The authors acknowledge the financial support from the programs of the Natural Science Foundation of the Jiangsu Higher Education (22KJB460033), and Jiangsu Science and Technology Programme - Young Scholar (BK20200251). This work is also partially supported by the XJTLU AI University Research Centre, Jiangsu Province Engineering Research Centre of Data Science and Cognitive Computation at XJTLU and SIP AI innovation platform (YZCXPT2022103). The support from State Key Laboratory for Manufacturing Systems Engineering via the open project (SKLMS2023019) and Key Laboratory of Bionic Engineering, Ministry of Education, are also acknowledged.

1. Microembossing process for microchannel patterning on nanopaper
<ol>
	<li>Mold preparation 
	NOTE: Refer to Yuan et al.12 for details on mold preparation.
	<ol>
		<li>Prepare a PTFE film as indicated in the Table of Materials.</li>
		<li>Laser-cut the prepared PTFE film to make a convex microchannel mold (Figure 1A-I). 
		NOTE: The dimensions of the PTFE mold determine the microchannel dimensions (Figure 2E,F) in a linear first-order function relationship.</li>
	</ol>
	</li>
	<li>Nanopaper preparation
	<ol>
		<li>Disperse 4.0 g of (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)-oxidized NFC gel (see Table of Materials) in distilled water (final concentration of 0.1 wt%).</li>
		<li>Stir the suspension heavily at 120.8 x g for 30 min at room temperature until no cellulose floc is visible.</li>
		<li>Vacuum-filter the clear suspension to obtain a nanopaper gel (Figure 1A-II). 
		NOTE: In this example, the diameter of the obtained nanopaper gel is 4 cm. NanoPADs can be tailored for various applications by selecting suction filtration devices with different radii, enabling the design of NanoPADs at different scales.</li>
	</ol>
	</li>
	<li>Embossing of nanopaper gel
	<ol>
		<li>Place the PTFE mold on the surface of the nanopaper gel.</li>
		<li>Emboss the nanopaper gel (Figure 1A-III) using the PTFE mold by the hot press for 10 min each time under optimized pressure and temperature (Figure 2A-D). 
		NOTE: Higher embossing pressure (250 kPa to 1000 kPa) improves fabrication accuracy but should not exceed 1000 kPa to prevent damage to the cellulose structure. Higher embossing temperatures (25-100 &#176;C) enhance microchannel accuracy by promoting dehydration and decarburization, but temperatures should not exceed 75 &#176;C to avoid gel wrinkling and reduced light transmittance7. In this example, optimized embossing parameters were 750 kPa and 75 &#176;C.</li>
	</ol>
	</li>
	<li>Mold releasing
	<ol>
		<li>Peel off an additional layer of filter nanopaper gel from the filter membrane (Figure 1A-IV).</li>
	</ol>
	</li>
	<li>Bonding
	<ol>
		<li>Attach the peeled layer on top of the embossed layer of nanopaper gel, stacking the two layers to create a hollow microchannel structure (Figure 1A-V). 
		NOTE: The stronger hydrogen bonding in &#39;gel-like&#39; nanopaper compared to fiber suspension and dried nanopaper enhances the entanglement and adhesion of nanocellulose fibers. Consequently, two layers of &#39;gel-like&#39; nanopaper can bond tightly through self-diffusion without external force.</li>
	</ol>
	</li>
	<li>Drying
	<ol>
		<li>Place the two layers of nanopaper gel in a drying oven at 75 &#176;C for approximately 30 min (Figure 1A-VI).</li>
	</ol>
	</li>
</ol>
2. Construction of fundamental microfluidic devices
<ol>
	<li>Construction of laminar-mixer
	<ol>
		<li>Prepare the NanoPADs with straight and curved channels (Figure 3A) following step 1. 
		NOTE: In this example, the dimensions of channels are 1 mm width and 50 &#181;m depth.</li>
		<li>Add red and blue droplets in the inlet zones simultaneously, allowing flow through the hollow channel automatically. 
		NOTE: The successful independent flow of the red and blue solutions in a straight channel and their mixing at the end of the curved channel can be attributed to the low Reynolds number of the layers in microfluidic devices and the radial flow induced by shear stress35.</li>
	</ol>
	</li>
	<li>Construction of droplet generator
	<ol>
		<li>Prepare the two-inlet NanoPADs with a T-junction channel (Figure 3D) according to step 1.</li>
		<li>Introduce water and hexadecane (oil), two immiscible liquids, into the two-inlet zones of the T-junction channel to generate droplets (Figure 3E). 
		NOTE: In this example, the dimensions of the T-junction channel are 1 mm width, 25 mm length, and 50 &#181;m depth.</li>
		<li>Fix the speed of Q1 at 6 &#181;L/min, and the speed of Q2 at n &#215; Q1 (n = 1-6). Use two syringe pumps and set them at the above speed to inject water and oil. This behavior is governed by the one simple scaling equation (provided below). 
		NOTE: In this example, oil and colored water were poured into the channel36. 
		<img alt="Equation 1" src="/files/ftp_upload/65965/65965eq01.jpg" style="margin: auto;" /> 
		Where &#945; = 1, &#946; = 1, L is the length, W is the width of the droplet, and Q1 and Q2 are the flow rates of water and hexadecane, respectively37,38.</li>
	</ol>
	</li>
</ol>
3. In-situ AgNP growth
<ol>
	<li>NanoPADs preparation
	<ol>
		<li>Prepare two-inlet NanoPADs with a converging detection zone (Figure 4A) according to step 1.</li>
	</ol>
	</li>
	<li>Successive ionic layer adsorption and reaction process
	<ol>
		<li>Prepare a 20 mM AgNO3 solution and a 20 mM NaBH4 solution (see Table of Materials).</li>
		<li>Drop 5 &#181;L of the 20 mM AgNO3 solution into the left inlet zone of the flow channel.</li>
		<li>Allow the AgNO3 solution to remain in the reaction zone for 30 s. 
		NOTE: Repeat steps 3.2.2. and 3.2.3. five times to ensure the uniform distribution of AgNPs without agglomeration, which could explain the higher band intensity.</li>
		<li>Drop 5 &#181;L of distilled water into the left inlet zone of the flow channel for rinsing. 
		NOTE: Repeat step 3.2.4. three times to ensure the removal of excessive, unadsorbed Ag ions through washing.</li>
		<li>Add 5 &#181;L of the 20 mM NaBH4 solution to the right inlet zone of the flow channel. 
		NOTE: Repeat step 3.2.5. until the AgNPs are generated evenly in the reaction zone. The chemical reactions involved in step 3 are represented by the following formula39: 
		<img alt="Equation 2" src="/files/ftp_upload/65965/65965eq02.jpg" style="margin: auto;" /> 
		 
