Mengmeng Ren

Fluorographene with high fluorine/carbon ratio: a nanofiller for preparing low-κ polyimide hybrid films.

Sufficient amounts of fluorographene sheets with different sheet-size and fluorine/carbon ratio were synthesized for preparing of fluorographene/polyimide hybrids in order to explore the effect of fluorographene on the dielectric properties of hybrid materials. It is found that the fluorine/carbon ratio, width of band gap, and sheet-size of fluorographene play the important roles in determining the final dielectric properties of hybrids. The fluorographene with high fluorine/carbon ratio (F/C ≈ 1) presents broaden band gap, enhanced hydrophobicity, good dispersity and thermal stability, etc. Even at a very low filling, only 1 wt %, its polyimide hybrids exhibited drastically reduced dielectric constants as low as 2.1 without sacrificing thermal stability, improved mechanical properties obviously and decreased water absorption by about 120% to 1.0 wt %. This provides a novel route for improving the dielectric properties of materials and a new thought to carry out the application of fluorographene as an advanced material.

Characterization of Conformation and Locations of C–F Bonds in Graphene Derivative by Polarized ATR-FTIR

It is still a challenge to explore the orientation and location of chemical groups in the two-dimensional derivative of graphene. In this study, polarized attenuated total reflectance Fourier transform infrared spectroscopy (polarized ATR-FTIR) was employed to investigate the orientation and location of C-F groups in the corresponding graphene derivative sheets, which facilitates building a relationship between the bonding nature and fine structure. There were two types of C-F bonding, (C-F)I and (C-F)II, in fluorinated graphene sheets. It was found that (C-F)II bonds were linked at the coplanar carbon atoms in the weakly fluorinated region (CxF, x ≥ 2), whereas the (C-F)I bonds cluster at the strongly deformed carbon framework with a F/C ratio of about 1. The thermostability of (C-F)II is lower than that of (C-F)I bonds. This is because the coplanar structure of the weakly fluorinated region tends to transform to the planar aromatic ring with the breaking of the C-F bond as compared with the strong fluorinated nonplanar region.

Various surface functionalizations of ultra-high-molecular-weight polyethylene based on fluorine-activation behavior

Ultra-high-molecular-weight-polyethylene (UHMWPE) is an excellent biological material, but covalently introducing a variety of functional groups on its surface is very difficult owing to its inherently inert structure. In this study, the surface functionalization of UHMWPE based on fluorine-activation and subsequent derivatization reactions is reported, and offers a simple and convenient pathway to the incorporation of useful functional groups and patterned surface functionality. A large number of carboxyl groups, –C–Fx and CC bonds are covalently bonded to the macromolecular chain structure through a fluorine-activated process in the presence of oxygen, greatly increasing the surface polarity and wettability. Its surface energy is increased from 34.5 mN m−1 to 57.5 mN m−1, and the polar component arises from 4.0 to 23.8 mN m−1. In contrast, only stable C–F forms when treated with only fluorine (no oxygen), producing a hydrophobic Teflon-like surface structure and poor wettability. Moreover, UHMWPE with carboxyl groups and double bonds, used as precursor, were further covalently functionalized through subsequent derivatization reactions with fluorine, bromine and amine-terminated molecules, by which the carbon–bromine bond and amino groups were successfully grafted onto a UHWMPE surface. The results demonstrate that the fluorine-activated strategy developed in this work is an effective means to improve the surface hydrophilicity and derivatization reaction capacity of UHMWPE.

The reaction kinetics and mechanism of crude fluoroelastomer vulcanized by direct fluorination with fluorine/nitrogen gas

A novel vulcanization method for crude fluoroelastomer by direct fluorination with fluorine/nitrogen gas has been investigated. The results show that the vulcanization reaction of fluoroelastomer is closely related with fluorination temperature, fluorination time and fluorine gas partial pressure. The maximum crosslink degree can be up to 97%, and the fluorine content of fluoroelastomer increased from 48.2% to 60% during the fluorination. The static friction coefficient of fluoroelastomer is decreased from 0.91 to 0.55, which is about 39.6% reduction after fluorination. The ATR-FTIR spectra indicate the crosslink reaction process of fluoroelastomer by direct fluorination, which arises from three reaction stages and successively goes through four elementary reactions: substitution reaction; elimination reaction; addition reaction; crosslink reaction. The increase of fluorine content takes place mainly in the first stage, and the crosslink reaction takes place mainly in the second stage and third stage.

A composite with excellent tribological performance derived from oxy-fluorinated UHMWPE particle/polyurethane

The thermoplastic polyurethane (TPU)/UHMWPE composite with good compatibility and strong interfacial adhesion is achieved by using direct fluorination surface modification technology. The obtained composite has excellent tribological performance enhancement efficiency with significant decrease in wear volume loss and friction coefficient.