This work is a part of the STW project "Integral solution for sustainable construction (IS2C, Fleur van Rossem for her support during the chip fabrication, Justyna Wiedemair for the chip design and Allison Bidulock for her support during the manuscript preparation.

1. Chip Fabrication
Note: The chip consists of an Ag/AgCl working electrode (WE), an Ag/AgCl pseudo-reference electrode (pseudo-RE) and a platinum counter electrode on a glass chip. The silver metal is deposited on a glass chip, using standard cleanroom processes16. It is then chloridized in 0.1 M FeCl3 solution for 30 sec to form an AgCl layer over the surface. The Ag/AgCl WE (area = 9.812 mm2) is located in the center, surrounded by the Ag/AgCl pseudo-RE as shown in Figure 1.
<ol>
	<li>Deposit the silver metal on glass to form a planar silver electrode. The step-by-step chip fabrication in a cleanroom is given as follows:
	<ol>
		<li>Lithography
		<ol>
			<li>For wafer cleaning, immerse the glass wafer first into conc. HNO3 bath to remove any organic contamination and then into 1 M KOH to clean the surface.</li>
			<li>Apply a positive photo resist (200 nm thick) to the wafer by spin coating and prebake the resist at 95 &#176;C for 15 min.</li>
			<li>Expose the wafer to UV light for 5 sec through a glass mask.</li>
			<li>Develop the photoresist in developer solution. This will expose the area of glass where electrodes will be deposited and the remaining area will be covered by the unexposed resist.</li>
		</ol>
		</li>
		<li>Glass Etching
		<ol>
			<li>Immerse the developed glass wafer in the KOH bath to etch the exposed area of the glass.</li>
		</ol>
		</li>
		<li>Metal Deposition (Sputtering)
		<ol>
			<li>Deposit silver metal on the exposed glass area.
			<ol>
				<li>First deposit a 20 nm titanium (Ti) layer (by sputtering) as an adhesion layer for glass.</li>
				<li>Then deposit 70 nm palladium (Pd) layer (by sputtering) as a diffusion barrier between silver and Ti.</li>
				<li>Finally deposit 500 nm of silver metal. This is the thickness of the deposited metal. The area of the working electrode is 4 mm2.</li>
				<li>Remove the remaining resist by lift-off process in an acetone bath.</li>
			</ol>
			</li>
			<li>Dice the wafer into the single chip size. The chip is now ready to be chloridized to form an on-chip Ag/AgCl electrode.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Place the chip in an in-house designed Polytetrafluoroethylene chip holder, as shown in Figure 1. The holder provides easy electrical connections via push-pins (or spring-loaded pins) and contains an electrochemical cell.</li>
	<li>Chloridize the silver electrode to form an Ag/AgCl electrode on the chip. For that, pour 0.1 M FeCl3 solution in the cell for 30 sec. or till the silver color of the electrode becomes dark grayish. Longer immersion is not critical whereas shorter immersion time can lead to no deposition of Ag/AgCl.</li>
	<li>Rinse the chip with deionized water to clean the remaining FeCl3.The chip is now ready to be used for the chronopotentiometric measurement.</li>
</ol>
2. Electrolyte Preparation
Note: The electrolytes were prepared with different concentration of potassium chloride in 0.5 M KNO3.
<ol>
	<li>Prepare 50 ml of 50 mM KCl electrolyte stock solution (0.186 g of KCl in 50 ml of solution).</li>
	<li>In the same solution add 2.52 g of KNO3 to form a 0.5 M KNO3 background electrolyte.</li>
	<li>Keep the starting concentration of chloride to zero and KNO3 to 0.5 M. In other words add 2.52 g of KNO3 in a 50 ml of deionized water.</li>
	<li>Add 50 mM KCl to increase the chloride ion concentration (from 1 mM to 6 mM) of the electrolyte, systematically, as shown in the following steps.
	<ol>
		<li>Add 100 &#181;l of the 50 mM KCl into a 4.9 ml of 0.5 M KNO3 to get 1 mM [Cl&#713;].</li>
		<li>Add 104 &#181;l of the 50 mM KCl solution into the solution of step 2.4.1 to get 2 mM [Cl&#713;].</li>
		<li>Add 108.41 &#181;l of the 50 mM KCl solution into the solution of step 2.4.2 to get 3 mM [Cl&#713;].</li>
		<li>Add 113.19 &#181;l of the 50 mM KCl solution into the solution of step 2.4.3 to get 4 mM [Cl&#713;].</li>
		<li>Add 118.2 &#181;l of the 50 mM KCl solution into the solution of step 2.4.4 to get 5 mM [Cl&#713;].</li>
		<li>Add 123.3 &#181;l of the 50 mM KCl solution into the solution of step 2.4.5 to get 6 mM [Cl&#713;].</li>
	</ol>
	</li>
</ol>
3. Experimental Setup
Note: The measurements were performed using a potentiostat (Biologic Science Instruments, France).
<ol>
	<li>Place the chip in the chip holder and connect the corresponding terminal of the potentiostat.</li>
	<li>Connect the working electrode terminal of the potentiostat to the Ag/AgCl electrode.</li>
	<li>Connect the reference electrode terminal of the potentiostat to another Ag/AgCl electrode.</li>
	<li>Connect the counter electrode terminal of the potentiostat to the platinum electrode.</li>
	<li>Place the complete experiment setup in a faraday cage to avoid ambient noise.</li>
</ol>
4. Instrument Operational Settings
