De-zhen Wu

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Name: 武德珍; DeZhen Wu

Organization: Beijing University of Chemical Technology , China

Department: State Key Laboratory of Chemical Resource Engineering

Title: Professor(PhD)

TOPICS

Material Chemistry

Graphene & Graphite

Polymer

Polyimide Polyphosphazene

Chemicals
References

Tensile modulus enhancement and mechanism of polyimide fibers by post-thermal treatment induced microvoid evolution

Co-reporter:Xiaolin Yi, Yunyun Gao, Mengying Zhang, Chunbo Zhang, Qiao Wang, Guoming Liu, Xia Dong, Dezhen Wu, Yongfeng Men, Dujin Wang

European Polymer Journal 2017 Volume 91(Volume 91) pp:

Publication Date(Web):1 June 2017

DOI:10.1016/j.eurpolymj.2017.03.063

•Mechanical property of PI fibers can be regulated by post annealing process.•Microvoid and liquid crystal-like structures determine primary mechanical property of PI fiber.•Annealing induced microvoid evolution enhances the PI fiber’s tensile modulus.•A simple method was proposed to improve PI fibers’ mechanical property.The correlation between mechanical property and the microstructure of two-step wet spinning polyimide (PI) fibers after thermal annealing was investigated. In-situ wide-angle X-ray diffraction (WAXD) and ex-situ small angle X-ray scattering (SAXS) methods were utilized to study the liquid crystal-like structure orientation and microvoids structure (the length and the orientation angle of microvoids) for PI fibers during annealing process. The effects of annealing temperature and time on the microstructure were systematically studied. The results reveal that the liquid crystal-like structure and the orientation degree keep nearly the same after annealing. Both of the molecular chain relaxation and the evolution of aligned microvoids are attributed to the change in tensile modulus. In low pre-drawing fiber, a slight decrease in microvoid length and an obvious rise in microvoid orientation angle lead to improved tensile modulus after annealing. In highly pre-drawn fiber, the tensile modulus decreases first due to de-orientation of polymer chains and then increase owing to disordering microvoids with decreasing size. Our work demonstrates the relationship between microvoids and mechanical properties in annealed PI fibers which provides a new avenue to access high performance PI fiber by facile annealing method and a deep insight into the structure and properties of high performance PI fibers.Download high-res image (118KB)Download full-size image

Surface decoration of polyimide fiber with carbon nanotubes and its application for mechanical enhancement of phosphoric acid-based geopolymers

Co-reporter:Tao Yang, Enlin Han, Xiaodong Wang, Dezhen Wu

Applied Surface Science 2017 Volume 416(Volume 416) pp:

Publication Date(Web):15 September 2017

DOI:10.1016/j.apsusc.2017.04.166

•A new methodology to decorate the PI fiber surface with CNTs is proposed.•The interfacial bonding force of PI fiber is improved in the presence of CNTs.•The CNTs-decorated PI fiber can reinforce geopolymers effectively.•PI fiber serves for the reinforcement of geopolymers by a fiber-bridging mechanism.A new methodology to decorate the surface of polyimide (PI) fiber with carbon nanotubes (CNTs) has been developed in this study. This surface decoration was carried out through a surface alkali treatment, a carboxylation modification, surface functionalization with acyl chloride groups and then with amino groups, and a surface graft of CNTs onto PI fiber. Fourier-transform infrared and X–ray photoelectron spectroscopic characterizations confirmed that CNTs were chemically grafted onto the surface of PI fiber, and scanning electron microscopic observation demonstrated the fiber surface was uniformly and densely covered with CNTs. The surface energy and wettability of PI fiber were improved in the presence of CNTs on the fiber surface, which made a contribution to enhance the interfacial adhesion of PI fiber with other inorganic matrices when used as a reinforcing fiber. The application of CNTs-decorated PI fiber for the reinforcement of phosphoric acid-based geopolymers was investigated, and the results indicated that the geopolymeric composites gained a noticeable reinforcement. Compared to unreinforced geopolymer, the geopolymeric composites achieved a remarkable increase in compressive strength by 120% and in flexural strength by 283%. Fractography investigation demonstrated that the interaction adhesion between the fibers and matrix was enhanced due to the surface decoration of PI fiber with CNTs, which contributed to an improvement in fracture-energy dissipation by fiber pullout and fiber debonding from the matrix. As a result, a significant reinforcement effect on geopolymeric composites was achieved through a fiber-bridging mechanism. This study provided an effective methodology to improve the interracial bonding force for PI fiber and also proves a highly efficient application of CNTs-decorated PI fiber for the mechanical enhancement of geopolymeric composites.Download high-res image (214KB)Download full-size image

Structural relationship between random copolyimides and their carbon fibers

Co-reporter:Li Cao;Mengying Zhang;Hongqing Niu;Jingjing Chang

Journal of Materials Science 2017 Volume 52( Issue 4) pp:1883-1897

Publication Date(Web):2017 February

DOI:10.1007/s10853-016-0477-4

A series of polyimide (PI) fibers synthesized from pyromellitic dianhydride (PMDA), 4,4′-oxydianiline (ODA), and p-phenylenediamine (p-PDA) were prepared by a two-step wet-spinning process. The prepared PI fibers were then carbonized with the increasing temperatures up to 1500 °C under a high-purity nitrogen atmosphere. The effects of ODA/p-PDA molar ratios on the chemical structure, microstructure, chain orientation, and structural evolutions of the PI fibers were systematically investigated. The elemental composition, morphology, and aggregation structure after carbonization were also analyzed. The results showed that different chemical compositions have greatly influenced the aggregation structures of the resulting PI and carbon fibers. The PI fibers showed increased crystallinity and orientation degree with the decreased ODA moieties, while the corresponding PI-based carbon fibers (CFs) exhibited perfect graphitic structures. The CFs derived from PMDA/p-PDA PI backbone with flat chains exhibited a well-defined graphite structure with d002 of 0.349 nm and ID/IG of 1.442. In addition, the carbon yield of the prepared PI-based carbon fibers reached more than 95 %.

