The authors acknowledge the support of the Air Force Research Labs under UES sub-contract #S-932-19-MR002. The authors further acknowledge equipment support from New York State Graduate Research and Teaching Initiative (GRTI/GR15).

1. Pre-analysis Sample Preparation
<ol>
	<li>Separation of functional particles from ink vehicle: centrifugation
	<ol>
		<li>Based on the initial ink formulation, calculate how much ink sample is needed to obtain a minimum of 2.0 g of particle sediment. For example, if the ink is 10 vol% ceramic and the density of the ceramic is 6.67 g/cm3, then a minimum of 3.0 ml of ink is needed to generate 2.0 g of sediment.</li>
		<li>Pipet at least the minimum required ink quantity into a centrifuge tube. Choice of centrifuge tube should be made based on quantity of ink required and on inertness of tube material to ink solvents.</li>
		<li>Place tube in centrifuge. Choice of centrifuge and rotational rate will be dictated by the gravitational force required to sediment the ink particle. A standard lab centrifuge like the Sorvall ST16 centrifuge with a TX-200 swinging bucket rotor is usually adequate.</li>
		<li>Program centrifuge to spin ink at a rotational rate and time necessary to produce a clear supernatant. For the centrifuge used here, typical rates and times are 3,000 &#8211; 4,000 rpm for between 30 min and 90 min. Arriving at the correct rotational speed and time necessary to sediment the ink may require trial and error because even inks of the same average particle sizes may have different particle size distributions.</li>
	</ol>
	</li>
	<li>Post-separation sample handling: removal of supernatant, sample washing, drying
	<ol>
		<li>Once a clear supernatant has been achieved, remove the centrifuge tube from the centrifuge.</li>
		<li>Decant the supernatant and save in a capped glass sample vial for possible future analysis. The functional particles are now residual in the centrifuge tube.</li>
		<li>After decanting, place the uncapped centrifuge tube upside down on a paper towel and allow additional supernatant to drip out for 1 min.</li>
		<li>Remove the tube from the paper towel and rinse the sedimented particles by adding to the tube approximately 2 ml of fresh solvent of the same composition used in the ink formulation. Note that this solvent will only touch the top most layer of the particles sedimented in the centrifuge tube. Decant solvent. Repeat the rinse cycle three times.</li>
		<li>After the final rinse cycle, place the uncapped centrifuge tube upside down on a paper towel and allow the additional solvent to drip out for approximately 5 min.</li>
		<li>Use a thin metal spatula to remove the sediment from the bottom of the centrifuge tube, and spread onto a clean, dry watch glass. Use a lint-free non-abrasive cotton swab or the tip of a clean spatula to remove excess particles from the spatula tip.</li>
		<li>Place the watch glass into a 50 &#176;C oven and allow the particles to dry for 24 hr. The temperature of the oven should be kept relatively low to minimize the possibility of decomposing adsorbed species. The time required for drying the particles will depend on the vapor pressure of the solvent. 24 hr is typical, but results are usually insensitive to wait times as short as 12 hr and as long as 3 weeks.</li>
	</ol>
	</li>
</ol>
2. Diffuse Reflectance Infrared Spectroscopy Measurement
<ol>
	<li>Preparation of infrared spectrometer: align accessory, purge compartment
	<ol>
		<li>Turn on IR spectrometer.</li>
		<li>To prepare for diffuse reflectance infrared spectroscopy measurements, place the diffuse reflectance sampling accessory into the infrared spectrometer sampling compartment. The infrared spectrometer may be any Fourier transform infrared spectrometer capable of interfacing with a diffuse reflectance sampling apparatus. A Shimadzu IR Prestige 21 spectrometer interfaced with a Pike Technologies EasiDiff accessory was utilized for this protocol. For most ink particles, a standard deuterated, L-alanine doped triglycine sulfate (DLaTGS) detector provides enough sensitivity for measurement. A liquid nitrogen cooled mercury cadmium telluride (MCT) detector provides a four to tenfold increase in sensitivity, but this is not usually necessary for identifying adsorbates on ink particle surfaces.</li>