Note: The operational parameters of the electrochemical cell are controlled via the user interface of the potentiostat. The potential response of the Ag/AgCl WE during an applied current pulse is measured for different concentrations of chloride ion.
<ol>
	<li>In the potentiostat program, open the technique chronopotentiometry and set the operational parameters.
	<ol>
		<li>Set the following parameter according to the requirements:
		<ol>
			<li>Current (Is)</li>
			<li>Time of applied current (ts)</li>
		</ol>
		</li>
		<li>Start this technique by clicking the play button in the potentiostat program. 
		Note: The potentiostat program displays the potential response as a function of time under the applied current pulse.</li>
	</ol>
	</li>
</ol>
5. Measurements and Data Analysis
<ol>
	<li>Draw the calibration curve of the transition time vs. Cl&#713; ion concentration in electrolyte.
	<ol>
		<li>Change the Cl&#713; concentration in the KCl electrolyte, systematically.
		<ol>
			<li>Start the measurement with 5 ml of 1 mM KCl with 0.5 M KNO3 background electrolyte in the electrochemical cell.</li>
			<li>Start the chronopotentiometric experiment by using the potentiostat and apply a current of 10 mA/cm-2 for 10 sec and store the data.</li>
			<li>Systematically change the concentration to 6 mM with 1 mM increments and repeat the measurements.</li>
		</ol>
		</li>
		<li>Store the measured data as a.mpt file and analyze the data file in data processing program.
		<ol>
			<li>Analyze the data using an in-house developed data processing program to calculate the first derivative of the potential response and calculate the peak of the first derivative. The peak of the first derivative is the transition time. 
			Note: The complete coding of data processing program is given in the supplementary information of Abbas et al., 2014.</li>
		</ol>
		</li>
		<li>Repeat the measurement three times with the interval of 1 hr each.</li>
		<li>Open all the data files in data processing program and calculate the transition time for each measurement. Detail steps of transition time calculation is given below:
		<ol>
			<li>Plot the potential difference vs. time obtained from the data files of chronopotentiometric measurement.</li>
			<li>Calculate the first derivative of the potential response.</li>
			<li>Indicate the maximum of the first derivative and the time of it. The time of the maximum of first derivative is the transition time.</li>
		</ol>
		</li>
		<li>For the calibration curve, plot the square root of the transition time with respect to the concentration of Cl&#713; ions.</li>
		<li>Along the measured data plot the theoretical curve based on the Sand equation25. Calculate back the diffusion coefficient from the data plot.
		<ol>
			<li>In the measured data plot between transition time and the [Cl&#713;] take any point on the line and record the value of transition time and the [Cl&#713;]. The Sand equation is given as: 
			&#964; = (FC*/2j(1-tCl-))2 D&#960; 
			Here, C* is the bulk Cl&#713; ion concentration, F is the Faraday constant, j is the current density, tCl- is the transport number and D is the diffusion coefficient. Neglect the tCl- since it approaches zero for higher background electrolyte concentration.</li>
			<li>The only remaining variable in the Sand equation in the diffusion coefficient; put the value of transition time, the chloride ion concentration and the applied current in the Sand equation getting the value of the diffusion coefficient.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Drift Measurement
	<ol>
		<li>Pour 5 ml of 1 mM of the KCl in the electrochemical cell.</li>
		<li>In the potentiostat, set the applied current to be 10 Am-2 and time to be 10 sec.</li>
		<li>Measure the potential response for 2 weeks with three measurement each day with an interval of 3 hr between measurements.</li>
		<li>Refresh the electrolyte, i.e.,&#160;1 mM KCl, every day before performing the measurements.</li>
		<li>Plot the transition time over two weeks of measurements. The change in the transition time per day is the drift of the transition time response.</li>
	</ol>
	</li>
	<li>Effect of the pseudo-reference electrode on the transition time measurements 
	Note: Various pseudo-references such as a Ag/AgCl wire, a platinum wire and a steel wire are tested to measure the transition time.
	<ol>
		<li>Pour 4 mM of KCl electrolyte in the electrochemical cell.</li>
		<li>Use Ag/AgCl as a pseudo-reference electrode and connect it to the reference electrode terminal of the potentiostat. Due to anodic current pulse the Cl&#713; ions are depleted near the Ag/AgCl working electrode.</li>
		<li>Perform the chronopotentiometric measurement by applying a current density of 15 Am-2 for 10 sec.</li>
		<li>Repeat the measurements with platinum as a pseudo-reference electrode and record the data.</li>
		<li>Repeat the measurements with steel bar as a pseudo-reference electrode and record the data.</li>
		<li>Plot the measured transition time for various pseudo-reference electrodes used.</li>
		<li>Repeat the complete set of measurement with 5 mM of KCl and plot the transition time using various pseudo-reference electrodes.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