Fabrication, mechanical performance and tribological behaviors of polyacetal-fiber-reinforced metakaolin-based geopolymeric composites

Co-reporter:Weiwei Zhao, Yatao Wang, Xiaodong Wang, Dezhen Wu

Ceramics International 2016 Volume 42(Issue 5) pp:6329-6341

Publication Date(Web):April 2016

DOI:10.1016/j.ceramint.2016.01.022

A type of new fiber-reinforced geopolymeric composites was developed by combining metakaolin and polyacetal (POM) fibers. High-strength POM fibers were first prepared through melt spinning followed by a hot-drawing procedure, and then a series of metakaolin-based geopolymeric composites with different contents of POM fibers were synthesized. The mechanical and tribological properties of the resulting composites were evaluated, and the morphology and microstructure were investigated. The POM fibers provided significant mechanical reinforcement for the metakaolin-based geopolymer. The composites were optimized for flexural and compressive strength with respect to fiber content and fiber length. Compared to unreinforced geopolymer, the composites obtained an optimum improvement by approximate 150% in flexural strength and by almost 26% in compressive strength. Moreover, the longer POM fibers exhibit a better reinforcement effect on the geopolymer, resulting in a lower optimal fiber content for the composites to achieve the maximum mechanical data. The reinforcing mechanisms were discussed on the basis of morphological investigation and considered as a cumulative energy-dissipating effect by fiber pullout and orientation, fiber rupture, fiber debonding from the matrix, and fiber bridging within cracks. The geopolymeric composites also achieved a considerable reduction in friction coefficient and abrasion loss rate in the presence of POM fibers. Such an enhancement of tribological performance is ascribed to the formation of self-lubricating transfer films between the contact surfaces of composites against the steel counterpart.

Design and fabrication of long-carbon-fiber-reinforced polyamide-6/nickel powder composites for electromagnetic interference shielding and high mechanical performance

Co-reporter:Shuangshuang Zhang;Xiaodong Wang;Dezhen Wu

Polymer Composites 2016 Volume 37( Issue 9) pp:2705-2718

Publication Date(Web):

DOI:10.1002/pc.23465

The long-carbon-fiber-reinforced polyamide-6/nickel powder composites were designed as electromagnetic interference (EMI) shielding materials and then were prepared through the joint processing of melt blending and thermoplastic pultrusion. The obtained composites show high conductivity and permittivity as well as a high dielectric loss with co-addition of carbon fiber and nickel powders, which makes the resulting composites a higher level of shielding effectiveness due to the combination of conductive and magnetic fillers. The composites are capable of shielding mainly through absorption rather than reflection. On the other hand, the composites achieved significant improvements in tensile, flexural, and impact strength due to the superiority of the long-carbon-fiber-reinforced technique. The residual fiber length in the injection-molded specimens is greatly superior to the critical one predicted by the Kelly–Tyson model. This takes full advantage of the strength of the reinforcing fiber itself, thus leading to a promising reinforcement effect. The enhancement of impact toughness is due to the energy dissipation by fiber fracture as a result of long fiber effect. The morphologic investigation indicated that the fiber fracture and fiber pullout concurred on the impact and tensile fracture surfaces, and the former preceded the latter. Highlighted with both good EMI shielding properties and excellent mechanical performance, the composites designed by this work exhibit potential applications for the automotive, electronic, aerospace, and military industries. POLYM. COMPOS., 37:2705–2718, 2016. © 2015 Society of Plastics Engineers

Structures and properties of polyimide/polyacrylonitrile blend fibers during stabilization process

Co-reporter:Jingjing Chang, Min He, Hongqing Niu, Gang Sui, Dezhen Wu

Polymer 2016 Volume 89() pp:102-111

Publication Date(Web):20 April 2016

DOI:10.1016/j.polymer.2016.02.056

•High-performance polyimide/polyacrylonitrile (PI/PAN) blend fibers were successfully prepared.•The effects of thermal treated time and PAN weight ratios were systematically investigated.•The mechanical and thermal properties of the blend fibers were obviously enhanced.•The PI and PAN macromolecules exhibited good compatibility with the fibers' glass transition temperature around 300 °C.The polyimide (PI)/polyacrylonitrile (PAN) blend fibers were successfully prepared through a wet-spinning method, derived from the blend of poly (amic acid) (PAA) and PAN precursors in dimethyl sulfoxide (DMSO) solvent. Herein, the effects of thermal treated time and PAN weight ratios on the structures and properties of the PI/PAN blend fibers were systematically explored. The increased thermal treated time favored the imidization of PAA and cyclization of PAN. As a consequence, the optimum mechanical properties of the PI/PAN blend fibers were obtained at a thermal treated time of 10 min with the tensile strength of 1.15 GPa and initial modulus of 50.87 GPa. On the other hand, the combination of PI and PAN facilitated the imidization process of PAA and the formation of ladder structures of PAN, while the optimum mechanical performances were achieved when the PAN weight ratio was 23 wt%. In addition, the PI and PAN macromolecules exhibited good compatibility in the blend fibers with the glass transition temperature around 300 °C.

