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 performing the chemical reactions and product processing steps including the use of fume hood and personal protective equipment (lab coat, gloves, safety glasses, closed shoes, full length pants) while suitable filtering facepiece respirators should be particularly used when potential nanotube dust may be generated (NIOSH approved N95 model, or European EN 149 certified FFP3 versions). Portions of the following procedure involve standard inert atmosphere handling techniques.24
1. Selective Hydroxylation of Multiwalled Carbon Nanotubes 22
<ol>
	<li>Biphasic Catalytically Mediated Oxidation of MWCNTs
	<ol>
		<li>Preparation of the Organic Phase
		<ol>
			<li>Add 2.5 g of pristine MWCNTs to a watch glass, Petri dish or beaker.</li>
			<li>Move the container into an 80 &#176;C vacuum oven and cover with a suitable watch glass. Turn on the vacuum pump of the oven and set the system to ca. 200 mmHg.</li>
			<li>Dry the nanotubes in the vacuum oven for 12 h. After this step, the water content in the MWCNTs will be eliminated.</li>
			<li>Pour the dried MWCNTs into a 100 mL round bottom flask with a glass funnel and a spatula and remove the funnel once finished.</li>
			<li>Introduce a magnetic stirring bar to the round bottom flask and add ~ 50 mL of 99% dichloromethane into the flask using a beaker. Stir at 60 rpm using a stirring plate until agglomerates disappear.</li>
			<li>If agglomerates remain in solution after stirring for 10 min, move the flask into an ultrasonic bath and turn on the system for 5 min. Repeat sonication if necessary. This solution will be the organic phase in the oxidation reaction stage.</li>
		</ol>
		</li>
		<li>Preparation of the Aqueous Phase
		<ol>
			<li>In a 25 mL beaker, dissolve 0.6 g of tetrapropylammonium bromide (TPABr) in 5 mL of distilled water using a magnetic stirring bar and a stirring plate.</li>
			<li>In a 10 mL volumetric flask, dissolve 0.253 g KMnO4 in distilled water (0.16 M solution) and keep the solution in a beaker at hand. This solution will be used in Step 1.1.2.4.</li>
			<li>Take 5 mL of glacial acetic acid (HOAc) and transfer the volume drop-wise to the TPABr solution. Using a graduated pipette and constant stirring in an ice bath may be helpful. 
			NOTE: The mixture process is exothermic, therefore, the addition should be carried out slowly to avoid possible injuries by projected droplets or an excessive warming.</li>
			<li>Transfer a 5 mL aliquot of the 0.16 M KMnO4 aqueous solution to the acidified TPABr solution. Using a clean graduated pipette and stirring may be helpful.</li>
			<li>Keep the previous solution covered with a watch glass until needed. This solution will be the aqueous phase in the oxidation reaction stage.</li>
		</ol>
		</li>
		<li>Oxidation Reaction
		<ol>
			<li>Pour the aqueous phase into the round bottom flask that contains the organic phase. This mixture will be the biphasic reaction mixture.</li>
			<li>Using the stirring plate, agitate the biphasic system at 80 rpm or more and leave the mixture under stirring at room temperature for 24 h. After this time, the violet aqueous phase turns pale pink and the nanotubes become hydroxylated (MWCNT-OH).</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Purification of MWCNT-OH
	<ol>
		<li>Liquid-Liquid Extraction
		<ol>
			<li>Transfer the biphasic reaction mixture to a 150 mL or 200 mL separatory funnel with the stopcock at the closed position. Use a glass funnel and a spatula if needed.</li>
			<li>Using a Beral pipette, a Pasteur pipette with a rubber bulb attached or a beaker, add ~ 0.25 mL of concentrated hydrochloric acid into the separatory funnel.</li>
			<li>Use the separatory funnel.
			<ol>
				<li>Close the separatory funnel with a Teflon stopper (do not use glass stoppers for carbon nanotubes) and agitate vigorously for 5 s in a fume hood with the sash window down. During agitation, always hold the stopper strongly attached to the funnel with one hand and grab the stopcock with the other hand.</li>
				<li>Immediately after the agitation step, turn the funnel upside down and release the pressure build-up by opening the stopcock with the respective hand. 