The transition time is the moment of inflection; it is theoretically independent of the reference potential i.e., the reference electrode. Therefore any metal wire can be used as a pseudo-reference electrode for transition time measurements. In contrast to the existing potentiometric measurement of chloride ions in concrete this method enables a long-term and calibration free measurement. Furthermore the sensitivity and the detection range of concentration can be tuned by adjusting the applied current pulse. For...

A chloride ion sensor based on the transition time measurement of an Ag/AgCl electrode is presented. The aim is to avoid the inherent drifts during the long-term continuous monitoring of the chloride ions in the electrolyte. Chronopotentiometric measurement, which is a dynamic measurement approach, of an Ag/AgCl electrode is used for this purpose. Here a rate of change of potential of an Ag/AgCl electrode is measured during a stimulus (galvanostatic pulse). The advantage of this approach is demonstrated by eluding the liquid-junction reference electrode and instead using any metal wire as a pseudo-reference electrode, therefore allowing the detection of Cl&#713; ions concentration for long-term (years) and in situ applications, such as measurement inside concrete structures.
Chloride ions in concrete structures is one of the major causes of degradation1,2. It initiates pitting corrosion in the reinforcement steel and results in the ultimate failure of the structure3. Therefore, measuring Cl&#713; ions in concrete is inevitable to predict the service life and maintenance cycle of a structure4,5. Different sensing principles have been reported for chloride ion measurement in concrete such as electrochemical6,7, optical8,9 and electromagnetic10,11. However, optical and electromagnetic methods have bulky setups, are difficult to integrate as a stand-alone system and have issues with selectivity12. In electrochemical technique, potentiometric measurement of an Ag/AgCl electrode is the state of the art approach6,7,13. Despite promising results, this approach is limited to lab-scale measurement since the drifts in reference potential and diffusion potential drop results in flawed data14,15. A transition time approach based on the dynamic electrochemical measurement (DEM) could alleviate the problem due to potential drift16.
In the DEM, a system&#39;s response to an applied stimulus is measured17-19. The example of such a system is chronopotentiometry. Here an applied current pulse is used as a stimulus depleting ions near the electrode surface and the corresponding potential response is measured. An anodic current at an Ag/AgCl electrode initiates a faradaic reaction (Ag + Cl&#713; <img alt="Figure 1" src="/files/ftp_upload/53312/arrow.jpg" />AgCl + e&#713;) resulting in a depletion of Cl&#713; ions near electrode surface. The potential change is a function of the applied current and the concentration of the (selective) ions in the electrolyte12,20. The moment these ions deplete completely near the electrode surface the rate of change of potential rises rapidly, giving an inflection point21. The inflection point on the potential-time response curve (chronopotentiogram) shows the transition time and can be determined from the maximum of the first derivative of the potential response22. The transition time is a characteristic of the ion concentration. This approach has been used to determine different ions concentration17 and the pH of electrolytes23,24. In case of an Ag/AgCl electrode as a working electrode (to which current is applied) the depleting ions will be chloride ions17. Therefore measuring its transition time will determine its concentration.