Preparation of high-performance polyimide fibers containing benzimidazole and benzoxazole units

Co-reporter:Meng Sun;Jingjing Chang;Guofeng Tian;Hongqing Niu

Journal of Materials Science 2016 Volume 51( Issue 6) pp:2830-2840

Publication Date(Web):2016 March

DOI:10.1007/s10853-015-9591-y

A series of aromatic copolyimide (co-PI) fibers containing benzimidazole and benzoxazole were prepared by introducing 5-amino-2-(4-aminobenzene)benzoxazole (BOA) and 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) into the rigid 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA)/p-phenylenediamine (p-PDA) backbone via a typical two-step wet-spinning method. The incorporated BOA and BIA moieties in the polymer chains resulted in significant changes on the comprehensive performances of the resulting PI fibers. The optimum tensile strength was 2.26 GPa with the BIA/BOA molar ratio of 3/1, whereas the optimum initial modulus was 145.0 GPa with the BIA/BOA molar ratio of 1/3. The drastically improved mechanical properties were originated from the hydrogen-bonding intermolecular interactions by BIA moieties and high molecular orientation by BOA moieties. FT-IR results confirmed the presence of hydrogen-bonding interaction in the fibers with high imidization degree. Two-dimensional wide-angle X-ray diffraction (2D WAXD) indicated the existence of highly oriented structures along the fiber axial direction, while this feature varied with different diamine ratios. SEM observations showed that the fibers were obtained with homogeneous and uniform structures at various diamine ratios. Meanwhile, the co-PI fibers exhibited excellent thermal properties with 5 % weight loss temperature ranging from 563 to 570 °C in nitrogen and glass transition temperature ranging from 308 to 321 °C.

Preparation, mechanical properties and microstructure of polyoxymethylene fiber through melt spinning and hot drawing by using injection-molding grade resins

Co-reporter:Yatao Wang;Weiwei Zhao;Xiaodong Wang;Dezhen Wu

Fibers and Polymers 2016 Volume 17( Issue 9) pp:1464-1474

Publication Date(Web):2016 September

DOI:10.1007/s12221-016-6586-5

The polyoxymethylene (POM) fiber was melt spun by use of different commercial grades of POM resin, and the effect of post-drawing on mechanical properties and microstructures was investigated extensively. The fiber obtained from the POM resin with a higher melt flow index (MFI) exhibits a better hot-drawing capability and also achieves a greater ultimate draw ratio. The mechanical evaluation reveals that the tensile strength and elastic modulus of POM fiber are improved significantly after post-drawing compared to the as-spun fibers. Although the greater draw ratios result in higher mechanical strength and modulus for the POM fiber, the fiber obtained from the POM resin with an MFI of 13.0 g/10 min achieves the optimal mechanical performance at the ultimate draw ratio. The morphologic and structural developments of POM fiber were studied by scanning electronic microscopy and X-ray powder diffraction. The results indicate that the POM fiber spun by the resin with an MFI of 13.0 g/10 min has a smooth lateral surface and a compact cross section after post-drawing. The fiber samples spun by the POM resins with low MFIs show some hollow disfigurements as well as a rough surface at the ultimate draw ratio, whereas the fiber obtained from the resin with a high MFI of 27.0 g/10 min presents the ununiformity of diameter after post-drawing. The POM fibers achieve a crystalline orientation during the hot-drawing process, which results in a transformation from the spherulitic crystals to the lamellar structure in the drawing direction. The level of crystalline orientation can be improved with an increase of draw ratio and thus results in a high modulus and strength for the resulting POM fiber samples. In addition, the thermal analysis indicates that the crystallinity of the as-spun fibers can be enhanced by post-drawing due to the orientation-induced crystallization.

Synthesis of a novel linear polyphosphazene-based epoxy resin and its application in halogen-free flame-resistant thermosetting systems

Co-reporter:Huan Liu, Xiaodong Wang, Dezhen Wu

Polymer Degradation and Stability 2015 Volume 118() pp:45-58

Publication Date(Web):August 2015

DOI:10.1016/j.polymdegradstab.2015.04.009

The synthesis of a novel linear polyphosphazene-based epoxy resin (LPN–EP) was performed via a six-step reaction pathway, and the chemical structures of the intermediate and target products were characterized by 1H and 31P NMR spectroscopy and Fourier transform infrared spectroscopy. A series of thermosetting systems consisting of diglycidyl ether of bisphenol–A and LPN–EP were prepared, and their mechanical properties, thermal stabilities, and flame retardant properties were investigated. The resulting thermosets exhibited excellent flame resistance with the UL–94 V-0 rating but also achieved a significant improvement in impact toughness as a result of the incorporation of rubbery LPN–EP. The thermosets also showed a good thermal stability highlighted for high char yields. The mechanism study indicates that the synergistic effect from the combination of phosphorus and nitrogen in polyphosphazene segments could effectively enhance the flame retardancy by acting in both condensed and gaseous phases to promote the formation of intumescent phosphorus-rich char on the surface of the thermosets. Such a char layer plays a role of insulating protective shell to prevent the volatiles from transferring to the surface of the thermosets as well as to shield the heat and oxygen diffusion, thus resulting in a self-extinguishing flame rating.

