Thanks to Wendy Zhang, Luuk Lubbers, Marc Miskin and Michelle Driscoll for many useful discussions and Qiti Guo for help with preparing experimental samples. This work was supported by the National Science Foundation&#39;s MRSEC program under Grant No. DMR-0820054.

1. Fast Imaging Setup (See Figure 1)
<ol>
	<li>Start by setting up a vertical track along which a container filled with the fluid to be studied can be freely moved to adjust the impact velocity. The fluid leaves the bottom of the container through a nozzle and then enters free fall. For this work the falling height was varied from 1-200 cm to give an impact velocity V0 = (0.4-6.3)&#177;0.15 m/sec.</li>
	<li>Construct and mount a frame to hold the horizontal impact plane, typically a glass plate, under which an inclined reflective mirror is positioned for visualizing the drop impact from the bottom.</li>
	<li>Place a clean and smooth glass plate onto the holder. Make sure the plate is leveled horizontally.</li>
	<li>Mount a syringe pump onto the vertical track.</li>
	<li>For liquid metal impact, place a transparent paper diffuser behind the nozzle for side-view imaging. At the same time, attach a white opaque paper above the syringe pump to generate reflection for bottom viewing (see Figure 1). Then, locate the light source behind the nozzle.</li>
	<li>For dense suspension impact, no diffuser is needed. Instead, just place the light source in front of the imaging plane.</li>
	<li>Select the macro lens with an appropriate focal length for desired magnification and optical working distance. Then, connect the lens to the camera.</li>
	<li>Mount the camera onto a tripod and adjust the height of camera according to the imaging perspective (side or bottom).</li>
</ol>
2. Sample Preparation
<ol>
	<li>Preparation of oxidized liquid metal
	<ol>
		<li>Store Gallium-Indium Eutectic (eGaIn) in a sealed container. Since its melting temperature is about 15 &#176;C, eGaIn stays in a liquid state at room temperature.</li>
		<li>Use a pipette to extract 3 ml eGaIn from the container and extrude it onto an acrylic plate. Wait 30 min for the sample to be fully oxidized in air. As a consequence, a thin layer of wrinkled oxidized skin completely covers the sample surface.</li>
		<li>Use hydrochloric acid (HCl; &#34;CAUTION&#34;) of different concentrations to prewash the eGaIn sample and to control the surface oxidation. Specifically, shear the sample, while it is in the acid bath, at 60 sec-1 shear rate with a rheometer. After 10 min of shear, the level of surface oxidation in the sample reaches equilibrium, set by the HCl concentration15,18.</li>
		<li>After this prewash, use a plastic syringe with a steel nozzle tip to extract eGaIn from the bath.</li>
		<li>Mount the syringe onto the syringe pump and be ready for the experiment.</li>
	</ol>
	</li>
	<li>Preparation of dense suspensions
	<ol>
		<li>Cut off the end of a commercial syringe (4.5 mm or 2.3 mm in radius) and use it as cylindrical tube for dispensing the dense suspension.</li>
		<li>Pull back the piston and fill the syringe with water all the way to the open end, making sure there is no air bubble entrained.</li>
		<li>Put spherical ZrO2 or glass beads into the syringe. With the sedimentation of particles, water will spill out from the nozzle. Fill the syringe with particles all the way to the open end. The suspension will jam under gravity.</li>
