Partial financial support for this work was provided by the U.S. National Science Foundation through the Industry/University Cooperative Research Center on Water Equipment &#38; Policy located at the University of Wisconsin-Milwaukee (IIP-0968887) and Marquette University (IIP-0968844). We thank Glenn M. Walker, Woo-Jin Chang and Shankar Radhakrishnan for helpful discussions.

1. Thermal Particle Detection (TPD)
<ol>
	<li>Prepare the micro-fabricated silicon device with a thin-film silicon nitride membrane and integrated temperature sensor by micromachining, using standard semiconductor processing technology2. Rinse the fabricated device with deionized (DI) water. 
	Note: The fabrication method for thermal particle detector microfluidic device is explained in prior publication2.</li>
	<li>To produce polydimethylsiloxane (PDMS) substrates with micro-channels, create an SU8 mold using standard lithography processes5. 
	Note: The channel size is designed for each specific particle&#8217;s dimension.
	<ol>
		<li>Make PDMS by mixing a 10:1 ratio of base (30 ml) and curing agent (3 ml). Pour the PDMS on to the mold and remove the bubbles by briefly exposing it to a vacuum (5-10 min). 
		Note: The vacuum level is not a critical value to the degasification and it should continue until gas bubbles are totally removed from mixed PDMS.</li>
		<li>Place the mold on a hotplate (~70 &#176;C) for 2 hr to cure the PDMS. Then peel off the PDMS very carefully so as not to damage the mold. 
		Note: The Vacuum level is not a critical value.</li>
	</ol>
	</li>
	<li>Using a manual punch, punch a tight hole (1 mm) for the PTFE tube at one end. Use a large punch (2 mm) at the other end to make the PDMS a reservoir. Place the punched micro-channel on top of the device under the microscope and align the RTD at the center of the micro-channel (Figure 1A).</li>
	<li>In the electrical interface, connect the electrical pins at the contact pad positions and tighten up the locking screws. Make sure the height-adjustable pins (Pogo pins) sit at the correct electrode pads on the device.</li>
	<li>Dilute 10 &#181;l of the concentrated PS beads in 100 &#181;l of DI water in a 1.5 ml tube.</li>
	<li>To ensure the PS beads remain neutrally buoyant, add 2.7 &#181;l of glycerol (1.26 g/cm3) to DI water to match the fluid density to the polystyrene (PS) bead density (1.05 g/cm3).</li>
	<li>Connect the PTFE tube to the channel at one end and the other end to a 1 ml glass syringe. Fill the glass syringe with 0.5 ml of DI water. 
	Note: Tight fitting made by selecting the right punch size will avoid leakage in tubes.</li>
	<li>Place the DI water filled syringe on the computer-controlled syringe pump. Push the water (5-20 &#181;l/min) into the channel to fill the whole channel with fluid all the way to the reservoir.</li>
	<li>Load 10 &#181;l of balanced bead solution to the reservoir and introduce the bead solution to the micro-channel by changing the flow direction on syringe pump.</li>
	<li>Turn on the RTD by biasing 1 mA of DC current through the computer controlled source/meter while measuring the resistance by source/meter and sorting the measured data (Figure 2). 
	Note: During the experiment, the sensor is biased; therefore, the temperature is continuously measured until the end of the counting experiment. The RTD sensor is electrically biased by applying a DC current in the range from 100 &#181;A to 1 mA to continuously measure the temperature until the end of the counting experiment. It is critical to select the correct current level since there is a trade-off between noise level and the detected signal amplitude. The syringe pump is used to generate the flow in micro-channel. Selecting an appropriate flow rate to perform the TPD experiment is limited to the speed of the measurement. This speed is a function of the thermal time constant of the device and electrical measurement speed. The results of thermal particle detection experiment are shown in Figure 3.</li>
	<li>Use the developed data processing software (LabVIEW) to convert the measured resistance data to temperature using the Callendar&#8211;Van Dusen equation6.</li>
</ol>
2. Thermal Characterization of Liquid Substances Using a Micro-calorimeter
<ol>
	<li>In this process, use the on-chip calorimeter device (Figure 4A) 3 to measure the thermal diffusivity and the specific heat of the samples. 
	Note: On each die, there are 2 micro-calorimeter chambers (Figure 4B). Each chamber has 2 inlets and one outlet. And each chamber has a heater and a RTD sensor integrated.</li>
	<li>Place the micro-calorimeter device on the device holder (Figure 4C). Align the device to the microfluidic inlets and outlets with the holder fittings. Place the PDMS seal layer on top of the device.</li>
	<li>Install electrical connection pins on the device holder and lock the holder screws. 
