The Surface Covlently Grafting Of Multi-Walled Carbon Nanotubes And Their Derivatives

Multi-walled carbon nanotubes(MWNT)have received increasing attention in the fields of reinforcement and conduction due to their excellent mechanical and electronic properties.In particular,MWNT are ideal candidates for nanocomposites in polymer matrix and have demonstrated large enhancement in physical properties with relatively low mass fractions.The properties of MWNT-reinforced polymer are substantially dependent of the degree of dispersion in the matrix and the interaction between MWNT and polymer matrix.However,MWNT tends to aggregate into a dense network owing to their high aspect ratio resulting in poor dispersion in polymer matrix.The atomically smooth surface of MWNT provides poor interfacial adhesion to the polymer matrix,which limited effective load transfer from the matrix to MWNT.For this reason,surface modification of MWNT must be performed before fabrication of nanotube-reinforced polymer composite.This paper presents an approach of covalently grafting of MWNT with polymer chains in order to effectively decrease the aggregation of MWNTs and improve the interfacial interaction.Research work in this dissertation include acid-modification, covalent grafting with various polymer chains of MWNT,and the preparation of nanocomposites using these modified MWNT,particularly:1.Oxidation of MWNT in a mixture of concentrated sulfuric and nitric acids(1:1,v/v)to generate an amount of hydroxyl groups on the surface of MWNT.2.Reacting the hydroxyl groups on the surface of acid-modified MWNT with acryloyl chloride leading to acrylate-functionalized MWNT, which was further copolymerized with styrene to form a polystyrene-matrix composite.Homogeneous dispersion of MWNT in polystyrene matrix was successfully achieved.3.Poly(acryloyl chloride)was covalently grafted onto the surface of MWNTs through esterification of polymer-bound acyl chloride with hydroxyl groups on the surface of acid-modified MWNT.Since only a small fraction of acyl chloride groups was consumed in the attachment of poly(acryloyl chloride)to MWNT,and the major remaining acyl chloride groups further reacted with hydroxyl-/amine-terminated organic molecules or polymers,leading to surface grafted corresponding polymers:(1)through hydrolysis of acyl chloride,poly(acrylic acid)-grafted MWNT were formed and demonstrated good solubility in water;(2)through amidation of acyl chloride with ethylenediamine, amine-functionalized MWNT was formed;(3)through esterification of acyl chloride with poly(ethylene glycol),poly(ethylene glycol)-grafted MWNT was obtained,which exhibited good solubility in many organic solvents;(4)treatment of acyl chloride in an aqueous solution of NaOH, sodium polyacrylated-grafted MWNT was formed.The product was further treated with cetyltrimethylammonium bromide and long alkyl chains were introduced onto the surface of MWNT resulting in good dispersibility in nonpolar solvents and polymers.4.Through esterification of poly(acrylonitrile-co-methyl methacrylate-co-itaconic acid)(PAMI)with hydroxyl groups on acid-modified MWNTs,the PAMI was grafted onto the surface of MWNT. The AMI-grafted MWNT was dispersed in a PAMI solution,which was electrospun to form a nanofiber sheet.The grafted MWNT exhibited good dispersion in the nanofiber sheet and well aligned along the fiber axis.At low loading of MWNT,the nanofiber sheet exhibited much higher tensile strength and modulus compared with the nanofiber membrane based on neat PAMI,with only slight decrease in elongation at break.5.A novel nanostructure of carbon nanotube-silica hybrid was presented.In this hybrid the carbon nanotube was covalently encapsulated with polymer and silica nanospheres were pending on the polymer layer.6.Carbon nanotubes-supported silver nanoparticles were synthesized through reduction of absorbed silver ions onto the nanotube surface by electrostatic interaction with polyacrylate grated on MWCNT. By simply tuning the Ag~+-to-carboxylate ratio,Ag nanoparticles with different sizes were synthesized and anchored on the surface of MWCNT.In summary,through the various approaches proposed in this dissertation,various modified MWNTs were prepared and employed in several important systems.The dispersibility and interface interaction of MWNT in the polymer matrix were significantly improved.This will pave a way for further investigation and practical application of carbon nanotube in the field reinforcement.