Name: grafting multiwalled carbon nanotubes with polystyrene to enable self-assembly and anisotropic patchiness
Uploaded: 2018-04-01T13:00:00
Description: Watch this Scientific Journal Video about Grafting Multiwalled Carbon Nanotubes with Polystyrene to Enable Self-Assembly and Anisotropic Patchiness at JoVE.com

We would like to acknowledge the FQ-PAIP and DGAPA-PAPIIT programs from National Autonomous University of Mexico (grant numbers 5000-9158, 5000-9156, IA205616 and IA205316) and the National Council for Science and Technology from Mexico -CONACYT- (grant number 251533).

Caution: Please consult all relevant material safety data sheets (MSDS) before use. Several of the chemicals used in this protocol are acutely toxic and carcinogenic. Carbon nanotube derivatives may have additional respiratory hazards compared to other traditional bulk carbon allotropes. It is suspected that carbon nanotubes in aerosol may affect lungs in a similar way than asbestos, though their carcinogenic properties have not been completely elucidated so far. Please use all appropriate safety practices when performin...

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In this method, there are some steps which result critical to guarantee a successful grafting process. First, the biphasic catalytically mediated oxidation reaction (Step 1.1) should be carried out with recently dispersed carbon nanotubes (Step 1.1.1.5). If dispersion results unviable according to the recommendations in the protocol, the use of an ultrasonic tip sonicator would be helpful if using the same indications (Step 1.1.1.6). Using shorter MWCNTs may also help in solving dispersion issues. Second, setting of the ...

Since the discovery of single-walled carbon nanotubes (SWCNTs),1,2 the scientific communities have applied their outstanding electrical, mechanical and thermal properties3 in a wide range of cutting-edge applications by modulating their surface properties via covalent4 and non-covalent5 strategies. Examples of those applications include their use as transducers in sensors,6,7 electrodes in solar cells,8 heterogeneous supports in catalysis,9 nanoreactors in synthesis,10 anti-fouling agents in protective films,11 fillers in composite materials,12etc. However, the possibility to modulate the surface properties of their more robust, yet industrially available multiwalled counterparts namely, MWCNTs, to control the directionality in their non-covalent interactions at the nanoscale, has remained a difficult task so far.13
Supramolecular self-assembly of molecular building blocks is one of the most versatile strategies to control the organization of matter at the nanoscale.14,15 In this sense, supramolecular interactions involve directional, short-range and mid-range non-covalent interactions such as H-bond, Van der Waals, dipole-dipole, ion-dipole, dipole-induced dipole, &#960;- &#960; stacking, cation-&#960;, anion-&#960;, coulombic, among others.16 Unfortunately, directionality in self-assembly for larger structures such as MWCNTs is not spontaneous and usually requires external motive forces (e.g. templates or energy dissipation systems).17 A recent report used non-covalent wrapping of nanotubes with tailored co-polymers to pursue the latter goal,18 but the use of covalent strategies to offer new alternatives to solve that problem have remained scarcely explored.
Chemical modification of carbon nanotubes can be selectively carried out to introduce different functional groups either to the termini or to the sidewalls of the same.19,20 One of the most useful approaches to tailor the surface properties in carbon nanostructures is polymer-grafting through standard polymerization routes. Typically, those approaches involve the preliminary introduction of polymerizable or initiator groups (acrylic, vinyl, etc.) on the nanostructure surface and their successive polymerization with a suitable monomer.21 In the case of MWCNTs, the covalent introduction of polymer chains on the sidewalls to control their patchiness in an anisotropic fashion has remained a challenge.
Here we will show how a series of straightforward chemical modification steps22,23 can be applied to insert PS chains on the sidewalls of MWCNTs in order to modify their surface patchiness and to promote their anisotropic self-assembly23 at the nanoscale. During the modification route, a first step allows for the selective hydroxylation of pristine MWCNTs at the sidewalls by following a biphasic catalytically mediated oxidation reaction to yield the hydroxylated counterparts namely, MWCNT-OH. A second step uses 3-(trimethoxysilyl)propyl methacrylate (TMSPMA) to introduce silylated methacrylic moieties to the previously created hydroxyl groups (MWCNT-O-TMSPMA). These inserts will provide surface reactive sites during a third step, when styrene monomer is polymerized from the methacrylic moieties thus yielding polymer chains grafted to the sidewalls of the nanotubes at the end (i.e. MWCNT-O-PS).

