Name: evaluation of the curing of adhesive systems by rheological and thermal testing
Uploaded: 2020-07-03T15:00:00
Description: Watch this Scientific Journal Video about Evaluation of the Curing of Adhesive Systems by Rheological and Thermal Testing at JoVE.com

This research has been partially supported by the Spanish Ministry of Science and Innovation [Grant MTM2014-52876-R], [MTM2017-82724-R] and by Xunta de Galicia (Unidad Mixta de Investigaci&#243;n UDC-Navantia [IN853B-2018/02]). We would like to thank TA Instruments for the image showing the scheme of the rheometer used. This image is included in the Table of Materials of the article.&#160;We also would like to thank Journal of Thermal Analysis and Calorimetry for its permission for using some data from reference [16],&#160;and the Centro de Investigaciones Cient&#237;ficas Avanzadas (CICA) for using its facilities.

1. Checking the manufacturer curing conditions
<ol>
	<li>Cure the adhesive sample following the manufacturer recommendations, and then evaluate it by a TGA and a DSC test. Record the specific curing conditions.</li>
	<li>TGA test of cured sample
	<ol>
		<li>Perform thermogravimetric tests in a TGA or in a simultaneous DSC+TGA equipment (SDT).</li>
		<li>Carry out a thermogravimetric test of the cured sample following the next steps&#160;to determine the inorganic filler content and the temperature at which the material...

<ol>
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R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multi-nationality+epoxy+adhesives+on+trial+for+future+nanocomposite+developments.">Multi-nationality epoxy adhesives on trial for future nanocomposite developments.</a> Progress in Organic Coatings. 133, 376-386 (2019).</li><li>Kozowyk, P. R. B., Poulis, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+new+experimental+methodology+for+assessing+adhesive+properties+shows+that+Neandertals+used+the+most+suitable+material+available.">A new experimental methodology for assessing adhesive properties shows that Neandertals used the most suitable material available.</a> Journal of Human Evolution. 137, 102664 (2019).</li><li>Tenorio-Alfonso, A., Pizarro, M. L., S&#225;nchez, M. C., Franco, J. 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J., Lee, Y. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adhesion+and+rheological+properties+of+EVA-based+hot-melt+adhesives.">Adhesion and rheological properties of EVA-based hot-melt adhesives.</a> International Journal of Adhesion and Adhesives. 26 (8), 571-576 (2006).</li><li>Kim, H., Kim, J., Kim, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+novel+carboxylic+acid-based+reductants+on+the+wetting+characteristics+of+anisotropic+conductive+adhesive+with+low+melting+point+alloy+filler.">Effects of novel carboxylic acid-based reductants on the wetting characteristics of anisotropic conductive adhesive with low melting point alloy filler.</a> Microelectronics Reliability. 50 (2), 258-265 (2010).</li><li>S&#225;nchez-Silva, B., 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=Thermal+and+rheological+comparison+of+adhesives.">Thermal and rheological comparison of adhesives.</a> Journal of Thermal Analysis and Calorimetry. 138 (5), 3357-3366 (2019).</li><li>Full, A. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Polymerization+of+tetrahydrofurfuryl+methacrylate+in+three-component+anionic+microemulsions.">Polymerization of tetrahydrofurfuryl methacrylate in three-component anionic microemulsions.</a> Macromolecules. 25, 5157-5164 (1992).</li><li>Pizzi, A., Mittal, K. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Handbook of adhesive technology. , (1992).</li><li>Keenan, M. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Autocatalytic+cure+kinetics+from+DSC+measurements:+Zero+initial+cure+rate.">Autocatalytic cure kinetics from DSC measurements: Zero initial cure rate.</a> Journal of Applied Polymer Science. 33 (5), 1725-1734 (1987).</li><li>Lee, J. Y., Shim, M. J., Kim, S. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Autocatalytic+cure+kinetics+of+natural+zeolite+filled+epoxy+composites.">Autocatalytic cure kinetics of natural zeolite filled epoxy composites.</a> Materials Chemistry and Physics. 48 (1), 36-40 (1997).</li><li>Hayaty, M., Beheshty, M. H., Esfandeh, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isothermal+differential+scanning+calorimetry+study+of+a+glass/epoxy+prepreg.">Isothermal differential scanning calorimetry study of a glass/epoxy prepreg.</a> Polymers for Advanced Technologies. 22 (6), 1001-1006 (2011).</li><li>Lee, E. J., Park, H. J., Kim, S. M., Lee, K. 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A preliminary TGA test of each adhesive is always a fundamental step as it gives information about the temperature range at which the material is stable. That information is crucial to correctly setting up further experiments. In addition, TGA may also inform about the filler content, which can be very insightful to understand that storage and loss modulus may not to cross along the cure.
On the other hand, DSC allows to study the cure of most thermosetting systems but not of those whose cure ...

