Xiangyang Liu

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Name: 刘向阳; Liu, XiangYang

Organization: Sichuan University , China

Department: College of Polymer Scienceand Engineering

Title: Professor(PhD)

TOPICS

Polymer

Polyimide Polybenzimidazoles

Chemicals
References

Activation effect of porous structure on fluorination of graphene based materials with large specific surface area at mild condition

Co-reporter:Xu Wang, Weimiao Wang, Dazhou Xu, Yang Liu, Wenchan Lai, Xiangyang Liu

Carbon 2017 Volume 124(Volume 124) pp:

Publication Date(Web):1 November 2017

DOI:10.1016/j.carbon.2017.08.076

Fluorinated 2D porous graphene-based materials, FPGMs, were synthesized by using porous activated graphene material as raw material. The fluorination of PGM was activated through the introduction of meso- and micropores which generated a large number of vacancy, edges and defects. The fluorinated sample FPGM-10 with a F/C ratio of 0.67 was obtained at room temperature. Meanwhile, the temperate fluorination conditions guaranteed the porous structure from destruction, which endowed the FPGMs with large specific surface area and well-defined micro- and mesopores, among which FPGM-10 exhibited a BET SSA value of around 1100 m2/g. It was found the bare C atoms near the CF bonds with unpaired electron showed high reactivity with F2 resulting in the clustering of fluorine atoms at the edges, thus highly fluorinated edge region was formed. The thermogravimetric analysis, electrochemical measurement and computer simulation results simultaneously confirmed this structural characteristic ensured FPGMs with high chemical and thermal stability.Download high-res image (162KB)Download full-size image

Towards efficient microwave absorption: intrinsic heterostructure of fluorinated SWCNTs

Co-reporter:Yichun Zhang;Yang Liu;Xu Wang;Yuehui Yuan;Wenchuan Lai;Zaoming Wang;Xiaojiao Zhang

Journal of Materials Chemistry C 2017 vol. 5(Issue 45) pp:11847-11855

Publication Date(Web):2017/11/23

DOI:10.1039/C7TC04141A

The construction of heterostructures is always effective to achieve efficient microwave absorption (MA) properties. Herein, different from conventional hybrid techniques, a novel microwave absorber with an intrinsic heterostructure is fabricated via direct heating fluorination of SWCNTs (F-SWCNTs) utilizing F2/N2. The as-prepared inhomogeneous F-SWCNTs are confirmed to contain both fluorinated domains and aromatic domains at the nanoscale. The evolution of the fluorinated domains is closely related to the development of the C–F groups, whereas the –CF2 groups have no effect. For MA, it is proposed that the aromatic domains function as attenuation regions, whereas the fluorinated domains serve as microwave transparent regions. When the area of aromatic domains is almost equal to that of fluorinated domains, the complementarity between attenuation ability and impedance match endows F-SWCNTs (fluorine content equals of 6.8%) with a good MA performance. Specifically, with only 4.8 wt% loading, the minimum reflection loss (RL) reaches −64.3 dB at the thickness of 1.61 mm, and the effective absorption region (RL < −10 dB) covers a range of 14.1–18 GHz at the thickness of 1.15 mm. The MA performances rely on the evolution of the physical heterostructure, instead of the introduced chemical bonds or fluorine-containing functional groups. The simplicity and feasibility of our design concept indicate the potential application of F-SWCNTs industrially.

The preparation of surface fluorinated polyethylene films with excellent properties similar to that of fluoropolymers

Co-reporter:Zaoming Wang, Shuliang Li, Baoyin Li, Wenchuan Lai, Yang Liu, Zheng Cheng, Xu Wang, Xiangyang Liu

Journal of Fluorine Chemistry 2017 Volume 200(Volume 200) pp:

Publication Date(Web):1 August 2017

DOI:10.1016/j.jfluchem.2017.07.003

•Fluorinated polyethylene films with properties similar to that of fluoropolymers are prepared by direct fluorination.•The chemical structure of fluorinated layer on surface of polyethylene can be tuned by different temperature.•The existence of surface fluorinated layer show improved weathering-resistant property and barrier properties.•Direct fluorination provides a new method for the manufacture of a new generation protect film product.Various surface fluorinated polyethylene films with different fluorination degree have been prepared by direct fluorination. The chemical structure of the resulted fluorinated polyethylene layer has been effectively tuned by direct fluorination, where the fluorination degree and chemical structures are highly dependent on fluorination temperature. Direct fluorination with low temperature mainly results in a formation of CHF groups, whereas CF2 groups are prevailing at high temperature, which plays a major role in the enhancement of weathering-resistant properties. The polyethylene films with highly fluorinated layers show better weathering-resistant property, which are much more stable against UV irradiation compared with the virgin. Moreover, better thermal stability could also been observed in air atmosphere (up to 428.8 °C) compared with the virgin (396.6 °C) for the fluorinated layer. The increasing fluorination degree also results in lower surface energy (from 34.5 to 14.3 mN m−1, 58.6% reduction), and higher contact angle of water (from 98.1° to 117.9°, 20.2% improvement) and diiodomethane (from 53.9° to 98.9°, 84.5% improvement), which contributing to the enhance of barrier properties towards O2 (30% reduction) and water as well as organic solvents. In addition, the corresponding apparent activation energy and pre-exponential factor of the direct fluorination process calculated from Arrhenius equation are 58.86 kJ mol−1 and 1.53 × 107 min−1, respectively.Download high-res image (225KB)Download full-size image

Characterization of the thermal/thermal oxidative stability of fluorinated graphene with various structures

Co-reporter:Wenchuan Lai;Dazhou Xu;Xu Wang;Zaoming Wang;Yang Liu;Xiaojiao Zhang

Physical Chemistry Chemical Physics 2017 vol. 19(Issue 29) pp:19442-19451

Publication Date(Web):2017/07/26

DOI:10.1039/C7CP03684A

Considering practical applications, the thermal/thermal oxidative stability of fluorinated graphene should be given sufficient attention. Herein, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR) were used to investigate in detail the differences in the thermal stabilities of two types of fluorinated samples, fluorinated graphene (FG) and fluorinated porous graphene (FPG) with various fluorine contents, respectively, as well as the reasons for these differences. It was demonstrated that the thermal stability of FG and FPG was improved upon increasing the fluorine content, which was mainly caused by the enhancement of bond energy of the covalent C–F bonds. Moreover, compared to that of the raw graphene samples, the thermal oxidative stability of FG was reduced due to the defects brought by fluorination, while the thermal oxidative stability of FPG was improved, originating from the inflaming retarding effect of the fluorine element. Interestingly, the thermal oxidative stability of the fluorinated samples was even better than their thermal stability. Using a comparison of the two types of fluorinated samples and support from the computational simulations of the model molecules, it was suggested that a greater amount of CFn (n = 2, 3) groups or defects in the FG samples resulted in its relatively worse thermal stabilities. Furthermore, electron paramagnetic resonance (EPR) spectroscopy was introduced to analyze the thermal stabilities of the fluorinated graphene samples as a novel method. The changes in the spin centers in samples after thermal treatment were studied, which indicated that the lower amount of the more stable spin centers of FPG was another reason leading to its more outstanding thermal stabilities in comparison to FG samples.

