The Research at Oak Ridge National Laboratory's Spallation Neutron Source and Center for Nanophase Materials Sciences was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. The author, Zhe Zhang, gratefully acknowledges the financial support from J&#252;lich Center for Neutron Science, Research center J&#252;lich.

Note: This protocol requires special care in the handling of nanomaterials. As-purchased single-walled carbon nanotubes (SWNTs) exist in the form of fine powder and thus, they should be considered as nano-hazardous materials before dispersing them in aqueous solutions. Please use appropriate safety equipment described in the material safety data sheets (MSDS).
1. Preparation of Poloxamer 407/SWNT Aqueous Suspensions
Note: Proceed with all the sample preparation procedures at a lower temperature than the critical micellization temperature (CMT) of the block copolymers used. The poloxamer 407/SWNT samples were prepared at 20 &#176;C, below the CMT of poloxamer 407 (30 &#176;C).21
<ol>
	<li>Preparation of Poloxamer 407 aqueous solutions (0.25% w/w)
	<ol>
		<li>Completely dissolve 0.175 g of poloxamer 407 powder in 70 g D2O. 
		Note: D2O is used for SANS measurements. 70 g D2O is approximately 63.2 ml at room temperature. For other purposes, H2O is recommended for use.</li>
	</ol>
	</li>
	<li>Preparation of crude Poloxamer 407/SWNT suspensions
	<ol>
		<li>Add 0.01 g SWNT powder to two 50 ml conical centrifuge tubes (tube 1 and tube 2) separately.</li>
		<li>Add 31.6 ml of the poloxamer 407 solution (1.1.1), into the tube 1 and 31.6 ml of the remaining solution into the tube 2.</li>
		<li>Mix the suspensions in the tube 1 and 2 by vortex-mixing for 5-10 min.</li>
		<li>Place the tube 1 in a water bath. Fix the tube position securely. (Figure 1) Dip the tube until the air-suspension interface reaches the surface of water in the bath.</li>
		<li>Dip the tip of an ultrasonicator into the suspension of the tube 1. Increase the sonication power gradually from 0% at least until the SWNTs deposited at the bottom of the tube start shattering and spreading due to the ultrasound propagated from the ultrasonicator tip. Treat the suspension with ultrasound for 60 min at 20 &#176;C, while keeping the suspension temperature below 25 &#176;C. 
		Note: Do not put the tip end deeper than 1 cm into the suspension. Keep the suspension temperature below 25 &#176;C, either by controlling the temperature of the water reservoir or by refilling the bath appropriately.</li>
		<li>Repeat steps 1.2.4 and 1.2.5 for the tube 2.</li>
	</ol>
	</li>
	<li>Preparation of Poloxamer 407/SWNT suspensions in the absence and presence of 5-Methylsalicylic acid
	<ol>
		<li>Centrifuge the crude suspensions in tubes 1 and 2 at 9,800 &#215; g for 2 hr at 20 &#176;C.</li>
		<li>Move 15 ml of the supernatants from each tube to a new tube, separately.</li>
		<li>Dissolve 0.015 g of 5-methylsalicylic acid (5MS) into the supernatant taken from tube 2, and label this mixture as Sample #2. Label the other supernatant from the tube 1 as Sample #1.</li>
	</ol>
	</li>
</ol>
2. Extended Q-range Small-angle Neutron Scattering (EQ-SANS) Measurements
Note: To work at the beamlines of Spallation Neutron Source (SNS), an accepted beamtime proposal is required. Radiological safety training and other instrument specific training are also required in advance. Access and training details are provided by the SNS User Office and can be found at neutrons.ornl.gov.
<ol>
	<li>Sample loading
	<ol>
		<li>Load 0.3 ml of Sample #1 of into an amorphous quartz banjo cell and Sample #2 into another banjo cell (Figure 2A-i). Put lids on the two cells and seal them by wrapping tape securely around the lids.</li>
		<li>Place one of the sealed cells between spacers (Figure 2A-ii) for an aluminum cell holder (Figure 2A-iii), and assemble the aluminum banjo cell holder (Figure 2B). Assemble the other cell with a different set of banjo cell holder in the same manner.</li>
		<li>Load the assembled cells into different sample positions of the EQ-SANS sample paddle (Figure 3A). Make the list of the sample positions of the paddle.</li>
	</ol>
	</li>
	<li>Measurements
	<ol>
		<li>Set the configurations for the SANS measurements in a script with the help of an instrument scientist, referring to the given example script. 
		Note: An example of the script used during the actual SANS measurements is provided in the supplementary material with brief comment. This example is specifically designed for SANS measurements of two samples (sample #1 and #2) using a wavelength band of 9.1 &#197; &#60; &#955; &#60; 13.2 &#197; at the fixed 1.3 m sample-to-detector distance with a 10 mm sample aperture and a 30 mm beam stop. The example script can be used without any modification for the sample #1 and #2.
		<ol>
			<li>To cover a q-range of 0.01 - 0.4 &#197;-1, select a wavelength band of 9.1 &#197; &#60; &#955; &#60; 13.2 &#197; and a sample-to-detector distance of 1.3 m by inputting 1300 into detector position and 9 into wavelength as shown in the example script.</li>
			<li>To use a 10 mm sample aperture and a 30 mm beam stop, set x-y positions of the beam stops and apertures in the script.</li>
			<li>Set the sample positions and the corresponding names for both transmission and sample scattering measurements.</li>
			<li>Save the script in the folder corresponding to the beam time.</li>
		</ol>
		</li>
		<li>Execute the script to perform measurements by clicking on &#39;Run Script&#39; on the right side of the PyDAS control window (Figure 3B) and loading the saved script.</li>
		<li>Inform the instrument team of the completion of measurements after the experiment is finished.</li>
	</ol>
	</li>
</ol>
3. SANS Data Reduction and Analysis
<ol>
	<li>SANS Data reduction process
	<ol>
		<li>For the reduction of the measured data, use MantidPlot23-24 software provided at analysis.sns.gov, with the help of the instrument team. 
		Note: Detailed instructions to run MantidPlot software can be found at analysis.sns.gov webpage.</li>
		<li>Within MantidPlot, open the EQSANS reduction interface from the interfaces menu. (interface&#62;SANS&#62;ORNL SANS). Input all necessary information for the data reduction process. 
		Note: Most of important information in the data reduction process is provided by the instrument team. For information, relevant screenshots are also provided in the supplementary materials.</li>
		<li>Input all necessary information in the &#39;Reduction Options&#39; tab.
		<ol>
			<li>Input the absolute scale factor from the standard sample measurement. Obtain the absolute intensity from the measurement of a well characterized standard sample whose scattering intensity is known (I(0)=450 cm-1) and fit with a Debye-Buche scattering model.</li>
			<li>Input the dark current file name, which is provided by the instrument team.</li>
			<li>Check options for the &#39;solid angle correction&#39;, &#39;Q resolution&#39;, &#39;use configuration file&#39;, &#39;Correct TOF&#39;, and &#39;user mask from configuration file as applicable&#39;.</li>