		<li>Use a razor blade to remove extra wetted particles from the top to keep that end flat.</li>
		<li>Flip over the nozzle and mount it onto the syringe pump. Surface tension will prevent the particles from falling out16.</li>
	</ol>
	</li>
</ol>
3. Calibration
Before collecting videos, the parameters of the imaging device have to be set and lighting alignment has to be completed. Also, the spatial resolution needs to be calibrated.
<ol>
	<li>Start the syringe pump at a speed of 20 ml/hr to push out the fluid (liquid metal or suspension) from the nozzle.</li>
	<li>Wait for the fluid to detach from the syringe, form a drop and fall off to make a test impact onto the glass substrate.</li>
	<li>Adjust the camera position, including its vertical position and imaging orientation, to find the splat in the computer monitor that connects to the camera. Modify the working distance to arrange the image to be in the focal plane when the reproduction ratio of the lens is fixed at 1:1.</li>
	<li>Vary the aperture size, exposure time and lighting angle to obtain the best image quality when the frame rate is high enough (&#62;6,000 fps). Figure 2(a) shows typical images taken by the camera for both liquid eGaIn and a dense suspension.</li>
	<li>Place a ruler in the field of view (see Figure 2(b)) and calculate the spatial resolution by counting how many pixels fit across 1 cm. Make sure there is no difference in resolution between horizontal and vertical directions.</li>
	<li>Follow a 3-step process to measure the packing fraction of dense suspension drop:
	<ol>
		<li>Measure the mass of the entire splat right after impact (e.g.&#160;by letting the drop fall into a measuring cup that can be weighed accurately).</li>
		<li>Then, evaporate all solvent with a heater and weigh the splat again to obtain the particle mass.</li>
		<li>Calculate the volume of particles and liquid to get the packing fraction. Typically, this volume fraction should be around 60%.</li>
	</ol>
	</li>
	<li>According to the observation direction (bottom or side), position the camera appropriately. In particular, put the camera next to the substrate for the side view or on the same level of the reflective mirror for bottom imaging.</li>
</ol>
4. Video Recording and Data Acquisition
<ol>
	<li>After imaging calibration, restart the syringe pump. At the same time, open the camera controlling software to monitor the impact process.</li>
	<li>Set the post-triggering frame numbers at roughly half of the video length. Watch carefully when the drop starts to form and manually trigger the camera at the moment when drop detaches from the nozzle. Perform a few practice tests before data recording.</li>
	<li>After the data is recorded, trim down the video to the portion containing the impact and save the videos as image sequences for analysis.</li>
</ol>
5. Image Post-processing and Analysis
<ol>
	<li>Use a boundary detection method to locate the moving front of liquid eGaIn as it spreads, which corresponds to a sharp transition in the average pixel value (see Figures 3(a-b)).</li>
	<li>From both bottom and side images, determine the splashing onset of dense suspension.</li>
	<li>Perform particle-tracking algorithms to obtain traces of individual particles that escaped from the splat (see Figure 3(c)). Then, calculate the ejecting velocity from such trajectories (Figure 3(d)).</li>
</ol>

