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.

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

Research

JoVE Journal

Chemistry

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 ...

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 ...

Capillary Electrophoresis to Monitor Peptide Grafting onto Chitosan Films in Real Time

Free-solution capillary electrophoresis (CE) separates analytes, generally charged compounds in solution through the application of an electric field. Compared to other analytical separation techniques, such as chromatography, CE is cheap, robust and effectively requires no sample preparation (for a number of complex natural matrices or polymeric samples). CE is fast and can be used to follow the evolution of mixtures in real time (e.g., chemical reaction kinetics), as the signals observed for the separated compounds are directly proportional to their quantity in solution.
Here, the efficiency of CE is demonstrated for monitoring the covalent grafting of peptides onto chitosan films for subsequent biomedical applications. Chitosan&#39;s antimicrobial and biocompatible properties make it an attractive material for biomedical applications such as cell growth substrates. Covalently grafting the peptide RGDS (arginine - glycine - aspartic acid - serine) onto the surface of chitosan films aims at improving cell attachment. Historically, chromatography and amino acid analysis have been used to provide a direct measurement of the amount of grafted peptide. However, the fast separation and absence of sample preparation provided by CE enables equally accurate yet real-time monitoring of the peptide grafting process. CE is able to separate and quantify the different components of the reaction mixture: the (non-grafted) peptide and the chemical coupling agents. In this way the use of CE results in improved films for downstream applications.
The chitosan films were characterized through solid-state NMR (nuclear magnetic resonance) spectroscopy. This technique is more time-consuming and cannot be applied in real time, but yields a direct measurement of the peptide and thus validates the CE technique.

Free solution capillary electrophoresis is a fast, cheap and robust analytical method that enables the quantitative monitoring of chemical reactions in real time. Its utility for rapid, convenient and precise analysis is demonstrated here through analysis of covalent peptide grafting onto chitosan films for improved cell adhesion.

Free-solution capillary electrophoresis (CE) separates analytes, generally charged compounds in solution through the application of an electric field. ...

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 ...