			<li>Set sample aperture diameter to 10 mm. Set number of Q bins to 200 with a linear Q binning scheme. Input the mask file name, which is also provided by the instrument team.</li>
		</ol>
		</li>
		<li>Input all necessary information to complete the &#39;Detector&#39; tab.
		<ol>
			<li>Check &#39;Use beam finder&#39; (with fit direct beam option) and &#39;perform sensitivity correction&#39;. Find a beam center &#39;data file&#39; using the run number of the empty beam measurement.</li>
			<li>Input the sensitivity data file name, which is provided by the instrument scientist. Set the allowed sensitivity range to 0.5 and 2.5 for the min and max, respectively. Check &#39;Use sample beam center&#39;.</li>
		</ol>
		</li>
		<li>Input all necessary information for the &#39;Data&#39; tab.
		<ol>
			<li>Enter sample scattering run number at &#39;Scattering data file&#39;. Specify the sample thickness in cm. Select &#39;Calculate transmission&#39;.</li>
			<li>Enter the sample transmission run number at &#39;Sample direct beam data file&#39;. Enter empty beam run number at &#39;Empty direct beam data file&#39;.</li>
			<li>Check &#39;Background data file&#39; and enter background scattering run number. Select &#39;Calculate transmission&#39;. Enter background transmission run number at &#39;Sample direct beam data file&#39;. 
			Note: In this case, the empty banjo cell scattering data file is the background scattering.</li>
			<li>Enter empty beam run number at &#39;Empty direct beam data file&#39;. Typically, this number is same as the empty beam run number (3.1.5.2).</li>
		</ol>
		</li>
		<li>Click on &#39;Reduce&#39; to execute the data reduction. 
		Note: The output is written in the designated folder as #####_Iq.txt where ##### is the run number of the sample scattering file. ASCII format is used for the data files.</li>
	</ol>
	</li>
	<li>Model fitting analysis 
	Note: SasView is a small-angle scattering analysis software package, which was originally developed as part of the NSF DANSE project, and is currently managed by an international collaboration of facilities (http://www.sasview.org/). The software package can be downloaded at http://sourceforge.net/projects/sasview/files/.
	<ol>
		<li>Run SasView, and load a data file by clicking on &#39;Load Data&#39; from the &#39;Data Explorer&#39; window.</li>
		<li>Click on &#39;Send To&#39; with the &#39;Fitting&#39; option, and check the data plot on the popup window.</li>
		<li>In the &#39;Fit Panel&#39;, select &#34;Shapes&#34; under the model category, and choose &#34;CoreShellCylinderModel&#34; from the model drop box.</li>
		<li>Adjust the parameter values, so the model curve is as close to the data curve as possible. 
		Note: Use the SLD (scattering length density) calculator from the Tool menu to calculate scattering length densities.</li>
		<li>Select &#34;Use dQ data&#34; and &#34;Use dI Data&#34; in the Fitting panel. Adjust Q range of the data for fitting. Click on &#39;Fit&#39; to execute data fitting.</li>
	</ol>
	</li>
</ol>
4. Real-space Observation Using Atomic Force Microscopy (AFM)
<ol>
	<li>Sample preparation on Si-wafers using spin coating
	<ol>
		<li>For AFM measurements, take 0.1 ml sample solution from the Sample #1 (1.3.3), and mix it with 1.9 ml de-ionized water.</li>
		<li>Place a clean Si-wafer (12 mm &#215; 12 mm) on a spin coater. Fix the wafer position using a vacuum chuck.</li>
		<li>Set the rotation speed and the running time at 1,500 revolutions per minute (rpm) and 60 sec, respectively. Wet the exposed surface of the wafer with the diluted sample. Start spin coating.</li>
		<li>Turn off the vacuum pump, and remove the coated wafer from the spin coater.</li>
	</ol>
	</li>
	<li>AFM measurements
	<ol>
		<li>Attach the spin-coated wafer (4.1.4) on an iron disk using a double-sided adhesive carbon tape.</li>
		<li>Bring the specimen disk (4.2.1) closer to the edge of the exposed area of the scanner first, and slide the disk toward the center until the bottom surface of the disk completely covers the top of the scanner. 
		Note: Avoid sudden contact because a magnet on the top of the scanner strongly attracts the iron disk. Gently make a contact between two edges of the disk and the scanner.</li>
		<li>Mount the scanning probe microscope (SPM) head on the scanner, and plug in the cable. 
		Note: Extreme care has to be paid while moving the SPM head or docking (removing) it to (from) the scanner. When the head is detached from the scanner stage, keep the bottom surface of the head facing upwards all the time.</li>
		<li>Run the instrument-supplied control software, and select the tapping mode in the &#39;System Configuration&#39; window.</li>
		<li>Place the cantilever tip at the center of the monitor window by adjusting the coarse and fine knobs of the optical microscope and by moving the x- and y- optical stages.</li>
		<li>Align the laser by adjusting the laser alignment knobs on the SPM head. Locate the red laser dot to the cantilever roughly, and move the dot to the middle of the cantilever tip by tracing the dot shown in the monitor. 
		Note: When the laser is properly aligned, the pink reflection spot appears on the laser alignment window.</li>
		<li>Align the detector by locating the pink reflection image at the center of the laser alignment window. Adjusting the photodetector knobs on the SPM head until the quadrant photodiode (QPD) signal sum is greater than 2 V at least (2.1 - 2.4 V).</li>
		<li>Tune the cantilever using AutoTune in the Cantilever Tuning window. Run AutoTune in a frequency range of 0 - 1,000 kHz.</li>
		<li>Bring the wafer surface into focus of the microscope by adjusting the focus knobs.</li>
		<li>Drive the cantilever tip slowly toward the wafer surface using the up and down arrows in the &#39;Motor Stage&#39; window. Stop the movement before the tip touches the sample surface. 
		Note: As the tip approaches the wafer, the blurred black image of the tip appears in the monitor and the image becomes clear when the tip and the wafer surface make contact. Never let the tip physically touch the specimen. It damages both sample and instrument. Stop the tip when the dark blurred image is shown.</li>
		<li>Click on the engage button on the toolbar.</li>
		<li>Select a scan size (5-10 &#181;m), a sampling number (512-1,024), and a scan rate (0.5-0.6 Hz) in the popup window, in order to acquire a large-scale image first.</li>
		<li>Start scanning. Gradually adjust P (proportional gain), I (integral gain), and D (vertical deflection) values if the contrast between the particles and the substrate background is too low to clearly recognize particle shapes and boundaries from the scanned image. 
		Note: When a new PID value set is entered, the scanning process will be automatically restarted.</li>
		<li>If there is any region of interest in the large-scale image, re-run the scan with a proper set of scan size, x-offset, y-offset, and sample number.</li>
		<li>Disengage the probe after measurement. 
		Note: Raise the probe head to prevent any damage on the cantilever tip and the sample. Remove the probe head first, and then, detach the specimen disk.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

