Functionalization Of Graphene And Polymer/Graphene Composites

Graphene is under the spotlight of the science and technology community owning to itsunparalleled properties. As nanofiller for polymer, graphene has exceptional reinforcingefficiency towards polymer matrix, and it can endow the composites with functionalproperties. However, the real-life applications of graphene in polymer composites are greatlylimited by the large-scale production, the uniform dispersibility of graphene in polymermatrix, the design of interfacial structures, and being lack of the understanding of therelationship between the structures and performances of the composites. Accordingly, in thepresent dissertation, we focused on the studies on the functionalization of graphene andpolymer/graphene composites.(1) The elastomeric hybrids consisting of graphene oxide (GO) sheets were fabricatedby utilizing butadiene-styrene-vinyl pyridine rubber (VPR) as the host through co-coagulationprocess and in situ formation of an ionic bonding interface. The VPR/GO composites with anormal hydrogen bonding interface were also prepared. The mechanical properties and gaspermeability of these hybrids with an ionic bonding interface were obviously superior to thoseof the composites with a hydrogen bonding interface, which was due to the fine dispersion ofGO and strong ionic interface in the hybrids.(2) Individually dispersed graphene colloid was prepared using common andcommercially available fluorescent whitening agents (FWAs) and dye as nano-covalentmodifiers. The modifiers were successfully anchored onto graphene sheets by π-π andcation-π interaction to prevent the aggregation of graphene. Subsequently, the obtainedgraphene was incorporated into polyvinly alcohol and chitosan (CS) by solution casting tofabricate PVA/graphene and CS/graphene composites. The concurrently significantimprovements in tensile strength and toughness of the composites were observed, which wasrelated to the uniqueness interfacial structure and morphology of the composites. It wasdemonstrated that graphene was homogeneous dispersed in the composites and was alignedparallel to the surface of composite films. Besides, the modifiers located in the graphene and polymer interface zone strengthened the interfacial interaction between them.(3) Graphene material with liquid-like behavior was synthesized through decoratinggraphene with a generic non-covalent fashion and subsequently combining them with bulkypolymer chains. Individually dispersed graphene core was first prepared through chemicalreduction of GO by using fluorescent whitening agent VBL as a non-covalent modifier. Thenegative groups of VBL which were anchored onto the graphene sheets imparted grapheneanionic characteristic. Combination of the modified graphene with bulky Jefamine2070chains through electrostatic interaction yielded homogeneous graphene fluid, i.e.graphene-based nanoparticle ionic materials (G-NIM). G-NIM could be stably dispersed in abroad spectrum of solvents at a super-high concentration of500mg/ml.(4) A kind of bio-based polyester (BE) was synthesized by poly-condensation betweenplant-derived diols and diacids. The individually dispersed GO sheets in DMF were obtainedby the solvent-exchange method. BE was then grafted onto GO via the easterification, whichwas then subjected to reduction by vitamin C. In the BE/graphene composites, graphenesheets were interconnected by the BE chains, which favored the formation of conductivepaths at very low graphene loading. The concurrently increased electrical and thermalconductivity were a consequence of well-dispersion of graphene in BE and the interconnectedstructure of graphene.(5) Graphene oxide was directly reduced into graphene in N-methyl-pyrrolidone with theassisted-dispersion of vapor grown carbon nanofibers (VGCF), resulting in a homogeneousdispersion of VGCF-graphene (VGCF-G) hybrid filler. In the hybrid filler, VGCF served aseffective stabilizers for graphene by adsorbing VGCF onto graphene through π-π interactionbetween them. The obtained hybrid filler was incorporated into a bio-based polyester (BE) toprepare BE/VGCF-G composites. In the BE/VGCF-G composites, the dispersion of VGCFand interfacial adhesion between BE and VGCF were greatly improved because that theincorporated graphene acted as “compatibilizer” between VGCF and BE, leading tosignificant synergistic effects in improving the electrical conductivity and mechanicalproperties of the composites. Furthermore, multi-stimuli responsive shape memory performances (electro-activated and infrared-triggered) of the composites were investigated,and it was showed that BE/VGCF-G composites had a combination of higher shape memoryrecovery, stronger recovery stress and faster response, compared with the compositescontaining VGCF alone.(6) Tannic acid functionalized graphene (TAG) aqueous dispersion was prepared andused to hybridize with tubular clay, halloysite nanotubes (HNTs), to prepare a hybrid colloid(HNTs-TAG). The driving force for the hybridization was disclosed to be the specificinteractions (hydrogen bond and bridged bidentate bond) between the catechols on TAG andalumina/siloxane surfaces of HNTs. The obtained hybrid colloid was then co-coagulated withstyrene-butadiene rubber (SBR) emulsion to prepare elastomeric composites. Results showedthat a3D hybrid filler network consisting of HNTs and TAG was developed and served as anovel networked reinforcement in the SBR matrix. The formed hybrid filler network, togetherwith the enhanced interfacial adhesion, was considered to be responsible for the extraordinarysynergetic effects on improving the modulus and strength of the composites.