Preparation of High Performance Copolyimide Fibers via Increasing Draw Ratios

Co-reporter:Mengying Zhang;Hongqing Niu;Zhiwei Lin;Shengli Qi;Jingjing Chang;Qiyan Ge;Dezhen Wu

Macromolecular Materials and Engineering 2015 Volume 300( Issue 11) pp:1096-1107

Publication Date(Web):

DOI:10.1002/mame.201500126

High performance fibers based on copolyimide (co-PI) containing benzimidazole and ether moieties were prepared via a two-step wet spinning method. The effects of draw ratio on the structures and properties of the ﬁbers are investigated. The mechanical properties of the co-PI fibers are improved greatly by increasing draw ratio at temperatures above 400 °C, reaching the optimum tensile strength of 2.8 GPa and modulus of 136 GPa, which is due to the development of the molecular orientation along the fiber direction. The hot drawing process roughens the fiber surface and stretches the molecules in the fibers. Moreover, the fiber structure evolutions during the drawing process were also discussed and a “smectic A liquid crystal-like” model was proposed.

Structures and properties of polyimide fibers containing fluorine groups

Co-reporter:Jingjing Chang, Weiwei Liu, Mengying Zhang, Li Cao, Qiyan Ge, Hongqing Niu, Gang Sui and Dezhen Wu

RSC Advances 2015 vol. 5(Issue 87) pp:71425-71432

Publication Date(Web):17 Aug 2015

DOI:10.1039/C5RA14115J

A series of copolyimide (co-PI) fibers containing fluorine groups were successfully obtained based on 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), p-phenylenediamine (p-PDA), 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) and 4,4′-oxydianiline (ODA) via a typical two-step wet-spinning method. The increased 6FDA moieties in the system resulted in unexpected great changes on the structures and properties of the resultant PI fibers. Regarding mechanical performances of the PI fibers, the tensile strength and initial modulus of the fibers decreased from 2.56 to 0.13 GPa and 91.55 to 2.99 GPa, respectively. Two-dimensional wide angle X-ray diffraction (2D WAXD) confirmed the existence of highly oriented structures along the fiber axial direction, while this feature gradually disappeared after the introduction of bulky trifluoromethyl pendant groups. SEM results suggested the presence of defects such as macrovoids structures with the increased 6FDA moieties. Besides, the dielectric permittivity was found to decrease from 3.46 to 2.78 in the frequency of 10 MHz as a result of the incorporation of 6FDA. Moreover, the co-PI fibers possessed excellent thermal-oxidative stabilities with the 5% weight loss temperature ranging from 495 to 552 °C under nitrogen atmosphere.

Effect of pre-imidization on the structures and properties of polyimide fibers

Co-reporter:Jingjing Chang, Qiyan Ge, Mengying Zhang, Weiwei Liu, Li Cao, Hongqing Niu, Gang Sui and Dezhen Wu

RSC Advances 2015 vol. 5(Issue 85) pp:69555-69566

Publication Date(Web):10 Aug 2015

DOI:10.1039/C5RA10943D

A series of polyimide (PI) fibers derived from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 4,4′-oxydiphthalic anhydride (ODPA) and p-phenylenediamine (p-PDA) were successfully prepared through a partially pre-imidization process, and the effects of different amount of dehydration reagents and initial poly(amic acid) (PAA) concentrations on the structure–property relationship of the resultant PI fibers were systematically investigated. The results showed that both the increased amount of dehydration reagents and PAA concentration could result in the ordered molecular packing arrangement of the polymer chains and gradually formed homogeneous structures in the fibers, which are proposed to be essentially dominated for the effectively enhancement in the mechanical properties of PI fibers. Moreover, the PI fibers obtained through the pre-imidization process still exhibited excellent thermal-oxidative stabilities, although the 5% weight loss temperature of the PI fibers was slightly decreased compared with that of the pure PI fibers as a result of the residual dehydration reagents in the fibers. Consequently, the present work provided a new approach in preparing high-performance PI fibers through a partially pre-imidization process.

Structureproperty relationship of polyimide fibers containing ether groups

Co-reporter:Jingjing Chang;Hongqing Niu;Min He;Meng Sun ;Dezhen Wu

Journal of Applied Polymer Science 2015 Volume 132( Issue 34) pp:

Publication Date(Web):

DOI:10.1002/app.42474

ABSTRACT

The copolyimide (co-PI) fibers with outstanding mechanical properties were prepared by a two-step wet-spinning method, derived from the design of combining 4,4′-oxydianiline (ODA) with the rigid 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA)/p-phenylenediamine (p-PDA) backbone. The mechanical properties of PI fibers were drastically improved with the optimum tensile strength of 2.53 GPa at a p-PDA/ODA molar ratio of 5/5, which was approximately 3.7 times the tensile strength of BPDA/p-PDA PI fibers. Two-dimensional wide-angle X-ray diffraction indicated that the highly oriented structures were formed in the fibers. Two-dimensional small-angle X-ray scattering revealed the existence of the needle-shaped microvoids aligned parallel to the fiber axis, and the introduction of ODA led to the reduction in the size of the microvoids. As a result, the significantly improved mechanical properties of PI fibers were mainly attributed to the gradually formed homogeneous structures. The co-PI fibers also exhibited excellent thermal stabilities of up to 563°C in nitrogen and 536°C in air for a 5% weight loss and glass transition temperatures above 279°C. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42474.