		<li>Align the diffuse reflectance sampling accessory as per the manufacturer&#8217;s instructions.</li>
	</ol>
	</li>
	<li>After alignment, close the infrared sampling compartment and begin purging with nitrogen or with CO2-free, dry air (purge rate of 10 L/min). A standard Parker Balston FT-IR purge gas generator provides air with less than 1 ppm water and CO2. The amount of purge time necessary to obtain a stable water and CO2 free chamber will depend on the sample compartment configuration and the humidity in the lab. The necessary purge time can be determined experimentally by comparing background spectra taken at 1 or 2 min intervals and assessing the intensities of the water and CO2 bands as a function of time.</li>
	<li>Prepare sample for diffuse reflectance infrared spectroscopy measurement
	<ol>
		<li>Obtain the following sample preparation accessories: small (35 mm) agate mortar and pestle, small metal spatula, straight razor blade, and two diffuse reflectance infrared sample cups. Wipe the accessories clean with ethanol, then acetone, and allow them to dry for 10 min in a 50 &#176;C oven.</li>
		<li>Remove clean, dry sample preparation accessories from the oven, place them on a large Kimwipe, and allow them to cool to RT.</li>
		<li>While the sample preparation accessories are cooling, remove the dried ink particles from the oven, and use an analytical balance to measure 0.025 g of the particle sample. Leave the sample sitting in the analytical balance.</li>
		<li>Return to the sample preparation accessories and pour 0.5 g of KBr into the agate mortar. Always use KBr sold for infrared applications. Pre-measured individual 0.5 g packets of KBr (Thermo Scientific) are recommended because they minimize weighing time and exposure of the hydroscopic KBr to the ambient water vapor. Grind the KBr to a uniform appearance, usually 1 min of continuous manual grinding.</li>
		<li>Completely fill one of the diffuse reflectance infrared sampling cups with the ground KBr powder. Lightly press the powder with the blunt end of the pestle, and top off the sampling cup with KBr.</li>
		<li>Use the side of the razor blade to flatten the top of the KBr in the sample cup. This filled and flattened sample is the reference or background.</li>
		<li>Dispose of any KBr remaining in the mortar, and wipe clean.</li>
		<li>Open a new 0.5 g packet of KBr powder (or add 0.5 g of KBr powder), and pour into the mortar.</li>
		<li>Add the previously weighed 0.025 g of ink particles to the 0.5 g of KBr, and grind with the pestle to form a uniform powder, usually 1 min of continuous manual grinding. This ratio of ink particles to KBr provides a 5 wt% sample during the measurement. This is within the standard range (1 &#8211; 10 wt%), but can be adjusted up or down depending on the absorptivity and signal strength of the sample.</li>
		<li>Follow steps 2.3.5 and 2.3.6 to create a sample cup filled with the particle/KBr mixture.</li>
	</ol>
	</li>
	<li>Infrared spectroscopic measurement
	<ol>
		<li>Place the reference and sample cups into the holder, and place the holder into the diffuse reflectance infrared spectroscopy sampling accessory. Position the holder so that the cup containing the background (pure KBr) material is exposed to the infrared radiation.</li>
		<li>Close the infrared sampling compartment and allow the compartment to purge for 5 min. This purge time may be adjusted depending on the amount of time determined to be necessary in step 2.2.</li>
		<li>After 5 min of purging, obtain an infrared spectrum of the background in the region of interest. The number of scans should be set to maximize the signal to noise ratio while minimizing measurement time. 128 scans at 4 cm-1 resolution is usually adequate.</li>
		<li>After the background scan is completed, open the infrared sample compartment and move the cup containing the particle/KBr mixture so that it is now exposed to the infrared radiation.</li>
		<li>Repeat steps 2.4.2 and 2.4.3 to obtain a spectrum of the particle/KBr mixture.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