Nowadays there is an increasing demand of adhesives. Today&#39;s industry demands that adhesives have increasingly varied properties, adapted to the growing diversity of possible new applications. It makes the selection of the most suitable option for each specific case a difficult task. Therefore, creating a standard methodology to characterize the adhesives according to their properties would facilitate the selection process. The analysis of the adhesive during the curing process and the final properties of the cured system are crucial to decide whether an adhesive is valid or not for a certain application.
Two of the most commonly used experimental techniques to study the behavior of adhesives are Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA). Rheological measurements and thermogravimetric tests are also widely used. Through them, the glass transition temperature (Tg) and the residual heat of curing, which are related to the degree of cure1,2, can be determined.
TGA provides information about the thermal stability of the adhesives3,4, which is very useful to establish further process conditions, on the other hand rheological measurements allows the determination of the gel time of the adhesive, analysis of the curing shrinkage, and the definition of the viscoelastic properties of a cured sample5,6,7, while the DSC technique allows measurement of the residual heat of curing, and discernment between one or more thermal processes that can take place simultaneously during the curing8,9. Therefore, the combination of DSC, TGA and rheological methodologies provide detailed and reliable information to develop a complete characterization of adhesives.
There is a number of studies of adhesives where DSC and TGA are applied together10,11,12. There are also some studies that complement the DSC with rheological measurements13,14,15. However, there is not a standardized protocol to address the comparison of adhesives in a systematic way. That comparison would all to better choose the right adhesives in different contexts. In this work, an experimental methodology is proposed for doing a characterization of the curing process through the combined use of the thermal analysis and rheology. Applying these techniques as an ensemble allows to gather information about the adhesive behavior during and after the curing process, also the thermal stability and the Tg of the material16.
The proposed methodology involving the three techniques, DSC, TGA and rheology is described in this work using three commercial adhesives as an example. One of the adhesives, hereinafter referred to as S2c, is a two-component adhesive: component A contains tetrahydrofurfuryl methacrylate and component B contains benzoyl peroxide. The component B acts as an initiator of the curing reaction by causing the tetrahydrofurfuryl methacrylate rings to open. Through a free radical polymerization mechanism, the C=C bond of the monomer reacts with the growing radical to form a chain with tetrahydrofurfuryl side groups17. The other adhesives, T1c and T2c, are the one- and two-component versions from the same commercial house of a modified silane polymer adhesive. The curing process begins by the hydrolysis of the silane group18, which can be initiated by ambient humidity (as in the case of T1c) or by the addition of a second component (as in the case of T2c).
Concerning the application areas of these three different systems: the adhesive S2c was designed to substitute, in some cases, welding, riveting, clinching and other mechanical fastening techniques and it is suitable for high strength fastening of concealed joints on different types of substrates including top coats, plastics, glass, etc. The T1c and T2c adhesives are used for elastic bonding of metals and plastics: in caravan manufacturing, in the railroad vehicle industry or in shipbuilding.