Preparation, isothermal kinetics, and performance of a novel epoxy thermosetting system based on phosphazene-cyclomatrix network for halogen-free flame retardancy and high thermal stability

Co-reporter:Huan Liu, Xiaodong Wang, Dezhen Wu

Thermochimica Acta 2015 Volume 607() pp:60-73

Publication Date(Web):10 May 2015

DOI:10.1016/j.tca.2015.04.002

•A novel phosphazene-based epoxy thermosetting system was designed.•The isothermal kinetics was studied for the thermosetting process.•A phosphazene-cyclomatrix network was built for this epoxy thermosetting system.•High flame resistance was obtained due to such a unique cyclomatrix structure.•The epoxy thermosets achieved a sound improvement in thermal stability.A novel epoxy thermosetting system based on a phosphazene-cyclomatrix network was designed and successfully prepared through the crosslinking reaction of diglycidyl ether of bisphenol-A with trispiro(ethylenediamino)-cyclotriphosphazene. The study of isothermal crosslinking kinetics indicated that the crosslinking process could be simulated by the Kamal’s model. The resultant thermosets exhibit excellent flame-retardant properties with a UL94 V-0 flame rating due to the presence of phosphazene-cyclomatrix network, whereas they show a higher thermal stability than the conventional epoxy thermoset. The mechanism study indicated that the phosphazene-cyclomatrix moieties could effectively enhance the flame retardancy by acting in both condensed and gaseous phases to promote the formation of an intumescent phosphorus-rich carbonaceous char layer on the surface of material. Such a char layer could prevent the volatiles from transferring to the surface of the thermosets as well as to shield the heat and oxygen diffusion, thus resulting in the self-extinguishing flame rating.

Effects of using polyacrylonitrile on the thermal, morphological and mechanical properties of polyimide/polyacrylonitrile blend fibers

Co-reporter:Mengying Zhang;Xin Zhao;Weiwei Liu;Min He;Hongqing Niu

Fibers and Polymers 2015 Volume 16( Issue 10) pp:2244-2250

Publication Date(Web):2015 October

DOI:10.1007/s12221-015-5569-2

High-performance polyimide/polyacrylonitrile (PI/PAN) blend fibers were prepared through wet-spinning of the polymer blends of polyamide acid (PAA) and PAN solutions followed by a thermal treatment in air. During the heat treatment process, PAA was imidized into its final heteroaromatic PI form with the concomitant evolution of PAN into its ladder-like preoxidized form, thus yielding PI/PAN blend fibers with desirable properties. The structure evolution was traced by fourier transform infrared radiation spectrometer, differential scanning calorimetry and thermogravimetry, implying that the PAA moiety in the blend fibers played a role as initiator for the cyclization of PAN. The final PI/PAN blend fibers exhibited a single glass-transition peak at 326 °C and a smooth surface without any pores. Moreover, the PI/PAN blend fibers possessed the tensile strength of 1.06 GPa and modulus of 59.9 GPa.

High-performance fibers based on copolyimides containing benzimidazole and ether moieties: Molecular packing, morphology, hydrogen-bonding interactions and properties

Co-reporter:Mengying Zhang;Hongqing Niu;Jingjing Chang;Qiyan Ge;Li Cao ;Dezhen Wu

Polymer Engineering & Science 2015 Volume 55( Issue 11) pp:2615-2625

Publication Date(Web):

DOI:10.1002/pen.24154

High-performance copolyimide (co-PI) fibers were prepared via the wet spinning process of co-polyamide acid precursors based on 3,3′,4,4′-biphenyldianhydride (BPDA) and a mixture of three diamines namely p-phenylene diamine (p-PDA), 2-(4-aminophenyl)-5-aminobenzimidazole (BIA), and 4,4′-oxidianiline (ODA), followed by drawing and imidization at high temperatures. Effects of the ODA and BIA contents on the molecular packing, morphology, hydrogen-bonding interactions, mechanical and thermal properties of the prepared fibers were investigated. The mechanical properties of the co-PI fibers were improved with the addition of ODA and BIA, and they reached the optimum tensile strength of 2.7 GPa and modulus of 94.3 GPa. Wide-angle X-ray diffraction results (WAXD) showed that the co-PI fibers exhibited highly oriented structure along the fiber direction with low degree of lateral packing orders in the transverse direction. Two-dimensional small-angle X-ray scattering (2D-SAXS) revealed that the incorporation of ODA resulted in the reduction in radius, length, misorientation, and internal surface roughness of the microvoids in the fibers. Fourier transform infrared (FTIR) results indicated that hydrogen-bonding formed between the BIA and cyclic imide units effectively strengthened the intermolecular interactions. The co-PI fibers exhibited excellent thermal and thermal-oxidative stability, with a 5%-weight-loss temperature of 578°C under N₂ and 572°C in air. POLYM. ENG. SCI., 55:2615–2625, 2015. © 2015 Society of Plastics Engineers

Enhanced dielectric permittivity of a flexible three-phase polyimide–graphene–BaTiO3 composite material

Co-reporter:Jingni Liu, Guofeng Tian, Shengli Qi, Zhanpeng Wu, Dezhen Wu

Materials Letters 2014 Volume 124() pp:117-119

Publication Date(Web):1 June 2014

DOI:10.1016/j.matlet.2014.02.105

•A flexible three-phase polymeric composite material with high dielectric permittivity was prepared by the incorporation of graphene and BaTiO3 into the polyimide (PI) matrix.•Significant improvement in dielectric permittivity of PI can be achieved attributing to the unique three-dimensional structure constructed by graphene and BaTiO3 inside the PI matrix.•The composite material maintains a lower dielectric loss than that only use graphene as fillers in the same volume concentration.A flexible three-phase composite material with enhanced dielectric permittivity was prepared with both graphene and BaTiO3 nanoparticles as fillers and polyimide (PI) as matrix. Studies on the dielectric properties of PI–graphene–BaTiO3 composite materials in the frequency range from 102 to 106 Hz show that they possess excellent dielectric permittivity (ε=170.39) and lower dielectric loss thanks to their unique dimensional structure. In consideration of the percolation theory and microcapacitor model, a percolation threshold of 1.11 vol% was calculated and the mechanism of the enhancement of the dielectric permittivity of the composite material was discussed.