<ol>
	<li>Chiechi, R. C., Weiss, E. A., Dickey, M. D., Whitsides, 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=Eutectic+Gallium-Indium+(EGaIn):+A+moldable+Liquid+Metal+for+Electrical+Characterization+of+Self-Assembled+Monolayers.">Eutectic Gallium-Indium (EGaIn): A moldable Liquid Metal for Electrical Characterization of Self-Assembled Monolayers.</a> Angew. Chem. Int. Ed. 47, 142 (2008).</li><li>Fukumoto, M., Huang, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flattening+Mechanism+in+Thermal+Sprayed+Ni+Particles+Impinging+on+Flat+Substrate+Surface.">Flattening Mechanism in Thermal Sprayed Ni Particles Impinging on Flat Substrate Surface.</a> J. Thermal Spray Tech. 8, (1999).</li><li>Seerden, K. A., Reis, N., Evans, J. R., Grant, P. S., Halloran, J. W., Derby, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ink-Jet+Printing+of+Wax-Based+Alumina+Suspensions.">Ink-Jet Printing of Wax-Based Alumina Suspensions.</a> J. Am. Ceram. Soc. 84, 2514 (2004).</li><li>Derby, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inkjet+printing+ceramics:+From+drops+to+solid.">Inkjet printing ceramics: From drops to solid.</a> J. Eur. Ceram. Soc. 31, 2543 (2011).</li><li>Xu, L., Zhang, W. W., Nagel, S. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Drop+Splashing+on+a+Dry+Smooth+Surface.">Drop Splashing on a Dry Smooth Surface.</a> Phys. Rev. Lett. 94, (2005).</li><li>Clanet, C., Beguin, C., Richard, D., Quere, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Maximal+deformation+of+an+impacting+drop.">Maximal deformation of an impacting drop.</a> J. Fluid. Mech. 517, 199 (2004).</li><li>Yarin, A. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Drop+Impact+Dynamics:+Splashing+Spreading,+Receding,+Bouncing.">Drop Impact Dynamics: Splashing Spreading, Receding, Bouncing.</a> Annu. Rev. Fluid Mech. 38, 159 (2006).</li><li>Chandra, S., Avedisian, C. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+the+collision+of+a+droplet+with+a+solid+surface.">On the collision of a droplet with a solid surface.</a> Proc. R. Soc. Lond. A. 432, 13-41 (1991).</li><li>Versluis, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-speed+imaging+in+fluids.">High-speed imaging in fluids.</a> Exp. Fluids. 54, 1458 (2013).</li><li>Thoraval, M. -. J., Takehara, K., Etoh, T. G., Thoroddsen, S. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Drop+impact+entrapment+of+bubble+rings.">Drop impact entrapment of bubble rings.</a> J. Fluid Mech. 724, 234-258 (2013).</li><li>Thoroddsen, S. T., Takehara, K., Etoh, T. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Micro-splashing+by+drop+impacts.">Micro-splashing by drop impacts.</a> J. Fluid Mech. 706, 560-570 (2012).</li><li>Thoroddsen, S. T., Etoh, T. G., Takehara, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-speed+imaging+of+drops+and+bubble.">High-speed imaging of drops and bubble.</a> Ann. Rev. Fluid Mech. 40, 257-285 (2008).</li><li>Driscoll, M., Stevens, C. S., Nagel, S. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thin+film+formation+during+splashing+of+viscous+liquids.">Thin film formation during splashing of viscous liquids.</a> Phys. Rev. E. 82, (2010).</li><li>Pregent, S., Adams, S., Butler, M. F., Waigh, T. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+impact+and+deformation+of+a+viscoelastic+drop+at+the+air-liquid+interface.">The impact and deformation of a viscoelastic drop at the air-liquid interface.</a> J. Non-Newtonian Fluid Mech. 166, 831 (2011).</li><li>Xu, Q., Brown, E., Jaeger, H. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Impact+dynamics+of+oxidized+liquid+metal+drops.">Impact dynamics of oxidized liquid metal drops.</a> Phys. Rev. E. 87, (2013).</li><li>Peters, I. R., Xu, Q., Jaeger, H. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Splashing+onset+in+dense+suspension+droplets.">Splashing onset in dense suspension droplets.</a> Phys. Rev. Lett. 111, (2013).</li><li>Luu, L., Forterre, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Drop+impact+of+yield-stress+fluids.">Drop impact of yield-stress fluids.</a> J. Fluid Mech. 632, 301 (2009).</li><li>Xu, Q., Oudalov, N., Guo, Q., Jaeger, H., Brown, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+oxidation+on+the+mechanical+properties+of+liquid+gallium+and+eutectic+gallium-indium.">Effect of oxidation on the mechanical properties of liquid gallium and eutectic gallium-indium.</a> Phys. Fluids. 24, (2012).</li><li>Turitsyn, K. S., Lai, L., Zhang, W. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Asymmetric+Disconnection+of+an+Underwater+Air+Bubble:+Persistent+Neck+Vibrations+Evolve+into+a+smooth+Contact.">Asymmetric Disconnection of an Underwater Air Bubble: Persistent Neck Vibrations Evolve into a smooth Contact.</a> Phys. Rev. Lett. 103, (2009).</li><li>Miskin, M. Z., Jaeger, H. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Droplet+Formation+and+Scaling+in+Dense+Suspensions.">Droplet Formation and Scaling in Dense Suspensions.</a> Proc. Natl. Acad. Sci. U.S.A. 109, 4389-4394 (2012).</li><li>Royer, J. R., 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=Birth+and+growth+of+a+granular+jet.">Birth and growth of a granular jet.</a> Phys. Rev. E. 78, (2008).</li><li>Paulsen, J. D., Burton, J. C., Nagel, S. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Viscous+to+Inertial+Crossover+in+Liquid+Drop+Coalescence.">Viscous to Inertial Crossover in Liquid Drop Coalescence.</a> Phys. Rev. Lett. 106, (2011).</li></ol>

