Study On Hybrid Functionalized Carbon Nanotube Polymer Composites

Carbon nanotubes (CNTs) are promising reinforcement material for structural polymercomposites due to their extraordinary mechanical and thermal properties. Mechanical propertiesof CNT polymer composites depend mainly on the interfacial interactions between CNT andmatrix, as well as the dispersion and alignment of CNTs in the matrix. However, pristine CNTsare prone to aggregation, and are insoluble in most solvents, rendering them difficult to bedispersed in the matrix. Moreover, the interfacial interactions between pristine CNT and matrixare rather weak. It was reported that CNT functionalization could be an effective way to improvethe dispersion and strengthen the interfacial interactions. Recently CNT functionalization andtheir application in polymer composites have become a new research interest. The purpose ofthis thesis is to explore new schemes for CNT functionalization, to study the effect of differentfunctionalizations on CNT dispersion, interfacial strength, and glass transition temperature (Tg)of composites, respectively. The completed works and the results are mainly summarized asfollows:Based on the analysis of advantages and disadvantages of covalent and noncovalentfunctionalizations, a scheme of hybrid system was proposed, in which polymer wrapping isintroduced to improve CNT dispersion in the matrix, and meanwhile, a small quantity ofcovalent functional groups are introduced onto CNT walls as anchors to pin the noncovalentpolymer wrappings from detachment. Molecular dynamics (MD) simulations are performed tovalidate the feasibility of the hybrid functionalization, and the dispersion capacity of hybridfunctionalized CNTs in matrix is also investigated. Results show that CNT dispersion can befurther improved by hybrid functionalization, in contrast with covalent or noncovalentfunctionalization.Effect of functionalizations on interfacial strength between CNT and polyethylene or epoxyresin, is investigated by pullout simulations of a pristine CNT, polymer wrapping (noncovalentfunctionalized) CNT, covalent functionalized CNT, and hybrid functionalized CNT, respectively.Results show that CNT-polymer interfacial strength can be improved by CNT functionalizations,best by hybrid functionalization, then by covalent, and then by noncovalent functionalizations, insequence. Thermodynamic properties of CNT-polymer composites prepared by different types of CNTfunctionalizations, or different degrees of functionalizations, or different loading of CNTs, arestudied. The effects of pressure on Tg are also studied. Results show that functionalizations ofCNTs improve thermostability of composites. The Tg of composites increased with the increasedegree of covalent functionalization of CNTs. The Tg for hybrid functionalization is slightlyhigher than that for covalent functionalization, in the case that both functionalizations have thesame quantity of chemical cross-links. When CNT loading is small, Tg of composites is almostlinearly dependent on CNT loading, whereas Tg of composites with higher CNT loadingapproaches constant. The Tg of CNT polymer composites also changes with pressure, and eachincrease (or decrease) of Tg of 50K or so for one order of magnitude of increase (or decrease) ofthe pressure for hybrid functionalized CNT-polyethylene composites.