Synthesis And Electroactivity Of Ionic Polymer Grafted Multiwalled Carbon Nanotubes

Carbon nanotubes (CNTs) are extremely promising for applications in materials science and medicinal chemistry, due to their extraordinary optical, electronic, thermal, mechanical and chemical properties. Especially, water-soluble carbon nanotubes (CNTs)-based composites have received much attention for investigations in the area of potential biological applications and environmentally compliant productions. But the defects of their insolubility and entanglements have imposed great limitations to the application and development of CNTs. The poor solubility of nanotubes in most solvents and matrices rendered a difficult processing ability, and the excellent properties of individual nanotube cannot show high efficiency in the matrices. How to obtain water-soluble CNTs is becoming a great challenge, which determined the commercial viability of the large-scale CNT processing. The most common way to overcome this above is the chemical modification of CNTs by oxidation followed by organic modification with hydrophilic substances.In the present dissertation, the synthesis of ionic polymer covalently modified CNTs, as well as the structure and the electroactive properties of the modified CNTs have been mainly studied. The organic small molecules with functional groups are preliminarily grafted onto the CNT surfaces via amidation to generate CNT-supported macroinitiators. Ionic polymer is then covalently grafted on the surface of CNTs via free radical in-situ polymerization of monomers and finally silver (Ag) nanoparticles are assembled on the surface of CNTs via water-soluble CNTs as template. The electrochemistry of water-soluble CNTs and Ag/CNTs was investigated. The actuation behaviors of ion-exchange membrane with water-soluble CNTs have been also discussed. Water-soluble poly (sodium styrene sulfonate-co-acrylic acid) (P(SSS-co-AA)) grafted CNTs (P(SSS-co-AA)-g-MWNT) have been successfully synthesized by an in-situ free radical copolymerization of sodium styrene sulfonate and acrylic acid in the presence of CNTs terminated with vinyl groups. P(SSS-co-AA)-g-MWNT showed a core-shell structure with a polymer layer thickness of 7-12 nm as shell and nanotube as core, and the grafting content of polymer was 82.3 wt.%. P(SSS-co-AA)-g-MWNT has good solubility and stable dispersibility in water with 4 mg/mL of dissolubility. The electrochemical sensor based on P(SSS-co-AA)-g-MWNT has strong catalytic ability, high electrochemical activity and fast electronic transfer capability. Low content of uric acid (UA), dopamine (DA) and 5-hydroxytryptamine (5-HT), respectively, can be detected by this sensor. It is very interesting that P(SSS-co-AA)-g-MWNT can detect the mixture of DA and 5-HT simultaneously.Ag and CNTs composite (Ag@MWNT) has been successfully synthesized by in-situ reducing Ag ion on the surface of nanotube with water-soluble CNTs as template. Ag crystal is composed of fcc unit cell structure with a =0.408 nm and has a narrow size distribution among 2-4 nm and adheres firmly on the surface of nanotube. The electrochemical sensor based on Ag@MWNT had good catalyst ability to the low concentration of dissolved oxygen (O2) and peroxide hydrogen (H2O2).Reinforced ion-exchange membrane (IEM) has been prepared by doping CNTs into the matrix of poly (vinyl alcohol) (PVA) and P(SSS-co-AA), generating good water-uptake and ionic exchange capability. Ionic polymer-functional CNTs had well-dispersed and was well good compatible in/with the matrix, resulting improve mechanical strength and conductivity of IEM.Electroactive actuators have been consisted of sandwich structure by sputtering gold (Au) on the two sides of IEM. All the actuators with four different contents of CNTs have more than 10 mm displacement of tip deflection under low square wave potential of±1.5 V with a frequency of 0.25 Hz. With the increasing of content of CNTs doped, the relaxation of actuator was gradually disappeared and the sensitivity of actuator to the electric filed increases.A novel actuator has been prepared with functional CNTs mat which served as electrode lays. The actuator shows maximum deflection displacement of 1 mm and 3 mm driven by±2.0 V or±3.0 V potential of square wave with a frequency of 0.25 Hz, respectively. Compared with Au metal as electrode, the CNTs mats improve the cycle life of the actuator with the continuous actuation of 3,000 cycles and the actuator is able to have a three months cycle life if driven 200 strokes each day.