We acknowledge Master Machinist Al Lance of the University of Delaware for machining the shear cell and Mr. Cedric Gagnon for design and drafting. This manuscript was prepared under cooperative agreement 70NANB7H6178 from NIST, U.S. Department of Commerce. This work utilized facilities supported in part by the National Science Foundation under Agreement No. DMR-0944772. The statements, findings, conclusions and recommendations are those of the author(s) and do not necessarily reflect the view of NIST or the U.S. Department of Commerce.&#160;

Figure 2 shows an assembled shear cell attached to the baseplate, which is mounted to the breadboard on the sample environment stage and aligned in the neutron beam for a SANS experiment. The stepper motor, gear box and belt drive, slit motor stage, shear cell and direction of the neutron beam are labeled in Figure 2. The present protocol provides directions for assembling the shear cell (section 1), mounting the shear cell onto the sample environment stage (section 2), calibrating the g...

<ol>
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A new instrument capable of measuring the microstructure of shearing complex fluids in the velocity-velocity gradient plane of shear via small angle neutron scattering is developed and validated. The shear cell design complements other instruments using radiation sources, such as X-ray and light scattering, as well as rheo-SANS instruments capable of characterizing the microstructure in the two other planes of shear (velocity-vorticity and velocity gradient-vorticity)8,10. This instrument...

Developing a scientific understanding of a natural phenomenon requires accurate and precise measurements. Metrology is also the basis of successful engineering and design of new processes and materials. Rheology is the science of the deformation and flow of matter. Rheology is central in our ability to process a wide variety of materials and is also used by product formulators to target specific material properties. Typical examples of the former include molding polymers or forming composites, whereas the latter includes the development of everyday consumer products such as paints, shampoos, and foods. Whether the viscosity of a molten polymer is controlled so that it can be effectively injection molded or the viscoelasticity of a shampoo is changed so it has the correct consistency for the consumer, the rheological properties are controlled by changing the formulation of the material1. The rheology of materials and products also depends on the structure in the fluid state and this structure ranges from the microscale to the nanoscale. Furthermore, this structure changes with the processing parameters, such as flow rate and time of flow, which challenges rheologists to measure the structure during flow. It is this challenge that is met, in part, by the novel instrumentation described in this article.
Novel techniques capable of probing the microstructure of soft materials under shear flow can benefit soft material product engineering and processing condition optimization. Many intriguing and long-standing challenges for the application of soft materials in a variety of industries and in fundamental science involve unusual flow behavior, such as shear thickening in colloidal suspensions2, shear and vorticity banding in wormlike micelles3, and heterogeneities inherent in the flow of colloidal gels4-6. Rheologists are constantly challenged to elucidate the microstructural origins of the nonlinearities in the rheological responses and sometimes even in the velocity field of shearing viscoelastic materials. This challenge requires simultaneous acquisition of the microstructure as a function of both the spatial location in the flow field and the time dependent behaviors, which has proven a formidable task for experimentalists.&#160;
Small angle neutron scattering (SANS) is particularly well suited for measuring the structure of complex fluids as it can probe materials that are opaque to light. Also selective deuteration can be used to provide contrast between components that may appear similar under X-ray scattering7. Furthermore, neutrons have an advantage over X-rays as there is no radiation damage of biological or other soft-matter samples. In the experiments illustrated here, cold neutrons generated by a reactor or a spallation source are collimated and illuminated upon a sample. The scattering intensity yields information about the structure of the material on length scales from the atomic to hundreds of nanometers (and with ultra-small angle neutron scattering up to tens of microns), but in the form of a Fourier transform of the real space structure. Therefore, interpretation of the data can be challenging and involves an inverse transform or comparison to microstructural models or simulations. More about SANS instrumentation, experiments, and contrast matching can be found on the tutorials posted on the web site of the Center for Neutron Science, www.cns.che.udel.edu.
Here we describe a shear cell designed to extend the SANS method to examine materials under flow. A recent overview of the general methodology and instrumentation, as well as a substantial literature review of recent applications can be found in reference8 and the cited references therein.&#160;A convenient and nearly ideal environment to probe fluid structure under shear flow with SANS is a narrow gap Couette geometry, also known as concentric cylinders9. This geometry applies a simple (i.e.&#160;laminar) shear flow to the sample while maintaining a sufficient unobstructed volume for the incident neutron beam. The application of flow breaks the symmetry of the microstructure; as such a complete characterization of the material microstructure under simple shear flow requires microstructural measurements in all three planes of shear. Two planes of shear may be investigated using the standard Couette geometry configuration (Figure 1a): the neutron beam is configured to travel along the velocity gradient direction and probe the velocity-vorticity (1-3) plane of shear (&#8220;radial&#8221; configuration); alternatively, the beam is collimated by a thin slit and aligned parallel to the flow direction, thereby probing the velocity gradient-vorticity (2-3) plane (&#8220;tangential&#8221; configuration). This instrument is available commercially and has been recently documented for examining complex fluids under shear10. The aforementioned review describes its use and that of related devices for structure-property determination across a broad range of materials and applications8. Time-resolved experiments, such as for oscillatory shear flows have also been reported11,12.
Often the most interesting and most important plane of flow is the velocity-velocity gradient (1-2) plane (Figure 1b) but it is also the most difficult to investigate as it requires special instrumentation. A custom shear cell has been designed to enable direct investigation of the velocity-velocity gradient (1-2) plane by SANS such that the neutron beam travels parallel to the vorticity axis of shear13-16. Measurements in the 1-2 plane of flow are critical to gaining a quantitative understanding for the shear viscosity because they elucidate the orientation of the structure relative to the flow direction15,17,18. This is important for materials such as polymers, self-assembled surfactants, colloids, and other complex fluids. In addition, it is possible to investigate the materials&#8217; microstructure as a function of position across the gap in the gradient direction of shear flow. With the addition of spatial resolution, the method provides a means for studying materials that exhibit microstructural changes along the gradient direction of shear. An example for which investigating changes in microstructure and composition along the gradient direction of flow is shear-banding. Shear banding is a phenomenon caused by a coupling between the microstructure and flow direction that results in an inhomogeneous flow field13. In this article, we describe the instrument, its assembly and the flow-SANS measurement technique as implemented at the NIST Center for Neutron Research (NCNR) at the National Institute of Standards and Technology (NIST) in Gaithersburg, MD. This sample environment is the result of a collaboration between the University of Delaware, NIST and the Institut Laue-Langevin (ILL), and has been successfully implemented at both ILL and NIST. For purposes of this article, where the SANS specific portions of the protocol are concerned, the technique is described as implemented at NIST. However, modifying those instrument specific details should be straightforward and the overall technique can be implemented on any SANS instrument for steady flow (section 5.1). In addition, instruments equipped with time-resolved SANS capabilities may also perform oscillatory shear flow-SANS experiments (section 5.2). Technical drawings of the shear cell components are provided as Figures 12-23. &#160;

