Dispersion of Single Walled Carbon Nanotubes by Self Assembly of Polymers
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Dispersion of Single Walled Carbon Nanotubes by Self Assembly of Polymers Ramasudhakar Babu Dhullipudi1, Yuri M Lvov1, and Tabbetha A Dobbins1,2 1 Institute For Micromanufacturing, Louisiana Tech University, Ruston, LA, 71270 2 Physics, Grambling State University, Grambling, LA, 71245 ABSTRACT Dispersion and stability of single walled nanotubes (SWNT) is one of the inhibiting factors affecting their tailorability for various electronic, chemical and mechanical applications1. The realization of these applications depends on dispersing the SWNTs in aqueous media by inducing high forces of repulsion among the SWNTs. Steric repulsions are induced between the SWNTs by attaching polyelectrolytes, like poly styrene sulfonate (PSS) and poly allyl amine hydrochloride (PAH). In this work, self assembly technique is employed to attach polyelectrolytes, and thereby enhance the dispersion of SWNTs in aqueous media. The steric forces produced by the attached polyelectrolytes overcome the high van der Waals’ force of attraction between the SWNTs and aid in the SWNTs dispersion. Characterization of the dispersions with UV-Vis spectrophotometer in kinetic mode revealed that SWNTs treated at pH 3 are seen to be more stable than the ones treated at pH 7. The effect of pH of the polyelectrolyte solutions in the assembly and its consequence on dispersion stability is also studied with zeta potential measurements. The morphology of the films produced by drying the SWNTs in vacuum on a silicon substrate is characterized by field emission scanning electron microscopy (FESEM). INTRODUCTION SWNTS, one of the most promising one-dimensional materials used in different applications in recent times, exhibit a very high van der Waals’ force of attraction resulting in their aggregation when submersed in aqueous media for processing2. Increasing number of SWNT applications ushered a greater significance being shown to their dispersion. Different methods have been employed to induce repulsive forces that can overcome the van der Waals’ attractive forces between SWNTs. Covalent modifications3, surfactant assisted dispersions4, non covalent functionalization5, acid treatment combined with ultrasonication6, are just few of the methods used to achieve SWNT dispersion. These methods either changed the intrinsic properties of the molecules or are complex and expensive. One non covalent method we employed in our earlier work is a self assembly technique to alternately attach oppositely charged polyelectrolytes7. We employed this technique to attach water soluble polyelectrolytes like PSS and PAH and thereby enhance the dispersion of the SWNTs in aqueous media. Once the films or structures are formed these polyelectrolytes may be removed by employing high temperatures to which SWNTs are inert. If left to exist in the films of these SWNTs, we can produce a uniform polymer nanotube composite material, which has numerous applications. One of the major requirements in our scientific endeavor to produce stable dispersion is a robust technique for ch
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