<table border="0" cellpadding="0" cellspacing="0" width="1009">
	<tbody>
		<tr height="25">
			<td height="25" style="height:25px;width:373px;">Platinum wire (&#8805;99.99% trace metals)</td>
			<td style="width:292px;">Sigma Aldrich, the Netherlands</td>
			<td style="width:172px;">EP1330-1EA</td>
			<td style="width:172px;"></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Potassium chloride (BioXtra, &#8805;99.0%)</td>
			<td>Sigma Aldrich, the Netherlands</td>
			<td>P9333-500G</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Potassium hydroxide (90% pure reagent grade)</td>
			<td>Sigma Aldrich, the Netherlands</td>
			<td>484016-1KG</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Ferric chloride&#160;</td>
			<td>Sigma Aldrich, the Netherlands</td>
			<td>451649-1G</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">potassium nitrate (&#62; 99% reagent grade)&#160;</td>
			<td>Sigma Aldrich, the Netherlands</td>
			<td>P6083-500G</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Ag/AgCl liquid junction reference electrode&#160;</td>
			<td>BASi, USA</td>
			<td>model MF-2079</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">VSP potentiostat</td>
			<td>Biologic Science Instruments, France</td>
			<td>VSP 300</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Steel wire</td>
			<td>Microlab TU Delft</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Silver wire&#160;</td>
			<td>Sigma Aldrich, the Netherlands</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

dynamic electrochemical measurement of chloride ions

This protocol describes the dynamic measurement of chloride ions using the transition time of a silver silver chloride (Ag/AgCl) electrode. Silver silver chloride electrode is used extensively for potentiometric measurement of chloride ions concentration in electrolyte. In this measurement, long-term and continuous monitoring is limited due to the inherent drift and the requirement of a stable reference electrode. We utilized the chronopotentiometric approach to minimize drift and avoid the use of a conventional reference electrode. A galvanostatic pulse is applied to an Ag/AgCl electrode which initiates a faradic reaction depleting the Cl&#713; ions near the electrode surface. The transition time, which is the time to completely deplete the ions near the electrode surface, is a function of the ion concentration, given by the Nernst equation. The square root of the transition time is in linear relation to the chloride ion concentration. Drift of the response over two weeks is negligible (59 &#181;M/day) when measuring 1 mM [Cl&#713;]using a current pulse of 10 Am-2. This is a dynamic measurement where the moment of transition time determines the response and thus is independent of the absolute potential. Any metal wire can be used as a pseudo-reference electrode, making this approach feasible for long-term measurement inside concrete structures.

The Ag/AgCl electrode is fabricated on a glass chip (Figure1) using a standard cleanroom process. The chronopotentiometric measurement setup (Figure 2) was used and response was measured using a potentiostat. To observe the effect of Cl&#713; ion concentration on the transition time, solutions containing 4, 5 and 6 mM of Cl&#713; ions in a 0.5 M KNO3 background are measured (Figure 3). The calibration curve of the square root o...