<table border="0" cellpadding="0" cellspacing="0" width="785">
	<tbody>
		<tr>
			<td>Deuterated Water (99.9%)</td>
			<td>Cambridge Isotopes</td>
			<td>7789-20-0</td>
			<td>83.3 wt % in formulation 
			D2O</td>
		</tr>
		<tr>
			<td>CTAB- Cetyl Trimethyl Ammonium Bromide&#160;</td>
			<td>Sigma-Aldrich</td>
			<td>57-09-0&#160;</td>
			<td>16.7 wt % in formulation 
			CH3(CH2)15N(Br)(CH3)3</td>
		</tr>
		<tr>
			<td>1/16&#34; Allen wrench</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>3/16&#34; Allen wrench</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>3/8&#34; open end wrench</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>tape</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>thread seal tape</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td style="font-size: 13px; line-height: 1.6em;">syringes (2)</td>
			<td style="font-size: 13px; line-height: 1.6em;"></td>
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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.

Representative results of a successful flow-SANS experiment are given in Figures 9, 10, and 11. These examples are from investigations made on a wormlike micelle solution (WLM) (Table 1) known to exhibit shear banding during certain conditions of shear. A complete discussion of the scientific findings can be found in references15-17.
Figure 10 represents results of a scattering pattern obtained under shear flow usin...

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

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 ...

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14.0K vistas.  University of Delaware.  Una célula de cizallamiento es desarrollado para mediciones de dispersión de neutrones de ángulo pequeño en el plano gradiente de velocidad-velocidad de cizallamiento y se usa para caracterizar fluidos complejos. Mediciones espacialmente resueltas en la dirección del gradiente de velocidad son posibles para el estudio de los materiales de cizalla-anillado. Las aplicaciones incluyen investigaciones de dispersiones coloidales, soluciones de polímeros, y estructuras a...