	Note: Make sure the height-adjustable Pogo pins are aligned with the electrical contact pads.</li>
	<li>Install the microfluidic interface layer with magnetic latches to the device holder (Figure 4D). Connect the PTFE tubes to both inlets and the outlet. Connect one inlet to the sample-loaded syringe pump and close the other one, as the enthalpy is not measured in this case.</li>
	<li>Use a developed computer-controlled program to load the sample into the micro-channel and chambers. 
	Note: The program will use discontinued flow to release excessive pressure on the thin-film suspended chamber.
	<ol>
		<li>Load the 300 &#181;l sample into the glass syringe and place it on the syringe pump. Use very slow (0.25 &#181;l/min) constant flow rates for high viscosity samples (e.g., glycerol and ionic liquids). Use a glycerol sample for thermal diffusivity measurements and ionic liquids for specific heat measurements.</li>
	</ol>
	</li>
	<li>Measurements
	<ol>
		<li>Thermal diffusivity measurements
		<ol>
			<li>Connect the measurements setup as shown in Figure 5A. Load the glycerol sample to the micro-calorimeter chamber. Run the modified computer controlled program for heat penetration time measurement.</li>
			<li>Use the calibrated heat penetration equation to calculate thermal diffusivity from the measured heat penetration time7: 
			<img alt="Equation 1" src="/files/ftp_upload/52828/52828eq1.jpg" width="100" /> 
			where &#945; is thermal diffusivity, L is thickness of the chamber, p is the thickness calibration factor due to fabrication process variation, and t0 is heat penetration time.</li>
		</ol>
		</li>
		<li>Specific heat measurements
		<ol>
			<li>Use the TWA measurement setup as shown in Figure 5B. Use the same sample loading program and load the ionic liquid in the chamber. Run the TWA program to get the amplitude of the AC temperature fluctuations (&#8706;TAC) and use the specific heat equation to calculate the specific, cp, heat for each ionic liquid sample8: 
			<img alt="Equation 2" src="/files/ftp_upload/52828/52828eq2.jpg" width="117" /> 
			where C0 is input power calibration factor, Pin is input power, &#969; is frequency of the actuation signal, and m is the mass of liquid sample.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
3. Calorimetric Biochemical Detection in Paper-based Microfluidic Device
<ol>
	<li>Use microfabricated thin film (40-50 nm nickel) RTD sensor. Fabrication steps for the RTD sensor are explained in previous works4.</li>
	<li>For paper-based channel fabrication4, use a knife plotter to cut the paper microfluidic channels with a designed pattern (L-shape). Place the paper on top of the cutting mat, load the paper and the cutting mat to the knife plotter, and use the appropriate recipe to cut the microfluidic paper channels4.</li>
	<li>For device and channel integration, use an acrylic adhesive layer (5 &#181;m) to integrate the paper on the RTD sensor. Use a clean blade to push the paper to the device and remove air bubbles (Figure 6A). The acrylic film is an adhesive layer to hold the paper over RTD sensor.</li>
	<li>For enzyme activation, use 50 mM sodium acetate buffer to activate the GOD enzyme. Add 1 mg of the GOD enzyme to 1 ml of sodium acetate buffer to make the 1 mg/ml solution. Adjust the pH of the solution to 5.1. 
	Note: Adjust the amount of acetic acid in the sodium acetate buffer to maintain the PH of solution 5.1.</li>
	<li>Bias the RTD with 1 mA of DC current to activate the RTD and start measuring the resistance source/meter continuously while the resistance settles down after the experiment (~4 min). 
	Note: Figure 6B shows the measurement setup for the paper-based calorimetric test.</li>
	<li>Introduce the 2 &#181;l of the prepared GOD solution to the center of the paper micro-channel (immobilization site) via pipette. The detected temperature (Figure 7A) must start to decrease. 
	Note: This cooling effect is due to the higher operation temperature of the RTD and evaporation of the sample together.</li>
	<li>To measure the glucose concentration, introduce standard glucose control solution9 to the channel inlet and measure the resistance change caused by the reaction. Repeat this experiment with all different glucose control solutions (high, normal and low concentrations) and save the resistance data.</li>
	<li>Using the temperature coefficient of resistance (TCR) for nickel RTD and Callendar&#8211;Van Dusen equation, convert the resistance change to the temperature. Calculate the concentration of the glucose in each sample by considering the reaction enthalpy of glucose and the GOD enzyme (&#916;H = -80 kJ/mole) and using the concentration equation10: 
	<img alt="Equation 3" src="/files/ftp_upload/52828/52828eq3.jpg" width="83" /> 
	where np is detected molar concentration, Cp is heat capacity of the system and&#160;&#916;T is calculated temperature.</li>
</ol>