		In this example, dense, uniform, well-structured AgNP arrays were formed on the NanoPADs (Figure 4B). The average diameter of the AgNPs was 55 nm (Figure 4C).</li>
	</ol>
	</li>
</ol>
4. SERS measurement
<ol>
	<li>Raman spectroscopy system preparation
	<ol>
		<li>Turn on the laser and launch the accompanying software for the Raman spectrometer (see Table of Materials).</li>
		<li>Employ a 50x objective for focusing and collecting Raman signals and a 532 nm laser for excitation.</li>
		<li>Set the spectral resolution to 2 cm-1 for accurate measurement. Set Raman spectrum measurement range from 400 cm-1 to 600 cm&#8722;1.</li>
		<li>Calibrate the Raman spectrometer using a silicon wafer12. 
		NOTE: Perform step 4.1. for step 4.2.</li>
	</ol>
	</li>
	<li>Rhodamine B (RhB) measurement
	<ol>
		<li>Dissolve 4.7 mg of RhB (see Table of Materials) in 10 mL of ethanol to prepare a 1 mM RhB solution.</li>
		<li>Prepare a series of RhB solutions with concentrations ranging from 10 &#181;M to 0.1 pM by diluting the 1 mM RhB solution in the ethanol.</li>
		<li>Add 5 &#181;L of the RhB solution onto the inlet zone of the NanoPADs channel and let it dry. 
		NOTE: Repeat step 4.2.3. for RhB solutions of different concentrations indicated in step 4.2.2.</li>
		<li>Set the excitation time to 10 s, the grating to 2 cm&#8722;1, and the number of cycles to 1. Set Raman spectrum measurement range from 500 cm-1 to 1800 cm&#8722;1.</li>
		<li>Adjust the coarse focus screw and fine focus screw individually to achieve proper focus, then click on stop to save the position.</li>
		<li>Click on start to begin the measurement.</li>
		<li>Repeat the measurements seven times and save the collected data.</li>
		<li>Turn off the laser.</li>
	</ol>
	</li>
	<li>Data analysis
	<ol>
		<li>Import the saved data into the data analysis software (see Table of Materials).</li>
		<li>Calculate the average spectrum from the saved data.</li>
		<li>Select the line draft option to plot Raman spectra.</li>
		<li>Utilize the Peak analyzer tool to set the baseline of the spectra.</li>
		<li>Apply the Signal process - Smooth function to smooth the spectra for final results.</li>
	</ol>
	</li>
</ol>