SANS and AFM measurements showed that SWNTs have been successfully de-bundled and individually dispersed in aqueous solution using a poloxamer 407 triblock copolymer. In this sample preparation method, ultra-sonication and centrifugation processes are the critical steps determining the characteristics of the final suspension. The strong interaction between the SWNTs, which forces uncoated SWNTs to bundle together in solution, must be overcome to stabilize the individual SWNTs with block copolymers. Providing a sufficient energy for a properly long time allows the polymers to overcome the energy barriers and stabilize the SWNT successfully. Nevertheless, it is too difficult to remove all the SWNT bundles in the suspension and thus, the fractionation process is also crucial to produce high purity and quality samples. Optimization in the sonication power, the centrifugation speed, and the collecting volume of supernatant is required if any improvement in the sample purity and yield rate is needed.
Using this method, thermo-reversible CNT/polymer nanoparticles of various sizes can be fabricated by varying the molecular weight of the triblock copolymer. It has been predicted that the stabilization of carbon nanotubes using amphiphilic block copolymers shows size selectivity so that carbon nanotubes with a specific diameter can be selectively solubilized.25 In this work, SANS analysis reveals that the SWNT core in the synthesized nanorods has a diameter of about 7.2 &#197; on average. This implies that poloxamer 407 could even solubilize SWNTs with a relatively small diameter around 7-8 &#197; among HiPCo (high-pressure carbon monoxide) SWNTs, which are known to have a diameter of 7-14 &#197;.26 Therefore, a rational selection of molecular weight and the PEO/PPO mass ratio in the PEO-PPO-PEO polymers enables researchers not only to utilize either single-walled or multi-walled carbon nanotubes regardless of their diameter but also to size-selectively fabricate polymer-CNT hybrid nanorods via this strategy.
Although a variety of PEO-PPO-PEO polymer-coated CNT nanorods can be prepared through the identical preparation procedure, the methods for characterization of the detailed structure in real space are quite limited. Commonly-used optical microscopy instruments are not appropriate because of the very small particle size. Electron microscopy (EM) and AFM techniques also have limitations. Solvent evaporation required in dry-EM and AFM techniques prevents the in-situ characterization and may cause a morphology change, and temperature quenching in cryo-EM prevents the real-time observation with temperature control. Thus, the structural characterization in q-space using small-angle scattering techniques is essential in this system, and it is also more powerful if any other real-space observation can be provided as a complementary approach.
Nevertheless, for this characterization method via SANS, there are two things to consider. First, the set of fitting parameters from SANS analysis may not be unique because there are uncertainties in SLDs. The obtained results should be consistent with other physical measurements as well as the amount and SLDs of the constituents. Second, this investigation is based on model-dependent analysis and thus, the fitting model should be chosen by carefully considering the inter-molecular interaction as well as possible macro-molecular geometries. The CoreShellCylinder model introduced in this protocol is one of the simplest models, which is appropriate for describing polymer-coated CNT structures. Although the CoreShellCylinder model provides information about the core and shell thicknesses of the synthesized nanorods, the oversimplified form factor in this model is not able to describe the actual distribution profiles of water and polymers surrounding the CNT core. For a better understanding, the modified CoreShellCylinder model, which employs the Gaussian chain model for the adsorbed polymers, is recommended.21
Through this work, it is demonstrated that the synthesized hybrid nanoparticles exhibit a sensitive temperature-dependent response of their encapsulation structure. These systems present an interesting model for smart functional building blocks which self-assemble into higher-ordered nanostructures and whose intra- and inter-particle structures are reversibly controlled as a response to external stimuli. While the technique presented lends itself to producing well-ordered, self-assembled systems, there are still challenges to be overcome before they can be utilized in devices. For example, after sonication the CNT&#39;s are not uniform in length limiting full three dimensional order. Nevertheless, successful design of fabrication of shape-tunable nano-building blocks provide a promising opportunity towards self-assembled smart functional materials.