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Dynamic Electrochemical Measurement of Chloride Ions

Dynamic measurement of chloride ions is presented. Transition time of an Ag/AgCl electrode, during a chronopotentiometric technique, can give the concentration of chloride ions in electrolyte. This method does not require a stable conventional reference electrode.

This protocol describes the dynamic measurement of chloride ions using the transition time of a silver silver chloride (Ag/AgCl) electrode. Silver silver ...

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11.4K visualizações.  University of Twente. Dynamic measurement of chloride ions is presented. Transition time of an Ag/AgCl electrode, during a chronopotentiometric technique, can give the concentration of chloride ions in electrolyte. This method does not require a stable conventional reference electrode.

Vídeo: Dynamic Electrochemical Measurement of Chloride Ions

Activating Molecules, Ions, and Solid Particles with Acoustic Cavitation

The chemical and physical effects of ultrasound arise not from a direct interaction of molecules with sound waves, but rather from the acoustic cavitation: the nucleation, growth, and implosive collapse of microbubbles in liquids submitted to power ultrasound. The violent implosion of bubbles leads to the formation of chemically reactive species and to the emission of light, named sonoluminescence. In this manuscript, we describe the techniques allowing study of extreme intrabubble conditions and chemical reactivity of acoustic cavitation in solutions. The analysis of sonoluminescence spectra of water sparged with noble gases provides evidence for nonequilibrium plasma formation. The photons and the "hot" particles generated by cavitation bubbles enable to excite the non-volatile species in solutions increasing their chemical reactivity. For example the mechanism of ultrabright sonoluminescence of uranyl ions in acidic solutions varies with uranium concentration: sonophotoluminescence dominates in diluted solutions, and collisional excitation contributes at higher uranium concentration. Secondary sonochemical products may arise from chemically active species that are formed inside the bubble, but then diffuse into the liquid phase and react with solution precursors to form a variety of products. For instance, the sonochemical reduction of Pt(IV) in pure water provides an innovative synthetic route for monodispersed nanoparticles of metallic platinum without any templates or capping agents. Many studies reveal the advantages of ultrasound to activate the divided solids. In general, the mechanical effects of ultrasound strongly contribute in heterogeneous systems in addition to chemical effects. In particular, the sonolysis of PuO2 powder in pure water yields stable colloids of plutonium due to both effects.

Acoustic cavitation in liquids submitted to power ultrasound creates transient extreme conditions inside the collapsing bubbles, which are the origin of unusual chemical reactivity and light emission, known as sonoluminescence. In the presence of noble gases, nonequilibrium plasma is formed. The "hot" particles and the photons generated by collapsing bubbles are able to excite species in solution.

The chemical and physical effects of ultrasound arise not from a direct interaction of molecules with sound waves, but rather from the acoustic ...

Measurement of Particle Size Distribution in Turbid Solutions by Dynamic Light Scattering Microscopy

A protocol for measuring polydispersity of concentrated polymer solutions using dynamic light scattering is described. Dynamic light scattering is a technique used to measure the size distribution of polymer solutions or colloidal particles. Although this technique is widely used for the assessment of polymer solutions, it is difficult to measure the particle size in concentrated solutions due to the multiple scattering effect or strong light absorption. Therefore, the concentrated solutions should be diluted before measurement. Implementation of the confocal optical component in a dynamic light scattering microscope1 helps to overcome this barrier. Using such a microscopic system, both transparent and turbid systems can be analyzed under the same experimental setup without a dilution. As a representative example, a size distribution measurement of a temperature-responsive polymer solution was performed. The sizes of the polymer chains in an aqueous solution were several tens of nanometers at a temperature below the lower critical solution temperature (LCST). In contrast, the sizes increased to more than 1.0 &#181;m when above the LCST. This result is consistent with the observation that the solution turned turbid above the LCST.