Micro-Embossed Fabrication of Nanocellulose Paper-Based Analytical Devices  

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T. H., Dien, N. D., Vu, X. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Facile+synthesis+of+silver/gold+alloy+nanoparticles+for+ultra-sensitive+rhodamine+B+detection.">Facile synthesis of silver/gold alloy nanoparticles for ultra-sensitive rhodamine B detection.</a> RSC Advances. 11 (35), 21475-21488 (2021).</li><li>Li, D., Li, D. W., Li, Y., Fossey, J. S., Long, Y. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cyclic+electroplating+and+stripping+of+silver+on+Au@SiO2+core/shell+nanoparticles+for+sensitive+and+recyclable+substrate+of+surface-enhanced+Raman+scattering.">Cyclic electroplating and stripping of silver on Au@SiO2 core/shell nanoparticles for sensitive and recyclable substrate of surface-enhanced Raman scattering.</a> Journal of Materials Chemistry. 20 (18), 3688-3693 (2010).</li><li>Sun, C. H., Wang, M. L., Feng, Q., Liu, W., Xu, C. X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface-enhanced+Raman+scattering+(SERS)+study+on+Rhodamine+B+adsorbed+on+different+substrates.">Surface-enhanced Raman scattering (SERS) study on Rhodamine B adsorbed on different substrates.</a> Russian Journal of Physical Chemistry A. 89 (2), 291-296 (2015).</li></ol>

The authors have nothing to disclose.

The primary focus of this study is to develop a simple method for fabricating microchannels on nanopaper. An efficient embossing technique was devised using PTFE as the mold to address this challenge12. By optimizing the temperature and embossing pressure, a series of experiments were conducted to establish a reliable fabrication process for NanoPADs. Additionally, the use of a quick-reference table to adjust the applications of NanoPADs in different fields was demonstrated. Although this method i...

