Jieyang Huang

High-Yield Production of Highly Fluorinated Graphene by Direct Heating Fluorination of Graphene-oxide

By employing honeycomb GO with large surface area as the starting materials and using elemental fluorine, we developed a novel, straightforward topotactic route toward highly fluorinated graphene in really large quantities at low temperature. The value of F/C molar ratio approaches to 1.02. Few-layer fluorinated graphene sheets are obtained, among which the yield of monolayered FG sheet is about 10% and the number of layers is mainly in the range of 2-5. Variations in morphology and chemical structure of fluorinated graphene were explored, and some physical properties were reported.

Facile preparation of highly hydrophilic, recyclable high-performance polyimide adsorbents for the removal of heavy metal ions

To obtain high-performance adsorbents that combine excellent adsorption ability, thermal stability, service life and recycling ability, polyimide (PI)/silica powders were prepared via a facile one-pot coprecipitation process. A benzimidazole unit was introduced into the PI backbone as the adsorption site. The benzimidazole unit induced more hydroxyls onto the silica, which provided hydrophilic sites for access by heavy metal ions. By comprehensively analyzing the effect of hydrophilcity, agglomeration, silica polycondensation, specific surface area and PI crystallinity, 10% was demonstrated to be the most proper feed silica content. The equilibrium adsorption amount (Qe) for Cu(2+) of PI/silica adsorbents was 77 times higher than that of pure PI. Hydrogen chloride (HCl) was used as a desorbent for heavy metal ions and could be decomplexed with benzimidazole unit at around 300°C, which was lower than the glass transition temperature of PI. The complexation and decomplexation process of HCl made PI/silica adsorbents recyclable, and the adsorption ability remained steady for more than 50 recycling processes. As PI/silica adsorbents possess excellent thermal stability, chemical resistance and radiation resistance and hydrophilicity, they have potential as superior recyclable adsorbents for collecting heavy metal ions from waste water in extreme environments.

Dependence of pretilt angle on orientation and conformation of side chain with different chemical structure in polyimide film surface

A series of polyimide films were synthesized based on various side-chained diamines, 4-phenylphenyl-3,5-diaminobenzoate (DABB), 6-(4-phenylphenoxy)hexyl-3,5-diaminobenzoate (C6BB), 6-(4-(4-butoxylphenyl)phenoxy)hexyl-3,5-diaminobenzoate (C6BBC4) and 4-(4-butoxylphenyl-phenyl-3,5-diaminobenzoate (BBC4), the side chains of which contain a rigid biphenyl linked with flexible alkyl. The pretilt angle of liquid crystal molecules on the side-chained polyimide films based on C6BBC4 or BBC4 (PI-C6BBC4 or PI-BBC4) increased obviously with increasing side chain content and even achieved 87–89°. In contrast, the polyimide film based on C6BB or BB (PI-C6BB or PI-BB) even with a high side chain content could only achieve the homogeneous alignment. The properties and microscopic structure of the functionalized polyimide films were analyzed by polarized ATR-FTIR, computer simulations and surface energy etc. It was found that the side chains with different chemical structure get the different orientation and conformation in the outmost layer of polymer film, affecting the pretilt angle of liquid crystal molecules on this film surface. For PI-BBC4 and PI-C6BBC4, the side chains with the non-polar group at the tail take the vertical conformation in the outer layer of the polymer surface, which benefited the liquid crystal to get a large pretilt angle, even vertical alignment on the film surface. The side chain of PI-C6BB with the flexible alkyl spacer is equipped with good mobility. It is easy for its polar mesogen groups at the surface to take the conformation parallel to the polymer film, which leads to the formation of homogeneous alignment of LC molecules.

Pre-drawing induced evolution of phase, microstructure and property in para-aramid fibres containing benzimidazole moiety

Copoly(p-phenylene-benzimidazole-terephthalamide) (PBIA) fibre was spun by wet-spinning and drawn in a coagulating bath with different pre-drawing ratios (R). The evolution of phase, microstructure structure and conformation induced by pre-drawing were studied by 2D-wide angle X-ray diffraction (2D-WAXD), attenuated total reflection-Fourier transform infrared (ATR-FTIR) and scanning electron microscope (SEM). WAXD results indicate that mesomorphic/amorphous coexisting phases transform to crystal/mesomorphic/amorphous coexisting phases when R is higher than 75%. Even when R reaches an ultimate value of 100%, the content of crystalline is only 10.7% but the mesomorphic phase content is higher than 40%, which indicates that the 3D well defined crystalline structure is disturbed by the introduction of asymmetric benzimidazole units. The ATR-FTIR results indicate that the increase of R leads to conformational order, contributing to phase transition. The results of SEM show that PBIA fibres have a typical skin–core morphology. The sizes of micro-fibrils in the core part become more homogeneous with the increase of R. Moreover, with the increasing R from 0% to 100%, the tensile strength and initial modulus of the PBIA fibre significantly increase from 7.8 cN dt−1 to 21.5 cN dt−1 and from 238 cN dt−1 to 884 cN dt−1, respectively. Dynamic mechanical analysis (DMA) of PBIA fibres shows two transition peaks, and some amorphous phase is confined by the order phases.