A protocol for the direct measurement of particle size distribution in concentrated solutions using dynamic light scattering microscopy is presented.

A protocol for measuring polydispersity of concentrated polymer solutions using dynamic light scattering is described. Dynamic light scattering is a ...

Fabrication and Testing of Photonic Thermometers

In recent years, a push for developing novel silicon photonic devices for telecommunications has generated a vast knowledge base that is now being leveraged for developing sophisticated photonic sensors. Silicon photonic sensors seek to exploit the strong confinement of light in nano-waveguides to transduce changes in physical state to changes in resonance frequency. In the case of thermometry, the thermo-optic coefficient, i.e., changes in refractive index due to temperature, causes the resonant frequency of the photonic device such as a Bragg grating to drift with temperature. We are developing a suite of photonic devices that leverage recent advances in telecom compatible light sources to fabricate cost-effective photonic temperature sensors, which can be deployed in a wide variety of settings ranging from controlled laboratory conditions, to the noisy environment of a factory floor or a residence. In this manuscript, we detail our protocol for the fabrication and testing of photonic thermometers.

We describe the process of fabrication and testing of photonic thermometers.

In recent years, a push for developing novel silicon photonic devices for telecommunications has generated a vast knowledge base that is now being ...

Electrochemical Impedance Spectroscopy as a Tool for Electrochemical Rate Constant Estimation

Electrochemical impedance spectroscopy (EIS) was used for advanced characterization of organic electroactive compounds along with cyclic voltammetry (CV). In the case of fast reversible electrochemical processes, current is predominantly affected by the rate of diffusion, which is the slowest and limiting stage. EIS is a powerful technique that allows separate analysis of stages of charge transfer that have different AC frequency response. The capability of the method was used to extract the value of charge transfer resistance, which characterizes the rate of charge exchange on the electrode-solution interface. The application of this technique is broad, from biochemistry up to organic electronics. In this work, we are presenting the method of analysis of organic compounds for optoelectronic applications.

Electrochemical impedance spectroscopy (EIS) of species that undergo reversible oxidation or reduction in solution was used for determination of rate constants of oxidation or reduction.

Electrochemical impedance spectroscopy (EIS) was used for advanced characterization of organic electroactive compounds along with cyclic voltammetry (CV). ...

Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles

Bicyclic aziridinium ions were generated by the removal of an appropriate leaving group through internal nucleophilic attack by nitrogen atom in the aziridine ring. The utility of bicyclic aziridinium ions, specifically 1-azoniabicyclo[3.1.0]hexane and 1-azoniabicyclo[4.1.0]heptane tosylate highlighted in the aziridine ring openings by the nucleophile with the release of the ring strain to yield the corresponding ring-expanded azaheterocycles such as pyrrolidine, piperidine and azepane with diverse substituents on the ring in regio- and stereospecific manner. Herein, we report a simple and convenient method for the preparation of the stable 1-azabicyclo[4.1.0]heptane tosylate followed by selective ring opening via a nucleophilic attack either at the bridge or at the bridgehead carbon to yield piperidine and azepane rings, respectively. This synthetic strategy allowed us to prepare biologically active natural products containing piperidine and azepane motif including sedamine, allosedamine, fagomine and balanol in highly efficient manner.

Bicyclic aziridinium ions such as 1-azoniabicyclo[4.1.0]heptane tosylate were generated from 2-[4-tolenesulfonyloxybutyl]aziridine, which was utilized for the preparation of substituted piperidines and azepanes via regio- and stereospecific ring-expansion with various nucleophiles. This highly efficient protocol allowed us to prepare diverse azaheterocycles including natural products such as fagomine, febrifugine analogue and balanol.

Bicyclic aziridinium ions were generated by the removal of an appropriate leaving group through internal nucleophilic attack by nitrogen atom in the ...

