Access to the NG3 VSANS was provided by the Center for High-Resolution Neutron Scattering, a partnership between the National Institute of Standards and Technology and the National Science Foundation under Agreement NO. DMR-2010792. M.H.L.N acknowledges the funding provided by Mitacs Globalink (Canada). The identification of any commercial products or trade names is to foster understanding and does not imply endorsement or recommendation by the National Institute of Standards and Technology.

1. Set up and initiate the stopped-flow system.
<ol>
	<li>Turn on all pump power supplies and dynamic mixers using the power switch.</li>
	<li>Initiate all pumps and valves in the stopped-flow system control graphical user interface (GUI) by entering the device configuration path and using the commands bus=qmixbus.Bus(), bus.open(), bus.start(), pump=qmixpump.Pump(), pump.enable(), and valve=ViciMultiposSelector()&#160;</strong...

The authors have no conflicts of interest to declare.

The current procedure describes the mixing device and the steps to perform stopped-flow TR-SANS measurements. The device and protocol are optimized for low-viscosity liquid samples where the time scales of interest are &#8776;1 s to 5 min. For time scales greater than 5 min, manually mixing the samples and loading them into standard scattering cells may be easier and desirable, especially for high-viscosity samples, gels, or pastes. Accessing time scales less than 1 s requires a different mixing apparatus, lower total vo...