<table border="0" cellpadding="0" cellspacing="0" width="1573">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:379px;">Tetrapropylammonium bromide, 99 % (TPABr)</td>
			<td style="width:181px;">Sigma-Aldrich</td>
			<td align="right" style="width:119px;">88104</td>
			<td style="width:895px;">Irritant, toxic</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:379px;">Potassium permanganate, 99 % (KMnO4)</td>
			<td style="width:181px;">Sigma-Aldrich</td>
			<td align="right" style="width:119px;">223468</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:379px;">Acetic acid, 99.5 %</td>
			<td style="width:181px;">Sigma-Aldrich</td>
			<td align="right" style="width:119px;">45726</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:379px;">Pristine multiwalled carbon nanotubes, 99 % (MWCNTs)</td>
			<td style="width:181px;">Bayer Technology Services</td>
			<td style="width:119px;">Donated sample</td>
			<td>Harmful dusts. &#62;1 mm in length and 13&#8211;16 nm in outer diameter. Alternative supplier: Nanocyl, Catalog N. NC7000, website: http://www.nanocyl.com/</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:379px;">Sodium Chloride, 98 % (NaCl)</td>
			<td style="width:181px;">Sigma-Aldrich</td>
			<td style="width:119px;">S3014</td>
			<td>Technical grade can also be used</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:379px;">Ethanol, 99.8 % (EtOH)</td>
			<td style="width:181px;">Sigma-Aldrich</td>
			<td align="right" style="width:119px;">32221</td>
			<td>Technical grade can also be used</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:379px;">Methanol, 99.8 % (MeOH)</td>
			<td style="width:181px;">Sigma-Aldrich</td>
			<td align="right" style="width:119px;">322415</td>
			<td>Highly toxic. Technical grade can also be used</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:379px;">Hydroquinone, 99 %</td>
			<td style="width:181px;">Sigma-Aldrich</td>
			<td style="width:119px;">H9003</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:379px;">Toluene, 99.8 %</td>
			<td style="width:181px;">Sigma-Aldrich</td>
			<td align="right" style="width:119px;">244511</td>
			<td>Anhydrous</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:379px;">3-(Trimethoxysilyl)propyl methacrylate, 98 % (TMSPMA)</td>
			<td style="width:181px;">Sigma-Aldrich</td>
			<td align="right" style="width:119px;">440159</td>
			<td>Air sensitive, toxic</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:379px;">Azobisisobutyronitrile, 99 % (AIBN)</td>
			<td style="width:181px;">Sigma-Aldrich</td>
			<td align="right" style="width:119px;">755745</td>
			<td>Explosive</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:379px;">Styrene, 99 %</td>
			<td style="width:181px;">Sigma-Aldrich</td>
			<td style="width:119px;">S4972</td>
			<td>Purified using an alumina gel preparative column and stored at 4 &#176;C</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:379px;">Acetone, 99.5 %</td>
			<td style="width:181px;">Sigma-Aldrich</td>
			<td align="right" style="width:119px;">179124</td>
			<td>Technical grade can also be used</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:379px;">Tetrahydrofuran, 99.9 % (THF)</td>
			<td style="width:181px;">Sigma-Aldrich</td>
			<td align="right" style="width:119px;">494461</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:379px;">Dichloromethane, 99.5 %</td>
			<td style="width:181px;">Sigma-Aldrich</td>
			<td align="right" style="width:119px;">443484</td>
			<td>Highly toxic</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:379px;">Hydrochloric acid, 37 %</td>
			<td style="width:181px;">Sigma-Aldrich</td>
			<td align="right" style="width:119px;">435570</td>
			<td>Harmful fumes</td>
		</tr>
	</tbody>
</table>

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.