				NOTE: Make sure to address the pressure direction to the rear of the fume food.</li>
				<li>Repeat the last two agitation/pressure-release steps in cycles of 3 - 5.</li>
				<li>Once the last cycle is finished, immediately remove the stopper and leave the funnel clamped and undisturbed until phase separation is evident. After liquid-liquid separation, the aqueous phase remains above the organic phase. The MWCNT-OH will remain at the organic phase.</li>
			</ol>
			</li>
			<li>If no phase separation occurs, add 1 - 5 mL of brine (10 - 20% NaCl in water, m/v) to the separatory funnel using a Beral pipette or a Pasteur pipette, mix gently and leave the mixture undisturbed until phase separation. Repeat until needed.</li>
			<li>Recover the organic phase on a 150 mL beaker keeping the stopcock open until the phase boundary reaches the stopcock position. A 150 mL Erlenmeyer flask can be alternatively used to recover the organic phase; however, retrieval of nanotubes from this container type is usually more difficult.</li>
			<li>Keep the recovered solution protected with a watch glass until filtration.</li>
			<li>Discard the aqueous phase appropriately.</li>
		</ol>
		</li>
		<li>Setting of the Vacuum Filtration System
		<ol>
			<li>Set the vacuum filtration system seating the stopper and base firmly into the neck of a clamped Kitasato flask.</li>
			<li>Keep a 47 mm diameter membrane filter at hand and, depending on the membrane material and indications from the manufacturer, optionally follow this step and the next two ones (Steps 1.2.2.2 - 1.2.2.4). Prepare a 100 mm diameter Petri dish with ethanol (EtOH) filling 50% of its capacity.</li>
			<li>With smooth-tip forceps, place the 47 mm diameter membrane filter on the Petri dish with EtOH. Leave the membrane in EtOH for 2 - 5 min. Make sure to use a membrane with a pore size 0.45 - 20 &#181;m. Smaller pore sizes will clog the filtration, while larger ones will reduce filtering efficiency.</li>
			<li>Remove the membrane from the EtOH using the smooth-tip forceps.</li>
			<li>Center the membrane on the sintered glass area of the filter support surface starting by the edge of the membrane. The optional wetting with EtOH may facilitate this step.</li>
			<li>Center the flange of the funnel on top of the assembly. Do not disturb the membrane. Lock the funnel and base together with the spring clamp.</li>
			<li>Connect the system to the vacuum source. Do not turn the vacuum on until needed.</li>
		</ol>
		</li>
		<li>Filtration of the MWCNT-OH
		<ol>
			<li>Pour the retrieved organic phase into the vacuum filtration funnel aided by a glass rod. Apply vacuum to filter the sample until dryness.</li>
			<li>Wash the solid with 40 - 50 mL of 95% methanol (MeOH) using a wash bottle. Using a glass rod may be helpful in this task. Repeat this process at least 5 times. Keep the vacuum on during this step.</li>
			<li>After washing, leave the system under vacuum for 20 min covered with a glass watch to dry the solid.</li>
			<li>In order to recover the solid from the membrane, follow the next Steps 1.2.3.5 - 1.2.3.8.</li>
			<li>Carefully, remove the spring clamp, then vertically remove the funnel without disturbing the membrane and the solid.</li>
			<li>Very carefully, remove the membrane together with the solid from the filter support surface aided by a spatula and the smooth-tip forceps.</li>
			<li>Transfer the membrane with the solid to a 100 mm diameter Petri dish or watch glass.</li>
			<li>Aided by two smooth-tip forceps and a spatula, recover the solid from the membrane surface until all the product is deposited on the Petri dish/watch glass.</li>
		</ol>
		</li>
		<li>Drying and Storage of MWCNT-OH
		<ol>
			<li>Cover the Petri dish/watch glass with a suitable watch glass (larger diameter is required). 
			NOTE: Do not use sealing film to avoid electrostatic charging.</li>
			<li>Introduce the Petri dish/watch glass into a vacuum oven heated at 80 &#176;C. Turn on the vacuum pump of oven and set the system to ca. 200 mm Hg.</li>
			<li>Dry the solid for 24 h. After this step, the solvent content in the product will be eliminated. If the product will not be used immediately, store the solid in a desiccator until needed.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
