Name: dielectric rheosans — simultaneous interrogation of impedance, rheology and small angle neutron scattering of complex fluids
Uploaded: 2017-04-10T12:30:00.000+00:00
Duration: 7 min 51 s
Description: Watch this Scientific Journal Video about Dielectric RheoSANS â€” Simultaneous Interrogation of Impedance, Rheology and Small Angle Neutron Scattering of Complex Fluids at JoVE.com

The authors would like to acknowledge the NIST Center for Neutron Research CNS cooperative agreement number #70NANB12H239 grant for partial funding during this time period as well as the National Research Council for support. Certain commercial equipment, instruments, or materials are identified in this paper in order to specify the experimental procedure adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the materials or equipment identified are necessarily the best available for the purpose.

1. Mounting the Rheometer onto the SANS Beamline
NOTE: See Figure 1 for definitions of named components.
<ol>
	<li>Ensure that the power to the rheometer is off, the transducer is locked and the motor air bearing protector is installed. Turn off the neutron beam, and close the oven door.</li>
	<li>Install the large base plate onto the table, remove the snout, install the window, and secure the 4 eyelets to the mounting brackets on the rheometer&#39;s crane adapter such that the cables do not tangle and are not twisted.</li>
	<li>Using the crane, lift the rheometer and maneuver it from the rheometer table to rest centered on the table with the LCD screen of the rheometer facing outward, taking care to guide the cables to minimize tangling.</li>
	<li>Using the SANS control software, send the table to the minimum Z position.</li>
	<li>Remove the rheometers&#39; crane adapter and lift away from the platform using the crane.</li>
</ol>
2. Dielectric Cell Assembly
NOTE: See Figure 2 for definitions of named components.
<ol>
	<li>Ensure that the power to the rheometer is off, the transducer is locked and the motor air bearing protector is installed. Before use, clean the dielectric cup and bob assemblies using detergent solution followed by several deionized water rinses, and allow to fully dry.</li>
	<li>Open the oven door, unlock the transducer and remove the motor bearing lock. Mount the dielectric geometry and dielectric bob assembly onto the upper and lower tool mounts of the rheometer. Loosen both set screws on the dielectric geometry using a 2-mm Allen key and place the dielectric cup assembly so that it is mounted on the dielectric geometry.</li>
	<li>Using the rheometer control software, zero the gap from the sample geometry drop-down menu, and apply 10 N normal force using the axial force drop-down menu. Under compression, tighten screws using a 3-mm Allen key until the dielectric cup assembly is fully secured to the dielectric geometry.</li>
	<li>Set the gap to the measurement gap using the rheometer control software, and close the oven door. Ensure that the oven can fully enclose the dielectric cell with adequate vertical clearance on the top and bottom of the geometry. If a height adjustment is needed, adjust the set screw so that the oven enclosure fits with adequate tolerance around the dielectric cell. Adequate clearance is achieved when the dielectric geometry fits within the oven and can undergo a full revolution without touching the oven walls.</li>
	<li>Remove both the dielectric bob assembly and the dielectric cup assembly/dielectric geometry as one piece and replace with the rheometer alignment tool on the lower tool head.</li>
</ol>
3. Install the Slip Ring
NOTE: See Figure 3 for step-by-step pictorial summary.
<ol>
	<li>Install the wire baffle onto the shaft of the dielectric geometry and connect the dielectric cup connector to the slip ring connector.</li>
	<li>Hold the slip ring so that it is concentric with the shaft of the dielectric cup assembly/dielectric geometry but above the flange on the dielectric geometry. Place the slip ring adapters (x2) such that their nobs insert into the holes drilled into the dielectric geometry and their base rests on the dielectric geometry flange.</li>
	<li>Gently slide the slip ring over the slip ring adapters. The slip ring should slide effortlessly around the slip ring adapters holding them in place.</li>
</ol>
4. Alignment of the Rheometer
NOTE: See Figure 4 for schematic of beam path.
<ol>