<table>
	<tbody>
		<tr>
			<td>2960 SDT</td>
			<td>TA Instruments</td>
			<td></td>
			<td>Simultaneous DSC/TGA device: Used to perform thermogravimetric tests.</td>
		</tr>
		<tr>
			<td>Discovery HR-2</td>
			<td>TA Instruments</td>
			<td></td>
			<td>Rheometer to perform rheological test.</td>
		</tr>
		<tr>
			<td>MDSC Q2000</td>
			<td>TA Instruments</td>
			<td></td>
			<td>Differential Scanning Calorimeter with optional temperature modulation. Used to peform DSC and MDSC tests.</td>
		</tr>
		<tr>
			<td>Sikafast 5211NT</td>
			<td>Sika</td>
			<td></td>
			<td>S2c: a two component system manufactured by Sika. It is based on tetrahydrofurfuryl methacrylate and contains an ethoxylated aromatic amine. 
			The second component contains benzoyl peroxide as the initiator for the crosslinking reaction.</td>
		</tr>
		<tr>
			<td>Teroson MS 939 FR</td>
			<td>Henkel</td>
			<td></td>
			<td>T1c: manufactured by Henkel, which is a one component sylil-modified-polymer, whose cure reaction is triggered by moisture.</td>
		</tr>
		<tr>
			<td>Teroson MS 9399</td>
			<td>Henkel</td>
			<td></td>
			<td>T2c: a two component system manufactured by Henkel. It is a sylil-modified-polymer too but the second component is aimed to make the curing rate a little more independent from the moisture content of air.</td>
		</tr>
		<tr>
			<td>TRIOS</td>
			<td>TA Instruments</td>
			<td></td>
			<td>Control Software for the rheometer. Version 4.4.0.41651</td>
		</tr>
	</tbody>
</table>

evaluation of the curing of adhesive systems by rheological and thermal testing

The analysis of thermal processes associated to the curing of adhesives and the study of mechanical behavior once cured, provide key information to choose the best option for any specific application. The proposed methodology for the curing characterization, based on thermal analysis and rheology, is described through the comparison of three commercial adhesives. The experimental techniques used here are Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC) and Rheology. TGA provides information about the thermal stability and filler content, DSC allows the evaluation of some thermal events associated to the cure reaction and to thermal changes of the cured material when subjected to temperature changes. Rheology complements the information of the thermal transformations from a mechanical point of view. Thus, the curing reaction can be tracked through the elastic modulus (mainly the storage modulus), the phase angle and the gap. In addition, it is also shown that although DSC is of no use to study the curing of moisture curable adhesives, it is a very convenient method to evaluate the low temperature glass transition of amorphous systems.

In order to show the application of the proposed method three adhesive systems are used (Table of Materials):
<ul>
	<li>S2c, a two-component system.</li>
	<li>T1c, a one-component silane-modified-polymer, whose cure reaction is triggered by moisture.</li>
	<li>T2c, a two-component system. It is a silane-modified-polymer too, but the second component is aimed to make the curing rate a little more independent from the moisture content of air.</li>
</ul>
The thermal stability and...

Watch this Scientific Journal Video about Evaluation of the Curing of Adhesive Systems by Rheological and Thermal Testing at JoVE.com

Evaluation of the Curing of Adhesive Systems by Rheological and Thermal Testing

An experimental methodology based on thermal and rheological measurements is proposed to characterize the curing process of adhesives with to obtain useful information for industrial adhesive selection.

The analysis of thermal processes associated to the curing of adhesives and the study of mechanical behavior once cured, provide key information to choose ...