The two critical factors for generating high quality infrared spectra using this procedure are: 1) minimizing the absolute quantity of water contamination and the differences in the quantity of water contamination between the sample and reference cups; and 2) creating sample and reference cups with uniform flat layers and similar KBr grain sizes. Both of these factors are achieved by paying particular attention to the sample preparation procedures outlined in section 2.3.
In order minimize the...

Additive manufacturing has recently emerged as a promising technique for fabrication of everything from ceramics to semiconductors to medical devices1. As the applications of additive manufacturing expand to printed ceramic, metal oxide, and metal parts, the need to formulate specialized functional inks arises. The question of how to formulate the required functional inks relates to a fundamental issue in surface and colloid science: what are the mechanisms by which particles in colloidal dispersion are stabilized against aggregation? Broadly, stabilization requires modification of the particle surfaces such that close approach of particles (and hence aggregation) is prevented either by Coulombic repulsion (electrostatic stabilization), by the entropic penalty of polymer entanglement (steric stabilization), or by a combination of the Coulombic and entropic forces (electrosteric stabilization)2. In order to achieve any of these mechanisms of stabilization, it is usually necessary to modify the particle surface chemistry through attachment of polymers or shorter chain functional groups. Thus, the rational formulation of stable functional inks demands that we know whether a given chemical additive attaches to the particle surface and what chemical group attaches to the particle surface.
The goal of the method presented in this protocol is to demonstrate rapid characterization of chemical species adsorbed on particle surfaces in functional inks. This goal is particularly important as functional ink formulation transitions from a specialized task for surface and colloid scientists to an activity broadly practiced by the range of scientists and engineers interested in printing ceramic, metal oxide, and metal devices. Achieving this goal requires designing an experiment that overcomes the challenges of characterizing opaque, high solids loadings dispersions. It also requires discriminating between chemical species that are present in the dispersion but not adsorbed on the particles from those that are actually adsorbed. It further requires distinguishing between those species that are chemically adsorbed on the particles from those that are weakly physisorbed. In this experimental protocol, we present the use of diffuse reflectance infrared spectroscopy for characterization of dispersant attachment in functional inks. The diffuse reflectance infrared spectroscopy measurement follows a pre-analysis sample preparation technique necessary to distinguish adsorbed species from those merely present in the dispersion.
A variety of methods are currently used to gain insight into the nature of the interactions between chemical ink components and colloidally dispersed particles. Some of these methods are indirect probes in which measured properties are presumed to correlate with surface functionalization. For example, changes in slurry rheology or sedimentation rates are presumed to correlate with adsorption of surface modifiers3. Particle size distribution, as characterized by dynamic light scattering (DLS), and zeta potential, as characterized by electrophoretic mobility, provide insight into the adsorption of polymers or species with surface charge4,5. Similarly, sample mass loss as probed by thermogravimetric analysis (TGA) relates to the presence of desorbing species and the strength of interaction between the adsorbate and the particle6. The information from the above mentioned indirect probes suggest changes in surface chemistry, but they do not provide direct insight into the identity of the adsorbing species or the mechanism of its adsorption. Direct insight is particularly important for functional inks in which a large number of components are present in the dispersion. To provide detailed molecular level information, X-ray photoelectron spectroscopy (XPS)7, 13C nuclear magnetic resonance (NMR) 4,6, and infrared spectroscopy8-12 have been explored. Of these three options, infrared spectroscopy is particularly promising. In comparison to 13C NMR, infrared spectroscopy does not require that inks be formulated with analytically pure solvents to prevent interferences during measurement13. In comparison to X-ray photoelectron spectroscopy, standard infrared spectroscopy can be conducted at ambient pressure, avoiding the need for ultrahigh vacuum conditions during measurement.
There is literature precedent for the use of infrared spectroscopy to probe the interaction between colloidally dispersed ceramic, metal oxide, and metal nanoparticles. These works can be separated into attempts to measure interfacial chemistry in situ using attenuated total reflectance infrared (ATR-IR)9, and attempts to measure interfacial chemistry ex situ using solid sampling8. While there are advantages to in situ measurements, the uncertainties that arise due to the necessity for spectral manipulation make the method difficult for multi-component inks in which there are solvents and multiple polymeric components. Therefore, this protocol focuses on solid sampling and ex situ measurement. All of the solid sampling methods entail a pre-treatment step where a solid is obtained by separating the particles from the solvent, and an analysis step where infrared measurements are performed on the solid particles. The difference between methods arises in the choice of sample pre-treatment and in the choice of experimental technique used for infrared analysis of the solid. Historically, the traditional way to use infrared spectroscopy to analyze solids was to grind small quantities (&#60; 1%) of the solid sample with potassium bromide (KBr) powder, and then subject the mixture to high pressure sintering. The result is a transparent KBr pellet. This procedure has been attempted successfully with powders derived from aqueous suspensions of zirconia nanoparticles functionalized with polyethyleneamine10, with fatty acid monolayers on cobalt nanoparticles7, and with catechol-derived dispersants on Fe3O4 nanoparticles14. Despite these successful applications of the KBr pelleting technique for detection of adsorbed dispersants, diffuse reflectance infrared spectroscopy provides several advantages. One advantage is simplified sample preparation. In contrast to KBr pelleting, the solid sample in diffuse reflectance can be simply ground by hand. There is no sintering step as the powder itself is loaded into the sample cup and the diffusely scattered infrared light is measured. The other advantage of diffuse reflectance over KBr pelleting is the increased surface sensitivity15. The increase in surface sensitivity is especially useful for the present application in which the critical questions are the presence and nature of adsorbates on the nanoparticle surfaces.
Among works that have used the diffuse reflectance sampling technique to probe the adsorption of chemical species on colloidally dispersed samples, the primary differences arise in the method of separating the nanoparticles from the liquid medium. This step is critical because, without the separation, it would be impossible to distinguish specifically adsorbed dispersants from dispersants simply dissolved in the liquid medium. In several examples, the method of separation is not obvious from the experimental protocol12,16,17. When specified, the most frequently practiced method involves gravitational separation. The rationale is that the ceramic, metal oxide, and metal nanoparticles are all more dense than the surrounding media. When they settle, they will drag down with them only the specifically adsorbed species. Chemical species not interacting with the particles will remain in solution. While dispersions may readily settle under normal gravitational force18, a stable inkjet ink should not observably settle over a time period of less than a year. As such, the method of employing centrifugation for pre-analysis separation is preferred. This has been demonstrated in several studies of dispersant adsorption on glass particles19,20, dispersant binder adsorption on alumina8, and anionic dispersant functionalization of CuO11. Most recently, we have used it to evaluate mechanisms of fatty acid binding in non-aqueous NiO dispersions used for inkjet and aerosol jet printing of solid oxide fuel cell layers21.