	<li>Close the oven around the rheometer alignment tool. Install the truncated snout and the sample aperture (1 mm wide &#215; 8 mm tall), and using rheometer control software, set the geometry displacement angle to 0.49 rad in the motor control drop-down menu.</li>
	<li>Using the SANS instrument control software, ensure that all the neutron guides are removed, and open the oven door so that the laser is visible. Perform a rough alignment of the rheometer by changing the height and angle of the table from the SANS instrument control software so that the beam passes through the oven and crosses through the slit in the center of the rheometer alignment tool.</li>
	<li>Using the SANS instrument control software, adjust the height of the table and its rotation to optimize laser alignment. Note the rheometer is aligned when the laser beam passes through the slit in the rheometer alignment tool with the geometry displacement set at 0.49 rad without impinging on its walls and the beam passes through the center line in the oven.</li>
</ol>
5. Calibration of the SANS Instrument
<ol>
	<li>Once the desired SANS instrument configuration is aligned by the instrument scientist, measure the open beam transmission, empty cell scattering, and dark current scattering measurements.
	<ol>
		<li>Perform the open beam transmission measurement by performing a beam transmission measurement at the desired detector position for 3 min.</li>
		<li>Perform the empty cell scattering measurement by installing the dielectric geometry and measuring a scattering measurement at the desired detector position.</li>
		<li>Perform the dark current scattering measurement using a 3-mm thick piece of cadmium that totally attenuates the main beam scattering signal.</li>
	</ol>
	</li>
</ol>
6. Connecting the Electric Components
<ol>
	<li>Set the gap using the LCD screen to 100 mm.</li>
	<li>Remove the rheometer alignment tool from the bottom tool flange. Reinstall the dielectric bob assembly on the upper tool head and the dielectric cup assembly/dielectric geometry/slip ring assembly onto the lower tool head as one piece and re-zero the gap.</li>
	<li>Ensure that the carbon brush assembly is secured to the carbon brush adapter using screws, and secure the carbon brush adapter and carbon brush assembly to the rheometer using screws. Ensure that the carbon brushes on the carbon brush assembly mate with the grooved metal rings of the slip ring. This ensures maintenance of the electrical contact.</li>
	<li>Connect the female pin connectors on the carbon brush assembly and the dielectric bob assembly to the male pin connectors of the top and bottom bus bars respectively. Ensure that the labeled shielded BNC cables connected to the bus bars and terminating at the LCR meter are installed in their corresponding BNC connectors.</li>
	<li>Connect the BNC cable labeled &#34;TO SANS&#34; to the BNC cable connected to the DAQ card labeled &#34;AO0&#34;. Connect the BNC cable labeled &#34;FROM SANS&#34; to the BNC cable connected to the DAQ card labeled &#34;AI0&#34;. Connect the BNC cable labeled &#34;TRIGGER&#34; to the BNC cable connected to the DAQ card labeled &#34;AO1&#34;. Connect the BNC cable connected to the 15 pin connector on the back of the rheometer to the BNC cable labeled &#34;AI3&#34;. Ensure that the LCR meter and rheometer are communicating with the control computer.</li>
</ol>
7. Preparing the Instrument for a Measurement
<ol>
	<li>Open the oven, set the gap to 100 mm, and load 4 mL of the carbon black dispersion in propylene carbonate into the temperature equilibrated dielectric cup assembly, taking care to minimize sample left on the cup wall.</li>
	<li>Lower the geometry to 40 mm using the front LCD screen. Set the velocity on the rheometer control software using the motor control settings to 1 rad/s. Using the slew option on the rheometer, lower the dielectric bob assembly until the gap distance is at 0.5 mm.</li>
	<li>Using the equipment software, go to dielectric geometry measurement gap, and set the motor velocity on rheometer control software using the motor control settings to 0 rad/s. At this stage, the sample is loaded. 
	Note: Check the sample fill level once more to ensure that the sample level fills all the way up the Couette wall without overfilling.</li>
	<li>Install the solvent trap by filling the inner dielectric bob assembly wall with the desired solvent and place the solvent trap on the rim of the dielectric cup assembly.</li>
</ol>
8. Running the Dielectric RheoSANS Experiment
<ol>