Our methodology combines thermal analysis and rheology to characterize the curing process of an adhesive and to obtain useful information for industrial adhesive selection. This technique allows the creation of a standard guide for the curing process study of adhesive systems, making it easier to compare different adhesives. This methodology can also be used as an accepting criterion in the quality control of adhesive systems.To perform a thermogravimetric test to determine the inorganic filler content and the temperature at which the material starts to degrade, open the procedure tab and click editor. Drag the ramp segment to the editor screen and establish the ramp as 10 or 20 degrees per minute to 900 degrees Celsius. Click OK and open the notes tab.Select air as the purge gas and set the flow rate to 100 milliliters per minute. Then close the furnace and start the experiment. To perform a differential scanning calorimetry test of a cured sample, open the procedure tab, click test, and select custom.Click editor and drag an equilibrate segment indicating the temperature at which to start the experiment. Drag a ramp segment to the editor screen and introduce a heating rate of 10 or 20 degrees per minute and the final temperature into the command editor window. Drag a ramp segment to the editor screen and introduce a 10 or 20 degrees per minute cooling rate to a temperature tentatively below the glass transition.Drag another ramp segment to the editor screen and introduce a 10 or 20 degrees Celsius per minute heating rate to a temperature slightly below the degradation temperature. Open the notes tab and select nitrogen as the flow gas. Set the flow rate to 50 milliliters per minute and click apply.Then place a reference pan and a pan with a sample inside the DSC cell and launch the experiment. To analyze the fresh sample through a heating-cooling-heating test, open the procedure tab and click test and custom. Click editor and drag an equilibrate at minus 80 degrees Celsius segment to the editor screen.Drag a ramp segment and set the heating rate to 10 or 20 degrees Celsius per minute to a temperature slightly below the degradation temperature and insert another equilibrate at minus 80 degrees Celsius segment. Then drag a ramp segment and set the heating rate to 10 or 20 degrees Celsius per minute to the same temperature as before. Click OK.Then place a reference pan and a pan with the sample inside the DSC cell and click start to launch the experiment.To perform an isothermal curing test, open the procedure tab, click test, and select custom. Click editor and drag a ramp segment to the editor screen. Introduce a 20 degrees Celsius per minute to the chosen isothermal temperature.Then introduce an isothermal segment with enough time to complete the cure. To check the degree of curing reached, introduce at equilibrium at zero degrees Celsius segment, add a ramp segment, and set the heating rate between 2 and 20 degrees Celsius per minute to the maximum temperature. Drag the mark end-of-cycle segment to the editor window and insert another equilibrate segment with a temperature of minus 80 degrees Celsius.To obtain the final glass transition, add a ramp segment with a heating rate between 2 and 20 degrees Celsius per minute to the same temperature as indicated before and click OK.In the tool tab, select instrument preferences and DSC, and set a temperature lower than the isotherm temperature of the experiment. Click apply and open the control tab to select go to standby temperature. Then place a reference pan and a pan with a sample inside the DSC cell and click start.To perform a logarithmic strain sweep test, open the procedure tab and select oscillation amplitude. Set the experimental temperature to room temperature, the frequency to one Hertz, and the logarithmic sweep from one times 10 to the negative three to 100%of strain. Place the sample on the bottom plate with the upper plate separated about 40 millimeters from the lower plate and lower the upper plate until a gap of about two millimeters is observed between both plates.Then trim the excess adhesive and start the experiment. To monitor the curing of the adhesive, click the procedure tab and select conditioning options. Set the mode to compression, the axial force to zero Newtons, and the sensitivity to 0.1 Newtons.Click advance and set the gap change limit to 2, 000 microns in both the up and down directions. Insert a new oscillatory time sweep step and set the experimental temperature to room temperature, the test duration as a function of the estimated curing time based on the data sheet of the adhesive and the strain percentage acquired from the previous logarithmic strain sweep test. Select discreet and set the frequencies one, three, and 10 Hertz for all of the samples.Then load a new sample and start the experiment. To perform a torque sweep test, open the procedure tab and select oscillation amplitude. Then set the temperature to room temperature, the frequency to one Hertz, and the logarithmic sweep from 10 to 10, 000 micronewton meters of torque and start the experiment.From the torque sweep test, choose a torque amplitude within the linear viscoelastic region to use in the temperature ramp test, then select temperature ramp and set up the experiment at room temperature with a ramp rate of one degree Celsius per minute to ensure a uniform distribution of the temperature into the sample, a frequency of one Hertz, and the torque amplitude determined from the torque sweep test. Close the furnace of the rheometer and open the air stopcock of the furnace. Then start the experiment.These thermogravimetric results showed different degradation temperatures and different inorganic fillers for each studied adhesive. The mass loss observed between 600 and 800 degrees Celsius suggest the presence of calcium carbonate as filler. For this two-component adhesive, in the heat flow curve, there was no evidence of residual cure and the small deviation cannot be assigned with certainty to the glass transition reported by the manufacturer.In this table, the degree of curing of a two-component system at different temperatures was calculated by comparing the curing enthalpy acquired at each temperature to that obtained in a heating ramp. Through a rheological multi-frequency test of a fresh two-component adhesive sample, the gelation time of the material can be observed as the point at which the phase angle becomes frequency independent. In these isothermal multi-frequency tests using the one and two-component silane polymer adhesive systems, no sign of gelation is observed and a comparison of the slopes of the moduli of both adhesives reveals that the two-component silane polymer adhesives cures faster.In this rheological temperature scan test of a two-component adhesive sample cured for one hour, the glass transition can be clearly observed. Do not delay starting the test when using a fresh sample and be sure to prepare a thoroughly mixed solution when using a two-component system.