TGA data were collected from pristine nanotubes, hydroxylated nanotubes, nanotubes modified with silylated methacrylic moieties and polystyrene-grafted nanotubes (Figure 1). FT-IR results were collected from hydroxylated nanotubes and nanotubes modified with silylated methacrylic moieties (Figure 2). TEM images were collected from pristine nanotubes and polystyrene-grafted nanotubes (Figure 3). TGA d...

Watch this Scientific Journal Video about Grafting Multiwalled Carbon Nanotubes with Polystyrene to Enable Self-Assembly and Anisotropic Patchiness at JoVE.com

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

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 ...

The overall goal of this procedure is to offer a straightforward strategy for grafting multiwalled carbon nanotubes by polystyrene chains, which mediates a pro-molecular self-assembly and anisotropic patchiness. This method can help to modulate the surface properties of multiwalled carbon nanotubes, so as to establish improved processing conditions of the same in the field of thermoplastic polymers. The grafting strategy offers a straightforward alternative in processing protocols for carbon nanotubes in order to compatibilize them with industrially relevant, yet challenging polymers, such as polystyrene.In general, the method starts with the traditional hydroxyl groups on the side walls of pristine carbon nanotubes followed by the coupling of silylated methacrylic moieties to the OH groups, and their sequential free radical polymerization with styrene on the inner atmosphere. To find the yield, nanotubes grafted with polystyrene chains. The main advantage of this technique is that it can be easily deployed to mole surface properties of carbon nanotubes.And consequently, promote their anisotropic self assembly, which in turn may facilitate their inclusion in a polymer matrix. This technique opens promising alternatives to improve the supply chain of nanostructure carbon nanotropes in industrial processes, thus allowing for the creation of electrical percolation networks in polymer composites, which could find direct applications in electromagnetic shielding systems, mechanically reinforced parts, and electrically conducting materials under attractive cost-benefit conditions. Dry to 5 grams of pristine multi-walled carbon nanotubes, by introducing them into a vacuum oven at 80 Celsius degrees and 200 millimeters of mercury for 12 hours.Pour the dried carbon nanotubes into a 100 milliliter round-bottom flask. Afterwards, transfer 50 milliliters of dichloromethane, 99 percent, into the flask, and set the mechanical stirring at 60 rpm. This will be the organic phase of a bi-faceted chotilitically mediated reaction.In order to prepare the aqueous phase, dissolve 0.6 grams of tetroaropyl ammonium bromide in five milliliters of distilled water. Add five milliliters of acetic acid and five milliliters of an aqueous solution, containing potassium permanganate, 0.16 molar. Pour the latter solution into the round-bottom flask, already containing the organic phase and agitate vigorously, for example, about 80 rpm at room temperature for 24 hours.After that time, transfer the reaction mixture into a separatory funnel. Then, agrigate around 0.25 milliliters of concentrated hydrochloric acid, 36 percent, and carefully agitate the system and purge. Then, discard the supernatant aqueous phase.Once the aqueous phase was retired, the organic phase can be filtered using a vacuum filtration system as it is further described. Set this topper on base firmly into the neck of the filtered flask. With the small-tip forceps, center out 47 millimeter diameter membrane filter on the support surface.Make sure to use a membrane with a pore size between 0.45 micrometers and 20 micrometers. Smaller pore sizes will easily block, while larger pore sizes will retain lower amounts of filtered nanotubes. Without disturbing the filter, center the flange of the holder on top of the assembly and lock the funnel and base together with a spring clamp.Connect the filtering flask to the vacuum source, pour the sample into the funnel, and apply vacuum to filter the sample. Once the filter solid looks to be dried, wash with methanol 95 percent for at least five times the volume of the filtered solution. Afterward, transfer the solute into a petri dish and let it dry under vacuum for 24 hours at 80 Celsius degrees, at 200 millimeters of mercury.In order to insert