<table><tbody><tr><td>FTIR bench</td><td>Shimadzu Scientific Instruments</td><td>IR_Prestige 21 used in this work; in 2013 IR-Tracer 100 model replaced Prestige-21</td><td>Any research grade FTIR with purgable sample compartment is acceptable</td></tr><tr><td>Purge gas generator for sample compartment</td><td>Parker Balston</td><td>74-5041NA Lab Gas Generator</td><td>Provides air with less than 1&amp;nbsp;ppm CO&lt;sub&gt;2&lt;/sub&gt; and water; also possible to purge compartment with N&lt;sub&gt;2&lt;/sub&gt; tank</td></tr><tr><td>Diffuse Reflectance Infrared Accessory</td><td>Pike Technologies</td><td>042-10XX</td><td>Includes sample preparation kit and mortar and pestle (these can also be purchased separately, described below)</td></tr><tr><td>Diffuse Reflectance Sample Preparation kit</td><td>Pike Technologies</td><td>042-3040</td><td>Includes sample holder cups, spatulas, alignment mirror, mirror brush, razor blades</td></tr><tr><td>Agate mortar and pestle</td><td>Pike Technologies</td><td>161-5035</td><td></td></tr><tr><td>Centrifuge</td><td>ThermoScientific</td><td>Sorvall ST16</td><td>Most benchtop centrifuges capable of ~5,000 rpm will be acceptable</td></tr><tr><td colspan="4">[header]</td></tr><tr><td colspan="4">Consumables</td></tr><tr><td>Centrifuge tubes</td><td>Evergreen Scientific</td><td>222-2470-G8K</td><td>Any centrifuge tube of compatible size and material is acceptable</td></tr><tr><td>KBr powder packets</td><td>ThermoScientific</td><td>50-465-317</td><td>Also possible to use alternative KBr supplier</td></tr></tbody></table>

diffuse reflectance infrared spectroscopic identification of dispersant/particle bonding mechanisms in functional inks

In additive manufacturing, or 3D printing, material is deposited drop by drop, to create micron to macroscale layers. A typical inkjet ink is a colloidal dispersion containing approximately ten components including solvent, the nano to micron scale particles which will comprise the printed layer, polymeric dispersants to stabilize the particles, and polymers to tune layer strength, surface tension and viscosity. To rationally and efficiently formulate such an ink, it is crucial to know how the components interact. Specifically, which polymers bond to the particle surfaces and how are they attached? Answering this question requires an experimental procedure that discriminates between polymer adsorbed on the particles and free polymer. Further, the method must provide details about how the functional groups of the polymer interact with the particle. In this protocol, we show how to employ centrifugation to separate particles with adsorbed polymer from the rest of the ink, prepare the separated samples for spectroscopic measurement, and use Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS) for accurate determination of dispersant/particle bonding mechanisms. A significant advantage of this methodology is that it provides high level mechanistic detail using only simple, commonly available laboratory equipment. This makes crucial data available to almost any formulation laboratory. The method is most useful for inks composed of metal, ceramic, and metal oxide particles in the range of 100 nm or greater. Because of the density and particle size of these inks, they are readily separable with centrifugation. Further, the spectroscopic signatures of such particles are easy to distinguish from absorbed polymer. The primary limitation of this technique is that the spectroscopy is performed ex-situ on the separated and dried particles as opposed to the particles in dispersion. However, results from attenuated total reflectance spectra of the wet separated particles provide evidence for the validity of the DRIFTS measurement.

The experimental procedure described in this protocol has been applied to gain insight into the mechanism of NiO particle stabilization in an ink used to print the anode of solid oxide fuel cells. This ink is a dispersion of NiO particles in 2-butanol, alpha terpineol, and a range of dispersants and binders22. Representative results are shown here for a simplified dispersion of NiO in 2-butanol with an oleic acid dispersant. In Figure 1A, we show raw diffuse reflectance infrared spectroscopy d...

