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Synthesis of Water-Soluble Carbon Nanotubes and Its Applications

Author LiChunYan
Tutor ZuoYeHai
School Qingdao University of Science and Technology
Course Materials Science
Keywords carbon nanotubes montmorillonite polymer composite nano-heterostructure hydrogel
Type Master's thesis
Year 2013
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It is a favorable way to apply two different nanofillers into one polymer matrix for fabricating the high-quality nanocomposites. However, how to strengthen the synergistic effect of mixed fillers so as to realize their effective application is a practical challenge. The reults already having been reported suggest that to firstly synthesize the nano-heterostructures of two or more nanofillers and then apply them into polymer composites is an operative strategy for-promoting Synergistic Effect. To address such issue, taking a typical filler suite of montmorillonite (MMT) and single-walled carbon nanotube (SWNT) as an example, this research group would like to present a bottom-up approach for designing and synthesizing MMT/SWNT nanohybrids, in which strong electrostatic interaction is proposed as driving force for the construction of nanohybrids. The obtained MMT/SWNT nanohybrids will be used for the future study of "Fabrication Of Polymer Nanocomposite At The Manometer Level By Using The MMT/SWNT Mixed Fillers". The present work’mainly focuses on the advance research of nanohybrid fabrication, that is, synthesis of water-soluble carbon nanotubes and its applications.In view of negative character of Na+-MMT’s surface, the modified SWNT should have the positively charged surface besides water-solubility in order to provide the strong electrostatic interaction between Na+-MMT and modified SWNT. To this end, the structure of alkyl quaternary ammonium has been chemically grafted onto the nanotube surface. Achieved SWNT (N+-SWNT) present the excellent water solubility, being able to disperse uniformly and stably in pure water in the dominant forms of individual tubes or tiny bundles. The saturated concentration is measured to be as high as111.1mg.L-1. More important, N+-SWNT could be reversibly dried and re-dissolved in water over many cycles. This advantage is absent from the other water-soluble SWNT reported previously.After the successful preparation of N+-SWNT, the MMT/SWNT nanohybrids were subsequently fabricated by using a simple mechanical blending method. The effect of mass feed ratio of Na+-MMT to N+-SWNT on the morphology and yield of nanohybrids was systematically studied. Experimental data suggested that the nanohybrids with the desired structures could be obtained over a wide range of MMT/SWNT=20:1-5:1. Taking the yield and practicability as criteria, the optimal feed ratio is determined to be MMT/SWNT=10:1in mass. With the nanohybrids as starting materials, the hydrogel of MMT/SWNT was further prepared by a grinding method. Presence of the right amount of water makes the MMT/SWNT nanohybrids to form a3D network structure through electrostatic interaction and weak hydrogen bonding. Such water-containing materials show some elastic behaviour, indicating the formation of hydrogels that have the water contents of75-90wt%。Also, N+-SWNT had been used as nanofillers to prepare polymeric composites in which a water-soluble polyvinyl alcohol (PVA) was selected as matrix resin. Owing to critical issues of uniform dispersion and enhanced interfacial PVA-nanotube interaction having been simultaneously resolved to a reasonable extent, the composite with only0.3wt%N+-SWNT has obtained tensile strength of99.3±6.3MPa and Young’s modulus of4.5±0.3GPa, representing an increase of33.3%and32.4%, respectively, over neat PVA.

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