Carbon nanotubes (CNTs) are hollow cylindrical nanoparticles formed by rolling a micrometer-scale graphite sheet into a nanotube. Because of their extraordinary mechanical, thermal, and electrical properties, CNTs have been extensively investigated as a novel candidate for functional nanoparticles in therapeutic and bio-sensing applications as well as nano-fillers in self-assembled nanocomposite materials.1-3 However, their poor solubility and strong preference toward making bundles in commonly used organic and aqueous solvents hinder easy and environmentally-friendly processing as well as advances in biological applications. Therefore, a variety of functionalization methods, such as ultra-sonication, chemical surface modification, and non-covalent functionalization by using surfactants and block copolymers,4-9 have been developed to modify the CNT surfaces and improve their dispersibility in a wide range of solvents. Non-covalent functionalization methods based on physical surface treatments, in particular, are considered to be a promising and robust strategy, because any surface-modification induced suppression in intrinsic CNT properties can be minimized.10 To date, there have been numerous efforts to improve the dispersion efficiency of non-covalent functionalization methods by employing various types of dispersive agents including basic surfactants (e.g., SDS, CTAB, NaDDBS),7,11 amphiphilic block copolymers,8 bio-materials (e.g., DNA),12,13 and synthetic functional polymers (e.g., conjugated polymer, aromatic polymer).14,15
PEO-PPO-PEO polymers, a kind of triblock copolymer consisting of two hydrophilic poly(ethylene oxide) (PEO) chains at both ends covalently bound to one hydrophobic poly(propylene oxide) (PPO) chain at the center, can extend the potential application of non-covalently functionalized CNTs in aqueous solution. These polymers provide the interface, which is friendly not only to the CNT surfaces but also to aqueous media and other polymer matrices and exhibits tremendous biocompatibility due to the minimal toxicity of the PEO chains. This facilitates easier processing in a wide range of dispersing environments as well as the utilization of polymer-coated CNTs in biomedical applications.12,16-17 Moreover, the rich thermodynamic phase behavior of these polymers based on their sensitive responses to external stimuli enables the fabrication of the smart block copolymer-CNT hybrid nanostructures in which intra- and inter-particle structures can be reversibly and precisely controlled.18-21 Here, we present a protocol for the fabrication of CNT-based hybrid nanoparticles with a tunable encapsulation layer of PEO105-PPO70-PEO105 (poloxamer 407). The resulting structure is characterized by small-angle neutron scattering (SANS). This work is expected to introduce the concept of smart functional building blocks and help non-specialists easily prepare block copolymer-functionalized CNT suspensions and use SANS for the detailed characterization at Oak Ridge National Laboratory.

<table><tbody><tr><td>HiPco Single-walled carbon nanotubes</td><td>Unidym</td><td>P2771</td><td></td></tr><tr><td>Pluronic F127</td><td>BASF</td><td>9003-11-6</td><td>Mw = 12.6 kg/mol</td></tr><tr><td>5-methylsalicylic acid</td><td>TCI America</td><td>C0410</td><td></td></tr><tr><td>Ultrasonic processor</td><td>Cole-Parmer</td><td>ML-04714-52</td><td></td></tr><tr><td>Sorvall 6 plus centrifuge</td><td>Thermo Scientific</td><td>46910</td><td></td></tr><tr><td>Innova AFM</td><td>Bruker</td><td></td><td></td></tr><tr><td>Si-wafer</td><td>Silicon Quest International</td><td></td><td>150 mm in diameter; N type &amp;lt;1-1-1&gt; cut; 1-10&amp;nbsp;Ohm/cm; Single-side polyshed (675 &amp;#177; 25 &amp;#956;m); Diced (12&amp;nbsp;mm x 12 mm)</td></tr></tbody></table>

functionalization of single-walled carbon nanotubes with thermo-reversible block copolymers and characterization by small-angle neutron scattering

We demonstrate a protocol for single-walled carbon nanotube functionalization using thermo-sensitive PEO-PPO-PEO triblock copolymers in an aqueous solution. In a carbon nanotube/PEO105-PPO70-PEO105 (poloxamer 407) aqueous solution, the amphiphilic poloxamer 407 adsorbs onto the carbon nanotube surfaces and self-assembles into continuous layers, driven by intermolecular interactions between constituent molecules. The addition of 5-methylsalicylic acid changes the self-assembled structure from spherical-micellar to a cylindrical morphology. The fabricated poloxamer 407/carbon nanotube hybrid particles exhibit thermo-responsive structural features so that the density and thickness of poloxamer 407 layers are also reversibly controllable by varying temperature. The detailed structural properties of the poloxamer 407/carbon nanotube particles in suspension can be characterized by small-angle neutron scattering experiments and model fit analyses. The distinct curve shapes of the scattering intensities depending on temperature control or addition of aromatic additives are well described by a modified core-shell cylinder model consisting of a carbon nanotube core cylinder, a hydrophobic shell, and a hydrated polymer layer. This method can provide a simple but efficient way for the fabrication and in-situ characterization of carbon nanotube-based nano particles with a structure-tunable encapsulation.