Small-angle neutron scattering (SANS) provides a unique way to measure the sizes, shapes, interactions, and organization of various materials on length scales from &#8776;1 nm to &#8776;100 nm1,2,3. Recent instruments, including VSANS (very small-angle neutron scattering) instruments with focusing mirrors, push the limits toward measuring even larger length scales up to &#8776;1000 nm4,5. In general, the unique scattering contrast inherent to neutron scattering methods offers several advantages in measuring the time-evolution of nanoscale structures, such as the aggregation of components in pharmaceutical formulations6, crosslinking and gelation reactions in polymer systems7,8, in meso crystallization of membrane proteins9,10, degradation and unfolding of proteins11,12, and growth of silica-based materials13,14,15. The unique scattering contrast makes time-resolved SANS (TR-SANS) a useful complement to other stopped-flow-based measurements.
Stopped-flow mixing methods often are implemented in small-angle X-ray scattering (SAXS)16,17,18,19,20,21, fluorescence spectroscopy22,23,24,25,26, and light scattering27,28,29,30,31,32 experiments to study kinetic processes on the millisecond time scales. An important difference between SANS and SAXS is that neutron scattering is a nondestructive characterization technique, and as such, SANS can be used to measure the same sample for hours or even days without ionizing radiation damage to the sample, which can happen during higher-flux X-ray scattering experiments33. As repeated SANS measurements will not alter the chemical structure of the probe molecule or sample, the time-evolution can be studied without effects of photobleaching, for example, which can complicate kinetics measurements that rely on fluorescence23,24. Moreover, SANS can be used to measure highly concentrated and optically opaque samples that are often difficult to characterize with light-based techniques such as dynamic light scattering.
In addition to providing structural information on the nanoscale, SANS can be used to probe the local composition of these structures through the variation in neutron scattering length density contrast. The scattering length density (SLD) of different elements varies randomly across the periodic table and varies with different isotopes of the same element. A commonly exploited example is hydrogen (1H or H) and deuterium (2H or D), which have vastly different neutron scattering lengths. Therefore, hydrogen-rich materials, such as surfactants, lipids, proteins, RNA, DNA, and other polymers, can be distinguished from deuterated solvents using SANS without significantly changing the physical properties of the system. However, it is important to note that H/D exchange can affect the density, hydrogen-bonding, and phase transition temperatures in the sample. Nevertheless, the unique sensitivity of SANS to hydrogen-rich materials is especially useful in soft matter research where the samples of interest have lower scattering contrast and signal in X-ray-based techniques such as SAXS. Isotopic substitution also makes SANS a powerful tool for studying molecular exchange kinetics in hydrogen-rich materials by simply mixing H-labeled and D-labeled molecules. Isotopic substitution is particularly useful in systems where bulky fluorescent dyes are larger than the surfactant or lipid molecules of interest and can influence the exchange kinetics34,35.
Time-resolved SANS measurements are advantageous because the measured intensity is a function of time, length scale, and SLD contrast. As such, TR-SANS experiments can be designed to probe the time-dependent changes in the spatial distributions and the compositions of the samples. These unique advantages of SANS have led to important insights into kinetic processes in many soft material systems such as surfactants36,37,38, emulsions39,40,41, lipids34,42,43,44,45,46,47,48,49,50, and polymers51,52,53,54,55,56,57,58,59,60,61,62. Most TR-SANS studies have focused on time scales of minutes to hours. However, many kinetic processes of interest occur on the second time scale and are essential for understanding the underlying mechanisms. Capturing these early time points requires that the solutions be rapidly mixed and measured in situ, in which the mixing is synced with data collection during stopped-flow light scattering27,28,29,30,31,32, fluorescence22,23,24,25,26, and X-ray16,17,18,19,20,21 experiments. This work describes the use of a sample environment designed to rapidly mix multiple liquid samples and inject the mixture into a quartz glass cell for TR-SANS measurements. The mixing device is an adaptation of the recently developed capillary rheoSANS device63 and uses multiple syringe pumps and valves to control the sample mixing and to automate cell cleaning. By connecting syringe pumps to a series of flow selector valves, multiple inlet streams can be repeatedly mixed, measured, rinsed, and dried to facilitate TR-SANS measurements on the seconds time scale.