The evolution of structure and properties for copolyamide fibers–containing benzimidazole units during the decomplexation of hydrogen chloride:

A diamine monomer 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ) was introduced to modify poly(p-phenylene terephthalamide) by copolymerization, and corresponding aromatic copolyamide fibers were prepared by wet spinning. Thermogravimetric analysis showed that the benzimidazole units of the as-spun copolyamide fibers can complex with hydrogen chloride (HCl) to form protonated benzimidazole units, and the decomplexation takes place above 280°C. It is interesting that the crystal orientation, crystallite size, and tensile strength increase significantly during the decomplexation. Fourier transform infrared spectroscopy proved that the decomplexation leads to the release of the electron donor C=N, which can form hydrogen bonding with NH in the PABZ unit. After removing HCl, the copolyamide fibers exhibit better planarity and stronger π–π conjugation between benzimidazole and benzene rings, which is conducive to the formation of π–π stacking. Thus, we suggest that the newly formed hydrogen bonding and the enhanced π–π stacking induce the closely packing and spontaneous orientation of the macromolecular chains, which lead to the sharp improvement of the tensile strength.

Ultrahigh strength and modulus copolyamide films with uniaxially cold-drawing induced molecular orientation:

The tensile strength of polymer films is generally lower than 200 MPa. Copolyamide (CPA) films with ultrahigh strength (approximately 317–865 MPa) and high modulus (approximately 3.96–11.76 GPa) were obtained by uniaxial cold-drawing and heat treatment. The relationship between structures and properties in the orientation state was also investigated. The results of Fourier transform infrared (FTIR) spectroscopy indicate that hydrogen bonding interactions change a little with drawing. Wide-angle X-ray diffraction patterns show orientational stretch induces π–π ordered packing after drawing 100%. The tensile strength and modulus of the drawn CPA films are improved approximately 41%–173% and 9%–197% compared to undrawn films. Dichroic ratios obtained under polarized FTIR spectroscopy represent overall orientation factors. The decrease of dichroic ratios at about 3300 cm−1 and 1650 cm−1 and the increase of dichroic ratios at 1515 cm−1 prove that the orientation of macromolecular chains is improved along stretch direction. What’s more, the degree of orientation is further increased after heat treatment, which is the phenomenon of spontaneous orientation. The degree of spontaneous orientation increases with the increase of cold-drawing ratio. Thus, the initial orientation in cold-drawing and spontaneous orientation during heat treatment leads to ultrahigh modulus and high strength.

Catalysis and Inhibition of Benzimidazole Units on Thermal Imidization of Poly(amic acid) via Hydrogen Bonding Interactions

The effect of benzimidazole units on thermal imidizaiton was studied when they were introduced into the main chain of poly(amic acid) (PAA). The thermal imidization process of PAA-PABZ synthesized by 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 2-(4-aminophenyl)-5(6)-aminobenzimidazole (PABZ) was studied by TGA, DSC, DMA, FTIR and in situ FTIR. The results of FTIR and in situ FTIR indicate benzimidazole units act as an “in situ” catalyst to accelerate thermal imidization of PAA to polyimide (PI) when the temperature is lower than 170 °C. FTIR and 1H-NMR results demonstrate that in situ catalysis is caused by the hydrogen bonding interactions between C=N of benzimidazole and -NH- in -CONH- of PAA and the semi-ionization of the H in imidazole ring of benzimidazole. However, when the imidization temperature is higher than 170 °C, the thermal imidization process is inhibited. DMA and in situ FTIR results illustrate that the decreased mobility of PI-PABZ macromolecular chains and the reduced reactive ability of anhydride formed during the intramolecular breakdown of polymer chains lead to the inhibition of thermal imidization process.

Increasing pretilt angle by grafting hexafluorobutyl acrylate into the surface of polyimide alignment films via electron beam irradiation

In this study, the polyimide (PI) alignment film whose surface contained fluorinated side chain was prepared by a new method. The fluorine compound, hexafluorobutyl acrylate (HFBA), was grafted into the surface of main-chained PI film as side chain via electron beam irradiation. The pretilt angle of liquid crystal (LC) was significantly improved from 2° to 20° or above. It was indicated by X-ray photoelectron spectroscopy spectra and attenuated total reflection Fourier transform infrared spectroscopy spectra that HFBA was successfully grafted into the thin surface layer of PI alignment films in the form of covalent bond. Scanning electron microscopy images showed that the irradiation process had no obvious influence on the surface morphology of the PI film. The surface energy of the PI film decreased from 49.85 to 31.50 mN/m after surface modification. Besides, the reason for the increase of pretilt angles was discussed.