	<li>Configure code labeled &#34;TA_ARES_FlowSweep.vi&#34;. A GUI will appear with modifiable fields that specify the experimental run conditions of the dielectric RheoSANS experiment. Set these fields in the following order.
	<ol>
		<li>Specify a path for the log file to and the base name of the log file. Run the code by pressing the &#34;Run&#34; arrow button on the menu bar.</li>
		<li>Select rheological parameters &#8212; the starting shear rate (25 rad/s), ending shear rate (1 rad/s), the number of shear rate points (6) and whether the points should be logarithmically or linear spaced (radio button). Select temperature to 25 &#176;C for this experiment. Select preshear conditions (if desired, enable radio button to &#34;ON&#34;) &#8212; in this experiment, use a 25 rad/s preshear for 600 s with a 300 s wait time after the preshear step.</li>
		<li>Specify time per shear rate and collection rate. Enable handshaking radio button. On test parameters tab select logarithmic or linear sweep &#8212; if radio button is green, a list of N number of points will be logarithmically spaced from min shear rate to max shear rate.</li>
		<li>Specify discrete shear rates and times via the &#34;Discrete Values&#34; tab if desired. Select the number of frequency points, the frequency minimum and the frequency maximum default. Set the time dependent frequency &#8212; specifies the desired time dependent frequency for all shear rates. Set the time for steady state &#8212; sets the amount of time that the code will measure dielectric parameters at a fixed frequency as a function of time for each shear rate.</li>
		<li>Specify the signal type and amplitude. Specify the number of cycles to average and the measurement time.</li>
	</ol>
	</li>
	<li>Turn on autoLogging on the SANS computer. Set the SANS configuration. Select the configuration and specify the run time to be at least 1 min longer than the total time contained within the shear rate list in the code. 
	Note: When the configuration is achieved VIPER should read &#34;dio stat 16&#34; which indicates that it will be waiting for the analogue signal from the data acquisition card to change.</li>
	<li>Configuring the rheometer control software. In the experiment tab, Press &#34;Open Procedure File&#34; in the &#34;Procedure&#34; drop down menu. Navigate to the procedure file labeled &#34;Dielectric RheoSANS Script File&#34;. Ensure that rheometer is ready to execute experiment.</li>
	<li>When the SANS is ready, ensure control software is configured and rheometer control software script file is open, press &#34;Parameters Set&#34;. This triggers execution of the specified experiment and all data should be logged throughout the preprogrammed sample run.</li>
</ol>
9. End of Experiment
<ol>
	<li>Turn off the neutron beam and disable auto-logging. Unload the sample and remove the dielectric cup and bob assemblies from the rheometer. Install the motor air bearing protector and lock the transducer.</li>
	<li>Power down the computer, LCR meter, and rheometer power supplies. Disconnect the air line. Disconnect all BNC cables and reinstall the crane lift onto the rheometer.</li>
	<li>Uninstall the truncated snout. Reinstall the rheometer&#39;s crane adapter. Lift the rheometer from the table and place onto the rheometer table ensuring that the cables remain untangled.</li>
</ol>
<img alt="Figure 1" src="/files/ftp_upload/55318/55318fig1.jpg" /> 
Figure 1: a.)-e.) Pictures of Components of the SANS Beamline and the Rheometer necessary to Install Rheometer on the Beamline that are Labelled and Defined Below. <a href="http://cloudfront.jove.com/files/ftp_upload/55318/55318fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/55318/55318fig2.jpg" /> 
Figure 2: Pictures of Components Dielectric RheoSANS Geometry with Labels Defining Terms Below. <a href="http://cloudfront.jove.com/files/ftp_upload/55318/55318fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/55318/55318fig3.jpg" /> 
Figure 3: a.-d.) Pictures of Procedure for Installing the Slip-ring onto the Dielectric RheoSANS Geometry, and e.) Picture of Fully Assembled Dielectric RheoSANS Geometry. <a href="http://cloudfront.jove.com/files/ftp_upload/55318/55318fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" src="/files/ftp_upload/55318/55318fig4.jpg" /> 
Figure 4: Schematic of Beam Path through Oven Geometry and Dielectric RheoSANS Geometry. <a href="http://cloudfront.jove.com/files/ftp_upload/55318/55318fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