<ol>
	<li>Zhang, H., Chon, C., Pan, X., Li, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Methods+for+counting+particles+in+microfluidic+applications.">Methods for counting particles in microfluidic applications.</a> Microfluid Nanofluid. 7 (6), 739-749 (2009).</li><li>Vutha, A. K., Davaji, B., Lee, C. H., Walker, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+microfluidic+device+for+thermal+particle+detection.">A microfluidic device for thermal particle detection.</a> Microfluid Nanofluid. 17 (5), 871-878 (2014).</li><li>Davaji, B., Bak, H. J., Chang, W. J., Lee, C. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Novel+On-chip+Three-dimensional+Micromachined+Calorimeter+with+Fully+Enclosed+and+Suspended+Thin-film+Chamber+for+Thermal+Characterization+of+Liquid+Samples.">A Novel On-chip Three-dimensional Micromachined Calorimeter with Fully Enclosed and Suspended Thin-film Chamber for Thermal Characterization of Liquid Samples.</a> Biomicrofluidics. 8 (3), 034101-034113 (2014).</li><li>Davaji, B., Lee, C. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+paper-based+calorimetric+microfluidics+platform+for+bio-chemical+sensing.">A paper-based calorimetric microfluidics platform for bio-chemical sensing.</a> Biosens. Bioelectron. 59, 120-126 (2014).</li><li>Liu, J., 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=Process+research+of+high+aspect+ratio+microstructure+using+SU-8+resist.">Process research of high aspect ratio microstructure using SU-8 resist.</a> Microsystem Technologies. 10, 265-268 (2004).</li><li>Dusen, M. S. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Platinum-resistance+thermometry+at+low+temperatures.">Platinum-resistance thermometry at low temperatures.</a> J. Am. Chem. Soc. 47 (2), 326-332 (1925).</li><li>Arpaci, V. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Conduction Heat Transfer. , (1966).</li><li>Garden, J. L., Chteau, E., Chaussy, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Highly+sensitive+ac+nanocalorimeter+for+microliter-scale+liquids+or+biological+samples.">Highly sensitive ac nanocalorimeter for microliter-scale liquids or biological samples.</a> Appl. Phys. Lett. 84, 3597-3599 (2004).</li><li>Kilo, C., 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=Evaluation+of+a+New+Blood+Glucose+Monitoring+System+with+Auto-Calibration.">Evaluation of a New Blood Glucose Monitoring System with Auto-Calibration.</a> Diabetes Technol. Ther. 7 (2), 283-294 (2005).</li><li>Scheper, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Thermal Biosensors Bioactivity Bioaffinity (Advances in Biochemical Engineering/Biotechnology). , (1999).</li></ol>

No conflicts of interest declared.

Different thermal measurement techniques in microfluidic devices and their respective setup procedures are presented in this work. These thermal measurement methods such as thermal conductivity monitoring, thermal penetration time, amplitude of AC thermal fluctuations, and amplitude measurement of the generated heat are used to detect specific substances and investigate different reactions and interactions. 
The thermal time constant plays a key role in the aforementioned thermal measurement t...