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The Preparation of Electrohydrodynamic Bridges from Polar Dielectric Liquids

Horizontal and vertical liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields (8-20 kV/cm) and polar dielectric liquids. These bridges are unique from capillary bridges in that they exhibit extensibility beyond a few millimeters, have complex bi-directional mass transfer patterns, and emit non-Planck infrared radiation. A number of common solvents can form such bridges as well as low conductivity solutions and colloidal suspensions. The macroscopic behavior is governed by electrohydrodynamics and provides a means of studying fluid flow phenomena without the presence of rigid walls. Prior to the onset of a liquid bridge several important phenomena can be observed including advancing meniscus height (electrowetting), bulk fluid circulation (the Sumoto effect), and the ejection of charged droplets (electrospray). The interaction between surface, polarization, and displacement forces can be directly examined by varying applied voltage and bridge length. The electric field, assisted by gravity, stabilizes the liquid bridge against Rayleigh-Plateau instabilities. Construction of basic apparatus for both vertical and horizontal orientation along with operational examples, including thermographic images, for three liquids (e.g., water, DMSO, and glycerol) is presented.

Horizontal and vertical electrohydrodynamic liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields and polar dielectric liquids. The construction of basic apparatus and operational examples, including thermographic images, for three liquids (e.g., water, DMSO, and glycerol) is presented.

Horizontal and vertical liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields (8-20 kV/cm) and ...

Making Record-efficiency SnS Solar Cells by Thermal Evaporation and Atomic Layer Deposition

Tin sulfide (SnS) is a candidate absorber material for Earth-abundant, non-toxic solar cells. SnS offers easy phase control and rapid growth by congruent thermal evaporation, and it absorbs visible light strongly. However, for a long time the record power conversion efficiency of SnS solar cells remained below 2%. Recently we demonstrated new certified record efficiencies of 4.36% using SnS deposited by atomic layer deposition, and 3.88% using thermal evaporation. Here the fabrication procedure for these record solar cells is described, and the statistical distribution of the fabrication process is reported. The standard deviation of efficiency measured on a single substrate is typically over 0.5%. All steps including substrate selection and cleaning, Mo sputtering for the rear contact (cathode), SnS deposition, annealing, surface passivation, Zn(O,S) buffer layer selection and deposition, transparent conductor (anode) deposition, and metallization are described. On each substrate we fabricate 11 individual devices, each with active area 0.25 cm2. Further, a system for high throughput measurements of current-voltage curves under simulated solar light, and external quantum efficiency measurement with variable light bias is described. With this system we are able to measure full data sets on all 11 devices in an automated manner and in minimal time. These results illustrate the value of studying large sample sets, rather than focusing narrowly on the highest performing devices. Large data sets help us to distinguish and remedy individual loss mechanisms affecting our devices.

Tin sulfide (SnS) is a candidate material for Earth-abundant, non-toxic solar cells. Here, we demonstrate the fabrication procedure of the SnS solar cells employing atomic layer deposition, which yields 4.36% certified power conversion efficiency, and thermal evaporation which yields 3.88%.

