Multiparameter Engineering of Layered Composites.

Many technological challenges facing humanity require the development of high performance nanocomposites. The desirable multiparameter combination of those composites relies on the inclusion of high content well-dispersed nanomaterials with tailored interface and ordered architecture. Natural biomaterials, such as wood, bone, silk, and nacre, exemplify such a design strategy, and accordingly give rise to satisfactory collective properties. Biomimicking such materials to obtain appealing synthetic composites, however, requires advanced manufacturing techniques with multiscale controllability, adaptability and scalability. This thesis shows that layer-by-layer assembly (LBL) and its alternatives as effective and versatile approaches to fabricate layered nanocomposites with attractive multifunctional properties. First, an LBL assembled single walled carbon nanotube (SWNT) transparent coating is designed as an indium tin oxide replacement. A new type of SWNT doping by sulfonated polyetheretherketone (SPEEK) led to a conductivity of 1.1×105 S/m. This property was better than those of other conventional SWNT composites and translated to a surface conductance of 920 ohms/sq and transmittance of 87%. The coating also revealed high temperature resilience up to 500 °C, low roughness of 3.5 nm, and high strength of 366 MPa. Next, a combination of better strength and toughness than other layered assemblies was shown for polyvinyl alcohol (PVA) /reduced graphene composites made by both LBL and vacuum assisted flocculation (VAF) technique. Composites by those methods showed similarities in the mechanical properties, but striking difference in the in-plane electrical conductivity. These observations were explained in terms of structures and interfaces. A unique pseudonegative thermal expansion was identified in the graphene oxide (GO) layered assemblies due to fast water exchange with the environment. This property was exploited to tune the thermal expansion of PVA/GO composites through VAF. Finally, aramid nanofiber (ANF) hydrogel network was constructed by a solvent-exchange process. This network was impregnated with epoxy by a gelation-assisted LBL technique. The resulting ANF/epoxy composite demonstrates an ultimate strength of 505 MPa, and toughness of 50.1 MJ/m3 with high damping property and close-to-zero thermal expansion. Either the strength or toughness is higher than those of quasi-isotropic carbon or aramid microfiber reinforced composites.PHDChemical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/100036/1/zhujian_1.pd