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The authors have nothing to disclose.

A dielectric RheoSANS experiment measures simultaneously the rheological, electrical and microstructural responses of a material as it undergoes a predefined deformation. The example shown here is an electrically conductive carbon black suspension that forms the conductive additive used in electrochemical flow cells. The dielectric RheoSANS instrument enables the interrogation of the radial plane of shear within a narrow gap Couette cell without compromising the fidelity of either the electrical or rheological measuremen...

Measurement of macroscopic properties are often used to gain fundamental insight into the nature of colloidal materials and self-assembled systems, usually with the goal of developing understanding in order to improve formulation performance. In particular, the field of rheology, which measures a fluid&#39;s dynamic response to an applied stress or deformation, provides valuable insight into colloidal behavior both under equilibrium conditions and also far from equilibrium, such as during processing1 Rheological tests of consumer and industrial fluids, gels, and glasses can also be used to measure rheological parameters, such as viscosity, that are targeted by formulators. While rheology is a powerful probe of material properties, it is an indirect measurement of colloidal information at the microscopic level, such that our understanding of fundamental colloidal behavior can be greatly enhanced by combining rheological measurements with complementary techniques.
One such orthogonal technique is impedance spectroscopy. Impedance spectroscopy is a bulk probe of dielectric relaxation behavior, which measures the response of a material to an applied oscillating electric field.2 The impedance spectrum results from electrical relaxation modes that are active within the material including charge transport and polarization.3,4 These measurements provide additional evidence for colloidal behavior particularly when combined with rheology.5 Therefore, the combination of these techniques is especially relevant when probing charged colloidal dispersions, proteins, ionic surfactants, nanocomposites, and other systems.6,7
A fundamental interest in investigations of colloidal behavior is the material&#39;s microstructure. The microstructure of a colloidal fluid is thought to encode all of the information necessary to reconstitute both its rheological and electrical behavior. Fundamentally, we seek to measure a snapshot of the nanoscale microstructural features that lead to a measured material response. Due to the complicated nature of many complex fluids&#39; dependence on their process history, much of the effort on microstructural characterization has focused on making in situ measurements of the material as it undergoes deformation. This has challenged experimentalists to devise methods to be able to make measurements of nano-sized particles under for example steady shear, where the velocities of the particles have made direct visualization intrinsically challenging. Direct measurement of material microstructure under flow has taken on many forms ranging from rheo-optics, rheo-microscopy and even rheo-NMR.8,9,10 Small angle scattering methods, and in particular small angle neutron scattering (SANS) techniques, have proven themselves effective at measuring the time-averaged microstructure of samples at steady state in a bulk shear field including all three planes of shear.11,12,13 However, new data acquisition techniques have allowed structural transients to be captured with time resolution as fine as 10 ms.14 Indeed combining rheology with various in situ scattering methods has proven invaluable in hundreds of recent studies.15
An emerging engineering challenge is the use of colloidal suspensions as conductive additives in semi-solid flow battery electrodes.16 In this application, conductive colloidal particles must maintain an electrically percolated network while the material is pumped through an electrochemical flow cell. The performance demands on these materials require that they maintain high conductivity without detrimental effect on the rheological performance over a wide range of shear rates.17 It is therefore highly desirable to be able to make measurements of the colloidal behavior under steady and time-dependent shear conditions in order to quantify and characterize the underlying rheological and electrical response of these materials far from their equilibrium state. A significant complicating factor that has hindered further theoretical development in this regard is the thixotropic nature of carbon black slurries.18 These history dependent rheological and electrical properties make experiments notoriously difficult to reproduce; thus, making it difficult to compare data sets measured using varying protocols. Furthermore, to date there is no single geometry capable of performing all three, dielectric, rheological, and microstructural characterizations, simultaneously. Simultaneous measurement is important as the flow can change the structure, such that rest measurements of processed materials may not provide accurate indications of the properties under flow, which are more relevant for their use. Additionally, as many of the measured properties of carbon black slurries are geometry dependent, there are complications with comparing data obtained from the same sample on different instruments.19
In order to meet this challenge in metrology, we have developed a new dielectric RheoSANS geometry at the NIST Center for Neutron Research and the University of Delaware capable of in situ impedance spectroscopy, rheology and SANS measurements of a material under arbitrary deformation on a commercial strain controlled rheometer. This is enabled by developing a Couette geometry capable of measuring the microstructural, electrical and rheological response of a material confined between the gap of two concentric cylinders. As the outer cylinder spins, torque imposed by the deformation of the sample is measured on the inner cylinder and the impedance measurement is made radially across the gap. The cylinders are machined from titanium so as to be transparent to neutrons and robust enough to withstand the shear stress experienced in the rheometer. We perform the SANS measurement through the radial position of the Couette, and have demonstrated that it is possible to measure high quality SANS patterns from the sample undergoing deformation. In this way, all three measurements are made on the same region of interest in the sample as it undergoes a well-defined deformation profile. The goal of this article is to describe the dielectric Couette geometry, its installation onto the RheoSANS instrument, and the successful execution of a simultaneous measurement. This rheometer is available at the NIST Center for Neutron Research at the National Institute of Standards and Technology. It has been designed to work on the NG-7 SANS beam line. We have provided drawings and a detailed description of the custom components that have been machined and assembled in order to enable this measurement.

<table><tbody><tr><td>ARES G2 Rheometer</td><td>TA Instruments</td><td>401000.501</td><td>Rheometer</td></tr><tr><td>ARES G2-DETA ACCY Kit</td><td>TA Instruments</td><td>402551.901</td><td>BNC Connectors</td></tr><tr><td>Geometry ARES 25 mm DETA</td><td>TA Instruments</td><td>402553.901</td><td>Dielectric Geometry</td></tr><tr><td>ARES G2 Forced Convection Oven</td><td>TA Instruments</td><td>401892.901</td><td>FCO</td></tr><tr><td>Agilent E4980A LCR Meter</td><td>TA Instruments</td><td>613.04946</td><td>LCR Meter</td></tr><tr><td>USB-6001</td><td>National Instruments</td><td>NI USB-6001</td><td>Data Acquisiton Card</td></tr><tr><td>Vulcan XC72R</td><td>Cabot</td><td>Vulcan XC72R</td><td></td></tr><tr><td>Propylene Carbonate</td><td>Aldrich</td><td>310328</td><td></td></tr><tr><td>LabVIEW&amp;nbsp; System Design Software</td><td>National Instruments</td><td>776671-35</td><td>Control Software&amp;nbsp;</td></tr></tbody></table>

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.

