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 proced...

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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...

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 border="0" cellpadding="0" cellspacing="0" width="634">
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">HiPco Single-walled carbon nanotubes</td>
			<td style="width:71px;">Unidym</td>
			<td style="width:119px;">P2771</td>
			<td style="width:228px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Pluronic F127</td>
			<td style="width:71px;">BASF</td>
			<td>9003-11-6</td>
			<td>Mw = 12.6 kg/mol</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">5-methylsalicylic acid</td>
			<td style="width:71px;">TCI America</td>
			<td>C0410</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Ultrasonic processor</td>
			<td style="width:71px;">Cole-Parmer</td>
			<td>ML-04714-52</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Sorvall 6 plus centrifuge</td>
			<td style="width:71px;">Thermo Scientific</td>
			<td align="right" style="width:119px;">46910</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Innova AFM&#160;</td>
			<td style="width:71px;">Bruker</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="89">
			<td height="89" style="height:89px;width:216px;">Si-wafer</td>
			<td style="width:71px;">Silicon Quest International</td>
			<td style="width:119px;"></td>
			<td style="width:228px;">150 mm in diameter&#160; ; N type &#60;1-1-1&#62; cut ; 1-10 Ohm/cm ; Single-side polyshed (675 +- 25 um) ; Diced (12 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 th...

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 ...

The overall goal of this procedure is to fabricate and characterize carbon nanotube based nanoparticles containing a thermal responsive encapsulation layer in aqueous solutions. This method can help answer key questions in the nano structure engineering field such as how to fabricate stimuli responsive nano particles and investigate in situ changes in their nanoscale structure induced by external stimuli. This method can provide insight into chemical assembly based fabrication of smart nano building blocks.It can be also applied to other systems consisting of different kinds of carbonated nanoparticles and block copolymers. To begin this procedure, add 0.175 grams of Poloxamer 407 powder in 70 grams of deuterium oxide. Then completely dissolve the polymer in solution using a magnetic stirrer for 30 minutes to one hour.Separately add 0.01 grams of single walled carbon nanotube powder to 250 milliliter conical centrifuge tubes. Then add 31.6 milliliters of the poloxamer 407 solution to each tube. Following this, mix the suspension in each tube by vortex mixing for 5 to 10 minutes.When finished, place tube one in a water bath and secure it using a clamp stand. Dip the tip of an ultrasonicator into the suspension of tube one. Increase the sonication power gradually from 0%until the carbon nanotubes 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 minutes at 20 degree Celsius while keeping the suspension temperature below 25 degree celsius using a water bath as a temperature reservoir. Next, centrifuge the crude suspensions in both tubes at 9800 times G for two hours at 20 degree celsius. After centrifugation, separately transfer 15 milliliters of each supernatant from the top of the solution to a new tube.Dissolve 0.015 grams of 5-methylsalicylic acid or 5-MS in the supernatant from tube two and label this mixture as sample two. Label the tube containing the supernatant from tube one as sample one. Load 0.3 milliliters of each sample into an amorphous cord-span-jo cell.Place lids on the two cells and seal them by wrapping tape securely around the lids. Following this, place one of the sealed cells between spacers from aluminum cell holder and assemble the aluminum banjo cell holder. Load the assembled cells into different sample positions of the EQ-SAN sample paddle.Make a list of the sample positions of the paddle on the sample list form. Start the measurement by loading and executing the experiment script in the PI-DAS control window. For AFM measurements, mix 0.1 milliliters of the solution from the sample one tube with 1.9 milliliters of deionized water.Next, place a clean silicon wafer on a spin coder. Fix the wafer position using a vacuum check. Set the rotation speed and the running time to 1500 revolutions per minute and 60 seconds respectively.Wet the exposed surface of the wafer with the diluted sample. Then start spin coding. When finished, turn off the vacuum pump and remove the coded wafer from the spin coder.At this point, attach the spin coded wafer on an iron disk using a double sided adhesive carbon tape. Move the disk closer to the edge of the exposed area of a scanner. Then slide the disk toward the center until the bottom surface completely covers the top of the scanner.Following this, mount the scanning probe microscope or SPM head on the scanner and plug in the cable. Open the instrument supply control software on the computer and select the tapping mode in the system configuration window. Next, 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.Align the laser by adjusting the laser alignment knobs on the SPM head. Roughly locate the red laser dot to the cantilever and move the dot to the middle of the cantilever tip by tracing the dots shown in the monitor. After laser alignment, align the detector using the photodetector knobs.Roughly adjust the knobs to turn off four red LED lights on the SPM head. Then finely adjust the knobs until the pink reflection image is located at the center of the laser alignment window and the quadrant photo diode signal sum is greater than at least two volts. Tune the cantilever using auto tune in the cantilever tuning window.Then run auto tune in a frequency range of zero to 1000 kilohertz. Following this, bring the wafer surface into focus of the microscope by adjusting the focus knobs. Once the wafer surface is in focus, click the engage button on the toolbar.Select a scan size, a sampling number, and a scan rate in the popup window. Start scanning. Gradually adjust the proportional gain, the integral gain, and the 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.Finally disengage the probe after measurement. By changing the temperature or by adding 5-MS additives, the SANS scattering intensities of the functionalized single walled carbon nanotube suspension show a shift to higher Q in the intermediate Q region and the development of a peak at high Q.The changes due to temperature control and 5-MS addition originate from the structural change of the poloxamer 407 encapsulation layer on the carbon nanotubes. The poloxamer carbon nanotube nanorod with the core shell cylinder structure undergoes a structural transformation from encapsulation by spherical micelles of poloxamer 407 at room temperature to encapsulation by a compact cylindrical layer of poloxamer 407 at higher temperature.During the structural change, the spherical poloxamer 407 micelle with a radius of gyration of 45 angstroms becomes a set of single chain blobs that surround the carbon nanotube core more compactly with the radius of gyration of 30 angstroms. Although AFM images only show a dried morphology of the poloxamer carbon nanotube nanorods without water they provide evidence of debundling and dispersion of carbon nanotubes as well as the length distribution of the nanorods. This procedure can be applied to different combinations of nanoparticles in block copolymers to fabricate various stimuli responsive nano building blocks.Following this procedure, other methods like cryo-EM or molecular dynamic simulation can be performed in order to answer questions such as the real space structure of polymer layers in solution state and detailed underlying physics related to the structure change. I hope that this video has demonstrated that a small angle neutron scattering is a very useful technique for in situ nano structure characterizations of solution samples. We also hope to see more scientists come to SNS for various neutron scattering experiment.

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9.1K vistas.  Oak Ridge National Laboratory. The overall goal of this procedure is to fabricate and characterize carbon nanotube based nanoparticles containing a thermal responsive encapsulation layer in aqueous solutions. This method can help answer key questions in the nano structure engineering field such as how to fabricate stimuli responsive nano particles and investigate in situ changes in their nanoscale structure induced by external stimuli. This method can provide insight into chemical assembly based fabrication of smart nano b...

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