Recently, nanofibrillated cellulose (NFC) paper (nanopaper) has emerged as a highly promising substrate material for various applications such as flexible electronics, energy devices, and biomedicals1,2,3,4. Derived from natural plants, nanopaper is cost-effective, biocompatible, and biodegradable, making it an appealing alternative to traditional cellulose paper5,6. Its exceptional properties include an ultra-smooth surface with a surface roughness of less than 25 nm and a dense cellulose matrix structure, allowing for the creation of highly structured nanostructures7. Abundant hydroxyl groups of nanopaper contribute to its compact and tightly packed nanocellulose structure8. Nanopaper exhibits excellent optical transparency and minimal optical haze, making it well-suited for optical sensors. Additionally, its inherent hydrophilicity enables pump-free flow, even with its thick structure, providing autonomous fluid motion9,10. Nanocellulose has diverse applications in biological sensors, conductive electronic devices, cell culture platforms, supercapacitors, batteries, and more, showcasing its versatility and potential11,12. Particularly, nanocellulose is promising for paper-based analytical microfluidic devices (&#181;PADs), offering unique advantages over conventional chromatography paper.
In the past decade, &#181;PADs have achieved significant attention due to their affordability, biocompatibility, pump-free operation, and ease of production13,14. These devices have emerged as effective point-of-care diagnostic tools, particularly in resource-limited settings15,16,17. A significant advancement in this field was the development of wax printing, pioneered by George Whitesides18 and the Bingcheng Lin group19, enabling the creation of functional &#181;PADs by incorporating microchannels on chromatography paper. Subsequently, &#181;PADs rapidly evolved, and various biosensing techniques, including electrochemical methods20, chemiluminescence21, and enzyme-linked immunosorbent assay (ELISA)22,23,24, were successfully implemented for the detection of diverse biomarkers such as proteins25,26, DNAs27,28, RNAs29,30, and exosomes31. Despite these achievements, &#181;PADs still face challenges, including slow flow speeds and solvent evaporation.
Several methods have been proposed for creating microchannels on nanopaper32,33,34. One approach involves 3D printing sacrificial ingredients into the material, but it requires a hydrophobic coating that limits pump-free operation33. Another technique involves manually stacking channel layers between nanopaper sheets using glue, which is labor-intensive32. Alternatively, spray-coating nanocellulose fibers onto pre-patterned molds can create microchannels, but it involves time-consuming and expensive mold preparation34. Notably, these methods are limited to millimeter-scale microchannels, compromising the advantages of microfluidic devices regarding reagent volume consumption and integration. Developing a simple nanopaper microchannel patterning process with micrometer-scale resolution remains a challenge.
This study presents a unique nanopaper microchannel patterning method based on practical microembossing. The approach offers several advantages over existing methods, as it requires no expensive or specialized equipment, is simple, cost-effective, and highly accurate. A convex microchannel mold is fabricated by laser cutting a polytetrafluoroethylene (PTFE) film, known for its chemical inertness and nonstick properties. This mold is then used to emboss microchannels onto a nanopaper gel membrane. A second layer of nanopaper gel is applied on top to create closed hollow channels. Using this patterning technique, fundamental microfluidic devices on nanopaper are developed, including a laminar mixer and droplet generator. Additionally, the fabrication of surface-enhanced Raman microscopy (SERS) NanoPADs is demonstrated. In-situ creation of a silver nanoparticle-based SERS substrate is achieved by introducing two chemical reagents (AgNO3 and NaBH4) into the channels, resulting in a remarkable performance with low limits of detection (LODs).

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>AgNO3&#160;</td>
			<td>Hushi (Shanghai, China)</td>
			<td>7761-88-8</td>
			<td>&#62;99%</td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>Hushi (Shanghai, China)</td>
			<td>64-17-5</td>
			<td>&#62;99%</td>
		</tr>
		<tr>
			<td>Hexadecane</td>
			<td>Macklin (Shanghai, China)</td>
			<td>544-76-3</td>
			<td>&#62;99%</td>
		</tr>
		<tr>
			<td>LabSpec software</td>
			<td>Horiba (Japan)</td>
			<td>LabSpec5</td>
			<td></td>
		</tr>
		<tr>
			<td>Melamine</td>
			<td>Macklin (Shanghai, China)</td>
			<td>108-78-1</td>
			<td>&#62;99%</td>
		</tr>
		<tr>
			<td>NaBH4</td>
			<td>Aladdin (Shanghai, China)</td>
			<td>16940-66-2</td>
			<td>&#62;99%</td>
		</tr>
		<tr>
			<td>Origin lab software</td>
			<td>OriginLab (USA)</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Polyethylene terephthalate (PET)&#160;</td>
			<td>Myers Industries (Akron, USA)</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Polytetrafluoroethylene films</td>
			<td>Shenzhen Huashenglong plastic material Co., Ltd. (Shenzhen, China)</td>
			<td></td>
			<td>Teflon film</td>
		</tr>
		<tr>
			<td>PVDF filter membrane</td>
			<td>EMD Millipore Corporation (USA)</td>
			<td>VVLP04700</td>
			<td>pore size: 0.1 &#956;m</td>
		</tr>
		<tr>
			<td>Raman spectrometer</td>
			<td>Horiba (Japan)</td>
			<td>Xplo RA</td>
			<td></td>
		</tr>
		<tr>
			<td>Rhodamine B</td>
			<td>Macklin (Shanghai, China)</td>
			<td>81-88-9</td>
			<td>&#62;95%</td>
		</tr>
		<tr>
			<td>Scanning electron microscopy (SEM)</td>
			<td>FEI(USA)</td>
			<td>Scios 2 HiVac</td>
			<td></td>
		</tr>
		<tr>
			<td>Silicon wafer</td>
			<td>Horiba (Japan)</td>
			<td></td>
			<td>diameter: 5 mm</td>
		</tr>
		<tr>
			<td>TEMPO-oxidized NFC slurry</td>
			<td>Tianjin University of Science and Technology</td>
			<td></td>
			<td>1.0 wt% solid, carboxylate level 2.0 mmol/g solid, average nanofiber diameter: 10 nm</td>
		</tr>
	</tbody>
</table>