Disentangling High Strength Copolymer Aramid Fibers to Enable the Determination of Their Mechanical Properties

Traditionally, soft body armor has been made from poly(p-phenylene terephthalamide) (PPTA) and ultra-high molecular weight polyethylene. However, to diversify the fiber choices in the United States body armor market, copolymer fibers based on the combination of 5-amino-2-(p-aminophenyl) benzimidazole (PBIA) and the more conventional PPTA were introduced. Little is known regarding the long-term stability of these fibers, but as condensation polymers, they are expected to have potential sensitivity to moisture and humidity. Therefore, characterizing the strength of the materials and understanding their vulnerability to environmental conditions is important for evaluating their use lifetime in safety applications. Ballistic resistance and other critical structural properties of these fibers are predicated on their strength. To accurately determine the strength of the individual fibers, it is necessary to disentangle them from the yarn without introducing any damage. Three aramid-based copolymer fibers were selected for the study. The fibers were washed with acetone followed by methanol to remove an organic coating that held the individual fibers in each yarn bundle together. This coating makes it difficult to separate single fibers from the yarn bundle for mechanical testing without damaging the fibers and affecting their strength. After washing, fourier transform infrared (FTIR) spectroscopy was performed on both washed and unwashed samples and the results were compared. This experiment has shown that there are no significant variations in the spectra of poly(p-phenylene-benzimidazole-terephthalamide-co-p-phenylene terephthalamide) (PBIA-co-PPTA1) and PBIA-co-PPTA3 after washing, and only a small variation in intensity for PBIA. This indicates that the acetone and methanol rinses are not adversely affecting the fibers and causing chemical degradation. Additionally, single fiber tensile testing was performed on the washed fibers to characterize their initial tensile strength and strain to failure, and compare those to other reported values. Iterative procedural development was necessary to find a successful method for performing tensile testing on these fibers.

The primary goal of the study is to develop a protocol to prepare consistent specimens for accurate mechanical testing of high strength copolymer aramid fibers, by removing a coating and disentangling the individual fiber strands without introducing significant chemical or physical degradation.

Traditionally, soft body armor has been made from poly(p-phenylene terephthalamide) (PPTA) and ultra-high molecular weight polyethylene. However, to ...

Electrochemical Roughening of Thin-Film Platinum Macro and Microelectrodes

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries of the metal. Using this method, a crack free, thin-film macroelectrode surface with up to 40 times increase in active surface area was obtained. The roughening is easy to do in a standard electrochemical characterization laboratory and incudes the application of voltage pulses followed by extended application of a reductive voltage in a perchloric acid solution. The protocol includes the chemical and electrochemical preparation of both a macroscale (1.2 mm diameter) and microscale (20 &#181;m diameter) platinum disc electrode surface, roughening the electrode surface and characterizing the effects of surface roughening on electrode active surface area. This electrochemical characterization includes cyclic voltammetry and impedance spectroscopy and is demonstrated for both the macroelectrodes and the microelectrodes. Roughening increases electrode active surface area, decreases electrode impedance, increases platinum charge injection limits to those of titanium nitride electrodes of same geometry and improves substrates for adhesion of electrochemically deposited films.

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries. The electrochemical techniques of cyclic voltammetry and impedance spectroscopy are demonstrated to characterize these electrode surfaces.

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries ...

Asymmetric Thermoelectrochemical Cell for Harvesting Low-grade Heat under Isothermal Operation

Low-grade heat is abundantly available in the environment as waste heat. The efficient conversion of low-grade heat into electricity is very difficult. We developed an asymmetric thermoelectrochemical cell (aTEC) for heat-to-electricity conversion under isothermal operation in the charging and discharging processes without exploiting the thermal gradient or the thermal cycle. The aTEC is composed of a graphene oxide (GO) cathode, a polyaniline (PANI) anode, and 1M KCl as the electrolyte. The cell generates a voltage due to the pseudocapacitive reaction of GO when heating from room temperature (RT) to a high temperature (TH, ~40-90 &#176;C), and then current is successively produced by oxidizing PANI when an external electrical load is connected. The aTEC demonstrates a remarkable temperature coefficient of 4.1 mV/K and a high heat-to-electricity conversion efficiency of 3.32%, working at a TH = 70 &#176;C with a Carnot efficiency of 25.3%, unveiling a new promising thermoelectrochemical technology for low-grade heat recovery.