The authors have&#160;nothing to disclose.

Several steps are critical for proper execution of the fast imaging. First, camera and lens have to be appropriately set up and calibrated. In particular, in order to get high spatial resolution, the reproduction ratio of the lens must be kept close to 1:1. This is especially important for the visualization of dense suspensions. Also, the aperture size needs to be carefully chosen for imaging. For instance, observation from the side in general requires a longer depth of field, therefore smaller aperture size. To maintain...

Drop impact onto a solid surface is a key process in many applications involving electronic fabrication1, spray coating2, and additive manufacturing using inkjet printing3,4, where a precise control of drop spreading and splashing is desired. However, direct observation of drop impact is technically challenging for two reasons. First, it is an intricate dynamic process that occurs within a timescale too short (~100 &#181;sec) to be imaged easily by conventional imaging systems, such as optical microscopes and DSLR cameras. Flash photography can of course image much faster, but does not allow for continuous recording, as required for detailed analysis of the evolution with time. Second, the length scale induced by impact instabilities can be as small as 10 &#181;m&#160;5. Therefore, to quantitatively study the impact process a system that combines ultrafast imaging along with reasonably high spatial resolution is often desired. In the absence of such system, early work on droplet impact focused mostly on the global geometric deformation after impact6-8, but was unable to gather information about the early time, nonequilibrium processes associated with impact, such as the onset of splashing. Recent advances in CMOS high speed videography of fluids9,12 have pushed the frame rate up to one million fps and exposure times down below 1 &#181;sec. Furthermore, newly developed CCD imaging techniques can push the frame rate well above one million fps9-12. Spatial resolution on the other hand, can be increased to the order of 1 &#181;m/pixel using magnifying lenses12. As a consequence, it has become possible to explore in unprecedented detail the influence of a wide range of physical parameters on various stages of drop impact and to systematically compare experiment and theory5,13-16.&#160;For instance, the splashing transition in Newtonian fluids was found to be set by atmosphere pressure5,&#160;while the intrinsic rheology decides the spreading dynamics of yield-stress fluids17.
Here a simple yet powerful fast imaging technique is introduced and applied to study the impact dynamics of two types of non-Newtonian fluids: liquid metals and densely packed suspensions. With exposure to air, essentially all liquid metals (except mercury) will spontaneously develop an oxide skin on their surface. Mechanically, the skin is found to alter effective surface tension and wetting ability of the metals18.&#160;In a previous paper15, several of the authors studied the spreading process quantitatively and were able to explain how the skin effect influences the impact dynamics, especially the scaling of the maximum spreading radius with impact parameters. Since liquid metal has high surface reflectivity, careful adjustment of the lighting is required in the imaging. Suspensions are composed of small particles in a liquid. Even for simple Newtonian liquids, the addition of particles results in non-Newtonian behavior, which becomes especially pronounced in dense suspensions, i.e.&#160;at high volume fraction of suspended particles. Particularly, the onset of splashing when a suspension droplet hits a smooth, hard surface was studied in the previous work16.&#160;Both liquid-particle and inter-particle interactions can change the splashing behavior significantly from what might be expected from simple liquids. To track particles as small as 80 &#181;m in these experiments a high spatial resolution is needed.
A combination of various technical requirements such as high temporal and spatial resolution, plus the capability for observing impacts both from the side and from below, can all be satisfied with the imaging setup described here. By following a standard protocol, described below, the impact dynamics can be investigated in a controlled fashion, as shown explicitly for spreading and splashing behavior.

<table border="0" cellpadding="0" cellspacing="0" style="width:604px;" width="605">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Name of Material/ Equipment</td>
			<td style="width:103px;">Company</td>
			<td style="width:119px;">Catalog Number</td>
			<td style="width:167px;">Comments/Description</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Gallium-Indium Eutectic</td>
			<td>Sigma Aldrich</td>
			<td>495425-25G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Hydrochloric Acid&#160;</td>
			<td>Sigma Aldrich</td>
			<td>320331-2.5L</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Zirconium oxide</td>
			<td>Glen Mills Inc.</td>
			<td>7200</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Phantom V12 &#38; V7 Fast Ccamera</td>
			<td>Vision Research</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">105mm Micro-Nikon</td>
			<td>Nikon</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">12V/200W light Source</td>
			<td>Dedolight</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Syringe Pump</td>
			<td>RAZEL</td>
			<td>MODEL R9-9E</td>
			<td></td>
		</tr>
	</tbody>
</table>