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Diffuse Reflectance Infrared Spectroscopic Identification of Dispersant/Particle Bonding Mechanisms in Functional Inks

Formulation of stable, functional inks is critical to expanding the applications of additive manufacturing. In turn, knowledge of the mechanisms of dispersant/particle bonding is required for effective ink formulation. Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS) is presented as a simple, inexpensive way to gain insight into these mechanisms.

In additive manufacturing, or 3D printing, material is deposited drop by drop, to create micron to macroscale layers.  A typical inkjet ink is a colloidal ...

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Research

JoVE Journal

Chemistry

13.7K Views.  New York City College of Technology, City University of New York (CUNY). Formulation of stable, functional inks is critical to expanding the applications of additive manufacturing. In turn, knowledge of the mechanisms of dispersant/particle bonding is required for effective ink formulation. Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS) is presented as a simple, inexpensive way to gain insight into these mechanisms.

Video: Diffuse Reflectance Infrared Spectroscopic Identification of Dispersant/Particle Bonding Mechanisms in Functional Inks

Biomolecular Detection employing the Interferometric Reflectance Imaging Sensor (IRIS)

The sensitive measurement of biomolecular interactions has use in many fields and industries such as basic biology and microbiology, environmental/agricultural/biodefense monitoring, nanobiotechnology, and more. For diagnostic applications, monitoring (detecting) the presence, absence, or abnormal expression of targeted proteomic or genomic biomarkers found in patient samples can be used to determine treatment approaches or therapy efficacy. In the research arena, information on molecular affinities and specificities are useful for fully characterizing the systems under investigation.
Many of the current systems employed to determine molecular concentrations or affinities rely on the use of labels. Examples of these systems include immunoassays such as the enzyme-linked immunosorbent assay (ELISA), polymerase chain reaction (PCR) techniques, gel electrophoresis assays, and mass spectrometry (MS). Generally, these labels are fluorescent, radiological, or colorimetric in nature and are directly or indirectly attached to the molecular target of interest. Though the use of labels is widely accepted and has some benefits, there are drawbacks which are stimulating the development of new label-free methods for measuring these interactions. These drawbacks include practical facets such as increased assay cost, reagent lifespan and usability, storage and safety concerns, wasted time and effort in labelling, and variability among the different reagents due to the labelling processes or labels themselves. On a scientific research basis, the use of these labels can also introduce difficulties such as concerns with effects on protein functionality/structure due to the presence of the attached labels and the inability to directly measure the interactions in real time.
Presented here is the use of a new label-free optical biosensor that is amenable to microarray studies, termed the Interferometric Reflectance Imaging Sensor (IRIS), for detecting proteins, DNA, antigenic material, whole pathogens (virions) and other biological material. The IRIS system has been demonstrated to have high sensitivity, precision, and reproducibility for different biomolecular interactions [1-3]. Benefits include multiplex imaging capacity, real time and endpoint measurement capabilities, and other high-throughput attributes such as reduced reagent consumption and a reduction in assay times. Additionally, the IRIS platform is simple to use, requires inexpensive equipment, and utilizes silicon-based solid phase assay components making it compatible with many contemporary surface chemistry approaches.
Here, we present the use of the IRIS system from preparation of probe arrays to incubation and measurement of target binding to analysis of the results in an endpoint format. The model system will be the capture of target antibodies which are specific for human serum albumin (HSA) on HSA-spotted substrates.

Biomolecular Detection employing the Interferometric Reflectance Imaging Sensor IRIS

Quantitative, high-throughput, real-time, and label-free biomolecular detection (DNA, protein, etc.) on SiO2 surfaces can be achieved using a simple interferometric technique which relies on LED illumination, minimal optical components, and a camera. The Interferometric Reflectance Imaging Sensor (IRIS) is inexpensive, simple to use, and amenable to microarray formats.

The sensitive measurement of biomolecular interactions has use in many fields and industries such as basic biology and microbiology, ...