Enhanced Conductivity and mechanical properties of polyimide based nanocomposite materials with carbon nanofibers via carbonization of electrospun polyimide fibers

Co-reporter:Guofeng Tian;Haipeng Zhang;Jingni liu;Shengli Qi;Dezhen Wu

Polymer Science, Series A 2014 Volume 56( Issue 4) pp:505-510

Publication Date(Web):2014 July

DOI:10.1134/S0965545X14040154

Carbon nanofibers (CNF) have been obtained by the thermal treatment of the electrospun polyimide fibers in our present work. The carbon structure and surface morphology of the as-received CNFs were investigated using X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. Investigations of the nanocomposite materials fabricated using these CNFs as conductive fillers and polyimide as matrix show that the presence of CNFs can improve both the mechanical and electrical properties of the material. The conductivity of the nanocomposite films increases with increases in the CNF content and a percolation threshold of about 6.3 vol % (0.0785 in weight fraction) is calculated according to percolation theory.

Preparation of polyimide/BaTiO3/Ag nanocomposite films via in situ technique and study of their dielectric behavior

Co-reporter:Jia-yu Zhan;Guo-feng Tian;Zhan-peng Wu;Sheng-li Qi

Chinese Journal of Polymer Science 2014 Volume 32( Issue 4) pp:424-431

Publication Date(Web):2014 April

DOI:10.1007/s10118-014-1413-1

Triphase polyimide nanocomposite films were fabricated using barium titanate (BaTiO3) with high dielectric constant and silver (Ag) with high conductivity as fillers. In situ method was utilized to obtain the homogeneous dispersion of nanoparticles. The in situ polymerization of polyimide precursor-poly(amic acid) was performed in the presence of BaTiO3 particles. Silver compound 1,1,1-trifluoro-2,4-pentadionato silver(I) was added into the BaTiO3 containing poly(amic acid) solution to achieve silver nanoparticles via in situ self metallization technique. The thermally induced reduction converted silver (I) to metallic silver with concomitant imidization of poly(amic acid) to polyimide. Both BaTiO3 and silver nanoparticles were uniformly dispersed in the polyimide substrate. The dependence of dielectric behavior on the BaTiO3 and Ag contents was studied. The incorporation of small amount of silver nanoparticles greatly increased dielectric constant of composite films.

Structure evolutions involved in the carbonization of polyimide fibers with different chemical constitution

Co-reporter:M.Y. Zhang, H.Q. Niu, S.L. Qi, G.F. Tian, X.D. Wang, D.Z. Wu

Materials Today Communications 2014 Volume 1(1–2) pp:1-8

Publication Date(Web):September–December 2014

DOI:10.1016/j.mtcomm.2014.08.001

Two polyimide (PI) fibers with different chemical structures, pyromellitic dianhydride (PMDA)/4,4′-oxydianiline (ODA) and 3,3′,4,4′-biphenyldianhydride (BPDA)/p-phenylenediamine (p-PDA)/2-(4-aminophenyl)-5-aminobenzimidazole (BIA) fibers, were prepared by wet-spinning process, and followed by carbonization with increasing temperature up to 1600 °C under a high-purity nitrogen atmosphere, resulting in PI-derived carbon fibers. The chemical structure evolutions were traced by Fourier transform infrared radiation spectrometer (FTIR), Elemental analyzer (EA), Thermogravimetry (TG) and the carbonization mechanism was discussed through the molecular simulation and thermo gravimetric-infrared radiation (TG-IR) analysis. The aggregation structure evolutions were characterized by X-ray diffraction (XRD), Raman and scanning electron microscope (SEM) analyses. The graphite structure was formed and gradually became ordered by increasing temperature, finally resulting in carbon fibers with high carbon contents over 95% and high carbon yields over 50 wt%. Moreover, the carbon yields and graphitization degrees strongly depended on the chemical structures of PI fibers. The carbon fiber derived from BPDA/p-PDA/BIA demonstrated higher carbon yields, more ordered and more well-defined graphite structures than that derived from PMDA/ODA.

Synthesis of silver nanocubes with controlled size using water-soluble poly(amic acid) salt as the intermediate via a novel ion-exchange self-assembly technique

Co-reporter:Shengli Qi, Xiangyue Shen, Zhiwei Lin, GuoFeng Tian, Dezhen Wu and Riguang Jin

Nanoscale 2013 vol. 5(Issue 24) pp:12132-12135

Publication Date(Web):10 Oct 2013

DOI:10.1039/C3NR03212D

Here, we report for the first time on the successful fabrication of monodispersed silver nanocubes with regular shape and controlled size in the solid phase via a novel ion-exchange self-assembly technique by using water-soluble poly(amic acid) salt as the intermediate and silver nitrate as the metal precursor. By simply altering the annealing times at high temperature, the size of the silver nanocubes could be finely tuned in the range of 90–160 nm in the present case. Further attempts with different metal salts show that the present method is also feasible for other metal species and might be universal.