The current procedure assumes that the samples of interest have been identified and prepared. We focus on the in situ mixing setup and methods to collect TR-SANS data. Neutron scattering data were collected on the VSANS instrument at the NIST Center for Neutron Research (NCNR); however, the procedure should be applicable to other SANS instruments. Readers interested in implementing similar protocols on other SANS instruments should consult with the local instrument scientists to determine the optimal instrument configuration to maximize neutron flux at the desired length scale and time scale most relevant to the kinetic processes of interest. The data presented here were collected using the high flux &#39;white beam&#39; configuration on VSANS to maximize neutron counts at the loss of spatial resolution5. The detector carriages were positioned to cover a range of scattering vectors (q), 0.005 &#197;-1 &#60; q &#60; 0.5 &#197;-1, corresponding to length scales of &#8776;130 nm to &#8776;13 nm. The scattering vector is defined as q = 4&#960;/&#955; sin (&#952;/2) in which &#955; is the neutron wavelength, and &#952; is the scattering angle.
The stopped-flow mixing device used for the TR-SANS measurements consists of multiple pumps, rinsing syringes, sample syringes, flow selectors, as well as adynamic mixer, sample cell, and mixed sample container, as shown in Figure 1. All sealed fluid paths are located inside an air-conditioned enclosure, which includes the syringes, valves, connection tubing, dynamic mixer, and sample cells. A programmable thermoelectric air conditioner is used to control the enclosure temperature in the range from 10 &#176;C to 50 &#176;C within &#177;1 &#176;C. Note that some of the enclosure insulation was removed to show the working parts of the device. The main mixing device enclosure is positioned on a translational stage on the NG3 VSANS beam line at the NCNR. The enclosure position is adjusted using the translation stage to position the sample cell in the path of the neutron beam (yellow dashed line).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/62873/62873fig1v2.jpg" /> 
Figure 1: An example setup for combining stopped-flow mixing and small-angle neutron scattering measurements at the VSANS beamline at the NIST Center for Neutron Research. The setup contains four syringe pumps, two syringes for solvent rinsing and two syringes for sample injection, four pump selector valves, two mixer selector valves, a dynamic mixer, a flow-through quartz cell, and a mixed sample container. Incident neutrons scatter off the mixed sample located inside the sample cell. An insulated enclosure with quartz windows and a thermoelectric air-conditioned unit is&#160;used to control the sample and all equipment at a constant temperature. The yellow dashed line shows the neutron beam path. Scale bar = 10 cm. <a href="https://www.jove.com/files/ftp_upload/62873/62873fig1v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The device depicted in Figure 1 is configured with two sample syringes, two rinsing syringes, and one sample cell. Corresponding flow diagrams for the different steps of the protocol are illustrated in Figure 2. The desired volumes of the two different samples are injected into the mixer and the sample cell (Figure 2A). Once the sample cell is filled, the Inlet Switch Valve (ISV) and Outlet Switch Valve (OSV) are closed to isolate the sample cell from the dynamic mixer and to prevent sample back diffusion into the cell during TR-SANS data collection (Figure 2B). Before the dynamic mixer, the connection tubing varies in length from 10 cm to 1 m and does not affect the mixing delay time. However, tubing connections between the dynamic mixer and the sample cell will affect the mixing delay time and the required sample injection volume. Precut stainless steel tubing with 0.04 inch (1 mm) inner diameter and 100 mm length are used to connect the dynamic mixer, the Mixer Selector Valves (MSV1 and MSV2), and the ISV and OSV. Fluorinated tubing with 1 mm inner diameter and 115 mm length is used to connect the ISV and OSV (or the dynamic mixer outlet) to the sample cell. The total void volume that influences the mixing delay time includes the mixer void volume (0.15 mL), the tubing between the mixer outlet and the sample cell inlet (0.09 mL), and the sample cell volume (0.16 mL). In this example, the total void volume is 0.4 mL. The internal void volumes of valves are negligible compared to the tubing, mixer, and sample cell void volumes. For example, the employed low-pressure selector valves (0.75 mm bore diameter) contain approximate void volumes of 4 &#181;L, while the high-pressure selector valves and switch valves (0.25 mm bore diameter) contain approximate void volumes of 0.5 &#181;L.