microembossing: a convenient process for fabricating microchannels on nanocellulose paper-based microfluidics

Nanopaper, derived from nanofibrillated cellulose, has generated considerable interest as a promising material for microfluidic applications. Its appeal lies in a range of excellent&#160;qualities, including an exceptionally smooth surface, outstanding optical transparency, a uniform nanofiber matrix with nanoscale porosity, and customizable chemical properties. Despite the rapid growth of nanopaper-based microfluidics, the current techniques used to create microchannels on nanopaper, such as 3D printing, spray coating, or manual cutting and assembly, which are crucial for practical applications, still possess certain limitations, notably susceptibility to contamination. Furthermore, these methods are restricted to the production of millimeter-sized channels. This study introduces a straightforward process that utilizes convenient plastic micro-molds for simple microembossing operations to fabricate microchannels on nanopaper, achieving a minimum width of 200 &#181;m. The developed microchannel outperforms existing approaches, achieving a fourfold improvement, and can be fabricated within 45 min. Furthermore, fabrication parameters have been optimized, and a convenient quick-reference table is provided for application developers. The proof-of-concept for a laminar mixer, droplet generator, and functional nanopaper-based analytical devices (NanoPADs) designed for Rhodamine B sensing using surface-enhanced Raman spectroscopy was demonstrated. Notably, the NanoPADs exhibited exceptional performance with improved limits of detection. These outstanding results can be attributed to the superior optical properties of nanopaper and the recently developed accurate microembossing method, enabling the integration and fine-tuning of the NanoPADs.

A unique method for creating microchannel patterns on nanopaper has been devised utilizing the practical plastic micro-molds through the convenient microembossing technique. Notably, this method accomplishes microchannel patterning at a scale as small as 200 &#181;m, which represents a fourfold improvement compared to existing methods32,33,34. After fine-tuning the patterning parameters, the provided guidelines exhibit excellent...

Watch this Scientific Journal Video about Revolutionizing Microfluidics Through Microchannel Fabrication on Nanopaper at JoVE.com

Author Spotlight: Revolutionizing Microfluidics Through Microchannel Fabrication on Nanopaper 

This protocol describes a straightforward process that utilizes convenient plastic micro-molds for simple microembossing operations to fabricate microchannels on nanofibrillated cellulose paper, achieving a minimum width of 200 &#181;m.

Microembossing: A Convenient Process for Fabricating Microchannels on Nanocellulose Paper-Based Microfluidics

Nanopaper, derived from nanofibrillated cellulose, has generated considerable interest as a promising material for microfluidic applications. Its appeal ...

microembossing-convenient-process-for-fabricating-microchannels-on

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1.4K Views.  Xi’an Jiaotong - Liverpool University. This protocol describes a straightforward process that utilizes convenient plastic micro-molds for simple microembossing operations to fabricate microchannels on nanofibrillated cellulose paper, achieving a minimum width of 200 µm.