Poloxamer 407-coated SWNT nanorod suspensions were fabricated using the sample preparation procedure (Figure 4), which can be divided into two important processes; the physical adsorption process of poloxamer 407 on SWNT surfaces using ultra-sonication, and the fractionation process of individually-stabilized SWNTs from bundled aggregates using centrifugation.
The SANS scattering intensities were obtained for the prepared poloxamer 407/SWNT/D2O sample in a temperature range of 20-60 &#176;C in the absence (Figure 5A) and presence (Figure 5B) of 5MS. The scattering intensities with the q-1 behavior in the low q regions (&#60; 0.02 &#197;-1) indicate the existence of cylindrical rod-like particles in the aqueous media. By changing the temperature from 20 &#176;C to 60 &#176;C or by adding 5MS additives, the scattering intensities show clear changes; a shift to higher q in the intermediate q-region (0.02-0.05 &#197;-1) and the development of a peak at high q (about 0.11 &#197;-1) are observed. These analogous changes due to temperature-control and 5MS-addition originate from the structural change of poloxamer 407-encapsulation layer on SWNTs. As summarized in Figure 6A-6D, the CNT core/hydrophobic inner shell/hydrated poloxamer 407 layer undergoes a structural transformation from an SWNT encapsulated by spherical micelles of poloxamer 407 at room temperature to an SWNT encapsulated by a compact cylindrical layer of poloxamer 407 at higher temperature. The structural change was reversible with varying temperature regardless of the existence of 5MS additives; the size of hydrated polymer blobs was reversibly controlled in a temperature range between 20 &#176;C and 60 &#176;C. During this structural change of the poloxamer 407 layer, the spherical poloxamer 407 micelle with a radius of gyration of 45 &#197;, which consists of several poloxamer 407 chains, becomes a set of single-chain blobs which surround the SWNT core more compactly with a radius of gyration of 30 &#197;.
The structural change upon both temperature control and aromatic additives is explicable by variations in intermolecular interactions among polymers, water, and SWNTs. Increasing hydrophobicity of PPO and PEO blocks with increasing temperature causes stronger interaction of adsorbed polymers with SWNT core surfaces than with water.21 As a result, the adsorbed polymers form more compact encapsulation layer at high temperature to cover the hydrophobic core more efficiently and reduce the interfacial free energy. This tendency can be more promoted in the presence of 5MS, because of the preferential interaction between SWNT and a benzene ring of 5MS as well as the strong tendency of 5MS to bind with poloxamer 407.21,22 Especially, the inner shell thickness (Figure 6B), which was measured to be about 3 &#197; close to the planar distance between 5MS molecules and SWNT surfaces,21 is in good agreement with the prediction that the added 5MS prefer to occupy the SWNT surface area and provide a friendly interface to the polymers.
As a complementary investigation to the SANS study, the poloxamer 407/SWNT nanorods were observed in real space using an AFM. Figures 7A and 7B are tapping mode AFM images of poloxamer 407/SWNT nanorods which were spin-coated onto a Si-wafer. Although these AFM images only show a dried morphology of the nanorods without water, they provide evidence of de-bundling and dispersion of SWNTs as well the length distribution of the nanorods.
<img alt="Figure 1" src="/files/ftp_upload/53969/53969fig1.jpg" /> 
Figure 1. Snapshot of the ultrasonication process for SWNT stabilization. A sample tube is put into a water bath with the tip dipped in. <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/53969/53969fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/53969/53969fig2.jpg" /> 
Figure 2. Aluminum banjo cell holder for the EQ-SANS experiment at SNS. (A) Disassembled parts including (i) a banjo cell (ii) spacers, and (iii) a holder. (B) Assembled parts. <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/53969/53969fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/53969/53969fig3.jpg" /> 
Figure 3. Standard EQ-SANS experiment environments. (A) Sample booth, and (B) control software at the beam line. <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/53969/53969fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" src="/files/ftp_upload/53969/53969fig4.jpg" /> 
Figure 4. Simplified sample preparation procedure for Poloxamer 407/SWNT (sample #1) and Poloxamer 407/SWNT/5MS (sample #2) suspensions. The mass ratio between SWNTs and Poloxamer 407 in these final suspensions was measured by thermogravimetric analysis (TGA) after freeze-drying (*). (This figure has been modified with permission from ref. 21. Copyright 2015, American Chemical Society.) <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/53969/53969fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" src="/files/ftp_upload/53969/53969fig5.jpg" /> 
Figure 5. SANS intensities measured in a temperature range from 20 &#176;C to 60 &#176;C. (A) Poloxamer 407/SWNT/D2O sample. (B) Poloxamer 407/SWNT/5MS/D2O sample. The solid lines are the curves obtained by fitting the SANS data using a modified core/shell/chain model. The q-1 behavior at low q regions around 0.01 &#197;-1 indicates the existence of rod-like particles in the suspensions. The curves have been shifted for clarity. (This figure has been modified with permission from ref. 21. Copyright 2015, American Chemical Society.) <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/53969/53969fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" src="/files/ftp_upload/53969/53969fig6.jpg" /> 
Figure 6. Detailed structures of encapsulation layers from a SANS model fit analysis. (A) Radius of gyration (Rg) of poloxamer 407 chain blobs and (B) thickness of hydrophobic inner shell layers (T1) on SWNT surfaces in the absence (diamond) and presence (square) of 5-Methylsalicylic acid (5MS) in a temperature range from 20 &#176;C to 60 &#176;C. Rg was reversibly changed by controlling temperature via heating (filled marker) and cooling (filled marker with a cross inside) processes regardless of the existence of 5MS. (C-D) Schematic cross-sectional diagrams suggested from SANS analysis for the poloxamer 407/SWNT nanorods at room temperature (top) and its structural changes with increasing temperature or adding additives (bottom). (This figure has been modified with permission from ref. 21. Copyright 2015, American Chemical Society.) <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/53969/53969fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" src="/files/ftp_upload/53969/53969fig7.jpg" /> 
Figure 7. Tapping mode AFM images of spin-coated Poloxamer 407/SWNT nanorods on Si-wafer. (A) The height channel image provides the z-directional thickness information. (B) The tapping amplitude channel image presents clear boundaries of deposited nanoparticles. Scale bar: 1 &#181;m. (This figure has been modified with permission from ref. 21. Copyright 2015, American Chemical Society.) <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/53969/53969fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Functionalization of Single-walled Carbon Nanotubes with Thermo-reversible Block Copolymers and Characterization by Small-angle Neutron Scattering at JoVE.com

Functionalization of Single-walled Carbon Nanotubes with Thermo-reversible Block Copolymers and Characterization by Small-angle Neutron Scattering

A method for the functionalization of carbon nanotubes with structure-tunable polymeric encapsulation layers and structural characterization using small-angle neutron scattering is presented.