fast imaging technique to study drop impact dynamics of non-newtonian fluids

In the field of fluid mechanics, many dynamical processes not only occur over a very short time interval but also require high spatial resolution for detailed observation, scenarios that make it challenging to observe with conventional imaging systems. One of these is the drop impact of liquids, which usually happens within one tenth of millisecond. To tackle this challenge, a fast imaging technique is introduced that combines a high-speed camera (capable of up to one million frames per second) with a macro lens with long working distance to bring the spatial resolution of the image down to 10 &#181;m/pixel. The imaging technique enables precise measurement of relevant fluid dynamic quantities, such as the flow field, the spreading distance and the splashing speed, from analysis of the recorded video. To demonstrate the capabilities of this visualization system, the impact dynamics when droplets of non-Newtonian fluids impinge on a flat hard surface are characterized. Two situations are considered: for oxidized liquid metal droplets we focus on the spreading behavior, and for densely packed suspensions we determine the onset of splashing. More generally, the combination of high temporal and spatial imaging resolution introduced here offers advantages for studying fast dynamics across a wide range of microscale phenomena.

The fast imaging technique can be used to quantify spreading and splashing for various impact scenarios. Figure 4(a), for instance, shows typical impact image sequences for liquid eGaIn with different oxide skin strength. By ejecting eGaIn from the same nozzle and at the same falling height, droplets with reproducible impact velocity V0 = 1.02&#177;0.12&#160;m/sec&#160;and radius R0 = 6.25&#177;0.10&#160;mm&#160;were generated. The left column shows the impact of an air-oxidized eGa...

Watch this Scientific Journal Video about Fast Imaging Technique to Study Drop Impact Dynamics of Non-Newtonian Fluids at JoVE.com

Fast Imaging Technique to Study Drop Impact Dynamics of Non-Newtonian Fluids

Drop impact of non-Newtonian fluids is a complex process since different physical parameters influence the dynamics over a very short time (less than one tenth of a millisecond). A fast imaging technique is introduced in order to characterize the impact behaviors of different non-Newtonian fluids.

In the field of fluid mechanics, many dynamical processes not only occur over a very short time interval but also require high spatial resolution for ...

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12.2K Views.  The University of Chicago. Drop impact of non-Newtonian fluids is a complex process since different physical parameters influence the dynamics over a very short time (less than one tenth of a millisecond). A fast imaging technique is introduced in order to characterize the impact behaviors of different non-Newtonian fluids.

Video: Fast Imaging Technique to Study Drop Impact Dynamics of Non-Newtonian Fluids

Experimental Measurement of Settling Velocity of Spherical Particles in Unconfined and Confined Surfactant-based Shear Thinning Viscoelastic Fluids

An experimental study is performed to measure the terminal settling velocities of spherical particles in surfactant based shear thinning viscoelastic (VES) fluids. The measurements are made for particles settling in unbounded fluids&#160;and fluids between parallel walls. VES fluids over a wide range of rheological properties are prepared and rheologically characterized. The rheological characterization involves steady shear-viscosity and dynamic oscillatory-shear measurements to quantify the viscous and elastic properties respectively. The settling velocities under unbounded conditions are measured in beakers having diameters at least 25x the diameter of particles. For measuring settling velocities between parallel walls, two experimental cells with different wall spacing are constructed. Spherical particles of varying sizes are gently dropped in the fluids and allowed to settle. The process is recorded with a high resolution video camera and the trajectory of the particle is recorded using image analysis software. Terminal settling velocities are calculated from the data.
The impact of elasticity on settling velocity in unbounded fluids is quantified by comparing the experimental settling velocity to the settling velocity calculated by the inelastic drag predictions of Renaud et al.1&#160;Results show that elasticity of fluids can increase or decrease the settling velocity. The magnitude of reduction/increase is a function of the rheological properties of the fluids and properties of particles. Confining walls are observed to cause a retardation effect on settling and the retardation is measured in terms of wall factors.