Video: Author Spotlight: Revolutionizing Microfluidics Through Microchannel Fabrication on Nanopaper 

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 ...

Development of an Experimental Setup for the Measurement of the Coefficient of Restitution under Vacuum Conditions

The Discrete Element Method is used for the simulation of particulate systems to describe and analyze them, to predict and afterwards optimize their behavior for single stages of a process or even an entire process. For the simulation with occurring particle-particle and particle-wall contacts, the value of the coefficient of restitution is required. It can be determined experimentally. The coefficient of restitution depends on several parameters like the impact velocity. Especially for fine particles the impact velocity depends on the air pressure and under atmospheric pressure high impact velocities cannot be reached. For this, a new experimental setup for free-fall tests under vacuum conditions is developed. The coefficient of restitution is determined with the impact and rebound velocity which are detected by a high-speed camera. To not hinder the view, the vacuum chamber is made of glass. Also a new release mechanism to drop one single particle under vacuum conditions is constructed. Due to that, all properties of the particle can be characterized beforehand.

The coefficient of restitution is a parameter that describes the loss of kinetic energy during collision. Here, a free-fall setup under vacuum conditions is developed to be able to determine the coefficient of restitution parameter for particles in micrometer range with high impact velocities.

The Discrete Element Method is used for the simulation of particulate systems to describe and analyze them, to predict and afterwards optimize their ...

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 ...

Adsorption Device Based on a Langatate Crystal Microbalance for High Temperature High Pressure Gas Adsorption in Zeolite H-ZSM-5

We present a high-temperature and high-pressure gas adsorption measurement device based on a high-frequency oscillating microbalance (5 MHz langatate crystal microbalance, LCM) and its use for gas adsorption measurements in zeolite H-ZSM-5. Prior to the adsorption measurements, zeolite H-ZSM-5 crystals were synthesized on the gold electrode in the center of the LCM, without covering the connection points of the gold electrodes to the oscillator, by the steam-assisted crystallization (SAC) method, so that the zeolite crystals remain attached to the oscillating microbalance while keeping good electroconductivity of the LCM during the adsorption measurements. Compared to a conventional quartz crystal microbalance (QCM) which is limited to temperatures below 80 &#176;C, the LCM can realize the adsorption measurements in principle at temperatures as high as 200-300 &#176;C (i.e., at or close to the reaction temperature of the target application of one-stage DME synthesis from the synthesis gas), owing to the absence of crystalline-phase transitions up to its melting point (1,470 &#176;C). The system was applied to investigate the adsorption of CO2, H2O, methanol and dimethyl ether (DME), each in the gas phase, on zeolite H-ZSM-5 in the temperature and pressure range of 50-150 &#176;C and 0-18 bar, respectively. The results showed that the adsorption isotherms of these gases in H-ZSM-5 can be well fitted by Langmuir-type adsorption isotherms. Furthermore, the determined adsorption parameters, i.e., adsorption capacities, adsorption enthalpies, and adsorption entropies, compare well to literature data. In this work, the results for CO2 are shown as an example.

A protocol for high-temperature and high-pressure gas adsorption measurements on zeolite H-ZSM-5 using an adsorption measurement device based on a langatate crystal microbalance is presented. Prior to the adsorption measurements, the synthesis of zeolite H-ZSM-5 on the langatate crystal microbalance sensor by the steam-assisted crystallization (SAC) method is demonstrated.

We present a high-temperature and high-pressure gas adsorption measurement device based on a high-frequency oscillating microbalance (5 MHz langatate ...