After the TR-SANS measurement is complete, the sample is pushed out of the cell with solvent, and rinse solvent is repeatedly pumped through the cell to remove the residual sample and clean the sample cell (Figure 2C). Note that the rinse syringes are connected to larger solvent&#160;reservoirs (e.g., water and ethanol) via pump selector values to ensure that adequate solvent volumes are available to clean the sample cell between measurement runs. Solvent sources, sample sources, and mixed sample containers that contain flammable liquids are positioned in a separate enclosure with no electrical equipment to eliminate all possible ignition sources. In addition, vapor-locking bottle caps are used to minimize flammable vapors and solvent evaporation. Finally, the sample cell is dried with a nitrogen gas stream to remove the residual rinse solvent (Figure 2D). The inlet nitrogen gas pressure to the mixer selector valve is regulated to approximately 2 bar (0.2 MPa, gauge pressure) using a manual pressure regulator located on the nitrogen gas cylinder. Once the sample cell is sufficiently cleaned and dried, a newly mixed sample is injected into the sample cell for the next measurement cycle (repeating the mixing and injection illustrated in the flow diagram in Figure 2A).
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/62873/62873fig2v2.jpg" /> 
Figure 2: Example flow diagram using one sample cell, two samples mixing, and two rinse solvents for cleaning. (A) Mixing of sample A (blue) and sample B (red), and then flowing the mixed sample (purple)&#160;into the sample cell. (B) During data collection, the stopped-flow device state where the ISV and OSV switch valves are closed to isolate the sample cell and prevent back diffusion of the sample during data collection. (C) The cleaning steps where the sample cell is rinsed with rinse solvent from SS1 (green) after data collection. (D) Drying step where the sample cell is dried with nitrogen gas (orange). Abbreviations: PSV = pump selector valve; MSV = mixer selector valve; OSV = outlet switch valve; ISV = inlet switch valve; SS1 = solvent source 1; SSA = sample source A; N2 = nitrogen gas source. <a href="https://www.jove.com/files/ftp_upload/62873/62873fig2v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Figure 3 shows flow diagrams for a slightly different version in which the mixing setup is configured with two separate sample cells connected to the same switch valves (Figure 3A). While TR-SANS data are collected in Sample Cell 1, Sample Cell 2 is rinsed (Figure 3B) and dried (Figure 3C). When the data collection is complete for Sample Cell 1, the Inlet Switch Valve directs a newly mixed sample into Sample Cell 2 for data collection (Figure 3D). While TR-SANS data are collected in Sample Cell 2, Sample Cell 1 is rinsed and dried (Figure 3E). This alternating, parallel process between two sample cells minimizes the time between subsequent sample injections and maximizes the use of neutron beam time.
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/62873/62873fig3v2.jpg" /> 
Figure 3: Example flow diagram using a two-sample cells, two samples mixing, and two rinse solvents for cleaning. (A) Mixing sample A (blue) and sample B (red) and then flowing the mixed sample (purple) into sample cell 1. (B) The stopped-flow device state during data collection on sample cell 1 while sample cell 2 is rinsed with solvent from SS1 (green). (C) The stopped-flow device state during data collection on sample cell 1 while sample cell 2 is dried with nitrogen gas (orange). (D) Once data collection of sample cell 1 is complete, a new sample (purple) is immediately mixed and flowed into sample cell 2. (E) The stopped-flow device state during data collection on sample cell 2 while sample cell 1 is rinsed with solvent from SS1 (green). While one sample cell is being measured, the other sample cell is being cleaned and dried. The stopped-flow measurement process alternates between two sample cells to minimize the time between subsequent sample mixing injections. Abbreviations: PSV = pump selector valve; MSV = mixer selector valve; OSV = outlet switch valve; ISV = inlet switch valve; SS1 = solvent source 1; SSA = sample source A; N2 = nitrogen gas source. <a href="https://www.jove.com/files/ftp_upload/62873/62873fig3v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