2. Grafting MWCNT-OH with Polystyrene Chains 22,23
<ol>
	<li>Modification of MWCNT-OH with Silylated Methacrylic Moieties
	<ol>
		<li>Pour 2.5 g MWCNT-OH and 5 g of hydroquinone into a clean 100 mL Schlenk flask using a glass funnel and a spatula, remove the funnel and introduce a magnetic stirring bar.</li>
		<li>Set the Schlenk flask into reflux mode according to the following indications:
		<ol>
			<li>Connect the Schlenk flask to the vacuum/inert gas manifold system using a suitable rubber tubing attached to the flask&#39;s glass joint. Keep the flask&#39;s manifold closed.</li>
			<li>Connect a suitable condenser to the tap water system using suitable rubber tubing, making sure to set the water income through the glass joint closest to the male joint.</li>
			<li>Lubricate the male joint of the condenser with an evenly applied fine layer of vacuum grease. 
			NOTE: The joint should not be over-greased to avoid product contamination.</li>
			<li>Attach the condenser&#39;s male joint to the Schlenk flask&#39;s neck. Close the condenser&#39;s female joint with a rubber stopper.</li>
			<li>Carefully, open the flask to the vacuum. Make sure that the nanotubes are not sucked up into the vacuum line during this process.</li>
			<li>Fill the Schlenk flask with N2 gas.</li>
			<li>Repeat the last two steps two more times.</li>
			<li>Keep the system under positive N2 gas flow.</li>
		</ol>
		</li>
		<li>Aided by a clean cannula and a suitable syringe, slowly inject 50 mL dry toluene through the rubber stopper.</li>
		<li>Using the stirring plate and a thermal bath, agitate the mixture vigorously at 80 rpm or more and leave the mixture under stirring for 5 - 10 min at room temperature.</li>
		<li>Using a clean cannula and a syringe, inject 5 mL of TMSPMA through the rubber stopper.</li>
		<li>Set the temperature to 100 &#176;C and leave the reaction under reflux and stirring for 12 h. After this time, silylated methacrylic moieties are chemically couple to the hydroxyl groups on the MWCNTs (namely MWCNT-O-TMSPMA).</li>
		<li>Once the reaction is over, carefully remove the rubber stopper, close the N2 flow and wait until the flask is at room temperature.</li>
		<li>Set a vacuum filtration system (Step 1.2.2).</li>
		<li>Filter the solid (Step 1.2.3). Wash with MeOH in excess.</li>
		<li>Dry and store the MWCNT-O-TMSPMA (Step 1.2.4).</li>
	</ol>
	</li>
	<li>Polymerization of Styrene on Modified MWCNTs
	<ol>
		<li>Pour 2.5 g of the MWCNT-O-TMSPMA and 75 mg of azobisisobutyronitrile (AIBN) into a clean 100 mL Schlenk flask using a glass funnel and a spatula and remove the funnel. 
		Caution: AIBN powder should not be exposed to heat or strongly oxidizing agents, as it may spontaneously explode.</li>
		<li>Introduce a magnetic stirring bar to the Schlenk flask.</li>
		<li>Set the Schlenk flask into reflux mode (Step 2.1.2).</li>
		<li>Using a clean cannula and a syringe, inject 50 mL dry toluene through the rubber stopper.</li>
		<li>Using the stirring plate and the thermal bath, agitate the mixture at 80 rpm or more and leave the mixture under stirring for 5 - 10 min at room temperature.</li>
		<li>Aided by a clean cannula and a syringe, inject 7.5 mL of styrene through the stopper.</li>
		<li>Set the temperature to 70 &#176;C and leave the reaction under reflux, stirring and N2 for 12 h. After this time, PS chains are grafted to the nanotube sidewalls (MWCNT-O-PS).</li>
		<li>Open the system to the air, close the N2 flow and cool the flask to room temperature.</li>
		<li>Set a vacuum filtration system (Step 1.2.2).</li>
		<li>Filter and wash the solid (Step 1.2.3). Use acetone instead of MeOH during the washing step. Wash the solid five times more with 20 mL THF to remove unbound polystyrene.</li>
		<li>Dry and store the MWCNT-O-PS (Step 1.2.4). 
		NOTE: The length of the polymer chain grafted to the nanotubes can be tuned by changing the concentration of styrene in toluene during the polymerization step; lower concentrations produce shorter chains. The polymerization reaction time can be used to adjust the polymer chain size; shorter reaction times reduce the length of the chains. See references 22 and 23 for details.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