This paper demonstrates the experimental procedure to measure terminal settling velocities of spherical particles in surfactant-based shear thinning viscoelastic fluids. Fluids over a wide range of rheological properties are prepared and settling velocities are measured for a range of particle sizes in unbounded fluids and fluids between parallel walls.

An experimental study is performed to measure the terminal settling velocities of spherical particles in surfactant based shear thinning viscoelastic ...

Time Multiplexing Super Resolving Technique for Imaging from a Moving Platform

We propose a method for increasing the resolution of an object and overcoming the diffraction limit of an optical system installed on top of a moving imaging system, such as an airborne platform or satellite. The resolution improvement is obtained in a two-step process. First, three low resolution differently defocused images are being captured and the optical phase is retrieved using an improved iterative Gerchberg-Saxton based algorithm. The phase retrieval allows to numerically back propagate the field to the aperture plane. Second, the imaging system is shifted and the first step is repeated. The obtained optical fields at the aperture plane are combined and a synthetically increased lens aperture is generated along the direction of movement, yielding higher imaging resolution. The method resembles a well-known approach from the microwave regime called the Synthetic Aperture Radar (SAR) in which the antenna size is synthetically increased along the platform propagation direction. The proposed method is demonstrated through laboratory experiment.

A method for overcoming the optical diffraction limit is presented. The method includes a two-step process: optical phase retrieval using iterative Gerchberg-Saxton algorithm, and imaging system shifting followed by repetition of the first step. A synthetically increased lens aperture is generated along the direction of movement, yielding higher imaging resolution.

We propose a method for increasing the resolution of an object and overcoming the diffraction limit of an optical system installed on top of a moving ...

Fabrication of Uniform Nanoscale Cavities via Silicon Direct Wafer Bonding

Measurements of the heat capacity and superfluid fraction of confined 4He have been performed near the lambda transition using lithographically patterned and bonded silicon wafers. Unlike confinements in porous materials often used for these types of experiments3, bonded wafers provide predesigned uniform spaces for confinement. The geometry of each cell is well known, which removes a large source of ambiguity in the interpretation of data.
Exceptionally flat, 5 cm diameter, 375 &#181;m thick Si wafers with about 1 &#181;m variation over the entire wafer can be obtained commercially (from Semiconductor Processing Company, for example). Thermal oxide is grown on the wafers to define the confinement dimension in the z-direction. A pattern is then etched in the oxide using lithographic techniques so as to create a desired enclosure upon bonding. A hole is drilled in one of the wafers (the top) to allow for the introduction of the liquid to be measured. The wafers are cleaned2 in RCA solutions and then put in a microclean chamber where they are rinsed with deionized water4. The wafers are bonded at RT and then annealed at ~1,100 &#176;C. This forms a strong and permanent bond. This process can be used to make uniform enclosures for measuring thermal and hydrodynamic properties of confined liquids from the nanometer to the micrometer scale.

A method for permanently bonding two silicon wafers so as to realize a uniform enclosure is described. This includes wafer preparation, cleaning, RT bonding, and annealing processes. The resulting bonded wafers (cells) have uniformity of enclosure ~1%1,2. The resulting geometry allows for measurements of confined liquids and gasses.

Measurements of the heat capacity and superfluid fraction of confined 4He have been performed near the lambda transition using lithographically patterned ...

The Preparation of Electrohydrodynamic Bridges from Polar Dielectric Liquids

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

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

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

Use of a Multi-compartment Dynamic Single Enzyme Phantom for Studies of Hyperpolarized Magnetic Resonance Agents

Imaging of hyperpolarized substrates by magnetic resonance shows great clinical promise for assessment of critical biochemical processes in real time. Due to fundamental constraints imposed by the hyperpolarized state, exotic imaging and reconstruction techniques are commonly used. A practical system for characterization of dynamic, multi-spectral imaging methods is critically needed. Such a system must reproducibly recapitulate the relevant chemical dynamics of normal and pathological tissues. The most widely utilized substrate to date is hyperpolarized [1-13C]-pyruvate for assessment of cancer metabolism. We describe an enzyme-based phantom system that mediates the conversion of pyruvate to lactate. The reaction is initiated by injection of the hyperpolarized agent into multiple chambers within the phantom, each of which contains varying concentrations of reagents that control the reaction rate. Multiple compartments are necessary to ensure that imaging sequences faithfully capture the spatial and metabolic heterogeneity of tissue. This system will aid the development and validation of advanced imaging strategies by providing chemical dynamics that are not available from conventional phantoms, as well as control and reproducibility that is not possible in vivo.

