Graphene:Functionalization And Macroscopic Assembled Nacre-mimic Fibers

Graphene, a sheet of monolayer carbon-atoms arranged in honeycomb lattice, exhibits long-range π-conjugation architecture that affords it outstanding mechanical, electrical, and thermal properties. Lots of papers on functionalized graphene, graphene composites and macroscopic assembled graphene materials have been published. However, there are still some challenges unresolved, such as,1) synthesis of highly soluble graphene,2) preparation of continuous macroscopic ordered graphene-based composite materials,3) exploration of facile and efficient assembly strategy to obtain macroscopic ordered graphene-based composite materials. Accordingly, this dissertation systemically studied on these problems, and obtained the main results listed below.1. Multihydroxyl hyerpbranched polyglycerol (HPG) was reacted with graphene oxide (GO) in one-step, giving rise to HPG-functionalized graphene. The resultant sandwich-like graphene hybrids possessed excellent dispersibility in polar solvents such as water, DMSO, DMF, and so on, especially as single layers at extremely high concentration. The fractions of HPG attached on graphene were 16,34,49, and 57 wt% calculated from thermal gravimetric analysis (TGA) curves, dependent on the molecular weights. The corresponding hydroxyl densities were 2.11, 4.54,6.57, and 7.75 mmol/g. Moreover, the hydroxyl groups on the nanosurface can be utilized for further modification. High-density, superfine Pt nanocrystals of 1～2 nm were loaded on the functionalized sheets, showing predominant catalytic activity in the reduction of 4-nitrophenol.2. Due to the high solubility, the obtained sandwich-like building blocks of HPG-functionalized graphene exhibited spontaneously liquid crystalline (LC) behavior as concentration increases. The first artificial nacre fibres up to tens of metres in length, with perfect "brick-and-mortar" (B&M) layered structures of graphene sheets and HPG binders, were continuously wet-spun from their concentrated LC dope. The supramolecular fibres constructed by hydrogen-bonding arrays showed eminent properties such as high tensile strength (125 MPa), fine conductivity, and excellent corrosion-resistance. After being immersed in hydrochloric acid (1 M), NaOH (1 M), and saturated LiCl solution in DMF for 3 days, the artificial nacre fibres still kept excellent mechanical strength and flexibility and they were knotted without breakage after being immersed for two weeks.3. Based on GO liquid crystals (LCs) with orientational ordering in fluid state, the thesis proposed liquid crystal self-templating (LCST) methodology to make the ultrastrong and tough nacre-mimics continuously. HPG guest compounds were homogeneously dispersed into the inter-channels of LC GO sheets. The incorporation of wet-spinning technology gave birth to nacre-mimetic fibres up to thirty meters long with highly ordered hierarchical structure. The integration of ultrahigh aspect ratio and well-preserved alignment of GO sheets, uniform single-molecule interlayer of polymers, and adaptive hydrogen bonding arrays guaranteed the macroscopic assembled artificial nacre ultrahigh tensile strength (652 MPa), five to eight times as high as that of nacre (80-135 MPa), and excellent ductility with toughness of 18 MJ/m3, one to two orders of magnitude greater than that of nacre (0.1～1.8 MJ/m3).4. To confirm the versatility of the LCST strategy, other guests such as polyvinyl alcohol, sodium alginate (SA) and Ag nanoparticles were utilized to mix with the host of GO LCs, and continuous strong fibres were also obtained by the same wet-spinning assembly protocol. LCST approach realized the precise control over GO content of biomimetic composites. GO-SA composites with different fractions of GO (10-80wt%) were fabricated and at an optimum fraction (40wt%) of GO, the highest tensile strength (785 MPa) of composites was achieved. The proposed LCST strategy is simple and can easily be scale-up, opening the avenue for large scale processing of macroscopic ordered graphene nanocomposites. The resultant nacre-mimic composite fibers exhibit good mechanical and electrical performance, providing wide application in the fields of high performance composites, conductive texitles, and flexible devices.