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

Summary

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.

Abstract

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.

Introduction

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,

Protocol

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 glass....

Results

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.......

Discussion

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 .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Tetrapropylammonium bromide, 99 % (TPABr)	Sigma-Aldrich	88104	Irritant, toxic
Potassium permanganate, 99 % (KMnO4)	Sigma-Aldrich	223468
Acetic acid, 99.5 %	Sigma-Aldrich	45726
Pristine multiwalled carbon nanotubes, 99 % (MWCNTs)	Bayer Technology Services	Donated sample	Harmful dusts. >1 micrometer in length and 13–16 nm in outer diameter. Alternative supplier: Nanocyl, Catalog N. NC7000, website: http://www.nanocyl.com/
Sodium Chloride, 98 % (NaCl)	Sigma-Aldrich	S3014	Technical grade can also be used
Ethanol, 99.8 % (EtOH)	Sigma-Aldrich	32221	Technical grade can also be used
Methanol, 99.8 % (MeOH)	Sigma-Aldrich	322415	Highly toxic. Technical grade can also be used
Hydroquinone, 99 %	Sigma-Aldrich	H9003
Toluene, 99.8 %	Sigma-Aldrich	244511	Anhydrous
3-(Trimethoxysilyl)propyl methacrylate, 98 % (TMSPMA)	Sigma-Aldrich	440159	Air sensitive, toxic
Azobisisobutyronitrile, 99 % (AIBN)	Sigma-Aldrich	755745	Explosive
Styrene, 99 %	Sigma-Aldrich	S4972	Purified using an alumina gel preparative column and stored at 4 °C
Acetone, 99.5 %	Sigma-Aldrich	179124	Technical grade can also be used
Tetrahydrofuran, 99.9 % (THF)	Sigma-Aldrich	494461
Dichloromethane, 99.5 %	Sigma-Aldrich	443484	Highly toxic
Hydrochloric acid, 37 %	Sigma-Aldrich	435570	Harmful fumes