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 ...

grafting-multiwalled-carbon-nanotubes-with-polystyrene-to-enable-self

Research

JoVE Journal

Chemistry

8.0K Views.  National Autonomous University of Mexico. 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.

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

Origami Inspired Self-assembly of Patterned and Reconfigurable Particles

There are numerous techniques such as photolithography, electron-beam lithography and soft-lithography that can be used to precisely pattern two dimensional (2D) structures. These technologies are mature, offer high precision and many of them can be implemented in a high-throughput manner. We leverage the advantages of planar lithography and combine them with self-folding methods1-20 wherein physical forces derived from surface tension or residual stress, are used to curve or fold planar structures into three dimensional (3D) structures. In doing so, we make it possible to mass produce precisely patterned static and reconfigurable particles that are challenging to synthesize.
In this paper, we detail visualized experimental protocols to create patterned particles, notably, (a) permanently bonded, hollow, polyhedra that self-assemble and self-seal due to the minimization of surface energy of liquefied hinges21-23 and (b) grippers that self-fold due to residual stress powered hinges24,25. The specific protocol described can be used to create particles with overall sizes ranging from the micrometer to the centimeter length scales. Further, arbitrary patterns can be defined on the surfaces of the particles of importance in colloidal science, electronics, optics and medicine. More generally, the concept of self-assembling mechanically rigid particles with self-sealing hinges is applicable, with some process modifications, to the creation of particles at even smaller, 100 nm length scales22, 26 and with a range of materials including metals21, semiconductors9 and polymers27. With respect to residual stress powered actuation of reconfigurable grasping devices, our specific protocol utilizes chromium hinges of relevance to devices with sizes ranging from 100 &mu;m to 2.5 mm. However, more generally, the concept of such tether-free residual stress powered actuation can be used with alternate high-stress materials such as heteroepitaxially deposited semiconductor films5,7 to possibly create even smaller nanoscale grasping devices.

We describe experimental details of the synthesis of patterned and reconfigurable particles from two dimensional (2D) precursors. This methodology can be used to create particles in a variety of shapes including polyhedra and grasping devices at length scales ranging from the micro to centimeter scale.

There are numerous techniques such as photolithography, electron-beam lithography and soft-lithography that can be used to precisely pattern two ...

Template Directed Synthesis of Plasmonic Gold Nanotubes with Tunable IR Absorbance

A nearly parallel array of pores can be produced by anodizing aluminum foils in acidic environments1, 2. Applications of anodic aluminum oxide (AAO) membranes have been under development since the 1990's and have become a common method to template the synthesis of high aspect ratio nanostructures, mostly by electrochemical growth or pore-wetting. Recently, these membranes have become commercially available in a wide range of pore sizes and densities, leading to an extensive library of functional nanostructures being synthesized from AAO membranes. These include composite nanorods, nanowires and nanotubes made of metals, inorganic materials or polymers 3-10. Nanoporous membranes have been used to synthesize nanoparticle and nanotube arrays that perform well as refractive index sensors, plasmonic biosensors, or surface enhanced Raman spectroscopy (SERS) substrates 11-16, as well as a wide range of other fields such as photo-thermal heating 17, permselective transport 18, 19, catalysis 20, microfluidics 21, and electrochemical sensing 22, 23. Here, we report a novel procedure to prepare gold nanotubes in AAO membranes. Hollow nanostructures have potential application in plasmonic and SERS sensing, and we anticipate these gold nanotubes will allow for high sensitivity and strong plasmon signals, arising from decreased material dampening 15.