We demonstrate a protocol for single-walled carbon nanotube functionalization using thermo-sensitive PEO-PPO-PEO triblock copolymers in an aqueous ...

functionalization-single-walled-carbon-nanotubes-with-thermo

Nanyang Technological University

Research

JoVE Journal

Chemistry

9.1K Views.  Oak Ridge National Laboratory. A method for the functionalization of carbon nanotubes with structure-tunable polymeric encapsulation layers and structural characterization using small-angle neutron scattering is presented.

Video: Functionalization of Single-walled Carbon Nanotubes with Thermo-reversible Block Copolymers and Characterization by Small-angle Neutron Scattering

Fabrication, Densification, and Replica Molding of 3D Carbon Nanotube Microstructures

The introduction of new materials and processes to microfabrication has, in large part, enabled many important advances in microsystems, lab-on-a-chip devices, and their applications. In particular, capabilities for cost-effective fabrication of polymer microstructures were transformed by the advent of soft lithography and other micromolding techniques 1, 2, and this led a revolution in applications of microfabrication to biomedical engineering and biology. Nevertheless, it remains challenging to fabricate microstructures with well-defined nanoscale surface textures, and to fabricate arbitrary 3D shapes at the micro-scale. Robustness of master molds and maintenance of shape integrity is especially important to achieve high fidelity replication of complex structures and preserving their nanoscale surface texture. The combination of hierarchical textures, and heterogeneous shapes, is a profound challenge to existing microfabrication methods that largely rely upon top-down etching using fixed mask templates. On the other hand, the bottom-up synthesis of nanostructures such as nanotubes and nanowires can offer new capabilities to microfabrication, in particular by taking advantage of the collective self-organization of nanostructures, and local control of their growth behavior with respect to microfabricated patterns. 
Our goal is to introduce vertically aligned carbon nanotubes (CNTs), which we refer to as CNT "forests", as a new microfabrication material. We present details of a suite of related methods recently developed by our group: fabrication of CNT forest microstructures by thermal CVD from lithographically patterned catalyst thin films; self-directed elastocapillary densification of CNT microstructures; and replica molding of polymer microstructures using CNT composite master molds. In particular, our work shows that self-directed capillary densification ("capillary forming"), which is performed by condensation of a solvent onto the substrate with CNT microstructures, significantly increases the packing density of CNTs. This process enables directed transformation of vertical CNT microstructures into straight, inclined, and twisted shapes, which have robust mechanical properties exceeding those of typical microfabrication polymers. This in turn enables formation of nanocomposite CNT master molds by capillary-driven infiltration of polymers. The replica structures exhibit the anisotropic nanoscale texture of the aligned CNTs, and can have walls with sub-micron thickness and aspect ratios exceeding 50:1. Integration of CNT microstructures in fabrication offers further opportunity to exploit the electrical and thermal properties of CNTs, and diverse capabilities for chemical and biochemical functionalization 3.

We present methods for fabrication of patterned microstructures of vertically aligned carbon nanotubes (CNTs), and their use as master molds for production of polymer microstructures with organized nanoscale surface texture. The CNT forests are densified by condensation of solvent onto the substrate, which significantly increases their packing density and enables self-directed formation of 3D shapes.

The introduction of new materials and processes to microfabrication has, in large part, enabled many important advances in microsystems, lab-on-a-chip ...

Engineering

Gyroid Nickel Nanostructures from Diblock Copolymer Supramolecules

Nanoporous metal foams possess a unique combination of properties - they are catalytically active, thermally and electrically conductive, and furthermore, have high porosity, high surface-to-volume and strength-to-weight ratio. Unfortunately, common approaches for preparation of metallic nanostructures render materials with highly disordered architecture, which might have an adverse effect on their mechanical properties. Block copolymers have the ability to self-assemble into ordered nanostructures and can be applied as templates for the preparation of well-ordered metal nanofoams. Here we describe the application of a block copolymer-based supramolecular complex - polystyrene-block-poly(4-vinylpyridine)(pentadecylphenol) PS-b-P4VP(PDP) - as a precursor for well-ordered nickel nanofoam. The supramolecular complexes exhibit a phase behavior similar to conventional block copolymers and can self-assemble into the bicontinuous gyroid morphology with two PS networks placed in a P4VP(PDP) matrix. PDP can be dissolved in ethanol leading to the formation of a porous structure that can be backfilled with metal. Using electroless plating technique, nickel can be inserted into the template&#39;s channels. Finally, the remaining polymer can be removed via pyrolysis from the polymer/inorganic nanohybrid resulting in nanoporous nickel foam with inverse gyroid morphology.

This article describes the preparation of well-ordered nickel nanofoams via electroless metal deposition onto nanoporous templates obtained from self-assembled diblock copolymer based supramolecules.

Nanoporous metal foams possess a unique combination of properties - they are catalytically active, thermally and electrically conductive, and furthermore, ...

Synthesis and Functionalization of Nitrogen-doped Carbon Nanotube Cups with Gold Nanoparticles as Cork Stoppers

Nitrogen-doped carbon nanotubes consist of many cup-shaped graphitic compartments termed as nitrogen-doped carbon nanotube cups (NCNCs). These as-synthesized graphitic nanocups from chemical vapor deposition (CVD) method were stacked in a head-to-tail fashion held only through noncovalent interactions. Individual NCNCs can be isolated out of their stacking structure through a series of chemical and physical separation processes. First, as-synthesized NCNCs were oxidized in a mixture of strong acids to introduce oxygen-containing defects on the graphitic walls. The oxidized NCNCs were then processed using high-intensity probe-tip sonication which effectively separated the stacked NCNCs into individual graphitic nanocups. Owing to their abundant oxygen and nitrogen surface functionalities, the resulted individual NCNCs are highly hydrophilic and can be effectively functionalized with gold nanoparticles (GNPs), which preferentially fit in the opening of the cups as cork stoppers. These graphitic nanocups corked with GNPs may find promising applications as nanoscale containers and drug carriers.

We discussed the synthesis of individual graphitic nanocups using a series of techniques including chemical vapor deposition, acid oxidation and probe-tip sonication. By citrate reduction of HAuCl4, the graphitic nanocups were effectively corked with gold nanoparticles due to the chemically reactive edges of the cups.