Effects of the oxygenic groups on the mechanism of fluorination of graphene oxide and its structure

Co-reporter:Teng Chen;Xu Wang;Yang Liu;Baoyin Li;Zheng Cheng;Zaoming Wang;Wenchuan Lai

Physical Chemistry Chemical Physics 2017 vol. 19(Issue 7) pp:5504-5512

Publication Date(Web):2017/02/15

DOI:10.1039/C6CP07665C

A facile way to prepare fluorinated graphene (FG) with a high fluorine content and controllable structure is important to achieve its full potential application. In this work, it was found that the fluorine to carbon (F/C) ratio of fluorinated graphene oxide (FGO) was nearly twice as much as that of fluorinated chemically reduced graphene oxide (FCrGO) after fluorination at the same temperature. Concerning the detailed effects of oxygenic groups on the fluorination and structure of fluorinated graphene (FG), graphene oxides with different oxygen contents were fluorinated under the same conditions. It was shown that oxygenic groups promote the fluorination reaction by activating the surrounding aromatic regions and taking part in the substitution reaction with fluorine radicals, among which, hydroxyls and carbonyls tend to be replaced by fluorine atoms. Moreover, the fluorination mainly occurs at the edges and defects of graphene sheets with a low oxygen content, while the highly oxidized graphene sheets are fluorinated both at the edges and basal planes simultaneously. This indicates that the quantity and location of the C–F bonds in FGO can be controlled by adjusting the species and content of oxygenic groups in the precursor graphene oxide.

One-Step Preparation of Oxygen/Fluorine Dual Functional MWCNTs with Good Water Dispersibility by the Initiation of Fluorine Gas

Co-reporter:Yang Liu, Xu Wang, Weimiao Wang, Baoyin Li, Peng Wu, Mengmeng Ren, Zheng Cheng, Teng Chen, and Xiangyang Liu

ACS Applied Materials & Interfaces 2016 Volume 8(Issue 12) pp:7991

Publication Date(Web):March 7, 2016

DOI:10.1021/acsami.5b12647

It is still a challenge to prepare water-dispersible carbon nanotubes which are proved to have great potential in numerous applications. In this present work, as low as 2% fluorine gas was used as initiator to prepare oxygen/fluorine dual functional MWCNTs (OF-MWCNTs) with good water dispersibility through a one-step method under oxygen atmosphere. The aromatic structure of OF-MWCNTs is reserved to some extent resulting in better electrical conductivity than pure fluorinated MWCNTs (F-MWCNTs). The amount of oxygen atoms and fluorine atoms (hereinafter referred to as “O-content” and “F-content”) of OF-MWCNTs is up to 8.8% and 7.5%. Fourier transform infrared spectroscopy (FTIR) manifests that - COOH is covalently bonded onto the surface of OF-MWCNTs. In addition, the OF-MWCNTs sample is pH-sensitive, which further validates the successful introduction of -COOH. The successful covalent attachment of -COOH onto MWCNTs dramatically improves the hydrophilia of MWCNTs which always present hydrophobic character. It is deduced that fluorine creates reactive sites for oxygen, increases the oxygen content, and eventually results in the dispersibility of OF-MWCNTs in water. The corresponding hydrophilic OF-MWCNTs film shows good performance for separating oil-in-water emulsions. Meanwhile, the good dispersibility of OF-MWCNTs in organic solvents also makes it possible to be applied in various composites.Keywords: carbon nanotubes; dispersibility; hydrophilic modification; initiation; oil/water separation; oxyfluorination; water

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

Co-reporter:Xu Wang, Weimiao Wang, Yang Liu, Mengmeng Ren, Huining Xiao, and Xiangyang Liu

Analytical Chemistry 2016 Volume 88(Issue 7) pp:3926

Publication Date(Web):March 9, 2016

DOI:10.1021/acs.analchem.6b00115

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.

Chemical reactivity of C–F bonds attached to graphene with diamines depending on their nature and location

Co-reporter:Baoyin Li, Taijun He, Zaoming Wang, Zheng Cheng, Yang Liu, Teng Chen, Wenchuan Lai, Xu Wang and Xiangyang Liu

Physical Chemistry Chemical Physics 2016 vol. 18(Issue 26) pp:17495-17505

Publication Date(Web):07 Jun 2016

DOI:10.1039/C6CP01929C

The attachment of fluorine to graphene is a facile means to activate the carbon bonds for subsequent covalent bonding to other molecules for the preparation of desired graphene derivatives. Therefore, an insight into the chemical reactivity of fluorinated graphene (FG) is very essential to enable precise control of the composition and structure of the final products. In this study, FG has been treated with various mass amounts of poly(oxypropylene)diamine (PEA) ranging from starvation to saturation to explore the dependence of a substitution reaction of diamines on the nature and location (attached onto the basal planes or along defects or edges) of C–F bonds. X-ray photoelectron spectroscopy directly tracked the atomic percentage of fluorine present and the carbon 1s bonding state, showing that the grafting ratio of diamines gradually increases with increased diamine mass ratio. The varying of the types and orientation of C–F bonds characterized by polarized attenuated total reflectance Fourier transform infrared spectroscopy indicates that “covalent” C–F bonds are more sensitive to the substitution reaction of diamines than ‘‘semi-ionic’’ C–F bonds, and the C–F bonds attached onto basal planes more preferably participate in the functionalization reaction of diamines than that of C–F bonded on non-coplanar regions (edges or defects). The one-dimensional expansion along the graphene c-axis shown by wide angle X-ray diffraction provides further evidence on the preferred functionalization reaction of C–F attached on the basal planes, resulting in a change of the average intersheet distance by various magnitudes.

Graphene-based porous materials with tunable surface area and CO2 adsorption properties synthesized by fluorine displacement reaction with various diamines

Co-reporter:Baoyin Li, Kun Fan, Xin Ma, Yang Liu, Teng Chen, Zheng Cheng, Xu Wang, Jiaxing Jiang, Xiangyang Liu

Journal of Colloid and Interface Science 2016 Volume 478() pp:36-45

Publication Date(Web):15 September 2016

DOI:10.1016/j.jcis.2016.05.062

•Graphene porous materials were constructed by intercalating fluorinated graphene.•Both amino end groups of diamines during intercalating show a different reactivity.•The porous properties depend on the size and structure of diamine intercalants.•The intercalation of ethylenediamine shows excellent CO2 absorption performance.A mild, operationally simple and controllable protocol for preparing graphene-based porous materials is essential to achieve a good pore-design development. In this paper, graphene-based porous materials with tunable surface area were constructed by the intercalation of fluorinated graphene (FG) based on the reaction of reactive CF bonds attached to graphene sheets with various amine-terminated molecules. In the porous materials, graphene sheets are like building blocks, and the diamines covalently grafted onto graphene framework act as pillars. Various diamines are successfully grafted onto graphene sheets, but the grafting ratio of diamines and reduction degree of FG differ greatly and depend on the chemical reactivity of diamines. Pillared diamine molecules chemically anchor at one end and are capable of undergoing a different reaction on the other end, resulting in three different conformations of graphene derivatives. Nitrogen sorption isotherms revealed that the surface area and pore distribution of the obtained porous materials depend heavily on the size and structure of diamine pillars. CO2 uptake capacity characterization showed that ethylenediamine intercalated FG achieved a high CO2 uptake density of 18.0 CO2 molecules per nm2 at 0 °C and 1.1 bars, and high adsorption heat, up to 46.1 kJ mol−1 at zero coverage.