A step-by-step protocol is described below for connecting the pumps and tubing lines, priming the system, rinsing and drying the sample cell, and injecting the mixed sample. Although the single-cell configuration is demonstrated for simplicity (Figure 2), the flexible modular setup, protocol, and scripts can be easily modified to implement more syringe pumps, valves, mixers, or sample cell configurations, such as the two-sample cell configuration shown in Figure 3. Representative raw neutron count rate data collected throughout mixing and cleaning injection cycles are shown in Figure 4, while lipid exchange kinetics measured at 3 different temperatures and the extracted normalized scattered intensity corresponding to the fraction of lipids exchanged are shown in Figure 5 and Figure 6, respectively.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Dynamic mixer</td>
			<td>Analytical Scientific Instruments</td>
			<td>462-0150A</td>
			<td>Magnetically coupled rotor, binary dynamic mixer assembly (ternary type available), 0.15 mL dead volume (larger dead volume available)</td>
		</tr>
		<tr>
			<td>Fluoropolymer tubing</td>
			<td>IDEX Health &#38; Science</td>
			<td>1507L</td>
			<td>PFA Tubing Natural 1/16 inch OD x 0.040 inch ID x 50 ft</td>
		</tr>
		<tr>
			<td>Fluoropolymer 1/4-28 flangeless fittings</td>
			<td>IDEX Health &#38; Science</td>
			<td>XP-245</td>
			<td>PFA flangeless fitting with ferrules, 1/4-28 threading, 1/16 inch OD tubing</td>
		</tr>
		<tr>
			<td>Glass syringes</td>
			<td>Hamilton Company</td>
			<td>81660</td>
			<td>Hamilton 1000 series syringes, 10 mL (81660), model 1010 C syr, 1/4&#34;-28 thread termination, other volumes available</td>
		</tr>
		<tr>
			<td>High-pressure flow selector valves</td>
			<td>Vici Valco</td>
			<td>C85X-1570EUTB</td>
			<td>Vici 10 position selector valves, 15000 psi max, 0.25 mm bore, 1/16 inch OD tubing, 10-32 coned threaded ports, USB universal actuator</td>
		</tr>
		<tr>
			<td>High-pressure switch valves</td>
			<td>Vici Valco</td>
			<td>C82X-1574EUHB</td>
			<td>Vici 4 port switch valves, 15000 psi max, 0.25 mm bore, 1/16 inch OD tubing, 10-32 coned threaded ports, USB universal actuator</td>
		</tr>
		<tr>
			<td>High-pressure syringes</td>
			<td>Cetoni</td>
			<td>A2019000358</td>
			<td>3 mL stainless steel syringe, 510 bar max, 21 mL/min flow rate max</td>
		</tr>
		<tr>
			<td>Low-pressure flow selector valves</td>
			<td>Vici Valco</td>
			<td>C25-3180EUHB</td>
			<td>Vici 10 position selector valves, max 250 psi liquid, 0.75 mm bore, 1/16 inch OD tubing, 1/4-28 threaded ports, USB universal actuator</td>
		</tr>
		<tr>
			<td>neMESYS high-pressure syringe pumps</td>
			<td>Cetoni</td>
			<td>A3921000103</td>
			<td>Max force 2600 N</td>
		</tr>
		<tr>
			<td>neMESYS mid-pressure syringe pumps</td>
			<td>Cetoni</td>
			<td>A3921000131</td>
			<td>Max force 1000 N</td>
		</tr>
		<tr>
			<td>Power supply</td>
			<td>Cetoni</td>
			<td>A3921000127</td>
			<td>Base 600, supplies power for up to 4 high pressure pumps</td>
		</tr>
		<tr>
			<td>Quartz flow-through sample cell</td>
			<td>Starna Scientific</td>
			<td>3-2.30-Q-1/TC</td>
			<td>Quartz micro flow cells, 2 mm path length (1 mm available), 2 mm by 2 mm by 30 mm internal dimension</td>
		</tr>
		<tr>
			<td>Quartz windows</td>
			<td>Technical Glass Products</td>
			<td>NA</td>
			<td>GE 124 Clear fused quartz ground and polished plates, 11.75 inch by 23.75 inch by 0.375 inch thick</td>
		</tr>
		<tr>
			<td>Stainless steel 10-32 coned compression fittings</td>
			<td>IDEX Health &#38; Science</td>
			<td>U-321X, U-320X</td>
			<td>316 stainless steel ferrule (U-321X) and nut (U-320X) -Valco type, 10-32 coned, for 1/16 inch OD stainless steel tubing</td>
		</tr>
		<tr>
			<td>Stainless steel tubing</td>
			<td>IDEX Health &#38; Science</td>
			<td>U-102</td>
			<td>Stainless Steel Tubing 1/16 inch OD x 0.020 inch ID, 10 cm, various precut lengths available</td>
		</tr>
		<tr>
			<td>Syringe pump control software</td>
			<td>Cetoni</td>
			<td>T6000000004</td>
			<td>QmixElements software for nemesys pumps, QmixSDK software development kit</td>
		</tr>
		<tr>
			<td>Thermoelectric air conditioner</td>
			<td>EIC Solutions</td>
			<td>AAC-140C-4XT-HC</td>
			<td>Thermoelectric air conditioner mounted on insulated enclosure to control the pump, valve, mixer, and sample temperature</td>
		</tr>
		<tr>
			<td>T-slot railing</td>
			<td>McMaster-Carr</td>
			<td>47065T103</td>
			<td>Aluminum t-slotted railing (1.5 inch by 1.5 inch) cut to various lengths</td>
		</tr>
		<tr>
			<td>Vapor locking bottle caps&#160;</td>
			<td>Cole-Parmer</td>
			<td>EW-12018-02</td>
			<td>Four 304 SS port inserts, 1/4&#34;-28 threads, GL45 bottle cap size, PTFE body, SS threads, PP collar</td>
		</tr>
	</tbody>
</table>