Solution-suspendable gold nanotubes with controlled dimensions can be synthesized by electrochemical deposition in porous anodic aluminum oxide (AAO) membranes using a hydrophobic polymer core. Gold nanotubes and nanotube arrays hold promise for applications in plasmonic biosensing, surface-enhanced Raman spectroscopy, photo-thermal heating, ionic and molecular transport, microfluidics, catalysis and electrochemical sensing.

A nearly parallel array of pores can be produced by anodizing aluminum foils in acidic environments1, 2. Applications of anodic aluminum oxide (AAO) ...

Formation of Ordered Biomolecular Structures by the Self-assembly of Short Peptides

In nature, complex functional structures are formed by the self-assembly of biomolecules under mild conditions. Understanding the forces that control self-assembly and mimicking this process in vitro will bring about major advances in the areas of materials science and nanotechnology. Among the available biological building blocks, peptides have several advantages as they present substantial diversity, their synthesis in large scale is straightforward, and they can easily be modified with biological and chemical entities1,2. Several classes of designed peptides such as cyclic peptides, amphiphile peptides and peptide-conjugates self-assemble into ordered structures in solution. Homoaromatic dipeptides, are a class of short self-assembled peptides that contain all the molecular information needed to form ordered structures such as nanotubes, spheres and fibrils3-8. A large variety of these peptides is commercially available.
This paper presents a procedure that leads to the formation of ordered structures by the self-assembly of homoaromatic peptides. The protocol requires only commercial reagents and basic laboratory equipment. In addition, the paper describes some of the methods available for the characterization of peptide-based assemblies. These methods include electron and atomic force microscopy and Fourier-Transform Infrared Spectroscopy (FT-IR). Moreover, the manuscript demonstrates the blending of peptides (coassembly) and the formation of a &#34;beads on a string&#34;-like structure by this process.9 The protocols presented here can be adapted to other classes of peptides or biological building blocks and can potentially lead to the discovery of new peptide-based structures and to better control of their assembly.

This paper describes the formation of highly ordered peptide-based structures by the spontaneous process of self-assembly. The method utilizes commercially available peptides and common lab equipment. This technique can be applied to a large variety of peptides and may lead to the discovery of new peptide-based assemblies.

In nature, complex functional structures are formed by the self-assembly of biomolecules under mild conditions. Understanding the forces that control ...

Self-assembly of Complex Two-dimensional Shapes from Single-stranded DNA Tiles

Current methods in DNA nano-architecture have successfully engineered a variety of 2D and 3D structures using principles of self-assembly. In this article, we describe detailed protocols on how to fabricate sophisticated 2D shapes through the self-assembly of uniquely addressable single-stranded DNA tiles which act as molecular pixels on a molecular canvas. Each single-stranded tile (SST) is a 42-nucleotide DNA strand composed of four concatenated modular domains which bind to four neighbors during self-assembly. The molecular canvas is a rectangle structure self-assembled from SSTs. A prescribed complex 2D shape is formed by selecting the constituent molecular pixels (SSTs) from a 310-pixel molecular canvas and then subjecting the corresponding strands to one-pot annealing. Due to the modular nature of the SST approach we demonstrate the scalability, versatility and robustness of this method. Compared with alternative methods, the SST method enables a wider selection of information polymers and sequences through the use of de novo designed and synthesized short DNA strands.

DNA tiling is an effective approach to make programmable nanostructures. We describe the protocols to construct complex two-dimensional shapes by the self-assembly of single-stranded DNA tiles.

Current methods in DNA nano-architecture have successfully engineered a variety of 2D and 3D structures using principles of self-assembly. In this ...

Transport of Surface-modified Carbon Nanotubes through a Soil Column

Carbon nanotubes (CNTs) are widely manufactured nanoparticles, which are being utilized in a number of consumer products, such as sporting goods, electronics and biomedical applications. Due to their accelerating production and use, CNTs constitute a potential environmental risk if they are released to soil and groundwater systems. It is therefore essential to improve the current understanding of environmental fate and transport of CNTs. The transport and retention of CNTs in both natural and artificial media have been reported in literature, but the findings widely vary and are thus not conclusive. There are a number of physical and chemical parameters responsible for variation in retention and transport. In this study, a complete procedure of selected multiwalled carbon nanotubes (MWCNTs) is presented starting from their surface modification to a complete set of laboratory column experiments at critical physical and chemical scenarios. Results indicate that the stability of the commercially available MWCNTs are critical with their attached surface functional group which can also influence the transport and retention of MWCNT through the surrounding medium.