Nitrogen-doped carbon  nanotubes consist of many cup-shaped graphitic compartments termed as  nitrogen-doped carbon nanotube cups (NCNCs).  These ...

Using Polystyrene-block-poly(acrylic acid)-coated Metal Nanoparticles as Monomers for Their Homo- and Co-polymerization

We present a template-free method for &#8220;polymerizing&#8221; nanoparticles into long chains without side branches. A variety of nanoparticles are encapsulated in polystyrene-block-poly(acrylic acid) (PSPAA) shells and then used as monomers for their self-assembly. Spherical PSPAA micelles upon acid treatment are known to assemble into cylindrical micelles. Exploiting this tendency, the core-shell nanoparticles are induced to aggregate, coalesce, and then transform into long chains. When more than one type of nanoparticles are used, random and block &#8220;copolymers&#8221; of nanoparticles can be obtained. Detailed procedures are reported for the PSPAA encapsulation of nanoparticles, homo- and co-polymerization of the core-shell nanoparticles, separation and purification of the resulting nanoparticle chains. Transformations of single-line chains into double- and triple-line chains are also presented. The synergy between the polymer shell and the embedded nanoparticles leads to an unusual chain-growth polymerization mode, giving long nanoparticle chains that are distinct from the products of the traditional step-growth aggregation process.

Using Polystyrene-block-polyacrylic acid-coated Metal Nanoparticles as Monomers for Their Homo- and Co-polymerization

We report protocols for &#8220;polymerizing&#8221; various types of polymer-encapsulated metal nanoparticles into long chains of &#8220;homo-&#8220; and &#8220;co-polymers&#8221;.

We present a template-free method for &#8220;polymerizing&#8221; nanoparticles into long chains without side branches. A variety of nanoparticles are ...

Preparation of Carbon Nanosheets at Room Temperature

Amphiphilic molecules equipped with a reactive, carbon-rich "oligoyne" segment consisting of conjugated carbon-carbon triple bonds self-assemble into defined aggregates in aqueous media and at the air-water interface. In the aggregated state, the oligoynes can then be carbonized under mild conditions while preserving the morphology and the embedded chemical functionalization. This novel approach provides direct access to functionalized carbon nanomaterials. In this article, we present a synthetic approach that allows us to prepare hexayne carboxylate amphiphiles as carbon-rich siblings of typical fatty acid esters through a series of repeated bromination and Negishi-type cross-coupling reactions. The obtained compounds are designed to self-assemble into monolayers at the air-water interface, and we show how this can be achieved in a Langmuir trough. Thus, compression of the molecules at the air-water interface triggers the film formation and leads to a densely packed layer of the molecules. The complete carbonization of the films at the air-water interface is then accomplished by cross-linking of the hexayne layer at room temperature, using UV irradiation as a mild external stimulus. The changes in the layer during this process can be monitored with the help of infrared reflection-absorption spectroscopy and Brewster angle microscopy. Moreover, a transfer of the carbonized films onto solid substrates by the Langmuir-Blodgett technique has enabled us to prove that they were carbon nanosheets with lateral dimensions on the order of centimeters.

We present the synthesis of an amphiphilic hexayne and its use in the preparation of carbon nanosheets at the air-water interface from a self-assembled monolayer of these reactive, carbon-rich molecular precursors.

Amphiphilic molecules equipped with a reactive, carbon-rich "oligoyne" segment consisting of conjugated carbon-carbon triple bonds self-assemble into ...

Functionalization and Dispersion of Carbon Nanomaterials Using an Environmentally Friendly Ultrasonicated Ozonolysis Process

Functionalization of carbon nanomaterials is often a critical step that facilitates their integration into larger material systems and devices. In the as-received form, carbon nanomaterials, such as carbon nanotubes (CNTs) or graphene nanoplatelets (GNPs), may contain large agglomerates. Both agglomerates and impurities will diminish the benefits of the unique electrical and mechanical properties offered when CNTs or GNPs are incorporated into polymers or composite material systems. Whilst a variety of methods exist to functionalize carbon nanomaterials and to create stable dispersions, many the processes use harsh chemicals, organic solvents, or surfactants, which are environmentally unfriendly and may increase the processing burden when isolating the nanomaterials for subsequent use. The current research details the use of an alternative, environmentally friendly technique for functionalizing CNTs and GNPs. It produces stable, aqueous dispersions free of harmful chemicals. Both CNTs and GNPs can be added to water at concentrations up to 5 g/L and can be recirculated through a high-powered ultrasonic cell. The simultaneous injection of ozone into the cell progressively oxidizes the carbon nanomaterials, and the combined ultrasonication breaks down agglomerates and immediately exposes fresh material for functionalization. The prepared dispersions are ideally suited for the deposition of thin films onto solid substrates using electrophoretic deposition (EPD). CNTs and GNPs from the aqueous dispersions can be readily used to coat carbon- and glass-reinforcing fibers using EPD for the preparation of hierarchical composite materials.

Here, a novel method for the functionalization and stable dispersion of carbon nanomaterials in aqueous environments is described. Ozone is injected directly into an aqueous dispersion of carbon nanomaterial that is continuously recirculated through a high-powered ultrasonic cell.

Functionalization of carbon nanomaterials is often a critical step that facilitates their integration into larger material systems and devices. In the ...

Environment

Nanosponge Tunability in Size and Crosslinking Density

We describe a protocol for the synthesis of linear polyesters containing pendant epoxide functionality and their incorporation into a nanosponge with controlled dimensions. This approach begins with synthesis of a functionalized lactone which is key to the pendant functionalization of the resulting polymer. Valerolactone (VL) and allyl-valerolactone (AVL) are then copolymerized using ring-opening polymerization. Post-polymerization modification is then used to install an epoxide moiety on some or all of the pendant allyl groups. Epoxy-amine chemistry is employed to form nanoparticles in a dilute solution of both polymer and small molecule diamine crosslinker based on the desired nanosponge size and crosslinking density. Nanosponge sizes can be characterized by transmission electron microscopy (TEM) imaging to determine the dimension and distribution. This method provides a pathway by which highly tunable polyesters can create tunable nanoparticles, which can be used for small molecule drug encapsulation. Due to the nature of the backbone, these particles are hydrolytically and enzymatically degradable for a controlled release of a wide range of hydrophobic small molecules.