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.

The representative neutron data shown here measure lipid exchange kinetics in the presence of methyl-&#946;-cyclodextrin (m&#946;CD), an additive that catalyzes the lipid exchange between vesicles with the exchange rate (ke)66,67. Previous fluorescence studies have shown that ke depends on the m&#946;CD concentration, and the half-life of the exchange process is on the order of minutes68. The present experiments use s...

Watch this Scientific Journal Video about Measuring the Time-Evolution of Nanoscale Materials with Stopped-Flow and Small-Angle Neutron Scattering at JoVE.com

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

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 ...

Stop flow small angle scattering or stop flow SANS allows us to study how nanoscale materials evolve on set timescales of seconds to minutes. The contrast between hydrogen and deuterium unique to neutron scattering makes this technique particularly useful for studying materials rich in hydrogen such as lipids, proteins, and polymers. If you're interested in using stop flow stands to study your materials of interest, contact US local instrument scientist at a scattering facility to help plan your experiment.Demonstrating the procedure will be Ryan Murphy a chemical engineer at the National Institute of Standards and Technology, or NIST, Center for Neutron Research, or the NCNR and Brian Maranville a physicist also at the NCNR. To begin turn on all pump power supplies and dynamic mixers. Using the power switch initiate all pumps and valves in the stopped flow system controlled GUI by entering the device configuration path and commands mentioned in the text manuscript calibrate the pumps before attaching syringes.After ensuring the pumps have been calibrated. Screw in clean syringe barrels to the connection at the top of the pump. Ensure the syringe mount head is loosened before dispensing the fill volume so that the syringe does not break due to excessive force from the syringe piston.Then screw the syringe piston into the connection at the bottom of the pump. After the syringe barrel and syringe piston are connected to the pump, dispense the fill volume. After the piston stops moving tighten the syringe mount head.Then connect the tubing to the sample and solvent sources, syringes, valves, mixers, sample cells and mixed sample container. Define all tubing and valve connections made in the stopped flow system controlled GUI by typing in the corresponding port number connections made to each valve. To load the sample aspirate the desired sample and solvent volumes from their sources into the sample syringes through the pump selector valves.Then prime the system by dispensing all air from the syringes, tubing lines, and valves, ensuring that enough liquid volume is dispensed from each syringe. To remove all the air bubbles, once the air has been purged from the system, perform at least one sample injection by clicking the cell labeled Start mixing experiment in the controlled GUI, with this cell actively selected. Click on the run button at the top of the controlled GUI or press the shift and enter keys together on the keyboard.Visually inspect the sample cell for air bubbles. If bubbles are present repeat the purging steps, otherwise proceed to define the remaining experiment protocol steps. To define the stopped flow mixing protocol.Enter the temperature set point of the programmable air conditioner unit that controls the temperature of the insulated enclosures surrounding the stopped flow device. Then enter all rinsing sequence steps by typing in the appropriate volumes, flow rates, times and number of repetitions into the controlled GUI. Next define all sample injection sequence steps by typing the appropriate volumes, flow rates and times into the stopped flow system controlled GUI finally calculate the total time of a single stopped flow data collection cycle to define the SANS parameters.Set the total VSANS data acquisition time in the SANS instrument controlled GUI to the previously calculated cycle time. Then set the sample transmission measurement time to 100 seconds and turn on the event mode data collection. To measure the background scattering.Ensure that the local instrument shutter is closed before attaching the blocked beam sample to the back of the sample aperture. Then after securing the local instrument environment open the local instrument shutter. Next, define the blocked beam scattering data acquisition time in the software and collect blocked beam scattering data counting for the same duration as the longest scattering data acquisition time.Once the data collection is complete close the instrument shutter and remove the blocked beam sample from the sample aperture. Then proceed to measure the empty cell scattering before beginning the stopped flow experiment. Ensure that the local instrument area is secure.Then open the local instrument beam shutter. Begin SANS data collection using the SANS instrument control software on the instrument computer by dragging and dropping the desired runs into the instrument queue. Next, start the stopped flow mixing experiment in the controlled GUI and confirm that the defined stopped flow mixing protocol has started operating.Then add the transmission run to the bottom of the queue. The transmission will be collected after the scattering run finishes. After downloading the scattering data file and associated event files from the server bin the scattering data to the desired time bins by entering the appropriate commands as indicated in the text manuscript.Then reduce the bin scattering data using the software provided in the beam line to analyze the time resolved SANS data, calculate the process time of interest from the measurement times using the equation provided in the text manuscript. Then extract the kinetic parameters of interest from the change in Q dependent intensity as a function of process time. The measured neutron count rates of salt buffer background over multiple injection cycles consisting of nine rinsing steps.One drawing step and one sample injection step are shown here. The individual H labeled and D labeled lipid solutions were mixed at time T mix and immediately flowed into the sample cell. The measurement neutron count rate spiked and reached a maximum value when the sample cell was filled at T fill.The neutron counts from the mixed lipid vesicles sample at three different temperatures are plotted as a function of the corrected process timescale which is the process time of interest corrected for the steady state flow period and delay time. SANS data were collected continuously in event mode which can then be post processed into the desired time bins. The lipid exchange kinetics were measured at 36 degrees 30 degrees and 20 degrees Celsius.These data were bend into equal time bins of three seconds and are representative of the time and length scale dependent information that can be gained from a TR SANS measurement. The normalized intensity is plotted as a function of the process time for the different temperatures. Combining stop flow mixing and time resolve SANS provides new opportunities to explore structural evolutions in nano scan materials ranging from the lipid nanoparticles and next generation medicines and vaccines to geo polymers used in green building materials.

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Engineering

2.0K 조회수.  National Institute of Standards and Technology. 정지 흐름, 작은 각도 산란 또는 정지 흐름 SANS를 사용하면 나노 스케일 재료가 몇 초에서 몇 분의 정해진 시간 척도에서 어떻게 진화하는지 연구 할 수 있습니다. 중성자 산란 특유의 수소와 중수소의 대비로 인해 이 기술은 지질, 단백질 및 폴리머와 같은 수소가 풍부한 물질을 연구하는 데 특히 유용합니다. 스톱 플로우 스탠드를 사용하여 관심 물질을 연구하는 데 관심이 ?...