A facile method to enhance UV stability of PBIA fibers with intense fluorescence emission by forming complex with hydrogen chloride on the fibers surface

Co-reporter:Ke Li, Liang Li, Jiaqiang Qin, Xiangyang Liu

Polymer Degradation and Stability 2016 Volume 128() pp:278-285

Publication Date(Web):June 2016

DOI:10.1016/j.polymdegradstab.2016.03.033

To date, the main method in improving UV stability of aramid fibers is to coat ultraviolet screening agent on the surface of fibers. However, this method has a disadvantage that the coating tends to fall off when the fibers are exposed to an external force. In the present research, A diamine monomer 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ) was introduced to modify poly (p-phenylene terephthalamide) by copolymerization, and corresponding modified aramid fibers (PBIA fibers) were prepared. we found that PBIA fibers can form complex with hydrogen chloride (HCl) which would not lead to the obvious decrease in mechanical properties, and the decomplexation of HCl can only be achieved at high temperature (higher than 280 °C). At the same time, PBIA/HCl complex molecule showed intense fluorescence emission, and which can provide an effective way to dissipate the harmful UV energy, thus, the UV resistance of PBIA fibers can be improved. In addition, the HCl have the ability to quench the photoactive triplet state of PBIA fibers, which can also contribute to improve the UV resistance of PBIA fibers. After 48 h UV irradiation, the PBIA/HCl complex fibers almost remained their tensile performances (only about 3% loss in tensile strength), and UV irradiation did not bring the obvious deterioration in structure and performance of the complex fibers. On the contrary, for PBIA fibers, its chemical structure and physical properties all suffered to obvious damages (about 15% loss in tensile strength). The UV resistance of PBIA/HCl complex fibers is approximately 5 times higher than that of PBIA fibers.

The Effect of Asymmetric Heterocyclic Units on the Microstructure and the Improvement of Mechanical Properties of Three Rigid-Rod co-PI Fibers

Co-reporter:Longbo Luo;Yazhe Wang;Jing Zhang;Jieyang Huang;Yan Feng;Chaorong Peng;Xu Wang

Macromolecular Materials and Engineering 2016 Volume 301( Issue 7) pp:853-863

Publication Date(Web):

DOI:10.1002/mame.201600113

Surface chain cleavage behavior of PBIA fiber induced by direct fluorination

Co-reporter:Zheng Cheng, Peng Wu, Baoyin Li, Teng Chen, Yang Liu, Mengmeng Ren, Zaoming Wang, Wenchuan Lai, Xu Wang, Xiangyang Liu

Applied Surface Science 2016 Volume 384() pp:480-486

Publication Date(Web):30 October 2016

DOI:10.1016/j.apsusc.2016.05.055

Highlights

•: The products of chain cleavage on fiber surface provides an increase of 11.5% for the adhesion of fiber/epoxy resin composite.
•: It is amide bond and benzimidazole that are likely to be attacked by gas fluorine.
•: Chain cleavage product from direct fluorination are made up of mix small molecules, containing polar groups like carboxyl and carbon fluorine bond.

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

Co-reporter:Longbo Luo, Yazhe Wang, Jieyang Huang, Dawei Hong, Xu Wang and Xiangyang Liu

RSC Advances 2016 vol. 6(Issue 67) pp:62695-62704

Publication Date(Web):22 Jun 2016

DOI:10.1039/C6RA10184D

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.

Antibacterial activities and mechanisms of fluorinated graphene and guanidine-modified graphene

Co-reporter:Xu Wang, Peng Lu, Yuan Li, Huining Xiao and Xiangyang Liu

RSC Advances 2016 vol. 6(Issue 11) pp:8763-8772

Publication Date(Web):15 Jan 2016

DOI:10.1039/C5RA28030C

The antibacterial properties and mechanism of three types of graphene derivatives, graphene oxide (GO), fluorinated graphene (FG), and guanidine-modified graphene (PHGH-G), were comparatively studied. The PHGH-G nano-sheets were synthesized using the FG as a substrate. The results obtained from atomic force microscopy (AFM) and confocal laser scanning microscopy (CLSM) demonstrated that antibacterial activity of FG sheets, similar to that of GO, depends on how they interact with bacterial cells. In contrast to GO and FG, the PHGH-G with a low grafting ratio, about 2%, had a high antibacterial activity while the nanosheets applied to the culture medium at a concentration of 20 μg mL−1 can lead to a 99.9% viability loss in Escherichia coli (E. coli). The local damage to E. coli cells was induced by PHGH-G upon contact, resulting in the collapse of bacteria. It is considered that the strong interaction between PHGH-G and the membrane of E. coli cells attracts the cells to the surface of the nano sheets, and then the local bonded PHGH oligomers with a high concentration destroy the cell membranes.

Structural evolution of fluorinated aramid fibers with fluorination degree and dominant factor for its adhesion property

Co-reporter:Zheng Cheng, Peng Wu, Jie Gao, Xu Wang, Mengmeng Ren, Baoyin Li, Longbo Luo, Xiangyang Liu

Journal of Fluorine Chemistry 2016 Volume 188() pp:139-146

Publication Date(Web):August 2016

DOI:10.1016/j.jfluchem.2016.06.018

•Different physical/chemical surface structures of aramid fibers are obtained.•Surface chemical structures play a dominant role in the adhesion of aramid fibers.•The adhesion of aramid fibers can be furthermore improved by a special treatment.Fluorination of aramid fibers using F2 is a useful method to improve the adhesion property which is of great important for the mechanical performance of fibers-reinforced composites. In this paper, eight kinds of aramid fibers with different fluorination degree were prepared. With the increasing of fluorination degree, surface morphology and chemical structure of fibers both varied dramatically, such as appearance of CF bond and COOH in the surface and the increased content, among which the variation of surface roughness and formation of CF bond and COOH groups all contributed to the enhancement of pull-out strength of fluorinated aramid fibers from 0.43 to about 0.60 N/tex mm. Based on the contrast analysis, the appearance of chemical group COOH and increasing of its content are the dominant factor for the gradually improving the adhesion properties. Meanwhile, it was found that water soaking treatment after direct fluorination was a feasible method to further increase the COOH content and thus improve the pull-out strength to a higher level of 0.62 N/tex mm.Direct fluorination of aramid fiber in different degree would generate different amount of polar groups, including CF bond and carboxyl groups, and also it would bring about the change on surface morphology. These changes in both chemical structure and physical morphology finally make a great contribution to the interfacial properties of fiber/epoxy composite.

The dominant factor for mechanical property of polyimide films containing heterocyclic moieties: In-plane orientation, crystallization, or hydrogen bonding

Co-reporter:Longbo Luo;Jing Zhang;Jieyang Huang;Yan Feng;Chaorong Peng;Xu Wang

Journal of Applied Polymer Science 2016 Volume 133( Issue 39) pp:

Publication Date(Web):

DOI:10.1002/app.44000

ABSTRACT

Crystallization, in-plane orientation, and hydrogen bonding interactions are three vital factors for enhancing mechanical properties of polyimide (PI) films. However, which is the dominant factor? In this study, three PI films containing heterocyclic moiety, poly(benzoxazole-imide), poly(benzimidazole-imide), and poly(pyrimidine-imide) were chosen to comparative study. The crystallinity of poly(benzoxazole-imide), poly(benzimidazole-imide), and poly(pyrimidine-imide) PI films are 36, 24, and 15%, respectively. The results of small angle X-ray scattering indicate poly(benzoxazole-imide) and poly(benzimidazole-imide) films show periodical lamellar structures, while poly(pyrimidine-imide) shows no long period due to low crystallinity. In-plane orientation (P₂₀₀) is calculated from polarized attenuated total reflection (ATR)-Fourier transform infrared and refractive indices. The order of in-plane orientation is poly(benzimidazole-imide) < poly(benzoxazole-imide) < poly(pyrimidine-imide). Hydrogen bonding interactions, which restrict chain motion and hinder spontaneous in-plane orientation, are only formed in poly(benzimidazole-imide). The relationship between mechanical properties and three influence factors are discussed, and the order of influence extent for mechanical properties of PI films is hydrogen bonding interactions < degree of crystallization < in-plane orientation. Two structure models for PI films are proposed in order to further confirm the dominant effect of in-plane orientation on the mechanical properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44000.