This article describes a process for tuning the size and crosslinking density of covalently crosslinked nanoparticles from linear polyesters containing pendant functionality. By tailoring synthesis parameters (polymer molecular weight, pendant functionality incorporation, and crosslinker equivalents), a desired nanoparticle size and crosslinking density can be achieved for drug delivery applications.

We describe a protocol for the synthesis of linear polyesters containing pendant epoxide functionality and their incorporation into a nanosponge with ...

Grafting Multiwalled Carbon Nanotubes with Polystyrene to Enable Self-Assembly and Anisotropic Patchiness

We demonstrate a straightforward protocol to graft pristine multiwalled carbon nanotubes (MWCNTs) with polystyrene (PS) chains at the sidewalls through a free-radical polymerization strategy to enable the modulation of the nanotube surface properties and produce supramolecular self-assembly of the nanostructures. First, a selective hydroxylation of the pristine nanotubes through a biphasic catalytically mediated oxidation reaction creates superficially distributed reactive sites at the sidewalls. The latter reactive sites are subsequently modified with methacrylic moieties using a silylated methacrylic precursor to create polymerizable sites. Those polymerizable groups can address further polymerization of styrene to produce a hybrid nanomaterial containing PS chains grafted to the nanotube sidewalls. The polymer-graft content, amount of silylated methacrylic moieties introduced and hydroxylation modification of the nanotubes are identified and quantified by Thermogravimetric Analysis (TGA). The presence of reactive functional groups hydroxyl and silylated methacrylate are confirmed by Fourier Transform Infrared Spectroscopy (FT-IR). Polystyrene-grafted carbon nanotube solutions in tetrahydrofuran (THF) provide wall-to-wall collinearly self-assembled nanotubes when cast samples are analyzed by transmission electron microscopy (TEM). Those self-assemblies are not obtained when suitable blanks are similarly cast from analogous solutions containing non-grafted counterparts. Therefore, this method enables the modification of the nanotube anisotropic patchiness at the sidewalls which results into spontaneous auto-organization at the nanoscale.

A procedure for the synthesis of polystyrene-grafted multiwalled carbon nanotubes using successive chemical modification steps to selectively introduce the polymer chains to the sidewalls and their self-assembly via anisotropic patchiness is presented.

We demonstrate a straightforward protocol to graft pristine multiwalled carbon nanotubes (MWCNTs) with polystyrene (PS) chains at the sidewalls through a ...

Synthesis of Monodisperse Cylindrical Nanoparticles via Crystallization-driven Self-assembly of Biodegradable Block Copolymers

The production of monodisperse cylindrical micelles is a significant challenge in polymer chemistry. Most cylindrical constructs formed from diblock copolymers are produced by one of three techniques: thin film rehydration, solvent switching or polymerization-induced self-assembly, and produce only flexible, polydisperse cylinders. Crystallization-driven self-assembly (CDSA) is a method which can produce cylinders with these properties, by stabilizing structures of a lower curvature due to the formation of a crystalline core. However, the living polymerization techniques by which most core-forming blocks are formed are not trivial processes and the CDSA process may yield unsatisfactory results if carried out incorrectly. Here, the synthesis of cylindrical nanoparticles from simple reagents is shown. The drying and purification of reagents prior to a ring-opening polymerization of &#949;-caprolactone catalyzed by diphenyl phosphate is described. This polymer is then chain extended by methyl methacrylate (MMA) followed by N,N-dimethyl acrylamide (DMA) using reversible addition&#8722;fragmentation chain-transfer (RAFT) polymerization, affording a triblock copolymer that can undergo CDSA in ethanol. The living CDSA process is outlined, the results of which yield cylindrical nanoparticles up to 500 nm in length and a length dispersity as low as 1.05. It is anticipated that these protocols will allow others to produce cylindrical nanostructures and elevate the field of CDSA in the future.

Crystallization-driven self-assembly (CDSA) displays the unique ability to fabricate cylindrical nanostructures of narrow length distributions. The organocatalyzed ring-opening polymerization of &#949;-caprolactone and subsequent chain extensions of methyl methacrylate and N,N-dimethyl acrylamide are demonstrated. A living CDSA protocol that produces monodisperse cylinders up to 500 nm in length is outlined.

The production of monodisperse cylindrical micelles is a significant challenge in polymer chemistry. Most cylindrical constructs formed from diblock ...

Engineering Molecular Recognition with Bio-mimetic Polymers on Single Walled Carbon Nanotubes

Semiconducting single-wall carbon nanotubes (SWNTs) are a class of optically active nanomaterial that fluoresce in the near infrared, coinciding with the optical window where biological samples are most transparent. Here, we outline techniques to adsorb amphiphilic polymers and polynucleic acids onto the surface of SWNTs to engineer their corona phases and create novel molecular sensors for small molecules and proteins. These functionalized SWNT sensors are both biocompatible and stable. Polymers are adsorbed onto the nanotube surface either by direct sonication of SWNTs and polymer or by suspending SWNTs using a surfactant followed by dialysis with polymer. The fluorescence emission, stability, and response of these sensors to target analytes are confirmed using absorbance and near-infrared fluorescence spectroscopy. Furthermore, we demonstrate surface immobilization of the sensors onto glass slides to enable single-molecule fluorescence microscopy to characterize polymer adsorption and analyte binding kinetics.

We present a protocol for engineering the corona phase of near infrared fluorescent single walled carbon nanotubes (SWNTs) using amphiphilic polymers and DNA to develop sensors for molecular targets without known recognition elements.

Semiconducting single-wall carbon nanotubes (SWNTs) are a class of optically active nanomaterial that fluoresce in the near infrared, coinciding with the ...