Three different micro-scale thermal measurement techniques are presented in this article. The three different configurations of microfluidic devices are used for thermal particle detection (TPD), thermal characterization (thermal conductivity and specific heat), and calorimetric detection of chemical reactions and interactions.
Thermal Particle Detection
Detecting and counting particles in microfluidic devices is widely used for environmental, industrial, and biological applications1. TPD is one of the novel applications of thermal measurements in microfluidic devices2. Using heat transfer for detecting and counting particles based on the particle size reduces the complexity, cost, and size of the system. In other methods, complex optics or complex electrical measurements and advanced signal processing software are used for detecting particles.
Thermal Characterization of Liquid Substances Using Micro-Calorimeter
Liquid sample thermal characterization is the second application of thermal measurement in microfluidic devices. Performing micro-scale calorimetry will reduce the sample consumption and increase the precision by offering higher repeatability compared to conventional, bulk calorimetry methods. The procedures for thermal conductivity and specific heat measurement using the on-chip micro-calorimeter device are presented elsewhere3. The details of the heat penetration time technique for thermal conductivity measurement and the thermal wave analysis (TWA) for specific heat measurements in microfluidic devices are described in the protocol section.
Calorimetric Bio-Chemical Detection in Paper-Based Microfluidic Device
Another application of thermal measurement is biochemical detection in paper-based microfluidics. The capillary action in the porous structure of paper carries the liquid and avoids bubble initiation problems in micro-channels. The most common detection mechanisms in paper-based microfluidic devices are optical or electrochemical techniques. Optical detection suffers from high complexity and the necessity of advanced image processing software to quantize the detected signal. Electrochemical detections are also limited because they can only be applied to reactions that produce active byproducts. The recently introduced calorimetric paper-based biochemical sensor platform4 takes advantage of the paper-based microfluidic system and the label-free thermal detection mechanism. The procedures of calorimetric detection of glucose using glucose oxidase (GOD) enzyme in a paper-based microfluidic platform are presented in the protocol section.
The goal of this paper is to demonstrate the capabilities of thermal measurement techniques in microfluidic devices. The device preparation, liquid sample handling and resistance temperature detector (RTD) sensor excitation and measurement are presented in the next sections.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Polydimethylsiloxane (PDMS)&#160;</td>
			<td>Dow Corning</td>
			<td>Sylgard 184</td>
			<td></td>
		</tr>
		<tr>
			<td>PS beads - 90 um&#160;</td>
			<td>Corpuscular</td>
			<td>100265</td>
			<td></td>
		</tr>
		<tr>
			<td>PS beads - 200 um&#160;</td>
			<td>Corpuscular</td>
			<td>100271</td>
			<td></td>
		</tr>
		<tr>
			<td>Glycerol</td>
			<td>SigmaAldrich</td>
			<td>G5516</td>
			<td></td>
		</tr>
		<tr>
			<td>GOD enzyme</td>
			<td>SigmaAldrich</td>
			<td>G7141</td>
			<td></td>
		</tr>
		<tr>
			<td>Glucose Control Solution-Low</td>
			<td>Bayer contour</td>
			<td>Low Control</td>
			<td></td>
		</tr>
		<tr>
			<td>Glucose Control Solution-Normal</td>
			<td>Bayer contour</td>
			<td>Normal Control</td>
			<td></td>
		</tr>
		<tr>
			<td>Glucose Control Solution-High</td>
			<td>Bayer contour</td>
			<td>High Control</td>
			<td></td>
		</tr>
		<tr>
			<td>Chromatography filter paper</td>
			<td>Whatman</td>
			<td>3001-845</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass</td>
			<td>VWR&#160;</td>
			<td>48393-106</td>
			<td></td>
		</tr>
		<tr>
			<td>Acrylic Film</td>
			<td>Nitto Denko</td>
			<td>5600</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass syringe (1 mL)</td>
			<td>Hamilton</td>
			<td>1001</td>
			<td></td>
		</tr>
		<tr>
			<td>Syringe pump</td>
			<td>New Era</td>
			<td>NE-500</td>
			<td></td>
		</tr>
		<tr>
			<td>knife plotter</td>
			<td>Silhouette</td>
			<td>portrait</td>
			<td></td>
		</tr>
		<tr>
			<td>Current Preamplifier</td>
			<td>Stanford Research</td>
			<td>SR-570</td>
			<td></td>
		</tr>
		<tr>
			<td>Ocilloscope</td>
			<td>Agilent</td>
			<td>DSO 2420A</td>
			<td></td>
		</tr>
		<tr>
			<td>Signal Generator</td>
			<td>HP</td>
			<td>HP3324A</td>
			<td></td>
		</tr>
		<tr>
			<td>Lock-in Amplifire</td>
			<td>Stanford Research</td>
			<td>SRS-830</td>
			<td></td>
		</tr>
		<tr>
			<td>Source/meter 2400</td>
			<td>Keithley</td>
			<td>2400</td>
			<td></td>
		</tr>
		<tr>
			<td>Source/meter 2600</td>
			<td>Keithley</td>
			<td>2436A</td>
			<td></td>
		</tr>
	</tbody>
</table>