Representative results from a dielectric RheoSANS experiment are shown in Figure 5 and 6. These data are taken on a suspension of conductive carbon black in propylene carbonate. These aggregates flocculate due to attractive interactions at relatively low solids loadings forming gels that are electrically conducting. The rheological and conductivity responses of such suspensions are an active area of research and current investigations seek to understand t...

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

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 ...

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Research

JoVE Journal

Engineering

10.3K Views.  National Institute of Standards and Technology.  Hier presenteren we een procedure voor de meting van gelijktijdige impedantie reologie en neutronenverstrooiing van zacht materiaal materialen onder schuifkracht. 

Video: Dielectric RheoSANS — Simultaneous Interrogation of Impedance, Rheology and Small Angle Neutron Scattering of Complex Fluids

Confocal Imaging of Confined Quiescent and Flowing Colloid-polymer Mixtures

The behavior of confined colloidal suspensions with attractive interparticle interactions is critical to the rational design of materials for directed assembly1-3, drug delivery4, improved hydrocarbon recovery5-7, and flowable electrodes for energy storage8. Suspensions containing fluorescent colloids and non-adsorbing polymers are appealing model systems, as the ratio of the polymer radius of gyration to the particle radius&#160;and concentration of polymer control the range and strength of the interparticle attraction, respectively. By tuning the polymer properties and the volume fraction of the colloids, colloid fluids, fluids of clusters, gels, crystals, and glasses can be obtained9.&#160;Confocal microscopy, a variant of fluorescence microscopy, allows an optically transparent and fluorescent sample to be imaged with high spatial and temporal resolution in three dimensions. In this technique, a small pinhole or slit blocks the emitted fluorescent light from regions of the sample that are outside the focal volume of the microscope optical system. As a result, only a thin section of the sample in the focal plane is imaged. This technique is particularly well suited to probe the structure and dynamics in dense colloidal suspensions at the single-particle scale: the particles are large enough to be resolved using visible light and diffuse slowly enough to be captured at typical scan speeds of commercial confocal systems10. Improvements in scan speeds and analysis algorithms have also enabled quantitative confocal imaging of flowing suspensions11-16,37.&#160;In this paper, we demonstrate confocal microscopy experiments to probe the confined phase behavior and flow properties of colloid-polymer mixtures. We first prepare colloid-polymer mixtures that are density- and refractive-index matched. Next, we report a standard protocol for imaging quiescent dense colloid-polymer mixtures under varying confinement in thin wedge-shaped cells. Finally, we demonstrate a protocol for imaging colloid-polymer mixtures during microchannel flow.

Confocal microscopy is used to image quiescent and flowing colloid-polymer mixtures, which are studied as model systems for attractive suspensions. Image analysis algorithms are used to calculate structural and dynamic metrics for the colloidal particles that measure changes due to geometric confinement.

The behavior of confined colloidal suspensions with attractive interparticle interactions is critical to the rational design of materials for directed ...

Chemistry

Measuring Material Microstructure Under Flow Using 1-2 Plane Flow-Small Angle Neutron Scattering

A new small-angle neutron scattering (SANS) sample environment optimized for studying the microstructure of complex fluids under simple shear flow is presented. The SANS shear cell consists of a concentric cylinder Couette geometry that is sealed and rotating about a horizontal axis so that the vorticity direction of the flow field is aligned with the neutron beam enabling scattering from the 1-2 plane of shear (velocity-velocity gradient, respectively). This approach is an advance over previous shear cell sample environments as there is a strong coupling between the bulk rheology and microstructural features in the 1-2 plane of shear. Flow-instabilities, such as shear banding, can also be studied by spatially resolved measurements. This is accomplished in this sample environment by using a narrow aperture for the neutron beam and scanning along the velocity gradient direction. Time resolved experiments, such as flow start-ups and large amplitude oscillatory shear flow are also possible by synchronization of the shear motion and time-resolved detection of scattered neutrons. Representative results using the methods outlined here demonstrate the useful nature of spatial resolution for measuring the microstructure of a wormlike micelle solution that exhibits shear banding, a phenomenon that can only be investigated by resolving the structure along the velocity gradient direction. Finally, potential improvements to the current design are discussed along with suggestions for supplementary experiments as motivation for future experiments on a broad range of complex fluids in a variety of shear motions.

