thick metal mesh. Flexible transparent electrodes fabricated by this process demonstrate among the highest reported performances, including ultra-low sheet resistance, high optical transmittance, mechanical stability under bending, strong substrate adhesion, surface smoothness, and environmental stability.

Here, the authors report the embedded metal-mesh transparent electrode (EMTE), a new transparent electrode (TE) with a metal mesh completely embedded in a ...

Detecting the Water-soluble Chloride Distribution of Cement Paste in a High-precision Way

To improve the accuracy of the chloride distribution along the depth of cement paste under cyclic wet-dry conditions, a new method is proposed to obtain a high-precision chloride profile. Firstly, paste specimens are molded, cured, and exposed to cyclic wet-dry conditions. Then, powder samples at different specimen depths are grinded when the exposure age is reached. Finally, the water-soluble chloride content is detected using a silver nitrate titration method, and chloride profiles are plotted. The key to improving the accuracy of the chloride distribution along the depth is to exclude the error in the powderization, which is the most critical step for testing the distribution of chloride. Based on the above concept, the grinding method in this protocol can be used to grind powder samples automatically layer by layer from the surface inward, and it should be noted that a very thin grinding thickness (less than 0.5 mm) with a minimum error less than 0.04 mm can be obtained. The chloride profile obtained by this method better reflects the chloride distribution in specimens, which helps researchers to capture the distribution features that are often overlooked. Furthermore, this method can be applied to studies in the field of cement-based materials, which require high chloride distribution accuracy.

A protocol for obtaining a water-soluble chloride profile by using a high precision milling method is presented.

To improve the accuracy of the chloride distribution along the depth of cement paste under cyclic wet-dry conditions, a new method is proposed to obtain a ...

Flow-assisted Dielectrophoresis: A Low Cost Method for the Fabrication of High Performance Solution-processable Nanowire Devices

Flow-assisted dielectrophoresis (DEP) is an efficient self-assembly method for the controllable and reproducible positioning, alignment, and selection of nanowires. DEP is used for nanowire analysis, characterization, and for solution-based fabrication of semiconducting devices. The method works by applying an alternating electric field between metallic electrodes. The nanowire formulation is then dropped onto the electrodes which are on an inclined surface to create a flow of the formulation using gravity. The nanowires then align along the gradient of the electric field and in the direction of the liquid flow. The frequency of the field can be adjusted to select nanowires with superior conductivity and lower trap density. 
In this work, flow-assisted DEP is used to create nanowire field effect transistors. Flow-assisted DEP has several advantages: it allows selection of nanowire electrical properties; control of nanowire length; placement of nanowires in specific areas; control of orientation of nanowires; and control of nanowire density in the device. 
The technique can be expanded to many other applications such as gas sensors and microwave switches. The technique is efficient, quick, reproducible, and it uses a minimal amount of dilute solution making it ideal for the testing of novel nanomaterials. Wafer scale assembly of nanowire devices can also be achieved using this technique, allowing large numbers of samples for testing and large-area electronic applications.

In this paper, flow assisted dielectrophoresis is demonstrated for the self-assembly of nanowire devices. The fabrication of a silicon nanowire field effect transistor is shown as an example.

Flow-assisted dielectrophoresis (DEP) is an efficient self-assembly method for the controllable and reproducible positioning, alignment, and selection of ...

Design and Fabrication of an Optical Fiber Made of Water

In this report, an optical fiber of which the core is made solely of water, while the cladding is air, is designed and manufactured. In contrast with solid-cladding devices, capillary oscillations are not restricted, allowing the fiber walls to move and vibrate. The fiber is constructed by a high direct current (DC) voltage of several thousand volts (kV) between two water reservoirs that creates a floating water thread, known as a water bridge. Through the choice of micropipettes, it is possible to control the maximal diameter and length of the fiber. Optical fiber couplers, at both sides of the bridge, activate it as an optical waveguide, allowing researchers to monitor the water fiber capillary body waves through transmission modulation and, therefore, deducing changes in surface tension.
Co-confining two important wave types, capillary and electromagnetic, opens a new path of research in the interactions between light and liquid-wall devices. Water-walled microdevices are a million times softer than their solid counterparts, accordingly improving the response to minute forces.

This protocol describes the design and manufacture of a water bridge and its activation as a water fiber. The experiment demonstrates that capillary resonances of the water fiber modulate its optical transmission.

In this report, an optical fiber of which the core is made solely of water, while the cladding is air, is designed and manufactured. In contrast with ...