Bioengineering

An Inverse Analysis Approach to the Characterization of Chemical Transport in Paints

The ability to directly characterize chemical transport and interactions that occur within a material (i.e., subsurface dynamics) is a vital component in understanding contaminant mass transport and the ability to decontaminate materials. If a material is contaminated, over time, the transport of highly toxic chemicals (such as chemical warfare agent species) out of the material can result in vapor exposure or transfer to the skin, which can result in percutaneous exposure to personnel who interact with the material. Due to the high toxicity of chemical warfare agents, the release of trace chemical quantities is of significant concern. Mapping subsurface concentration distribution and transport characteristics of absorbed agents enables exposure hazards to be assessed in untested conditions. Furthermore, these tools can be used to characterize subsurface reaction dynamics to ultimately design improved decontaminants or decontamination procedures. To achieve this goal, an inverse analysis mass transport modeling approach was developed that utilizes time-resolved mass spectroscopy measurements of vapor emission from contaminated paint coatings as the input parameter for calculation of subsurface concentration profiles. Details are provided on sample preparation, including contaminant and material handling, the application of mass spectrometry for the measurement of emitted contaminant vapor, and the implementation of inverse analysis using a physics-based diffusion model to determine transport properties of live chemical warfare agents including distilled mustard (HD) and the nerve agent VX.

In this paper, a procedure for quantifying the mass transport parameters of chemicals in various materials is presented. This process involves employing an inverse-analysis based diffusion model to vapor emission profiles recorded by real-time, mass spectrometry in high vacuum.

The ability to directly characterize chemical transport and interactions that occur within a material (i.e., subsurface dynamics) is a vital component in ...

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices have used devices prepared by spin coating, a process that is not amenable to large-scale fabrication. This mismatch in device fabrication makes it difficult to translate quantitative results obtained in the laboratory to the commercial level, making optimization difficult. Using a mini-slot die coater, this mismatch can be resolved by translating the commercial process to the laboratory and characterizing the structure formation in the active layer of the device in real time and in situ as films are coated onto a substrate. The evolution of the morphology was characterized under different conditions, allowing us to propose a mechanism by which the structures form and grow. This mini-slot die coater offers a simple, convenient, material efficient route by which the morphology in the active layer can be optimized under industrially relevant conditions. The goal of this protocol is to show experimental details of how a solar cell device is fabricated using a mini-slot die coater and technical details of running in situ structure characterization using the mini-slot die coater.

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Here, we present a protocol to fabricate organic thin film solar cells using a mini-slot die coater and related in-line structure characterizations using synchrotron scattering techniques.

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices ...

Engineering

Inkjet-printed Polyvinyl Alcohol Multilayers

Inkjet printing is a modern method for polymer processing, and in this work, we demonstrate that this technology is capable of producing polyvinyl alcohol (PVOH) multilayer structures. A polyvinyl alcohol aqueous solution was formulated. The intrinsic properties of the ink, such as surface tension, viscosity, pH, and time stability, were investigated. The PVOH-based ink was a neutral solution (pH 6.7) with a surface tension of 39.3 mN/m and a viscosity of 7.5 cP. The ink displayed pseudoplastic (non-Newtonian shear thinning) behavior at low shear rates, and overall, it demonstrated good time stability. The wettability of the ink on different substrates was investigated, and glass was identified as the most suitable substrate in this particular case. A proprietary 3D inkjet printer was employed to manufacture polymer multilayer structures. The morphology, surface profile, and thickness uniformity of inkjet-printed multilayers were evaluated via optical microscopy.

An inkjet printer was used to manufacture polyvinyl alcohol multilayers. Polyvinyl alcohol water-based ink was formulated, and the main physical properties were investigated.

Inkjet printing is a modern method for polymer processing, and in this work, we demonstrate that this technology is capable of producing polyvinyl alcohol ...

Reactive Inkjet Printing and Propulsion Analysis of Silk-based Self-propelled Micro-stirrers

In this study, a protocol for using reactive inkjet printing to fabricate enzymatically propelled silk swimmers with well-defined shapes is reported. The resulting devices are an example of self-propelled objects capable of generating motion without external actuation and have potential applications in medicine and environmental sciences for a variety of purposes ranging from micro-stirring, targeted therapeutic delivery, to water remediation (e.g., cleaning oil spills). This method employs reactive inkjet printing to generate well-defined small-scale solid silk structures by converting water soluble regenerated silk fibroin (silk I) to insoluble silk fibroin (silk II). These structures are also selectively doped in specific regions with the enzyme catalase in order to produce motion via bubble generation and detachment. The number of layers printed determines the three-dimensional (3D) structure of the device, and so here the effect of this parameter on the propulsive trajectories is reported. The results demonstrate the ability to tune the motion by varying the dimensions of the printed structures.

This protocol demonstrates the ability to utilize reactive inkjet printing to print self-motile biocompatible and environmentally friendly micro-stirrers for use in biomedical and environmental applications.

In this study, a protocol for using reactive inkjet printing to fabricate enzymatically propelled silk swimmers with well-defined shapes is reported. The ...