A shear cell is developed for small-angle neutron scattering measurements in the velocity-velocity gradient plane of shear and is used to characterize complex fluids. Spatially resolved measurements in the velocity gradient direction are possible for studying shear-banding materials. Applications include investigations of colloidal dispersions, polymer solutions, and self-assembled structures.

A new small-angle neutron scattering (SANS) sample environment optimized for studying the microstructure of complex fluids under simple shear flow is ...

Quantitative and Qualitative Examination of Particle-particle Interactions Using Colloidal Probe Nanoscopy

Colloidal Probe Nanoscopy (CPN), the study of the nano-scale interactive forces between a specifically prepared colloidal probe and any chosen substrate using the Atomic Force Microscope (AFM), can provide key insights into physical interactions present within colloidal systems. Colloidal systems are widely existent in several applications including, pharmaceuticals, foods, paints, paper, soil and minerals, detergents, printing and much more.1-3 Furthermore, colloids can exist in many states such as emulsions, foams and suspensions. Using colloidal probe nanoscopy one can obtain key information on the adhesive properties, binding energies and even gain insight into the physical stability and coagulation kinetics of the colloids present within. Additionally, colloidal probe nanoscopy can be used with biological cells to aid in drug discovery and formulation development. In this paper we describe a method for conducting colloidal probe nanoscopy, discuss key factors that are important to consider during the measurement, and show that both quantitative and qualitative data that can be obtained from such measurements.

Colloidal probe nanoscopy can be used within a variety of fields to gain insight into the physical stability and coagulation kinetics of colloidal systems and aid in drug discovery and formulation sciences using biological systems. The method described within provides a quantitative and qualitative means to study such systems.

Colloidal Probe Nanoscopy (CPN), the study of the nano-scale interactive forces between a specifically prepared colloidal probe and any chosen substrate ...

An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids

An analog, macroscopic method for studying molecular-scale hydrodynamic processes in dense gases and liquids is described. The technique applies a standard fluid dynamic diagnostic, particle image velocimetry (PIV), to measure: i) velocities of individual particles (grains), extant on short, grain-collision time-scales, ii) velocities of systems of particles, on both short collision-time- and long, continuum-flow-time-scales, iii) collective hydrodynamic modes known to exist in dense molecular fluids, and iv) short- and long-time-scale velocity autocorrelation functions, central to understanding particle-scale dynamics in strongly interacting, dense fluid systems. The basic system is composed of an imaging system, light source, vibrational sensors, vibrational system with a known media, and PIV and analysis software. Required experimental measurements and an outline of the theoretical tools needed when using the analog technique to study molecular-scale hydrodynamic processes are highlighted. The proposed technique provides a relatively straightforward alternative to photonic and neutron beam scattering methods traditionally used in molecular hydrodynamic studies.

An experimentally accessible analog method for studying molecular hydrodynamic processes in dense fluids is presented. The technique uses particle image velocimetry of vibrated, high-restitution grain piles and allows direct, macroscopic observation of dynamical processes known and predicted to exist in strongly interacting, high density gases and liquids.

An analog, macroscopic method for studying molecular-scale hydrodynamic processes in dense gases and liquids is described. The technique applies a ...

Combining Microfluidics and Microrheology to Determine Rheological Properties of Soft Matter during Repeated Phase Transitions

The microstructure of soft matter directly impacts macroscopic rheological properties and can be changed by factors including colloidal rearrangement during previous phase changes and applied shear. To determine the extent of these changes, we have developed a microfluidic device that enables repeated phase transitions induced by exchange of the surrounding fluid and microrheological characterization while limiting shear on the sample. This technique is &#181;2rheology, the combination of microfluidics and microrheology. The microfluidic device is a two-layer design with symmetric inlet streams entering a sample chamber that traps the gel sample in place during fluid exchange. Suction can be applied far away from the sample chamber to pull fluids into the sample chamber. Material rheological properties are characterized using multiple particle tracking microrheology (MPT). In MPT, fluorescent probe particles are embedded into the material and the Brownian motion of the probes is recorded using video microscopy. The movement of the particles is tracked and the mean-squared displacement (MSD) is calculated. The MSD is related to macroscopic rheological properties, using the Generalized Stokes-Einstein Relation. The phase of the material is identified by comparison to the critical relaxation exponent, determined using time-cure superposition. Measurements of a fibrous colloidal gel illustrate the utility of the technique. This gel has a delicate structure that can be irreversibly changed when shear is applied. &#181;2rheology data shows that the material repeatedly equilibrates to the same rheological properties after each phase transition, indicating that phase transitions do not play a role in microstructural changes. To determine the role of shear, samples can be sheared prior to injection into our microfluidic device. &#181;2rheology is a widely applicable technique for the characterization of soft matter enabling the determination of rheological properties of delicate microstructures in a single sample during phase transitions in response to repeated changes in the surrounding environmental conditions.