Challenges in Rheological Characterization of Highly Concentrated Suspensions &#8212; A Case Study for Screen-printing Silver Pastes

A comprehensive rheological characterization of highly concentrated suspensions or pastes is mandatory for a targeted product development meeting the manifold requirements during processing and application of such complex fluids. In this investigation, measuring protocols for a conclusive assessment of different process relevant rheological parameters have been evaluated. This includes the determination of yield stress, viscosity, wall slip velocity, structural recovery after large deformation and elongation at break as well as tensile force during filament stretching.
The importance of concomitant video recordings during parallel-plate rotational rheometry for a significant determination of rheological quantities is demonstrated. The deformation profile and flow field at the sample edge can be determined using appropriate markers. Thus, measurement parameter settings and plate roughness values can be identified for which yield stress and viscosity measurements are possible. Slip velocity can be measured directly and measuring conditions at which plug flow, shear banding or sample spillover occur can be identified clearly. 
Video recordings further confirm that the change in shear moduli observed during three stage oscillatory shear tests with small deformation amplitude in stage I and III but large oscillation amplitude in stage II can be directly attributed to structural break down and recovery. For the pastes investigated here, the degree of irreversible, shear-induced structural change increases with increasing deformation amplitude in stage II until a saturation is reached at deformations corresponding to the crossover of G' and G'', but the irreversible damage is independent of the duration of large amplitude shear. 
A capillary breakup elongational rheometer and a tensile tester have been used to characterize deformation and breakup behavior of highly filled pastes in uniaxial elongation. Significant differences were observed in all experiments described above for two commercial screen-printing silver pastes used for front side metallization of Si-solar cells.

A protocol for a robust and application relevant rheological characterization of highly concentrated suspensions is presented. Silver pastes used for screen-printing application in solar cell production are employed as model systems.

A comprehensive rheological characterization of highly concentrated suspensions or pastes is mandatory for a targeted product development meeting the ...

Fabrication Procedures and Birefringence Measurements for Designing Magnetically Responsive Lanthanide Ion Chelating Phospholipid Assemblies

Bicelles are tunable disk-like polymolecular assemblies formed from a large variety of lipid mixtures. Applications range from membrane protein structural studies by nuclear magnetic resonance (NMR) to nanotechnological developments including the formation of optically active and magnetically switchable gels. Such technologies require high control of the assembly size, magnetic response and thermal resistance. Mixtures of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and its lanthanide ion (Ln3+) chelating phospholipid conjugate, 1,2-dimyristoyl-sn-glycero-3-phospho-ethanolamine-diethylene triaminepentaacetate (DMPE-DTPA), assemble into highly magnetically responsive assemblies such as DMPC/DMPE-DTPA/Ln3+ (molar ratio 4:1:1) bicelles. Introduction of cholesterol (Chol-OH) and steroid derivatives in the bilayer results in another set of assemblies offering unique physico-chemical properties. For a given lipid composition, the magnetic alignability is proportional to the bicelle size. The complexation of Ln3+ results in unprecedented magnetic responses in terms of both magnitude and alignment direction. The thermo-reversible collapse of the disk-like structures into vesicles upon heating allows tailoring of the assemblies&#39; dimensions by extrusion through membrane filters with defined pore sizes. The magnetically alignable bicelles are regenerated by cooling to 5 &#176;C, resulting in assembly dimensions defined by the vesicle precursors. Herein, this fabrication procedure is explained and the magnetic alignability of the assemblies is quantified by birefringence measurements under a 5.5 T magnetic field. The birefringence signal, originating from the phospholipid bilayer, further enables monitoring of polymolecular changes occurring in the bilayer. This simple technique is complementary to NMR experiments that are commonly employed to characterize bicelles.

Fabrication procedures for highly magnetically responsive lanthanide ion chelating polymolecular assemblies are presented. The magnetic response is dictated by the assembly size, which is tailored by extrusion through nanopore membranes. The assemblies&#39; magnetic alignability and temperature-induced structural changes are monitored by birefringence measurements, a complimentary technique to nuclear magnetic resonance and small angle neutron scattering.

Bicelles are tunable disk-like polymolecular assemblies formed from a large variety of lipid mixtures. Applications range from membrane protein structural ...