A Two-Step Pyrolysis-Gas Chromatography Method with Mass Spectrometric Detection for Identification of Tattoo Ink Ingredients and Counterfeit Products

Tattoo inks are complex mixtures of ingredients. Each of them possesses different chemical properties which have to be addressed upon chemical analysis. In this method for two-step pyrolysis online coupled to gas chromatography mass spectrometry (py-GC-MS) volatile compounds are analyzed during a first desorption run. In the second run, the same dried sample is pyrolyzed for analysis of non-volatile compounds such as pigments and polymers. These can be identified by their specific decomposition patterns. Additionally, this method can be used to differentiate original from counterfeit inks. Easy screening methods for data evaluation using the average mass spectra and self-made pyrolysis libraries are applied to speed up substance identification. Using specialized evaluation software for pyrolysis GS-MS data, a fast and reliable comparison of the full chromatogram can be achieved. Since GC-MS is used as separation technique, the method is limited to volatile substances upon desorption and after pyrolysis of the sample. The method can be applied for quick substance screening in market control surveys since it requires no sample preparation steps.

This method for two-step pyrolysis online coupled to gas chromatography with mass spectrometric detection and data evaluation protocol can be used for multi-component analysis of tattoo inks and discrimination of counterfeit products.

Tattoo inks are complex mixtures of ingredients. Each of them possesses different chemical properties which have to be addressed upon chemical analysis. ...

In situ FTIR Spectroscopy as a Tool for Investigation of Gas/Solid Interaction: Water-Enhanced CO2 Adsorption in UiO-66 Metal-Organic Framework

In situ infrared spectroscopy is an inexpensive, highly sensitive, and selective valuable tool to investigate the interaction of polycrystalline solids with adsorbates. Vibrational spectra provide information on the chemical nature of adsorbed species and their structure. Thus, they are very useful for obtaining molecular level understanding of surface species. The IR spectrum of the sample itself gives some direct information about the material. General conclusions can be drawn concerning hydroxyl groups, some stable surface species and impurities. However, the spectrum of the sample is &#34;blind&#34; with respect to the presence of coordinatively unsaturated ions and gives rather poor information about the acidity of surface hydroxyls, species decisive for the adsorption and catalytic properties of the materials. Furthermore, no discrimination between bulk and surface species can be made. These problems are solved by the use of probe molecules, substances that interact specifically with the surface; the alteration of some spectral features of these molecules as a result of adsorption provides valuable information about the nature, properties, location, concentration, etc., of the surface sites.
The experimental protocol for in-situ IR studies of gas/sample interaction includes preparation of a sample pellet, activation of the material, initial spectral characterization through the analysis of the background spectra, characterization by probe molecules, and study of the interaction with a particular set of gas mixtures. In this paper we investigate a zirconium terephthalate metal organic framework, Zr6O4(OH)4(BDC)6 (BDC = benzene-1,4-dicarboxylate), namely UiO-66 (UiO refers to University of Oslo). The acid sites of the UiO-66 sample are determined by using CO and CD3CN as molecular probes. Furthermore, we have demonstrated that CO2 is adsorbed on basic sites exposed on dehydroxylated UiO-66. Introduction of water to the system produces hydroxyl groups acting as additional CO2 adsorption sites. As a result, CO2 adsorption capacity of the sample is strongly enhanced.

In situ FTIR Spectroscopy as a Tool for Investigation of Gas/Solid Interaction: Water-Enhanced CO2 Adsorption in UiO-66 Metal-Organic Framework

The use of FTIR spectroscopy for investigation of the surface properties of polycrystalline solids is described. Preparation of sample pellets, activation procedures, characterization with probe molecules and model studies of CO2 adsorption are discussed.

In situ infrared spectroscopy is an inexpensive, highly sensitive, and selective valuable tool to investigate the interaction of polycrystalline solids ...

Vibrational Spectra of a N719-Chromophore/Titania Interface from Empirical-Potential Molecular-Dynamics Simulation, Solvated by a Room Temperature Ionic Liquid

The accurate molecular simulation prediction of vibrational spectra, and other structural, energetic and spectral characteristics, of photo-active metal-oxide surfaces in contact with light-absorbing dyes is an ongoing thorny and elusive challenge in physical chemistry. With this in mind, a molecular-dynamics (MD) simulation were performed by using optimized empirical potentials for a well-representative and prototypical dye-sensitized solar cell (DSC) solvated by a widely-studied room temperature ionic liquid (RTIL), in the guise of a [bmim]+[NTf2]- RTIL solvating an N719-sensitizing dye adsorbed onto 101 anatase-titania. In doing so, important insights were gleaned into how using a RTIL as the electrolytic hole acceptor modulates the dynamical and vibrational properties of a N719 dye, estimating the spectra for the DSC photo-active interface via Fourier transformation of mass-weighted velocity autocorrelation functions from MD. The acquired vibrational spectra were compared with the experiment spectra and those sampled from ab initio molecular dynamics (AIMD); in particular, various empirical-potential spectra generated from MD provide insight into how partial-charge charge parameterization of the ionic liquid affects vibrational spectra prediction. In any event, careful fitting of empirical force-field models has been shown to be an effective tool in handling DSC vibrational properties, when validated by AIMD and an experiment.