We demonstrate the fabrication and use of a microfluidic device that enables multiple particle tracking microrheology measurements to study the rheological effects of repeated phase transitions on soft matter.

The microstructure of soft matter directly impacts macroscopic rheological properties and can be changed by factors including colloidal rearrangement ...

Studying Large Amplitude Oscillatory Shear Response of Soft Materials

We investigate the sequence of physical processes exhibited during large amplitude oscillatory shearing (LAOS) of polyethylene oxide (PEO) in dimethyl sulfoxide (DMSO) and xanthan gum in water &#8212; two concentrated polymer solutions used as viscosifiers in foods, enhanced oil recovery, and soil remediation. Understanding the nonlinear rheological behavior of soft materials is important in the design and controlled manufacturing of many consumer products. It is shown how the response to LAOS of these polymer solutions can be interpreted in terms of a clear transition from linear viscoelasticity to viscoplastic deformation and back again during a period. The LAOS results are analyzed via the fully quantitative Sequence of Physical Processes (SPP) technique, using free MATLAB-based software. A detailed protocol of performing a LAOS measurement with a commercial rheometer, analyzing nonlinear stress responses with the freeware, and interpreting physical processes under LAOS is presented. It is further shown that, within the SPP framework, a LAOS response contains information regarding the linear viscoelasticity, the transient flow curves, and the critical strain responsible for the onset of nonlinearity.

We present a detailed protocol outlining how to perform nonlinear oscillatory shear rheology on soft materials, and how to run the SPP-LAOS analysis to understand the responses as a sequence of physical processes.

We investigate the sequence of physical processes exhibited during large amplitude oscillatory shearing (LAOS) of polyethylene oxide (PEO) in dimethyl ...

Assembly and Characterization of Polyelectrolyte Complex Micelles

Polyelectrolyte complex micelles (PCMs), core-shell nanoparticles formed by self-assembly of charged polymers in aqueous solution, provide a powerful platform for exploring the physics of polyelectrolyte interactions and also offer a promising solution to the pressing problem of delivering therapeutic oligonucleotides in vivo. Developing predictive structure-property relationships for PCMs has proven difficult, in part due to the presence of strong kinetic traps during nanoparticle self-assembly. This article discusses criteria for choosing polymers for PCM construction and provides protocols based on salt annealing that enable assembly of repeatable, low-polydispersity nanoparticles. We also discuss PCM characterization using light scattering, small-angle X-ray scattering, and electron microscopy.

We provide protocols and representative data for designing, assembling, and characterizing polyelectrolyte complex micelles, core-shell nanoparticles formed by polyelectrolytes and hydrophilic charged-uncharged block copolymers.

Polyelectrolyte complex micelles (PCMs), core-shell nanoparticles formed by self-assembly of charged polymers in aqueous solution, provide a powerful ...

Study of Protein Dynamics via Neutron Spin Echo Spectroscopy

Most human body proteins' activity and functionality are related to configurational changes of entire subdomains within the protein crystal structure. The crystal structures build the basis for any calculation that describes the structure or dynamics of a protein, most of the time with strong geometrical restrictions. However, these restrictions from the crystal structure are not present in the solution. The structure of the proteins in the solution may differ from the crystal due to rearrangements of loops or subdomains on the pico to nanosecond time scale (i.e., the internal protein dynamics time regime). The present work describes how slow motions on timescales of several tens of nanoseconds can be accessed using neutron scattering. In particular, the dynamical characterization of two major human proteins, an intrinsically disordered protein that lacks a well-defined secondary structure and a classical antibody protein, is addressed by neutron spin echo spectroscopy (NSE) combined with a wide range of laboratory characterization methods. Further insights into protein domain dynamics were achieved using mathematical modeling to describe the experimental neutron data and determine the crossover between combined diffusive and internal protein motions. The extraction of the internal dynamic contribution to the intermediate scattering function obtained from NSE, including the timescale of the various movements, allows further vision into the mechanical properties of single proteins and the softness of proteins in their nearly natural environment in the crowded protein solution.