thermal measurement techniques in analytical microfluidic devices

Thermal measurement techniques have been used for many applications such as thermal characterization of materials and chemical reaction detection. Micromachining techniques allow reduction of the thermal mass of fabricated structures and introduce the possibility to perform high sensitivity thermal measurements in the micro-scale and nano-scale devices. Combining thermal measurement techniques with microfluidic devices allows performing different analytical measurements with low sample consumption and reduced measurement time by integrating the miniaturized system on a single chip. The procedures of thermal measurement techniques for particle detection, material characterization, and chemical detection are introduced in this paper.

Figure 3 shows the plot of the measured thermal signal. The generated signals in the presence of the beads with corresponding optical images show the successful detection of the microsphere PS beads in the micro-channel. The thermal conductivity of the liquid passing through the micro-channel is changing due to the presence of PS beads. This change in the thermal conductivity of the channel is affecting the heat transfer in the micro-channel. The change in the heat transfer in the micro-channel is detect...

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Thermal Measurement Techniques in Analytical Microfluidic Devices

Here, we present three protocols for thermal measurements in microfluidic devices.

Thermal measurement techniques have been used for many applications such as thermal characterization of materials and chemical reaction detection. ...

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9.5K Views.  Marquette University. Here, we present three protocols for thermal measurements in microfluidic devices. 

Video: Thermal Measurement Techniques in Analytical Microfluidic Devices

Characterization of Thermal Transport in One-dimensional Solid Materials

The TET (transient electro-thermal) technique is an effective approach developed to measure the thermal diffusivity of solid materials, including conductive, semi-conductive or nonconductive one-dimensional structures. This technique broadens the measurement scope of materials (conductive and nonconductive) and improves the accuracy and stability. If the sample (especially biomaterials, such as human head hair, spider silk, and silkworm silk) is not conductive, it will be coated with a gold layer to make it electronically conductive. The effect of parasitic conduction and radiative losses on the thermal diffusivity can be subtracted during data processing. Then the real thermal conductivity can be calculated with the given value of volume-based specific heat (&#961;cp), which can be obtained from calibration, noncontact photo-thermal technique or measuring the density and specific heat separately. In this work, human head hair samples are used to show how to set up the experiment, process the experimental data, and subtract the effect of parasitic conduction and radiative losses.

The TET (transient electro-thermal) technique is an effective approach developed to measure the thermal diffusivity of solid materials.

The TET (transient electro-thermal) technique is an effective approach developed to measure the thermal diffusivity of solid materials, including ...

Optical Trap Loading of Dielectric Microparticles In Air

We demonstrate a method to trap a selected dielectric microparticle in air using radiation pressure from a single-beam gradient optical trap. Randomly scattered dielectric microparticles adhered to a glass substrate are momentarily detached using ultrasonic vibrations generated by a piezoelectric transducer (PZT). Then, the optical beam focused on a selected particle lifts it up to the optical trap while the vibrationally excited microparticles fall back to the substrate. A particle may be trapped at the nominal focus of the trapping beam or at a position above the focus (referred to here as the levitation position) where gravity provides the restoring force. After the measurement, the trapped particle can be placed at a desired position on the substrate in a controlled manner. 
In this protocol, an experimental procedure for selective optical trap loading in air is outlined. First, the experimental setup is briefly introduced. Second, the design and fabrication of a PZT holder and a sample enclosure are illustrated in detail. The optical trap loading of a selected microparticle is then demonstrated with step-by-step instructions including sample preparation, launching into the trap, and use of electrostatic force to excite particle motion in the trap and measure charge. Finally, we present recorded particle trajectories of Brownian and ballistic motions of a trapped microparticle in air. These trajectories can be used to measure stiffness or to verify optical alignment through time domain and frequency domain analysis. Selective trap loading enables optical tweezers to track a particle and its changes over repeated trap loadings in a reversible manner, thereby enabling studies of particle-surface interaction.

A protocol for launching and stably trapping selected dielectric microparticles in air is presented.

We demonstrate a method to trap a selected dielectric microparticle in air using radiation pressure from a single-beam gradient optical trap. Randomly ...