Tin sulfide (SnS) is a candidate absorber material for Earth-abundant, non-toxic solar cells. SnS offers easy phase control and rapid growth by congruent ...

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.

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

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 of 3D Carbon Microelectromechanical Systems (C-MEMS)

A wide range of carbon sources are available in nature, with a variety of micro-/nanostructure configurations. Here, a novel technique to fabricate long and hollow glassy carbon microfibers derived from human hairs is introduced. The long and hollow carbon structures were made by the pyrolysis of human hair at 900 &#176;C in a N2 atmosphere. The morphology and chemical composition of natural and pyrolyzed human hairs were investigated using scanning electron microscopy (SEM) and electron-dispersive X-ray spectroscopy (EDX), respectively, to estimate the physical and chemical changes due to pyrolysis. Raman spectroscopy was used to confirm the glassy nature of the carbon microstructures. Pyrolyzed hair carbon was introduced to modify screen-printed carbon electrodes ; the modified electrodes were then applied to the electrochemical sensing of dopamine and ascorbic acid. Sensing performance of the modified sensors was improved as compared to the unmodified sensors. To obtain the desired carbon structure design, carbon micro-/nanoelectromechanical system (C-MEMS/C-NEMS) technology was developed. The most common C-MEMS/C-NEMS fabrication process consists of two steps: (i) the patterning of a carbon-rich base material, such as a photosensitive polymer, using photolithography; and (ii) carbonization through the pyrolysis of the patterned polymer in an oxygen-free environment. The C-MEMS/NEMS process has been widely used to develop microelectronic devices for various applications, including in micro-batteries, supercapacitors, glucose sensors, gas sensors, fuel cells, and triboelectric nanogenerators. Here, recent developments of a high-aspect ratio solid and hollow carbon microstructures with SU8 photoresists are discussed. The structural shrinkage during pyrolysis was investigated using confocal microscopy and SEM. Raman spectroscopy was used to confirm the crystallinity of the structure, and the atomic percentage of the elements present in the material before and after pyrolysis was measured using EDX.

Fabrication of 3D Carbon Microelectromechanical Systems C-MEMS

Long and hollow glassy carbon microfibers were fabricated based on the pyrolysis of a natural product, human hair. The two fabrication steps of carbon microelectromechanical and carbon nanoelectromechanical systems, or C-MEMS and C-NEMS, are: (i) photolithography of a carbon-rich polymer precursor and (ii) pyrolysis of the patterned polymer precursor.

A wide range of carbon sources are available in nature, with a variety of micro-/nanostructure configurations. Here, a novel technique to fabricate long ...

Subsurface Defect Localization by Structured Heating Using Laser Projected Photothermal Thermography

The presented method is used to locate subsurface defects oriented perpendicularly to the surface. To achieve this, we create destructively interfering thermal wave fields that are disturbed by the defect. This effect is measured and used to locate the defect. We form the destructively interfering wave fields by using a modified projector. The original light engine of the projector is replaced with a fiber-coupled high-power diode laser. Its beam is shaped and aligned to the projector&#39;s spatial light modulator and optimized for optimal optical throughput and homogeneous projection by first characterizing the beam profile, and, second, correcting it mechanically and numerically. A high-performance infrared (IR) camera is set up according to the tight geometrical situation (including corrections of the geometrical image distortions) and the requirement to detect weak temperature oscillations at the sample surface. Data acquisition can be performed once a synchronization between the individual thermal wave field sources, the scanning stage, and the IR camera is established by using a dedicated experimental setup which needs to be tuned to the specific material being investigated. During data post-processing, the relevant information on the presence of a defect below the surface of the sample is extracted. It is retrieved from the oscillating part of the acquired thermal radiation coming from the so-called depletion line of the sample surface. The exact location of the defect is deduced from the analysis of the spatial-temporal shape of these oscillations in a final step. The method is reference-free and very sensitive to changes within the thermal wave field. So far, the method has been tested with steel samples but is applicable to different materials as well, in particular to temperature sensitive materials.