Study of Protein Dynamics via Neutron Spin Echo Spectroscopy

The present protocol describes methods for investigating the structure and dynamics of two model proteins that have an important role in human health. The technique combines bench-top biophysical characterization with neutron spin echo spectroscopy to access the dynamics at time and length scales relevant for protein interdomain motions.

Most human body proteins' activity and functionality are related to configurational changes of entire subdomains within the protein crystal structure. The ...

Studying Soft-matter and Biological Systems over a Wide Length-scale from Nanometer and Micrometer Sizes at the Small-angle Neutron Diffractometer KWS-2

The KWS-2 SANS diffractometer is dedicated to the investigation of soft matter and biophysical systems covering a wide length scale, from nm to &#181;m. The instrument is optimized for the exploration of the wide momentum transfer Q range between 1x10-4 and 0.5 &#197;-1 by combining classical pinhole, focusing (with lenses), and time-of-flight (with chopper) methods, while simultaneously providing high-neutron intensities with an adjustable resolution. Because of its ability to adjust the intensity and the resolution within wide limits during the experiment, combined with the possibility to equip specific sample environments and ancillary devices, the KWS-2 shows a high versatility in addressing the broad range of structural and morphological studies in the field. Equilibrium structures can be studied in static measurements, while dynamic and kinetic processes can be investigated over time scales between minutes to tens of milliseconds with time-resolved approaches. Typical systems that are investigated with the KWS-2 cover the range from complex, hierarchical systems that exhibit multiple structural levels (e.g., gels, networks, or macro-aggregates) to small and poorly-scattering systems (e.g., single polymers or proteins in solution). The recent upgrade of the detection system, which enables the detection of count rates in the MHz range, opens new opportunities to study even very small biological morphologies in buffer solution with weak scattering signals close to the buffer scattering level at high Q.
In this paper, we provide a protocol to investigate samples with characteristic size levels spanning a wide length scale and exhibiting ordering in the mesoscale structure using KWS-2. We present in detail how to use the multiple working modes that are offered by the instrument and the level of performance that is achieved.

Here, we present a protocol to investigate soft matter and biophysical systems over a wide mesoscopic length scale, from nm to &#181;m that involves the use of the KWS-2 SANS diffractometer at high intensities and an adjustable resolution.

The KWS-2 SANS diffractometer is dedicated to the investigation of soft matter and biophysical systems covering a wide length scale, from nm to &#181;m. ...

Bioengineering

Measuring the Time-Evolution of Nanoscale Materials with Stopped-Flow and Small-Angle Neutron Scattering

This paper presents the use of a stopped-flow small-angle neutron-scattering (SANS) sample environment to quickly mix liquid samples and study nanoscale kinetic processes on time scales of seconds to minutes. The stopped-flow sample environment uses commercially available syringe pumps to mix the desired volumes of liquid samples that are then injected through a dynamic mixer into a quartz glass cell in approximately 1 s. Time-resolved SANS data acquisition is synced with the sample mixing to follow the evolution of the nanostructure in solution after mixing. 
To make the most efficient use of neutron beam time, we use a series of flow selector valves to automatically load, rinse, and dry the cell between measurements, allowing for repeated data collection throughout multiple sample injections. Sample injections are repeated until sufficient neutron scattering statistics are collected. The mixing setup can be programmed to systematically vary conditions to measure the kinetics at different mixing ratios, sample concentrations, additive concentrations, and temperatures. The minimum sample volume required per injection is approximately 150 &#181;L depending on the path length of the quartz cell. 
Representative results using this stopped-flow sample environment are presented for rapid lipid exchange kinetics in the presence of an additive, cyclodextrin. The vesicles exchange outer-leaflet (exterior) lipids on the order of seconds and fully exchange both interior and exterior lipids within hours. Measuring lipid exchange kinetics requires in situ mixing to capture the faster (seconds) and slower (minutes) processes and extract the kinetic rate constants. The same sample environment can also be used to probe molecular exchange in other types of liquid samples such as lipid nanoparticles, proteins, surfactants, polymers, emulsions, or inorganic nanoparticles. Measuring the nanoscale structural transformations and kinetics of exchanging or reacting systems will provide new insights into processes that evolve at the nanoscale.

This protocol presents the use of a stopped-flow sample environment to quickly mix multiple liquid solutions in situ during a small-angle neutron scattering measurement and to study kinetic processes on nanometer length scales and second time scales.

This paper presents the use of a stopped-flow small-angle neutron-scattering (SANS) sample environment to quickly mix liquid samples and study nanoscale ...

Dielectric RheoSANS — Simultaneous Interrogation of Impedance, Rheology and Small Angle Neutron Scattering of Complex Fluids

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