Effect of molecular rigidity and hydrogen bond interaction on mechanical properties of polyimide fibers

Co-reporter:Yan Feng;Long Bo Luo;Jieyang Huang;Ke Li;Baoying Li;Huina Wang

Journal of Applied Polymer Science 2016 Volume 133( Issue 28) pp:

Publication Date(Web):

DOI:10.1002/app.43677

ABSTRACT

Six kinds of polyimide (PI) fibers with different molecular rigidity and hydrogen bond interactions were designed and prepared in order to investigate the relationship between structure and mechanical properties. The rigidity, aggregation structure, fracture morphology, hydrogen bond, and charge transfer (CT) interactions were investigated in detail. Conformational rigidity of six PI fibers were simulated and measured by D-values of energy barrier and bottom in potential energy curves of PI units. Rigid rod-like PI macromolecules tend to pack in order and show better mechanical properties. However, with the increase of D-values, fracture mechanisms change from ductile fracture to brittle fracture. Brittle fracture resulting from high conformational rigidity is adverse to improvement of mechanical properties of PI fibers. Besides, strength of hydrogen bond and CT interactions are characterized by infrared spectroscopy and ultraviolet absorption spectra, respectively. The results indicate that higher interactions lead to higher tensile strength and initial modulus. Finally, PI fibers, which possess moderate conformational rigidity and strong hydrogen bond interactions, exhibit highest tensile strength (1.82 GPa) and initial modulus (85.7 GPa) in six kinds of PI fibers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43677.

Direct fluorination of para-aramid fibers 1: Fluorination reaction process of PPTA fiber

Co-reporter:Longbo Luo, Peng Wu, Zheng Cheng, Dawei Hong, Baoyin Li, Xu Wang, Xiangyang Liu

Journal of Fluorine Chemistry 2016 Volume 186() pp:12-18

Publication Date(Web):June 2016

DOI:10.1016/j.jfluchem.2016.04.002

•The PPTA fiber was fluorinated with different partial pressure of F2.•The reaction of F2 with the amide bonds is easier at low Fp (Fp ≤10 kPa) while the reaction of F2 with benzene rings is more favorable at high Fp.•The results of FTIR prove that the reaction of F2 with benzene rings is mainly an addition reaction, rather than a substitution reaction.Fluorination reaction process of PPTA fiber is studied in detail by means of X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) spectra. We prove that the reaction of F2 with the amide groups is easier than that with benzene rings at the low partial pressure of F2 (Fp ≤10 kPa) due to higher charge density of N atom. With the further increase of Fp, the increase of reaction degree of F2 with the amide group gradually decreases, which may be due to the decrease of the concentration of amide groups. On the contrary, the reaction of F2 with benzene rings gradually becomes more favorable when Fp is higher than 10 kPa resulting from the saving high concentration of benzene rings. The results of FTIR prove that the reaction of F2 with benzene rings is mainly an addition reaction, rather than a substitution reaction. As the value of Fp is lower than 10 kPa, fiber surface morphology is smooth with few grooves. However, more and more lengthwise furrows and grooves are observed on the surface of fluorinated fiber with the further increase of Fp. Moreover, the mechanical properties of fluorinated PPTA fibers almost keep constant at the low Fp (Fp ≤10 kPa). However, when the Fp is higher than 10 kPa, the tensile strength of fluorinated PPTA fibers gradually decreases while the initial modulus and crystallinity have a little change.The PPTA fiber was fluorinated with different partial pressure of F2. The reaction of F2 with the amide bonds is easier at low Fp (Fp ≤10 kPa) while the reaction of F2 with benzene rings is more favorable at high Fp. The results of FTIR prove that the reaction of F2 with benzene rings is mainly an addition reaction, rather than a substitution reaction.

Reduction and transformation of fluorinated graphene induced by ultraviolet irradiation

Co-reporter:Mengmeng Ren, Xu Wang, Changshuai Dong, Baoyin Li, Yang Liu, Teng Chen, Peng Wu, Zheng Cheng and Xiangyang Liu

Physical Chemistry Chemical Physics 2015 vol. 17(Issue 37) pp:24056-24062

Publication Date(Web):20 Aug 2015

DOI:10.1039/C5CP03473F

The effect of ultraviolet irradiation on fluorinated graphene (FG) dispersed in toluene was investigated for the first time. The chemical and physical characteristics of FG before and after ultraviolet irradiation were analyzed by UV-vis, FTIR, XPS,EDS, oxygen flask combustion (OFC), XRD, TGA, Raman, SEM, TEM and fluorescence spectroscopy. It is found that the F/C ratio initially decreases rapidly and then slowly with irradiation time, finally to 0.179 after irradiation for 48 h. The nature of partial C–F bonds transforms from covalent to “semi-covalent” bonding in the process of irradiation. The restoration of new sp2 clusters is fast at the early stage within 6 h of irradiation, promoting the structural rearrangement. The morphology of irradiated fluorinated graphene (iFG) is not significantly destroyed by ultraviolet while more overlapped sheets are formed due to quick defluorination. Photoluminescence (PL) properties show that “blue emission” located at 432 nm is enhanced due to the recovery of sp2 domains. In particular, compared to non-aromatic solvents, there is a “synergistic effect” between aromatic solvents and ultraviolet in the defluorination process. FG is unstable and shows some structural transformations under ultraviolet irradiation, which can be used to tune its structure and properties.

Releasing and Freezing Phase Separation of Polyvinyl Alcohol/Silica To Control Polymorphs of Silica

Co-reporter:Jieyang Huang, Ke Li, Longbo Luo, Huina Wang, Xu Wang, Yan Feng, and Xiangyang Liu

Crystal Growth & Design 2015 Volume 15(Issue 5) pp:2072-2078

Publication Date(Web):March 23, 2015

DOI:10.1021/cg501511s

Crystalline silica is prepared beyond 1500 °C in a traditional process. Here, we prepared both cristobalite-rich and quartz-rich silica by calcinating polyvinyl alcohol (PVA)/silica films at 900 °C. Results of characterizations show that polymorphisms of silica were dependent on the phase separation of PVA and silica before calcinations. The phase separation is controlled by a coagulation bath. By soaking PVA/silica hybrid films in a coagulation bath before thermal treatment, phase separation of PVA and silica was frozen and prevented. When PVA/silica hybrid films were not soaked in a coagulation bath before thermal treatment, phase separation of PVA and silica was released. Further research reveals that different phase structures of PVA and silica generate distinct microscopical morphologies and molecular structures of silica, leading to variation of the final polymorphs.

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

Co-reporter:Cong Fan, Baoyin Li, Mengmeng Ren, Peng Wu, Yang Liu, Teng Chen, Zheng Cheng, Jiaqiang Qin and Xiangyang Liu

RSC Advances 2015 vol. 5(Issue 24) pp:18932-18938

Publication Date(Web):28 Jan 2015

DOI:10.1039/C4RA15096A

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.