Solvent Bonding for Fabrication of PMMA and COP Microfluidic Devices

Thermoplastic microfluidic devices offer many advantages over those made from silicone elastomers, but bonding procedures must be developed for each thermoplastic of interest. Solvent bonding is a simple and versatile method that can be used to fabricate devices from a variety of plastics. An appropriate solvent is added between two device layers to be bonded, and heat and pressure are applied to the device to facilitate the bonding. By using an appropriate combination of solvent, plastic, heat, and pressure, the device can be sealed with a high quality bond, characterized as having high bond coverage, bond strength, optical clarity, durability over time, and low deformation or damage to microfeature geometry. We describe the procedure for bonding devices made from two popular thermoplastics, poly(methyl-methacrylate) (PMMA), and cyclo-olefin polymer (COP), as well as a variety of methods to characterize the quality of the resulting bonds, and strategies to troubleshoot low quality bonds. These methods can be used to develop new solvent bonding protocols for other plastic-solvent systems.

Solvent bonding is a simple and versatile method for fabricating thermoplastic microfluidic devices with high quality bonds. We describe a protocol to achieve strong, optically clear bonds in PMMA and COP microfluidic devices that preserve microfeature details, by a judicious combination of pressure, temperature, an appropriate solvent, and device geometry.

Thermoplastic microfluidic devices offer many advantages over those made from silicone elastomers, but bonding procedures must be developed for each ...

Micro/Nano-scale Strain Distribution Measurement from Sampling Moir&#233; Fringes

This work describes the measurement procedure and principles of a sampling moir&#233; technique for full-field micro/nano-scale deformation measurements. The developed technique can be performed in two ways: using the reconstructed multiplication moir&#233; method or the spatial phase-shifting sampling moir&#233; method. When the specimen grid pitch is around 2 pixels, 2-pixel sampling moir&#233; fringes are generated to reconstruct a multiplication moir&#233; pattern for a deformation measurement. Both the displacement and strain sensitivities are twice as high as in the traditional scanning moir&#233; method in the same wide field of view. When the specimen grid pitch is around or greater than 3 pixels, multi-pixel sampling moir&#233; fringes are generated, and a spatial phase-shifting technique is combined for a full-field deformation measurement. The strain measurement accuracy is significantly improved, and automatic batch measurement is easily achievable. Both methods can measure the two-dimensional (2D) strain distributions from a single-shot grid image without rotating the specimen or scanning lines, as in traditional moir&#233; techniques. As examples, the 2D displacement and strain distributions, including the shear strains of two carbon fiber-reinforced plastic specimens, were measured in three-point bending tests. The proposed technique is expected to play an important role in the non-destructive quantitative evaluations of mechanical properties, crack occurrences, and residual stresses of a variety of materials.

Micro/Nano-scale Strain Distribution Measurement from Sampling Moir&amp;#233; Fringes

A sampling moir&#233; technique featuring 2-pixel and multi-pixel sampling methods for high-accuracy strain distribution measurements at the micro/nano-scale is presented here.

This work describes the measurement procedure and principles of a sampling moir&#233; technique for full-field micro/nano-scale deformation measurements. ...

Generation of Size-controlled Poly (ethylene Glycol) Diacrylate Droplets via Semi-3-Dimensional Flow Focusing Microfluidic Devices

Uniform and size-controllable poly (ethylene glycol) diacrylate (PEGDA) droplets could be produced via the flow focusing process in a microfluidic device. This paper proposes a semi-three-dimensional (semi-3D) flow-focusing microfluidic chip for droplet formation. The polydimethylsiloxane (PDMS) chip was fabricated using the multi-layer soft lithography method. Hexadecane containing surfactant was used as the continuous phase, and PEGDA with the ultraviolet (UV) photo-initiator was the dispersed phase. Surfactants allowed the local surface tension to drop and formed a more cusped tip which promoted breaking into tiny micro-droplets. As the pressure of dispersed phase was constant, the size of droplets became smaller with increasing continuous phase pressure before dispersed phase flow was broken off. As a result, droplets with size variation from 1 &#181;m to 80 &#181;m in diameter could be selectively achieved by changing the pressure ratio in two inlet channels, and the average coefficient of variation was estimated to be below 7%. Furthermore, droplets could turn into micro-beads by UV exposure for photo-polymerization. Conjugating biomolecules on such micro-beads surface have many potential applications in the fields of biology and chemistry.