A multi-compartment dynamic phantom is used to simulate some biology of interest for metabolic studies using hyperpolarized magnet resonance agents.

Imaging of hyperpolarized substrates by magnetic resonance shows great clinical promise for assessment of critical biochemical processes in real time. Due ...

Emission Spectroscopic Boundary Layer Investigation during Ablative Material Testing in Plasmatron

Ablative Thermal Protection Systems (TPS) allowed the first humans to safely return to Earth from the moon and are still considered as the only solution for future high-speed reentry missions. But despite the advancements made since Apollo, heat flux prediction remains an imperfect science and engineers resort to safety factors to determine the TPS thickness. This goes at the expense of embarked payload, hampering, for example, sample return missions. 
Ground testing in plasma wind-tunnels is currently the only affordable possibility for both material qualification and validation of material response codes. The subsonic 1.2MW Inductively Coupled Plasmatron facility at the von Karman Institute for Fluid Dynamics is able to reproduce a wide range of reentry environments. This protocol describes a procedure for the study of the gas/surface interaction on ablative materials in high enthalpy flows and presents sample results of a non-pyrolyzing, ablating carbon fiber precursor. With this publication, the authors envisage the definition of a standard procedure, facilitating comparison with other laboratories and contributing to ongoing efforts to improve heat shield reliability and reduce design uncertainties.
The described core techniques are non-intrusive methods to track the material recession with a high-speed camera along with the chemistry in the reactive boundary layer, probed by emission spectroscopy. Although optical emission spectroscopy is limited to line-of-sight measurements and is further constrained to electronically excited atoms and molecules, its simplicity and broad applicability still make it the technique of choice for analysis of the reactive boundary layer. Recession of the ablating sample further requires that the distance of the measurement location with respect to the surface is known at all times during the experiment. Calibration of the optical system of the applied three spectrometers allowed quantitative comparison. At the fiber scale, results from a post-test microscopy analysis are presented.

Development of new ablative materials and their numerical modeling requires extensive experimental investigation. This protocol describes procedures for material response characterization in plasma flows with the core techniques being non-intrusive methods to track the material recession along with the chemistry in the reactive boundary layer by emission spectroscopy.

Ablative Thermal Protection Systems (TPS) allowed the first humans to safely return to Earth from the moon and are still considered as the only solution ...

Dynamic Pore-scale Reservoir-condition Imaging of Reaction in Carbonates Using Synchrotron Fast Tomography

Underground storage permanence is a major concern for carbon capture and storage. Pumping CO2 into carbonate reservoirs has the potential to dissolve geologic seals and allow CO2 to escape. However, the dissolution processes at reservoir conditions are poorly understood. Thus, time-resolved experiments are needed to observe and predict the nature and rate of dissolution at the pore scale. Synchrotron fast tomography is a method of taking high-resolution time-resolved images of complex pore structures much more quickly than traditional &#181;-CT. The Diamond Lightsource Pink Beam was used to dynamically image dissolution of limestone in the presence of CO2-saturated brine at reservoir conditions. 100 scans were taken at a 6.1 &#181;m resolution over a period of 2 hours. The images were segmented and the porosity and permeability were measured using image analysis and network extraction. Porosity increased uniformly along the length of the sample; however, the rate of increase of both porosity and permeability slowed at later times.

Synchrotron fast tomography was used to dynamically image dissolution of limestone in the presence of CO2-saturated brine at reservoir conditions. 100 scans were taken at a 6.1 &#181;m resolution over a period of 2 h.

Underground storage permanence is a major concern for carbon capture and storage. Pumping CO2 into carbonate reservoirs has the potential to dissolve ...