Predicting Catalyst Extrudate Breakage Based on the Modulus of Rupture

The mechanical strength of extruded catalysts and their natural or forced breakage by either collision against a surface or by a compressive load in a fixed bed are important phenomena in catalyst technology. The mechanical strength of the catalyst is measured here by its bending strength or flexural strength. This technique is relatively new from the perspective of applying it to commercial catalysts of typical sizes used in the industry. Catalyst breakage by collision against a surface is measured after a fall of the extrudates through the ambient air in a vertical pipe. Quantifying the impact force is done theoretically by applying Newton's second law. Measurement of catalyst breakage due to stress in a fixed bed is done following the standard procedure of the bulk crush strength test. Novel here is the focus on measuring the reduction in the length to diameter ratio of the extrudates as a function of the stress.

Here we present a protocol to measure the modulus of rupture of an extruded catalyst and the breakage of said catalyst extrudates by collision against a surface or by compression in a fixed bed.

The mechanical strength of extruded catalysts and their natural or forced breakage by either collision against a surface or by a compressive load in a ...

A Soft Tooling Process Chain for Injection Molding of a 3D Component with Micro Pillars

The purpose of this paper is to present the method of a soft tooling process chain employing Additive Manufacturing (AM) for fabrication of injection molding inserts with micro surface features. The Soft Tooling inserts are manufactured by Digital Light Processing (vat photo polymerization) using a photopolymer that can withstand relatively high temperaturea. The part manufactured here has four tines with an angle of 60&#176;. Micro pillars (&#216;200 &#181;m, aspect ratio of 1) are arranged on the surfaces by two rows. Polyethylene (PE) injection molding with the soft tooling inserts is used to fabricate the final parts. This method demonstrates that it is feasible to obtain injection-molded parts with microstructures on complex geometry by additive manufactured inserts. The machining time and cost is reduced significantly compared to conventional tooling processes based on computer numerical control (CNC) machining. The dimensions of the micro features are influenced by the applied additive manufacturing process. The lifetime of the inserts determines that this process is more suitable for pilot production. The precision of the inserts production is limited by the additive manufacturing process as well.

A protocol for fabricating injection molding inserts for complex geometry with micro features on surfaces employing Additive Manufacturing (AM) is presented.

The purpose of this paper is to present the method of a soft tooling process chain employing Additive Manufacturing (AM) for fabrication of injection ...

Combining Microfluidics and Microrheology to Determine Rheological Properties of Soft Matter during Repeated Phase Transitions

The microstructure of soft matter directly impacts macroscopic rheological properties and can be changed by factors including colloidal rearrangement during previous phase changes and applied shear. To determine the extent of these changes, we have developed a microfluidic device that enables repeated phase transitions induced by exchange of the surrounding fluid and microrheological characterization while limiting shear on the sample. This technique is &#181;2rheology, the combination of microfluidics and microrheology. The microfluidic device is a two-layer design with symmetric inlet streams entering a sample chamber that traps the gel sample in place during fluid exchange. Suction can be applied far away from the sample chamber to pull fluids into the sample chamber. Material rheological properties are characterized using multiple particle tracking microrheology (MPT). In MPT, fluorescent probe particles are embedded into the material and the Brownian motion of the probes is recorded using video microscopy. The movement of the particles is tracked and the mean-squared displacement (MSD) is calculated. The MSD is related to macroscopic rheological properties, using the Generalized Stokes-Einstein Relation. The phase of the material is identified by comparison to the critical relaxation exponent, determined using time-cure superposition. Measurements of a fibrous colloidal gel illustrate the utility of the technique. This gel has a delicate structure that can be irreversibly changed when shear is applied. &#181;2rheology data shows that the material repeatedly equilibrates to the same rheological properties after each phase transition, indicating that phase transitions do not play a role in microstructural changes. To determine the role of shear, samples can be sheared prior to injection into our microfluidic device. &#181;2rheology is a widely applicable technique for the characterization of soft matter enabling the determination of rheological properties of delicate microstructures in a single sample during phase transitions in response to repeated changes in the surrounding environmental conditions.

We demonstrate the fabrication and use of a microfluidic device that enables multiple particle tracking microrheology measurements to study the rheological effects of repeated phase transitions on soft matter.

The microstructure of soft matter directly impacts macroscopic rheological properties and can be changed by factors including colloidal rearrangement ...

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 ...