Surface properties of a nanoparticle are important for their interaction with the surrounding medium. Therefore the surface modification of carbon nanotubes can be critical for their transport and retention through porous media. Here, lab scale column experiments are used to understand the possible transport and retention of these nanoparticles.

Carbon nanotubes (CNTs) are widely manufactured nanoparticles, which are being utilized in a number of consumer products, such as sporting goods, ...

Facile Preparation of Internally Self-assembled Lipid Particles Stabilized by Carbon Nanotubes

We present a facile method to prepare nanostructured lipid particles stabilized by carbon nanotubes (CNTs). Single-walled (pristine) and multi-walled (functionalized) CNTs are used as stabilizers to produce Pickering type oil-in-water (O/W) emulsions. Lipids namely, Dimodan U and Phytantriol are used as emulsifiers, which in excess water self-assemble into the bicontinuous cubic Pn3m phase. This highly viscous phase is fragmented into smaller particles using a probe ultrasonicator in presence of conventional surfactant stabilizers or CNTs as done here. Initially, the CNTs (powder form) are dispersed in water followed by further ultrasonication with the molten lipid to form the final emulsion. During this process the CNTs get coated with lipid molecules, which in turn are presumed to surround the lipid droplets to form a particulate emulsion that is stable for months. The average size of CNT-stabilized nanostructured lipid particles is in the submicron range, which compares well with the particles stabilized using conventional surfactants. Small angle X-ray scattering data confirms the retention of the original Pn3m cubic phase in the CNT-stabilized lipid dispersions as compared to the pure lipid phase (bulk state). Blue shift and lowering of the intensities in characteristic G and G&#39; bands of CNTs observed in Raman spectroscopy characterize the interaction between CNT surface and lipid molecules. These results suggest that the interactions between the CNTs and lipids are responsible for their mutual stabilization in aqueous solutions. As the concentrations of CNTs employed for stabilization are very low and lipid molecules are able to functionalize the CNTs, the toxicity of CNTs is expected to be insignificant while their biocompatibility is greatly enhanced. Hence the present approach finds a great potential in various biomedical applications, for instance, for developing hybrid nanocarrier systems for the delivery of multiple functional molecules as in combination therapy or polytherapy.

We report on a smart application of carbon nanotubes for kinetic stabilization of lipid particles that contain self-assembled nanostructures in their cores. The preparation of lipid particles requires rather low concentrations of carbon nanotubes permitting their use in biomedical applications such as drug delivery.

We present a facile method to prepare nanostructured lipid particles stabilized by carbon nanotubes (CNTs). Single-walled (pristine) and multi-walled ...

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.

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 ...

Synthesis and Characterization of Fe-doped Aluminosilicate Nanotubes with Enhanced Electron Conductive Properties

The goal of the protocol is to synthesize Fe-doped aluminosilicate nanotubes of the imogolite type with the formula (OH)3Al2-xFexO3SiOH. Doping with Fe aims at lowering the band gap of imogolite, an insulator with the chemical formula (OH)3Al2O3SiOH, and at modifying its adsorption properties towards azo-dyes, an important class of organic pollutants of both wastewater and groundwater.
Fe-doped nanotubes are obtained in two ways: by direct synthesis, where FeCl3 is added to an aqueous mixture of the Si and Al precursors, and by post-synthesis loading, where preformed nanotubes are put in contact with a FeCl3&#8226;6H2O aqueous solution. In both synthesis methods, isomorphic substitution of Al3+ by Fe3+ occurs, preserving the nanotube structure. Isomorphic substitution is indeed limited to a mass fraction of ~1.0% Fe, since at a higher Fe content (i.e., a mass fraction of 1.4% Fe), Fe2O3 clusters form, especially when the loading procedure is adopted. The physicochemical properties of the materials are studied by means of X-ray powder diffraction (XRD), N2 sorption isotherms at -196 &#176;C, high resolution transmission electron microscopy (HRTEM), diffuse reflectance (DR) UV-Vis spectroscopy, and &#950;-potential measurements. The most relevant result is the possibility to replace Al3+ ions (located on the outer surface of the nanotubes) by post-synthesis loading on preformed imogolite without perturbing the delicate hydrolysis equilibria occurring during nanotube formation. During the loading procedure, an anionic exchange occurs, where Al3+ ions on the outer surface of the nanotubes are replaced by Fe3+ ions. In Fe-doped aluminosilicate nanotubes, isomorphic substitution of Al3+ by Fe3+ is found to affect the band gap of doped imogolite. Nonetheless, Fe3+ sites on the outer surface of nanotubes are able to coordinate organic moieties, like the azo-dye Acid Orange 7, through a ligand-displacement mechanism occurring in an aqueous solution.