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

Co-reporter:Baoyin Li, Jiahui Zhang, Mengmeng Ren, Peng Wu, Yang Liu, Teng Chen, Zheng Cheng, Xu Wang and Xiangyang Liu

RSC Advances 2015 vol. 5(Issue 96) pp:79081-79089

Publication Date(Web):08 Sep 2015

DOI:10.1039/C5RA11810G

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.

Enhancing mechanical properties of aromatic polyamide fibers containing benzimidazole units via temporarily suppressing hydrogen bonding and crystallization

Co-reporter:Ke Li;Longbo Luo;Jieyang Huang;Huina Wang;Yan Feng

Journal of Applied Polymer Science 2015 Volume 132( Issue 35) pp:

Publication Date(Web):

DOI:10.1002/app.42482

ABSTRACT

The copolymerization modified poly(p-phenylene terephthalamide) containing 2-(4-aminophenyl)−5-aminobenzimidazole (PABZ) units in the main chain was synthesized and the corresponding poly-p-phenylene-benzimidazole-terephthalamide (PBIA) fibers were prepared by wet spinning. The HCl, the by-product released during polymerization, can complex with PABZ units to prevent the formation of hydrogen bonding between PABZ units, resulting in amorphous PBIA fibers and a lower glass transition temperature (T_g). Therefore, for the purpose of gaining strong hydrogen bonding and high orientation degree at the same time in PBIA fibers, two-step drawing–annealing processing was adopted. The as-spun PBIA/HCl complex fibers were drawn first at 280°C, higher than the T_g of the PBIA/HCl complex fibers and lower than the decomplexed temperature of HCl, which temporarily suppresses the formation of hydrogen bonding and crystallization. Subsequently, the fibers were annealed to reform hydrogen bonding between PABZ units and crystallization via decomplexation of HCl at 400°C. However, when the drawing is above the decomplexed temperature of HCl, the decomplexation of HCl begins to occur which leads to the reform of hydrogen bonding and crystallization, and the tensile strength of the drawn-annealed PBIA/HCl complex fibers decreases with a decrease in the HCl content of fibers. The tensile strength of two-step drawn-annealed fibers increased by approximately 15% compared to that of one-step drawn PBIA/HCl complex fibers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42482.

High-performance copoly(benzimidazole-benzoxazole-imide) fibers: Fabrication, structure, and properties

Co-reporter:Longbo Luo;Yaxin Zheng;Jieyang Huang;Ke Li;Huina Wang;Yan Feng;Xu Wang

Journal of Applied Polymer Science 2015 Volume 132( Issue 22) pp:

Publication Date(Web):

DOI:10.1002/app.42001

ABSTRACT

Novel high-performance copolyimide (co-PI) fibers containing benzimidazole and benzoxazole ring in the main chain were prepared by a two-step spinning via the poly(amic acid)s. Effects of the incorporated benzimidazole and benzoxazole units on the micro-structure and properties of co-PI fibers were investigated. Fourier transform infrared (FTIR) results indicated that hydrogen bonding is formed in the co-PI fibers. The co-PI fibers exhibited discernible crystallization peaks at 14°∼15° and 23°∼26° (2θ), showing crystalline-like structure. Moreover, the packing type of benzimidazole-imide units determined the macromolecules packing of co-PIs. It was amazedly found that the co-PI fibers exhibited higher tensile strength and initial modulus than those of corresponding homo-PI fibers, reaching tensile strength of 2.2–2.6 GPa, initial modulus of 99.1–113.2 GPa. The results of dynamic mechanical analysis (DMA) indicated co-PI2 fiber had a positive T_g deviation due to the presence of strong intermolecular hydrogen bonding between benzimidazole-imide and benzoxazole-imide units, which maybe lead to the effective stress transfer between benzimidazole-imide units and benzoxazole-imide units. In addition, the obtained PI fibers exhibited excellent thermal properties with the 10% weight loss temperatures under N₂ in the range of 574–585°C. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42001.

Catalysis and inhibition of benzimidazole units on thermal imidization of poly(amic acid) via hydrogen bonding interactions

Co-reporter:Hui-na Wang;Ming-xi Yang;Long-bo Luo

Chinese Journal of Polymer Science 2015 Volume 33( Issue 4) pp:621-632

Publication Date(Web):2015 April

DOI:10.1007/s10118-015-1614-2

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.

Fluorographene with High Fluorine/Carbon Ratio: A Nanofiller for Preparing Low-κ Polyimide Hybrid Films

Co-reporter:Xu Wang, Yunyang Dai, Weimiao Wang, Mengmeng Ren, Baoyin Li, Cong Fan, and Xiangyang Liu

ACS Applied Materials & Interfaces 2014 Volume 6(Issue 18) pp:16182

Publication Date(Web):September 4, 2014

DOI:10.1021/am5042516

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.Keywords: dielectric constant; fluorographene; hybrid; polyimide; semiconductor; water absorption

Releasing silica-confined macromolecular crystallization to enhance mechanical properties of polyimide/silica hybrid fibers

Co-reporter:Jieyang Huang, Xuhui Li, Longbo Luo, Huina Wang, Xu Wang, Ke Li, Chaoliang Zhang, Xiangyang Liu

Composites Science and Technology 2014 Volume 101() pp:24-31

Publication Date(Web):12 September 2014

DOI:10.1016/j.compscitech.2014.06.022

Polyimide (PI)/silica hybrid fibers containing 1% silica were prepared by the sol–gel method. Under tension-free thermal treatment at 300 °C, PI fibers and PI/silica hybrid fibers possess 0.98 GPa and 1.38 GPa respectively. However, it is found that the silica-reinforced effect is almost disappeared after the temperature of tension-free thermal treatment increasing to 420 °C. Wide angel X-ray diffraction (WAXD) patterns indicated that, by 420 °C tension-free treatment, PI fibers are reinforced due to crystallization of PI; PI/silica hybrid fibers are still amorphous since dispersed silica inhibits the crystallization of PI, which counteracts the silica reinforced effect. Through a hot-drawing process at 420 °C, PI fibers cannot obtain additional reinforcement, while tensile strength of hybrid fibers increases from 1.83 GPa to 2.34 GPa for crystallization. Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) tests revealed that the dispersed silica transforms into larger particles after hot-drawing, so the confinement of macromolecular crystallization is released for further reinforcing. As a result, the advantages of silica reinforcing in amorphous domain and macromolecules crystallizing are combined together, resulting in excellent mechanical properties of fibers.

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

Co-reporter:Baoyin Li, Cong Fan, Huina Wang, Mengmeng Ren, Peng Wu, Xu Wang and Xiangyang Liu

RSC Advances 2014 vol. 4(Issue 18) pp:9321-9325

Publication Date(Web):23 Jan 2014

DOI:10.1039/C3RA47715K

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.

Surface modification of fluoroelastomer by direct fluorination with fluorine gas

Co-reporter:Jie Gao, Xiaolu Xu, Cong Fan, Xu Wang, Yunyang Dai, Xiangyang Liu

Materials Letters 2014 Volume 121() pp:219-222

Publication Date(Web):15 April 2014

DOI:10.1016/j.matlet.2014.01.149

•The surface modification of fluoroelastomer by direct fluorination was investigated.•The surface of fluoroelastomer becomes smoother and cleaner after fluorination.•A greater number of CF3, CF2 and CF groups are formed after fluorination.•The surface of fluoroelastomer becomes more hydrophobic after fluorination.•Mechanical properties changed a little, while the friction coefficient is decreased.The surface modification of fluoroelastomer by using direct fluorination with fluorine gas was investigated. The results of X-ray photoelectron spectroscopy (XPS) indicate that a greater number of CF3, CF2 and CF groups are formed on the surface after fluorination and the photographs of both scanning electronic microscopy (SEM) and three-dimensional digital microscope reveal that the surface of fluoroelastomer becomes smoother and cleaner after fluorination. In addition, the surface energy of fluoroelastomer is decreased and more hydrophobic surface is explored after fluorination due to the more fluorine-contained chemical structures. However, the mechanical properties of fluorinated fluoroelastomer have not been changed apparently, while the friction coefficient is sharply decreased.