Generation of Size-controlled Poly ethylene Glycol Diacrylate Droplets via Semi-3-Dimensional Flow Focusing Microfluidic Devices

Here, we present a protocol to illustrate the fabrication processes and verifying experiments of a semi-three-dimensional (semi-3D) flow-focusing microfluidic chip for droplet formation.

Uniform and size-controllable poly (ethylene glycol) diacrylate (PEGDA) droplets could be produced via the flow focusing process in a microfluidic device. ...

Simultaneous Measurement of Turbulence and Particle Kinematics Using Flow Imaging Techniques

Numerous problems in scientific and engineering fields involve understanding the kinematics of particles in turbulent flows, such as contaminants, marine micro-organisms, and/or sediments in the ocean, or fluidized bed reactors and combustion processes in engineered systems. In order to study the effect of turbulence on the kinematics of particles in such flows, simultaneous measurements of both the flow and particle kinematics are required. Non-intrusive, optical flow measurement techniques for measuring turbulence, or for tracking particles, exist but measuring both simultaneously can be challenging due to interference between the techniques. The method presented herein provides a low cost and relatively simple method to make simultaneous measurements of the flow and particle kinematics. A cross section of the flow is measured using a particle image velocimetry (PIV) technique, which provides two components of velocity in the measurement plane. This technique utilizes a pulsed-laser for illumination of the seeded flow field that is imaged by a digital camera. The particle kinematics are simultaneously imaged using a light emitting diode (LED) line light that illuminates a planar cross section of the flow that overlaps with the PIV field-of-view (FOV). The line light is of low enough power that it does not affect the PIV measurements, but powerful enough to illuminate the larger particles of interest imaged using the high-speed camera. High-speed images that contain the laser pulses from the PIV technique are easily filtered by examining the summed intensity level of each high-speed image. By making the frame rate of the high-speed camera incommensurate with that of the PIV camera frame rate, the number of contaminated frames in the high-speed time series can be minimized. The technique is suitable for mean flows that are predominantly two-dimensional, contain particles that are at least 5 times the mean diameter of the PIV seeding tracers, and are low in concentration.

The technique described herein offers a low cost and relatively simple method to simultaneously measure particle kinematics and turbulence in flows with low particle concentrations. The turbulence is measured using particle image velocimetry (PIV), and particle kinematics are calculated from images obtained with a high-speed camera in an overlapping field-of-view.

Numerous problems in scientific and engineering fields involve understanding the kinematics of particles in turbulent flows, such as contaminants, marine ...

Method Development for Contactless Resonant Cavity Dielectric Spectroscopic Studies of Cellulosic Paper

The current analytical techniques for characterizing printing and graphic arts substrates are largely ex situ and destructive. This limits the amount of data that can be obtained from an individual sample and renders it difficult to produce statistically relevant data for unique and rare materials. Resonant cavity dielectric spectroscopy is a non-destructive, contactless technique which can simultaneously interrogate both sides of a sheeted material and provide measurements which are suitable for statistical interpretations. This offers analysts the ability to quickly discriminate between sheeted materials based on composition and storage history. In this methodology article, we demonstrate how contactless resonant cavity dielectric spectroscopy may be used to differentiate between paper analytes of varying fiber species compositions, to determine the relative age of the paper, and to detect and quantify the amount of post-consumer waste (PCW) recycled fiber content in manufactured office paper.

A protocol for the non-destructive analysis of the fiber content and relative age of paper.

The current analytical techniques for characterizing printing and graphic arts substrates are largely ex situ and destructive. This limits the amount of ...

Fabrication of Nanoheight Channels Incorporating Surface Acoustic Wave Actuation via Lithium Niobate for Acoustic Nanofluidics

Controlled nanoscale manipulation of fluids is known to be exceptionally difficult due to the dominance of surface and viscous forces. Megahertz-order surface acoustic wave (SAW) devices generate tremendous acceleration on their surface, up to 108 m/s2, in turn responsible for many of the observed effects that have come to define acoustofluidics: acoustic streaming and acoustic radiation forces. These effects have been used for particle, cell, and fluid manipulation at the microscale, although more recently SAW has been used to produce similar phenomena at the nanoscale through an entirely different set of mechanisms. Controllable nanoscale fluid manipulation offers a broad range of opportunities in ultrafast fluid pumping and biomacromolecule dynamics useful for physical and biological applications. Here, we demonstrate nanoscale-height channel fabrication via room-temperature lithium niobate (LN) bonding integrated with a SAW device. We describe the entire experimental process including nano-height channel fabrication via dry etching, plasma-activated bonding on lithium niobate, the appropriate optical setup for subsequent imaging, and SAW actuation. We show representative results for fluid capillary filling and fluid draining in a nanoscale channel induced by SAW. This procedure offers a practical protocol for nanoscale channel fabrication and integration with SAW devices useful to build upon for future nanofluidics applications.