polymerizable methacrylic moieties into the hydroxilated carbon nanotube walls, disperse about 2.5 grams of the nanotubes and five grams of hydrochinoin 99 percent, using a 100 milliliters schlenk flask. Then, with the aid of a cannula, carefully add 50 milliliters of Toluene under nitrogen atmosphere, using a vacuum inner gas manifold. Later, put it under vigorous mechanical agitation.Then, incorporate five milliliters of 3-thremethyl silane propel methacrylate 98 percent, and take it to reflux at 100 Celsius degrees for 12 hours. Once the reaction is complete, wash the obtained product with methanol in excess, using the vacuum filtration system and dry it overnight under vacuum at 80 Celsius degrees and 200 millimeters of mercury and store until needed. In order to graft the methacrylic modified nanotubes with acetoground polystyrene chains, disperse about 2.5 grams of the modified carbon nanotubes and 75 milligrams of AIBN in 50 milliliters of toluene.Using a shlenk flask, improach the system with nitrogen atmosphere, using the vacuum inner gas manifold. Then, add freshly purified 7.5 milliliters of styrene monomer. AIBN will act as the initiator of the free-radical polymerization.Subsequently, set the heating system at 70 Celsius degrees and stir it for 12 hours, under nitrogen atmosphere and reflux. Afterwards, filter the reaction mixture using the vacuum filtration system. Wash it with acetone, and finally wash it again with DHF 99 percent for at least five times to remove unbound polystyrene.Dry the product under vacuum for 24 hours at 80 Celsius degrees and 200 millimeters of mercury. The solid will contain carbon nanotubes grafted with polystyrene chains. The polymer grafted carbon nanotubes were characterized by TM.Here are representative TM images for dropcast samples in which polystyrene wraps its carbon nanotubes appear as partially aligned and self-assembled by the side walls.Such behavior is absent when pristine nanotubes are analyzed in a similar form. The values curve of thermogramemetric analysis for polymer-modified carbon nanotubes showed that the first weight loss, due to the loss of polystyrene chains starts at 270 Celsius degrees. Then, a second moderated step, which starts around 400 Celsius degrees, is caused by the loss of the siliyated methracrylic moieties, where as the final remark weight loss starting at around 600 Celsius degrees, corresponds to the carbon nanotubes.Here we show our representative weight loss present-age curve of grafted carbon nanotubes with polyester range in comparison with pristine ones, which confirms that the most significant alteration in the samples weighed is comprised between 270 Celsius degrees and 775 Celsius degrees. From TGA, it is possible to affirm that after the hydroxilation step, carbon nanotube-side walls will typically contain hydroxyl moieties at two percent to five percent in weight. It is important to mention that after co-insulating material moieties to the OH groups, modified carbon nanotubes will typically contain between eight and ten percent weight for methracrylic in comparison with the nanotube content.Once accomplished, the free radical polymerization with styrene, it is typically expected a grafting degree of about 30 to 40 percent relative to the nanotube weight. So, a selective modification of the surface properties of the nanotubes is obtained by successive chemical modification in steps to insert reactive functional robselectively to the side walls. We expect that this strategy can be reapplied to other acrylic or vinyl derivative polymer types and new hybrid materials and composites could arise in the future.After watching this video, you should have a good understanding of the different steps needed to chemically modify carbon nanotubes with acetogram polyester range chains, which might play an important role in the surface properties of that kind of carbon nanotubes via super-molecular forces. This can result in the creation of self-assembly nanotubes through anisotropic nanoscale interactions, with potential applications in wide areas, such as material science and engineering, nanoscience and nanotechnology, or macromolecular chemistry. While attempting this procedure, it is important to be aware of the hazardous conditions of all reactants used in this technique, and ensure the use of suitable laboratory equipment.

Research

JoVE Journal

Chemistry

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