Low-grade heat is abundant, but its efficient recovery is still a great challenge. We report an asymmetric thermoelectrochemical cell using graphene oxide as a cathode and polyaniline as an anode with KCl as the electrolyte. This cell works under isothermal heating, exhibiting a high heat-to-electricity conversion efficiency in low-temperature regions.

Low-grade heat is abundantly available in the environment as waste heat. The efficient conversion of low-grade heat into electricity is very difficult. We ...

Fabrication of Thin Film Silver/Silver Chloride Electrodes with Finely Controlled Single Layer Silver Chloride

This paper aims to present a protocol to form smooth and well-controlled films of silver/silver chloride (Ag/AgCl) with designated coverage on top of thin film silver electrodes. Thin film silver electrodes sized 80 &#181;m x 80 &#181;m and 160 &#181;m x 160 &#181;m were sputtered on quartz wafers with a chromium/gold (Cr/Au) layer for adhesion. After passivation, polishing and cathodic cleaning processes, the electrodes underwent galvanostatic oxidation with consideration of Faraday&#39;s Law of Electrolysis to form smooth layers of AgCl with a designated degree of coverage on top of the silver electrode. This protocol is validated by inspection of scanning electron microscope (SEM) images of the surface of the fabricated Ag/AgCl thin film electrodes, which highlights the functionality and performance of the protocol. Sub-optimally fabricated electrodes are fabricated as well for comparison. This protocol can be widely used to fabricate Ag/AgCl electrodes with specific impedance requirements (e.g., probing electrodes for impedance sensing applications like impedance flow cytometry and interdigitated electrode arrays).

This paper aims to present a method to form smooth and well-controlled films of silver chloride (AgCl) with designated coverage on top of thin film silver electrodes.

This paper aims to present a protocol to form smooth and well-controlled films of silver/silver chloride (Ag/AgCl) with designated coverage on top of thin ...

Probing Surface Electrochemical Activity of Nanomaterials using a Hybrid Atomic Force Microscope-Scanning Electrochemical Microscope (AFM-SECM)

Scanning electrochemical microscopy (SECM) is used to measure the local electrochemical behavior of liquid/solid, liquid/gas and liquid/liquid interfaces. Atomic force microscopy (AFM) is a versatile tool to characterize micro- and nanostructure in terms of topography and mechanical properties. However, conventional SECM or AFM provides limited laterally resolved information on electrical or electrochemical properties at nanoscale. For instance, the activity of a nanomaterial surface at crystal facet levels is difficult to resolve by conventional electrochemistry methods. This paper reports the application of a combination of AFM and SECM, namely, AFM-SECM, to probe nanoscale surface electrochemical activity while acquiring high-resolution topographical data. Such measurements are critical to understanding the relationship between nanostructure and reaction activity, which is relevant to a wide range of applications in material science, life science and chemical processes. The versatility of the combined AFM-SECM is demonstrated by mapping topographical and electrochemical properties of faceted nanoparticles (NPs) and nanobubbles (NBs), respectively. Compared to previously reported SECM imaging of nanostructures, this AFM-SECM enables quantitative assessment of local surface activity or reactivity with higher resolution of surface mapping.

Probing Surface Electrochemical Activity of Nanomaterials using a Hybrid Atomic Force Microscope-Scanning Electrochemical Microscope AFM-SECM

Atomic force microscopy (AFM) combined with scanning electrochemical microscopy (SECM), namely, AFM-SECM, can be used to simultaneously acquire high-resolution topographical and electrochemical information on material surfaces at nanoscale. Such information is critical to understanding heterogeneous properties (e.g., reactivity, defects, and reaction sites) on local surfaces of nanomaterials, electrodes and biomaterials.

Scanning electrochemical microscopy (SECM) is used to measure the local electrochemical behavior of liquid/solid, liquid/gas and liquid/liquid interfaces. ...

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Dynamic Electrochemical Measurement of Chloride Ions