We demonstrate fabrication of nanoheight channels with the integration of surface acoustic wave actuation devices upon lithium niobate for acoustic nanofluidics via liftoff photolithography, nano-depth reactive ion etching, and room-temperature plasma surface-activated multilayer bonding of single-crystal lithium niobate, a process similarly useful for bonding lithium niobate to oxides.

Controlled nanoscale manipulation of fluids is known to be exceptionally difficult due to the dominance of surface and viscous forces. Megahertz-order ...

In Situ Surface Temperature Measurement in a Conveyor Belt Furnace via Inline Infrared Thermography

Measuring the surface temperature of objects that are processed in conveyor belt furnaces is an important tool in process control and quality assurance. Currently, the surface temperature of objects processed in conveyor belt furnaces is typically measured via thermocouples. However, infrared (IR) thermography presents multiple advantages compared to thermocouple measurements, as it is a contactless, real-time, and spatially resolved method. Here, as a representative proof-of-concept example, an inline thermography system is successfully installed into an IR lamp powered solar firing furnace, which is used for the contact firing process of industrial Si solar cells. This protocol describes how to install an IR camera into a conveyor belt furnace, conduct a customer correction of a factory calibrated IR camera, and perform the evaluation of spatial surface temperature distribution on a target object.

This protocol describes how to install an infrared camera into a conveyor belt furnace, conduct a customer correction of a factory calibrated IR camera, and evaluate the spatial surface temperature distribution of an object of interest. The example objects are industrial silicon solar cells.

Measuring the surface temperature of objects that are processed in conveyor belt furnaces is an important tool in process control and quality assurance. ...

Microfluidic Fabrication Techniques for High-Pressure Testing of Microscale Supercritical CO2 Foam Transport in Fractured Unconventional Reservoirs

Pressure limitations of many microfluidic platforms have been a significant challenge in microfluidic experimental studies of fractured media. As a result, these platforms have not been fully exploited for direct observation of high-pressure transport in fractures. This work introduces microfluidic platforms that enable direct observation of multiphase flow in devices featuring surrogate permeable media and fractured systems. Such platforms provide a pathway to address important and timely questions such as those related to CO2 capture, utilization and storage. This work provides a detailed description of the fabrication techniques and an experimental setup that may serve to analyze the behavior of supercritical CO2 (scCO2) foam, its structure and stability. Such studies provide important insights regarding enhanced oil recovery processes and the role of hydraulic fractures in resource recovery from unconventional reservoirs. This work presents a comparative study of microfluidic devices developed using two different techniques: photolithography/wet-etching/thermal-bonding versus Selective Laser-induced Etching. Both techniques result in devices that are chemically and physically resistant and tolerant of high pressure and temperature conditions that correspond to subsurface systems of interest. Both techniques provide pathways to high-precision etched microchannels and capable lab-on-chip devices. Photolithography/wet-etching, however, enables fabrication of complex channel networks with complex geometries, which would be a challenging task for laser etching techniques. This work summarizes a step-by-step photolithography, wet-etching and glass thermal-bonding protocol and, presents representative observations of foam transport with relevance to oil recovery from unconventional tight and shale formations. Finally, this work describes the use of a high-resolution monochromatic sensor to observe scCO2 foam behavior where the entirety of the permeable medium is observed simultaneously while preserving the resolution needed to resolve features as small as 10 &#181;m.

Microfluidic Fabrication Techniques for High-Pressure Testing of Microscale Supercritical CO2 Foam Transport in Fractured Unconventional Reservoirs

This paper describes a protocol along with a comparative study of two microfluidic fabrication techniques, namely photolithography/wet-etching/thermal-bonding and Selective Laser-induced Etching (SLE), that are suitable for high-pressure conditions. These techniques constitute enabling platforms for direct observation of fluid flow in surrogate permeable media and fractured systems under reservoir conditions.

Pressure limitations of many microfluidic platforms have been a significant challenge in microfluidic experimental studies of fractured media. As a ...