Here, we present a protocol to synthesize and characterize Fe-doped aluminosilicate nanotubes. The materials are obtained by either sol-gel synthesis upon addition of FeCl3&#8226;6H2O to the mixture containing the Si and Al precursors or by post-synthesis ionic exchange of preformed aluminosilicate nanotubes.

The goal of the protocol is to synthesize Fe-doped aluminosilicate nanotubes of the imogolite type with the formula (OH)3Al2-xFexO3SiOH. Doping with Fe ...

Facet-to-facet Linking of Shape-anisotropic Colloidal Cadmium Chalcogenide Nanostructures

Here, we describe a protocol that allows for shape-anisotropic cadmium chalcogenide nanocrystals (NCs), such as nanorods (NRs) and tetrapods (TPs), to be covalently and site-specifically linked via their end facets, resulting in polymer-like linear or branched chains. The linking procedure begins with a cation-exchange process in which the end facets of the cadmium chalcogenide NCs are first converted to silver chalcogenide. This is followed by the selective removal of ligands at their surface. This results in cadmium chalcogenide NCs with highly reactive silver chalcogenide end facets that spontaneously fuse upon contact with each other, thereby establishing an interparticle facet-to-facet attachment. Through the judicious choice of precursor concentrations, an extensive network of linked NCs can be produced. Structural characterization of the linked NCs is carried out via low- and high-resolution transmission electron microscopy (TEM), as well as energy-dispersive X-ray spectroscopy, which confirm the presence of silver chalcogenide domains between chains of cadmium chalcogenide NCs.

A protocol detailing how shape-anisotropic colloidal cadmium chalcogenide nanocrystals can be covalently linked via their end facets is presented here.

Here, we describe a protocol that allows for shape-anisotropic cadmium chalcogenide nanocrystals (NCs), such as nanorods (NRs) and tetrapods (TPs), to be ...

Liquid-cell Transmission Electron Microscopy for Tracking Self-assembly of Nanoparticles

Drying a nanoparticle dispersion is a versatile way to create self-assembled structures of nanoparticles, but the mechanism of this process is not fully understood. We have traced the trajectories of individual nanoparticles using liquid-cell transmission electron microscopy (TEM) to investigate the mechanism of the assembly process. Herein, we present the protocols used for liquid-cell TEM studies of the self-assembly mechanism. First, we introduce the detailed synthetic protocols used to produce uniformly sized platinum and lead selenide nanoparticles. Next, we present the microfabrication processes used to produce liquid cells with silicon nitride or silicon windows and then describe the loading and imaging procedures of the liquid-cell TEM technique. Several notes are included to provide helpful tips for the entire process, including how to manage the fragile cell windows. The individual motions of nanoparticles tracked by liquid-cell TEM revealed that changes in the solvent boundaries caused by evaporation affected the self-assembly process of nanoparticles. The solvent boundaries drove nanoparticles to primarily form amorphous aggregates, followed by flattening of the aggregates to produce a 2-dimensional (2D) self-assembled structure. These behaviors are also observed for different nanoparticle types and different liquid-cell compositions.

Here we introduce experimental protocols for the real-time observation of a self-assembly process using liquid-cell transmission electron microscopy.

Drying a nanoparticle dispersion is a versatile way to create self-assembled structures of nanoparticles, but the mechanism of this process is not fully ...