This method aims at locating vertical subsurface defects. Here, we couple a laser with a spatial light modulator and trigger its video input to heat a sample surface deterministically with two anti-phased modulated lines while acquiring highly resolved thermal images. The defect position is retrieved from evaluating thermal wave interference minima.

The presented method is used to locate subsurface defects oriented perpendicularly to the surface. To achieve this, we create destructively interfering ...

Protocol for the Evaluation of MRI Artifacts Caused by Metal Implants to Assess the Suitability of Implants and the Vulnerability of Pulse Sequences

As the number of magnetic resonance imaging (MRI) scanners and patients with medical implants is constantly growing, radiologists increasingly encounter metallic implant-related artifacts in MRI, resulting in reduced image quality. Therefore, the MRI suitability of implants in terms of artifact volume, as well as the development of pulse sequences to reduce image artifacts, are becoming more and more important. Here, we present a comprehensive protocol which allows for a standardized evaluation of the artifact volume of implants on MRI. Furthermore, this protocol can be used to analyze the vulnerability of different pulse sequences to artifacts. The proposed protocol can be applied to T1- and T2-weighted images with or without fat-suppression and all passive implants. Furthermore, the procedure enables the separate and three-dimensional identification of signal loss and pile-up artifacts. As previous investigations differed greatly in evaluation methods, the comparability of their results was limited. Thus, standardized measurements of MRI artifact volumes are necessary to provide better comparability. This may improve the development of the MRI suitability of implants and better pulse sequences to finally improve patient care.

We describe a standardized method to evaluate magnetic resonance imaging artifacts caused by implants to estimate the suitability of the implants for magnetic resonance imaging and/or the vulnerability of different pulse sequences to metallic artifacts simultaneously.

As the number of magnetic resonance imaging (MRI) scanners and patients with medical implants is constantly growing, radiologists increasingly encounter ...

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 ...

Multi-material Ceramic-Based Components &#8211; Additive Manufacturing of Black-and-white Zirconia Components by Thermoplastic 3D-Printing (CerAM - T3DP)

To combine the benefits of Additive Manufacturing (AM) with the benefits of Functionally Graded Materials (FGM) to ceramic-based 4D components (three dimensions for the geometry and one degree of freedom concerning the material properties at each position) the Thermoplastic 3D-Printing (CerAM -&#160;T3DP) was developed. It is a direct AM technology which allows the AM of multi-material components. To demonstrate the advantages of this technology black-and-white zirconia components were additively manufactured and co-sintered defect-free.
Two different pairs of black and white zirconia powders were used to prepare different thermoplastic suspensions. Appropriate dispensing parameters were investigated to manufacture single-material test components and adjusted for the additive manufacturing of multi-color zirconia components.

Multi-material Ceramic-Based Components &amp;#8211; Additive Manufacturing of Black-and-white Zirconia Components by Thermoplastic 3D-Printing (CerAM - T3DP)

Here we describe a protocol for additively manufacturing black-and-white zirconia components by Thermoplastic 3D-Printing (CerAM -&#160;T3DP) and co-sintering defect-free.

To combine the benefits of Additive Manufacturing (AM) with the benefits of Functionally Graded Materials (FGM) to ceramic-based 4D components (three ...

Additive Manufacturing of Functionally Graded Ceramic Materials by Stereolithography

An additive manufacturing technology is applied to obtain functionally graded ceramic parts. This technology, based on digital light processing/stereolithography, is developed within the scope of the CerAMfacturing European research project. A three-dimensional (3-D) hemi-maxillary bone-like structure is 3-D printed using custom aluminum oxide polymeric mixtures. The powders and mixtures are fully analyzed in terms of rheological behavior in order to ensure proper material handling during the printing process. The possibility to print functionally graded materials using the Admaflex technology is explained in this document. Field-emission scanning electron microscopy (FESEM) show that the sintered aluminum oxide ceramic part has a porosity lower than 1% and no remainder of the original layered structure is found after analysis.

This manuscript describes the processing of single multifunctional ceramic components (e.g., combinations of dense-porous structures) additively manufactured by stereolithography.