High-performance copolyimide fibers containing quinazolinone moiety: Preparation, structure and properties

Co-reporter:Hongqing Niu, Mingjun Huang, Shengli Qi, Enlin Han, Guofeng Tian, Xiaodong Wang, Dezhen Wu

Polymer 2013 Volume 54(Issue 6) pp:1700-1708

Publication Date(Web):8 March 2013

DOI:10.1016/j.polymer.2013.01.047

Copolyimide (co-PI) fibers with superior mechanical properties and high thermal stability were developed via a two-step polymerization/imidization process based on a new design of introducing an aromatic heterocyclic diamine monomer, 2-(4-aminophenyl)-6-amino-4(3H)-quinazolinone (AAQ) into rigid homopolyimide backbones of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and p-phenylenediamine (p-PDA). Effects of the incorporated AAQ moieties on the micro-structure and properties of the prepared fibers were investigated. Fourier transform infrared (FTIR) results indicated that hydrogen bonding is formed between the AAQ and cyclic imide units that effectively strengthens the intermolecular interactions. This has been considered to be the key factor responsible for the significantly enhanced mechanical properties of the co-PI fibers. Two-dimensional wide angle X-ray diffraction (2D WAXD) spectra showed that the co-PI fibers are highly oriented with well-ordered 2D structures along both the fiber and transverse directions. The co-PI fibers reached the optimum tensile strength and modulus of 2.8 GPa and 115 GPa, respectively, at the AAQ/p-PDA molar ratio of 5/5. The fiber also exhibited high thermal stability, with a 5%-weight-loss temperature of 599 °C under N2 and 564 °C in air.Highlights► High-performance copolyimide fibers containing quinazolinone moiety were prepared. ► Fibers’ tensile strength and modulus can reach 2.8 GPa and 115 GPa, respectively. ► Effects of the AAQ on the fibers' microstructure and properties were studied. ► Fibers' properties can be improved by hydrogen bonding interactions significantly. ► The copolyimide fibers are highly oriented with mesophase-like ordered structures.

Synthesis and characterization of amino functionalized ladder-like polysilsesquioxanes and their hybrid films with polyimide

Co-reporter:Qiu-shuang Gao;Guo-feng Tian;Sheng-li Qi

Chinese Journal of Polymer Science 2013 Volume 31( Issue 3) pp:427-433

Publication Date(Web):2013 March

DOI:10.1007/s10118-013-1187-x

Ladder-like polysilsesquioxanes (LPSQs) with different amino contents have been synthesized by controlling of the dosage of Pd/C catalyst. The concentration and activity of amino groups were investigated by Fourier transform infrared spectroscopy. Polyimide (PI)/LPSQ hybrid films have been prepared by incorporating of the obtained LPSQs with different amino contents into PI matrix, respectively. The interfacial interactions between PI matrix and LPSQ were studied with scanning electron microscopy and X-ray photoelectron spectroscopy, meanwhile the thermal and mechanical properties of the hybrid films were studied using dynamic mechanical analysis and tensile tests. The results indicate that the functionality of LPSQ has great effects on the interfacial interactions and the properties of hybrid films. With the increase of amino content, both the interfacial interactions and the cross-linking density of hybrids enhanced, which results in the decline of surface silicon concentration, increase of Young’s modulus and drop of elongation at break. Excessive amino content makes the hybrid films brittle and leads to incomplete imidization.

Fabrication and mechanism study of CuO layers on double surfaces of polyimide substrate using surface modification

Co-reporter:Jiayu Zhan, Guofeng Tian, Shengli Qi, Zhanpeng Wu, Dezhen Wu, Riguang Jin

Composites Science and Technology 2012 Volume 72(Issue 9) pp:1020-1026

Publication Date(Web):21 May 2012

DOI:10.1016/j.compscitech.2012.03.014

Formation process and mechanism of continuous CuO layers on double surfaces of polyimide films were studied. The composite films were prepared using the facile surface modification and ion exchange technique. By alkaline-induced chemical modification and ion-exchange reaction, Cu2+ ions were incorporated into the surface of polyimide substrate. Thermal treatment in ambient atmosphere resulted in the formation of CuO particles that further agglomerated on the film surface and produced well-defined CuO thin layers on the double surfaces of polyimide films. The changes in the chemical structure, surface morphology, crystalline state and the surface roughness with the increase of ambient temperature were investigated. It was interesting to find that the conversion of metallic copper and low valence sub-oxide Cu2O to high valence oxide CuO was observed in the thermal treatment process. The agglomeration mechanism for the CuO particles was proposed and proved by three steps, which illustrated that copper-catalyzed and oxygen-assisted decomposition of the polyimide overlayer resulted in the agglomeration of CuO particles. The final composite films retained the thermal stability of the pure polyimide.