Influence of hydrogen-bonding interaction introduced by filled oligomer on bulk properties of blended polyimide films

Co-reporter:Baoyin Li;Yuwei Pang;Cong Fan;Jie Gao;Xu Wang;Chaoliang Zhang

Journal of Applied Polymer Science 2014 Volume 131( Issue 13) pp:

Publication Date(Web):

DOI:10.1002/app.40498

ABSTRACT

Specific structure oligomer is designed and synthesized to fill “blank interaction points” left among polyimide (PI) rigid-rod structure in order to further enhance the interaction between PI macromolecules. An oligomer, 4,4′-bisbenzamide diphenyl ether (BADE) containing amide groups as proton donor, was blended with polyamic acid (PAA) solution to modify PI of pyromellitic dianhydride and 4,4′-oxydianiline. Fourier transform infrared and dynamic mechanical analyses show that hydrogen-bonding interaction occurs between NH groups and PI chains. This resulted interchain interaction increases the tensile strength of blended PI films from 115.9 to 135.6 MPa, about 17.0% improvement, with BADE content surprisingly up to 20 wt %. BADE is uniformly dispersed without aggregation within a saturated amount of 20 wt % through wide angle X-ray diffraction and morphology characterization. Moreover, rheological measurements indicate that the processability of PAA solution is maintained after introduction of BADE. The obtained PI films still have excellent thermal stability. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40498.

The effect of Trimethylchlorosilane as a reactive additive on solution behavior of polyamide acid and properties of corresponding polyimide

Co-reporter:Jing Yao;Longbo Luo;Xu Wang;Ke Li;Jieyang Huang;Jie Gao

Journal of Polymer Research 2014 Volume 21( Issue 3) pp:

Publication Date(Web):2014 March

DOI:10.1007/s10965-014-0372-0

Trimethylchlorosilane (TMSCL) with different volume ratios was added to polyamide acid (PAA) solutions which were obtained by polymerization of Pyromellitic dianhydride (PMDA) and 4, 4′-Oxydianiline (ODA) in N-methyl-2-pyrrolidone (NMP) solvent. With the addition of TMSCL, the apparent viscosity of PAA solutions shows a sharp fall ranging from 137.6 × 104 to 1.0 × 104 cP with a substantial decline up to about 99 %. Gel permeation chromatography (GPC) measurements indicate that the molecular weights change little with the different addition ratios of TMSCL. The results of X-ray photoelectron (XPS) and Fourier Transform Infrared (FTIR) show that TMSCL reacts with carboxyl groups of PAAs to form silicon ester bonds, which results in two aspects of positive effects. For one hand, the consuming of carboxyl groups weakens the intensity of interchain hydrogen bonds among macromolecules, which leads to a sharp fall in apparent viscosity of PAA solutions. For the other hand, as carboxyl groups were consumed, the decomposition in a rational way of hydrolysis and exchange reactions catalyzed by carboxyl groups is prevented. Therefore the storage stability of PAA solution is also improved. The results of X-ray diffraction (XRD) show that the mean intermolecular distance of PAA chains increases with increase in TMSCL, which farther confirms the intensity of interchain hydrogen bonds among macromolecules decreases with the addition of TMSCL. The results of mechanical properties measurements, thermo gravimetric analysis (TGA) and dynamic mechanical analysis (DMA) indicate that the outstanding mechanical and thermal properties of polyimide films corresponding to PAA with TMSCL were still maintained well.

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

Co-reporter:Xu Wang, Yunyang Dai, Jie Gao, Jieyang Huang, Baoyin Li, Cong Fan, Jin Yang, and Xiangyang Liu

ACS Applied Materials & Interfaces 2013 Volume 5(Issue 17) pp:8294

Publication Date(Web):August 9, 2013

DOI:10.1021/am402958p

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.Keywords: chemical structure; direct fluorination; fluorinated graphene;

Preparing Highly Fluorinated Multiwall Carbon Nanotube by Direct Heating-Fluorination during the Elimination of Oxygen-Related Groups

Co-reporter:Xu Wang, Yi Chen, Yunyang Dai, Qin Wang, Jie Gao, Jieyang Huang, Jin Yang, and Xiangyang Liu

The Journal of Physical Chemistry C 2013 Volume 117(Issue 23) pp:12078-12085

Publication Date(Web):May 23, 2013

DOI:10.1021/jp312801p

Pristine and oxidized multiwalled carbon nanotubes (MWCNTs) were separately prepared and directly fluorinated with F2 through two different routes: heating-fluorination and isothermal-fluorination. The amount of fluorine atoms (hereinafter referred to as “F-content”) bonding to the fluorinated samples was largely dependent on the modifing route and chemical bonding of MWCNTs. The F-content of heating-fluorinated pristine and oxidized MWCNTs was 3.2% and 9.2% respectively, which were about 8 times and 18 times that of the corresponding isothermal-fluorinated MWCNTs. According to structural analysis of samples before and after fluorination, it was found that thermal elimination of oxygen-related groups bonding to MWCNTs contributed to the formation of strongly covalent C–F bonds during heating-fluorination. It was considered that the oxygen-related groups provided reactive sites for the fluorination. The fluorination reaction took place at an sp3 carbon linking with the oxygen-related groups and did not increase the density of defect on MWCNTs. A radical-mediated mechanism is accepted for this reaction. Thus, MWCNTs could be first oxidized to increase the number of oxygen-related groups and then heating-fluorinated by F2 directly to get highly fluorinated MWCNTs with stable C–F bonds.

Crystallization of inorganic silica based on interaction between polyimide and silica by sol–gel method

Co-reporter:Jieyang Huang;Peng Zhang;Xu Wang;Longbo Luo

Journal of Sol-Gel Science and Technology 2013 Volume 66( Issue 2) pp:193-198

Publication Date(Web):2013 May

DOI:10.1007/s10971-013-2989-6

Crystalline silica in cristobalite phase was successfully prepared at a relatively low temperature of 800 °C by calcinating polyimide/silica hybrid films under ambient air. X-ray photoelectron spectroscopy measurements show that the product is silica after calcination. It is found that the crystallinity is dependent on the removing rate and the strength of the interaction between polyimide and silica. The presence of polyimide plays an important role in the growth of silica. Calcination to remove polyimide with rapid heating results in lower crystallinity compared with calcination with slow heating. For samples with the same content of silica, the crystallinity changes with the strength of the interaction between polyimide and silica molecules.

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

Co-reporter:Xu Wang, Huina Wang, Longbo Luo, Jieyang Huang, Jie Gao and Xiangyang Liu

RSC Advances 2012 vol. 2(Issue 25) pp:9463-9472

Publication Date(Web):29 Aug 2012

DOI:10.1039/C2RA21647G

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.