A dye-sensitized solar cell was solvated by RTILs; using optimized empirical potentials, a molecular dynamics simulation was applied to compute vibrational properties. The obtained vibrational spectra were compared with experiment and ab initio molecular dynamics; various empirical potential spectra show how partial-charge charge parameterization of the ionic liquid affects vibrational spectra prediction.

The accurate molecular simulation prediction of vibrational spectra, and other structural, energetic and spectral characteristics, of photo-active ...

Exploring Multiphase Polymeric Systems by Nanoscale Infrared Spectroscopy

Advances in Nanoscale Infrared Spectroscopy to Explore Multiphase Polymeric Systems

Multiphase polymeric systems encompass local domains with dimensions that can vary from a few tens of nanometers to several micrometers. Their composition is commonly assessed using infrared spectroscopy, which provides an average fingerprint of the various materials contained in the volume probed. However, this approach does not offer any details on the arrangement of the phases in the material. Interfacial regions between two polymeric phases, often in the nanoscale range, are also challenging to access. Photothermal nanoscale infrared spectroscopy monitors the local response of materials excited by infrared light with the sensitive probe of an atomic force microscope (AFM). While the technique is suitable for interrogating small features, such as individual proteins on pristine gold surfaces, the characterization of three-dimensional multicomponent materials is more elusive. This is due to a relatively large volume of material undergoing photothermal expansion, defined by the laser focalization onto the sample and by the thermal properties of the polymeric constituents, compared to the nanoscale region probed by the AFM tip. Using a polystyrene (PS) bead and a polyvinyl alcohol (PVA) film, we evaluate the spatial footprint of photothermal nanoscale infrared spectroscopy for surface analysis as a function of the position of PS in the PVA film. The effect of the feature position on the nanoscale infrared images is investigated, and spectra are acquired. Some perspectives on the future advances in the field of photothermal nanoscale infrared spectroscopy are provided, considering the characterization of complex systems with embedded polymeric structures.

Author Spotlight: Advances in Nanoscale Infrared Spectroscopy to Explore Multiphase Polymeric Systems  

This protocol describes the application of atomic force microscopy and nanoscale infrared spectroscopy to evaluate the performance of photothermal nanoscale infrared spectroscopy in the characterization of three-dimensional multi-polymeric samples.

Multiphase polymeric systems encompass local domains with dimensions that can vary from a few tens of nanometers to several micrometers. Their composition ...

Visualizing Polymer Dynamics for Optimizing 3D Printing Quality

Real-Time Imaging of Bonding in 3D-Printed Layers

In recent times, 3D printing technology has revolutionized our ability to design and produce products, but optimizing the print quality can be challenging. The process of extrusion 3D printing involves pressuring molten material through a thin nozzle and depositing it onto previously extruded material. This method relies on bonding between the consecutive layers to create a strong and visually appealing final product. This is no easy task, as many parameters, such as the nozzle temperature, layer thickness, and printing speed, must be fine-tuned to achieve optimal results. In this study, a method for visualizing the polymer dynamics during extrusion is presented, giving insight into the layer bonding process. Using laser speckle imaging, the plastic flow and fusion can be resolved non-invasively, internally, and with high spatiotemporal resolution. This measurement, which is easy to perform, provides an in-depth understanding of the underlying mechanics influencing the final print quality. This methodology was tested with a range of cooling fan speeds, and the results showed increased polymer motion with lower fan speeds and, thus, explained the poor printing quality when the cooling fan was turned off. These findings show that this methodology allows for optimizing the printing settings and understanding the material behavior. This information can be used for the development and testing of novel printing materials or advanced slicing procedures. With this approach, a deeper understanding of extrusion can be built to take 3D printing to the next level.

Author Spotlight: Real-Time Imaging of Bonding in 3D-Printed Layers  

With a non-invasive and real-time technique, nanoscopic polymer motion inside a polymer filament is imaged during 3D printing. Fine-tuning this motion is crucial for producing constructs with optimal performance and appearance. This method reaches the core of plastic layer fusion, thus offering insights into optimal printing conditions and material design criteria.

Diffuse Reflectance Infrared Spectroscopic Identification of Dispersant/Particle Bonding Mechanisms in Functional Inks

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