Dielectric RheoSANS &#8212; Simultaneous Interrogation of Impedance, Rheology and Small Angle Neutron Scattering of Complex Fluids

A procedure for the operation of a new dielectric RheoSANS instrument capable of simultaneous interrogation of the electrical, mechanical and microstructural properties of complex fluids is presented. The instrument consists of a Couette geometry contained within a modified forced convection oven mounted on a commercial rheometer. This instrument is available for use on the small angle neutron scattering (SANS) beamlines at the National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR). The Couette geometry is machined to be transparent to neutrons and provides for measurement of the electrical properties and microstructural properties of a sample confined between titanium cylinders while the sample undergoes arbitrary deformation. Synchronization of these measurements is enabled through the use of a customizable program that monitors and controls the execution of predetermined experimental protocols. Described here is a protocol to perform a flow sweep experiment where the shear rate is logarithmically stepped from a maximum value to a minimum value holding at each step for a specified period of time while frequency dependent dielectric measurements are made. Representative results are shown from a sample consisting of a gel composed of carbon black aggregates dispersed in propylene carbonate. As the gel undergoes steady shear, the carbon black network is mechanically deformed, which causes an initial decrease in conductivity associated with the breaking of bonds comprising the carbon black network. However, at higher shear rates, the conductivity recovers associated with the onset of shear thickening. Overall, these results demonstrate the utility of the simultaneous measurement of the rheo-electro-microstructural properties of these suspensions using the dielectric RheoSANS geometry.

Here, we present a procedure for the measurement of simultaneous impedance, rheology and neutron scattering from soft matter materials under shear flow.

A procedure for the operation of a new dielectric RheoSANS instrument capable of simultaneous interrogation of the electrical, mechanical and ...

Measurements of Soil Carbon by Neutron-Gamma Analysis in Static and Scanning Modes

The herein described application of the inelastic neutron scattering (INS) method for soil carbon analysis is based on the registration and analysis of gamma rays created when neutrons interact with soil elements. The main parts of the INS system are a pulsed neutron generator, NaI(Tl) gamma detectors, split electronics to separate gamma spectra due to INS and thermo-neutron capture (TNC) processes, and software for gamma spectra acquisition and data processing. This method has several advantages over other methods in that it is a non-destructive in situ method that measures the average carbon content in large soil volumes, is negligibly impacted by local sharp changes in soil carbon, and can be used in stationary or scanning modes. The result of the INS method is the carbon content from a site with a footprint of ~2.5 - 3 m2 in the stationary regime, or the average carbon content of the traversed area in the scanning regime. The measurement range of the current INS system is &#62;1.5 carbon weight % (standard deviation &#177; 0.3 w%) in the upper 10 cm soil layer for a 1 hmeasurement.

Here, we present the protocol for in situ measurement of soil carbon using the neutron-gamma technique for single point measurements (static mode) or field averages (scanning mode). We also describe system construction and elaborate data treatment procedures.

The herein described application of the inelastic neutron scattering (INS) method for soil carbon analysis is based on the registration and analysis of ...

Film Control to Study Contributions of Waves to Droplet Impact Dynamics on Thin Flowing Liquid Films

Droplet impact is a very common phenomenon in nature and attracts attention due to its aesthetic fascination and wide-ranging applications. Previous studies on flowing liquid films have neglected the contributions of spatial structures of waves to the impact outcome, while this has recently been shown to have a significant influence on the drop impact dynamics. In this report, we outline a step-by-step procedure to investigate the effect of periodic inlet forcing of a flowing liquid film leading to the production of spatiotemporally regular wave structures on drop impact dynamics. A function generator in connection with a solenoid valve is used to excite these spatiotemporally regular wave structures on the film surface while the impact dynamics of uniform-sized droplets are captured using a high-speed camera. Three distinct regions are then studied; viz. the capillary wave region preceding the large wave peak, the flat film region, and the wave hump region. The effects of important dimensionless quantities such as film Reynolds, drop Weber and Ohnesorge numbers parameterized by the film flow rate, drop speed, and drop size are also examined. Our results show interesting, hitherto undiscovered dynamics brought about by this application of film inlet forcing of the flowing film for both low and high inertia drops.

A protocol to study the contributions of waves to droplet impact dynamics on flowing liquid films is presented.

Droplet impact is a very common phenomenon in nature and attracts attention due to its aesthetic fascination and wide-ranging applications. Previous ...