Enhancement of properties of polyimide/silica hybrid nanocomposites by benzimidazole formed hydrogen bond

Co-reporter:Peng Zhang;Yi Chen;Guoqiang Li;Longbo Luo;Yuwei Pang;Xu Wang;Chaorong Peng

Polymers for Advanced Technologies 2012 Volume 23( Issue 10) pp:1362-1368

Publication Date(Web):

DOI:10.1002/pat.2055

Polyimide/silica hybrid nanocomposites were prepared by sol–gel method without coupling agent. A novel diamine with a benzimidazole group, 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ), was introduced to copolymerize with 4,4'-oxydianiline (ODA) and pyromellitic dianhydride (PMDA) to synthesize polyimide (PI) matrix. The compatibility between PI and silica was improved by hydrogen bonds formed between silica phase and the –NH– group on benzimidazole of the new diamine. Highly transparent hybrid films were obtained when silica content reached as high as 30 wt%. SEM results show that silica particles with sizes much smaller than that in PMDA-ODA/silica system disperse homogeneously in the PI matrix. Differing from most hybrid systems without coupling agent, the tensile strength of PABZ system increases from 152 MPa to 165 MPa with silica content increasing from 0 to 20 wt%, while, it decreases linearly in PMDA-ODA system. DMA analysis shows that the introduction of PABZ largely increases the glass transition temperature (Tg) for all silica contents, which is suggested to be due to the more rigid structures and stronger interaction between the two phases. Meanwhile, the decomposition temperature and char yields at 800 °C are both higher than that of pure PIs. The structures of the hybrid films were identified by FTIR spectra, which indicate that different silica morphologies are developed, resulted from the hydrogen bonds between benzimidazole and silica phase. Copyright © 2011 John Wiley & Sons, Ltd.

Preparation and characterization of novel polyimide films containing amide groups

Co-reporter:Longbo Luo;Yuwei Pang;Xue Jiang;Xu Wang;Peng Zhang

Journal of Polymer Research 2012 Volume 19( Issue 1) pp:

Publication Date(Web):2012 January

DOI:10.1007/s10965-011-9783-3

A novel diamine monomer 4-amino-N-(4-amino-phenyl)-benzamide (DABA) containing amide group was introduced to modify the polyimide of pyromellitic dianhydride (PMDA) and 4, 4′-oxydianiline (ODA) by copolymerization. A series of homo- and co-polyamic acid were synthesized by DABA and ODA in different molar ratio with PMDA, and polyimide films were obtained by thermal imidization. The films were characterized by tensile testing, dynamic mechanical analysis (DMA), thermal gravimetry analysis (TGA), fourier transform infrared (FTIR) and wide x-ray diffraction (WAXD). All of the obtained polyimide films show excellent mechanical properties and thermal stability. With the content of DABA increasing from 0% to 100%, the tensile strength and initial modulus are highly improved from 124.72 MPa and 4.70 GPa to 286.46 MPa and 22.06 GPa respectively. The polyimides have 5% weight loss temperature in the range of 530.0–555.5 °C. The glass transition temperatures are in the range of 387.90–409.16 °C and the tanδ values decrease from 0.3721 to 0.08316. The results of WAXD and FTIR indicate that the introduction of DABA containing amide group can improve the order degree of macromolecule and form hydrogen bonds between the main chains, which results in the improvement of mechanical properties.

Characterization of Alignment Correlation between LC Molecules and Chemical Groups on/in the Surface of Polyimide Films with Biphenyl Side Chains

Co-reporter:Xu Wang, Peng Zhang, Yi Chen, Longbo Luo, Yuwei Pang, and Xiangyang Liu

Macromolecules 2011 Volume 44(Issue 24) pp:9731-9737

Publication Date(Web):November 29, 2011

DOI:10.1021/ma201781s

In this study, the surface chemical structure and molecular conformation of one kind of PI alignment film achieving vertical alignment were investigated by XPS, ATR-FTIR, and polarized ATR-FTIR, and the LC alignment on PI film was studied by transmission polarized FTIR. It was found that some chemical groups, such as biphenyl and imide ring, oriented perpendicular to the plane of alignment film while the molecular backbones took the conformation parallel to the plane of film. At the same time, the biphenyl groups of LC molecules in LC cell were aligned perpendicular to the alignment film. Thus, the alignment consistency between the biphenyl in the surface and LC molecules was proved first, which powerfully indicated that the chemical groups in the surface taking a vertical conformation on the surface play an essential role in producing a vertical LC alignment and the conformation of groups in the surface determines the size of pretilt angle.

Novel inorganic morphologies formed in polyimide/silica hybrid films

Co-reporter:Yuyuan Deng, Min Wu, Xiangyang Liu, Yi Gu

European Polymer Journal 2010 Volume 46(Issue 12) pp:2255-2260

Publication Date(Web):December 2010

DOI:10.1016/j.eurpolymj.2010.09.039

2-(4-Aminophenyl)-5-aminobenzimidazole was used to prepare polyimide/silica hybrid films via sol–gel process. At 40 wt.% silica content, hybrid films were still translucent. No noticeable silica particle has been observed. Unexpectedly, after treating at 800 °C, novel morphologies of silica were observed on the surface of inorganic films, which changed from homogeneous to sea-island and to co-continuous structure with increasing silica content in the matrix. Hydrogen bonding between NH in imidazole and silanol group results that silica tends to linear structures, which is considered as the main reason for this morphological change.No obvious particles were found in PI/SiO2 hybrid films using PABZ. After calcinations, novel morphologies were found. There were only silicon and oxygen left, generally, there out to be spherical particles (d, PDA-20, 60000×), actually, two phases were observed and morphologies changed from homogeneous (a, PABZ-20, 700×) to sea-island (b, PABZ-30, 700×) and to co-continuous structure (c, PABZ-40, 700×).

Correlation of pretilt angles and surface chemical structures of polyimide alignment films after direct fluorination

Co-reporter:Xu Wang;Shengliang Chen,;Yijun Yang;Yi Chen;Ming Li

Polymer International 2010 Volume 59( Issue 12) pp:1622-1629

Publication Date(Web):

DOI:10.1002/pi.2895

Abstract

A series of polyimides (PIs) with side chains were fabricated from 6-(4-phenylphenoxy)hexyl-3,5-diaminobenzoate of various ratios with 4,4′-oxydianiline and 4,4′-oxydiphthalic anhydride. After PI alignment, films were directly fluorinated using a 10 vol% fluorine/nitrogen mix. The pretilt angle of liquid crystals on the PI films is much improved to more than 20°, and can be continuously controlled by changing the side-chain content of the PI films from 20 to 100%. The change of the pretilt angles is ascribed to the fluorinated microstructure of molecules at the surface rather than to the surface energy or surface morphology. Moreover, the improvement of rigidity and the steric repulsion of the fluorinated side chains result in an upright conformation of the side chains that leads to the high pretilt angle. Copyright © 2010 Society of Chemical Industry

Structure and properties of novel PMDA/ODA/PABZ polyimide fibers

Co-reporter:Guanqun Gao;Liang Dong;Guangdou Ye ;Yi Gu

Polymer Engineering & Science 2008 Volume 48( Issue 5) pp:912-917

Publication Date(Web):

DOI:10.1002/pen.21036

Abstract

A series of random copolyamic acid were synthesized from various ratios of two diamines 4, 4′-oxydianiline (ODA) and 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ) by polycondensation with pyromellitic dianhydride (PMDA) in N-methyl-2-pyrrolidone (NMP). Their inherent viscosities were in the range of 1.89–2.91 dl/g. The polyamic acid (PAA) solution drops were spun into fibers by the wet spinning process. The polyimide (PI) fibers were obtained from PAA fibers after drawn and treated in heating tube. The fibers were characterized by fourier transform infrared (FTIR), wide X-ray diffraction (WAXD), scanning electron microscope (SEM), thermal gravimetry analysis (TGA), dynamic mechanical analysis (DMA), and tensile testing. WAXD showed these PI fibers were basically amorphous. The tensile strength and initial modulus of the PI fiber reached 1.53 and 220.5 GPa when diamine ratio of PABZ/ODA was 7/3, which were almost three times and 30 times over that of the PMDA/ODA PI fibers. TGA showed that the PI fibers were thermally stable with 10% weight losses recorded in the range of 492–564°C under nitrogen atmosphere, and their glass transition temperature (T_g) were found to be 410–440°C by DMA with increasing PABZ content from 30 to 70%. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Surface modification of polypropylene battery separator by direct fluorination with different gas components

Co-reporter:Baoyin Li, Jie Gao, Xu Wang, Cong Fan, Huina Wang, Xiangyang Liu

Applied Surface Science (30 January 2014) Volume 290() pp:

Publication Date(Web):30 January 2014

DOI:10.1016/j.apsusc.2013.11.015

•The alkali absorption ratio is substantially enhanced by direct fluorination.•The effect of direct fluorination with oxygen employed is more obvious.•Correlation between alkali absorption ratio and chemical structure is established.•The size and shape of micropores is still kept after direct fluorination.Improvement in hydrophilicity of polypropylene (PP) separator and its stability is essential for enhancing the comprehensive performance of battery. In this study, the PP separators were surface modified by direct fluorination with F2/N2 and F2/O2/N2 gas atmosphere. The alkali absorption ratios (AARs) of these two kinds of fluorinated separators are 302.7% and 418.4%, respectively, which is about nine and twelve times than that of the virgin PP separator. At the same time, the AARs of the fluorinated separators stored for 90 days at ambient temperature in air environment still remain. The surface energy of PP separators is increased from 37.8 mN/m to 47.7 mN/m and 48.9 mN/m determined by contact angle measurement after direct fluorination. X-ray photoelectron spectroscopy (XPS) and attenuated total reflection infrared spectroscopy (ATR-FTIR) results indicate that polar groups, such as CO(OH) and CFx, are introduced into the polymeric structures of the two fluorinated separator surfaces. Larger quantity of polar groups, especially CO(OH), are introduced on separator surface by the F2/O2/N2 modified route, which results in the difference of the AARs and behavior of alkali absorption. Scanning electron microscope (SEM) demonstrates that the size and shape of micropores of PP separators remain almost unchanged after direct fluorination.

Nondestructive grafting of PEI on aramid fiber surface through the coordination of Fe (Ⅲ) to enhance composite interfacial properties

Co-reporter:Zheng Cheng, Can Chen, Jieyang Huang, Teng Chen, Yang Liu, Xiangyang Liu

Applied Surface Science (15 April 2017) Volume 401() pp:

Publication Date(Web):15 April 2017

DOI:10.1016/j.apsusc.2017.01.051

•A none-damage method was studied for the functionalization of aramid fiber.•Coordination reactions were utilized in the modification.•The whole modification process was strongly confirmed by the simulating reaction of fiber’s model compound.•The IFSS value measured by single fiber pull-out test of aramid fiber has an increase by 47% after modification.The nondestructive functionalization of aramid fiber is an important research direction. In this study, a kind of benzimidazole-contained aramid fiber, Poly-p-phenylene-benzimidazole-terephthalamide (PBIA) fiber, was modified by the coordination of benzimidazole unit in fiber structure with Fe3+. Further, the coordinatively unsaturated sites of Fe3+ endow the modified fiber with active sites for the grafting of PEI. Model compound of PBIA unit, PBA, was utilized to confirm the whole process of modification. In comparison with that of the untreated fiber, the IFSS value of fiber with PEI grafted has an increase by 47%, owing to the chemical bond formed on the fiber/epoxy interface and the better wettability of resin to fiber. In all, the study presents a nondestructive functionalization of aramid fiber and can be employed in the modification of other benzimidazole-contained substrates.

Effects of different fluorination routes on aramid fiber surface structures and interlaminar shear strength of its composites

Co-reporter:Jie Gao, Yunyang Dai, Xu Wang, Jieyang Huang, Jin Yao, Jin Yang, Xiangyang Liu

Applied Surface Science (1 April 2013) Volume 270() pp:

Publication Date(Web):1 April 2013

DOI:10.1016/j.apsusc.2013.01.099

Poly-p-phenylene-benzimidazole-terephthalamide (PBIA) fiber was surface modified by direct fluorination under three different routes. The fiber was dried under vacuum to remove physisorbed water trapped on it and then fluorinated by the fluorine and oxygen gases or by the fluorine gas only. Results show that the interlaminar shear strength (ILSS) value of these two kinds of fluorinated fiber reinforced epoxy resin was 43.9 MPa and 51.0 MPa, which was improved about 14.0% and 32.5% compared with that of the virgin fiber (38.5 MPa), respectively. In the third route, the fiber was fluorinated by the fluorine and oxygen gases without removing physisorbed water, and the ILSS value decreased for nearly 31.2%, i.e. from 38.5 MPa to 26.5 MPa. X-ray photoelectron spectroscopy (XPS) showed that oxygen-containing and fluorine-containing chemical groups were introduced onto the fiber surface after fluorination, providing a stronger chemical bonding to polymeric matrices. Scanning electronic microscopy (SEM) indicated that the surface morphology of the fluorinated PBIA fiber varied with the different fluorination routes. A mass of compact micro groove structures was formed by the route that the fiber was dried to remove physisorbed water and then fluorinated with fluorine gas only. And these structures would markedly improve the ILSS of the composites. But, a mass of unstable flake surface structures was formed by the route that the fiber was fluorinated with the fluorine and oxygen gases without removing physisorbed water. And these structures would be the weak interface between the fiber and matrix and decrease the ILSS, even a lot of polar chemical groups were bonded onto the fiber surface as well.Graphical abstractHighlights► The ILSS is improved by appropriate fluorination routes. ► The inappropriate fluorination route sharply decreases the ILSS. ► Different fluorination routes lead to different fiber surface morphology structures. ► Physisorbed water accelerates chain scission and leads to formation of unstable structures. ► These unstable structures became weak interface between the fiber and matrix.

Reduction and transformation of fluorinated graphene induced by ultraviolet irradiation

Co-reporter:Mengmeng Ren, Xu Wang, Changshuai Dong, Baoyin Li, Yang Liu, Teng Chen, Peng Wu, Zheng Cheng and Xiangyang Liu

Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 37) pp:NaN24062-24062

Publication Date(Web):2015/08/20

DOI:10.1039/C5CP03473F

Characterization of the thermal/thermal oxidative stability of fluorinated graphene with various structures

Co-reporter:Wenchuan Lai, Dazhou Xu, Xu Wang, Zaoming Wang, Yang Liu, Xiaojiao Zhang and Xiangyang Liu

Physical Chemistry Chemical Physics 2017 - vol. 19(Issue 29) pp:NaN19451-19451

Publication Date(Web):2017/06/30

DOI:10.1039/C7CP03684A

Chemical reactivity of C–F bonds attached to graphene with diamines depending on their nature and location

Co-reporter:Baoyin Li, Taijun He, Zaoming Wang, Zheng Cheng, Yang Liu, Teng Chen, Wenchuan Lai, Xu Wang and Xiangyang Liu