Fabrication of high-performance copolyimide fibers from 3,3',4,4'-biphenyltetracarboxylic dianhydride, p-phenylenediamine and 2-(4-aminophenyl)-6-amino-4(3H)-quinazolinone

Co-reporter:Hongqing Niu, Shengli Qi, Enlin Han, Guofeng Tian, Xiaodong Wang, Dezhen Wu

Materials Letters 2012 Volume 89() pp:63-65

Publication Date(Web):15 December 2012

DOI:10.1016/j.matlet.2012.08.088

High-performance copolyimide (co-PI) fibers synthesized by 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), p-Phenylenediamine (p-PDA) and 2-(4-aminophenyl)-6-amino-4(3H)-quinazolinone (AAQ) were prepared via a two-step spinning technology. The influences of the thermal treatment temperatures on the structure, and mechanical and thermal properties of the co-PI fibers were studied. The co-PI fibers with excellent mechanical and thermal properties were obtained by heating the co-PAA fibers under a drawing ratio of 1.05 at 240 °C and subsequently at 390 °C. The tensile strength and modulus reach 2.6 GPa and 112.3 GPa, respectively. The 5%-weight-loss temperatures of the co-PI fibers under nitrogen and air achieve 611 °C and 565 °C, respectively, and the glass transition temperature is over 400 °C.Highlights► New high-performance co-PI fibers were prepared via a two-step technology. ► Influences of thermal treatment temperature on structure and properties were studied. ► co-PI fibers showed excellent mechanical and thermal properties.

Fabrication of surface silvered polyimide/iron oxide composite films with both superparamagnetism and electrical conductivity

Co-reporter:Jiayu Zhan, Zhanpeng Wu, Shengli Qi, Dezhen Wu, Wantai Yang

Thin Solid Films 2011 Volume 519(Issue 6) pp:1960-1965

Publication Date(Web):3 January 2011

DOI:10.1016/j.tsf.2010.10.034

Surface silvered polyimide (PI)/Fe2O3 composite films with both superparamagnetic and surface electrically conductive properties have been fabricated by an in situ technique. Iron (III) 2,4-pentanedionate was incorporated into a PI precursor poly(amic acid) solution and thermally decomposed to form iron oxide nanoparticles in the process of thermal imidization, preparing PI/Fe2O3 nanocomposite films. The establishment of a silver layer on the PI/Fe2O3 film surface involved the steps of chemical etching by the alkaline aqueous solution, ion exchange with silver ions and chemical reduction by glucose. The formed Fe2O3 particles of the nano scale endow the film with typical superparamagnetic response. By employing the etching time of only 10 min and a reduction time of no more than 15 min, the well-established silver layers have formed on the upside surface. The corresponding reflectivity and resistivity reached to the value of 76.15% and 0.7 Ω/square respectively.

Synthesis and characterization of functional ladder-like polysilsesquioxane and their hybrid films with polyimide

Co-reporter:Qiushuang Gao, Shengli Qi, Zhanpeng Wu, Dezhen Wu, Wantai Yang

Thin Solid Films 2011 Volume 519(Issue 19) pp:6499-6507

Publication Date(Web):29 July 2011

DOI:10.1016/j.tsf.2011.05.002

Ladder-like polyphenylsilsesquioxane has been synthesized by a convenient two-step approach and then modified to ladder-like poly(nitrophenyl)silsesquioxane (LPNPSQ) and poly(aminophenyl)silsesquioxane (LPAPSQ) by nitration and reduction reaction. These ladder-like polysilsesquioxanes (LPSQs) were characterized by Fourier transform infrared, nuclear magnetic resonance and X-ray diffraction (XRD). The results confirm the ladder-like structures of LPSQs and suggest the decrease of regularity after the chemical modification. Then high performance polyimide/ladder-like polysilsesquioxane (PI/LPSQ) hybrid films have been prepared by incorporating synthetic LPSQs with different functional groups into PI matrix, respectively, using conventional techniques. The interfacial interactions between PI matrix and LPSQ were investigated with XRD and scanning electron microscopy. Then the thermal and mechanical properties of the hybrid films were studied using dynamic mechanical analysis and tensile tests. The results indicate that different functional groups in LPSQs have great effects on the interfacial interactions and the properties of the hybrids. Both LPNPSQ and LPAPSQ can be dispersed uniformly in PI matrix because of the physical or chemical interaction between functional groups and PI. With these strong interfacial interactions, PI/LPNPSQ and PI/LPAPSQ hybrid films show higher glass transition temperatures and better mechanical properties.

Polyimide/sepiolite nanocomposite films: Preparation, morphology and properties

Co-reporter:Yun Yu, Shengli Qi, Jiayu Zhan, Zhanpeng Wu, Xiaoping Yang, Dezhen Wu

Materials Research Bulletin 2011 46(10) pp: 1593-1599

Publication Date(Web):

DOI:10.1016/j.materresbull.2011.06.009

Preparation of electrically conductive polyimide/silver composite fibers via in-situ surface treatment

Co-reporter:Shuxiang Mu, Zhanpeng Wu, Shengli Qi, Dezhen Wu, Wantai Yang

Materials Letters 2010 Volume 64(Issue 15) pp:1668-1671

Publication Date(Web):15 August 2010

DOI:10.1016/j.matlet.2010.05.005

Polyimide (PI)/silver composite fibers with high electrical conductivity were prepared via an in-situ surface treatment method. The following procedures were included: hydrolyzing the PI fibers in alkali solution, followed by silver ion loading through ion exchange in silver salt solution and finally reducing the silver ion-loaded PI fibers in ascorbic acid solution. The effects of alkali treatment and ion-exchange conditions on the surface morphology, electrical conductivity and mechanical properties of the final composite fibers were studied. Excellent surface electrical conductivity was achieved on PI fiber surface with an electrical resistance of about 102 Ω/cm. The mechanical properties of the PI composite fibers were essentially similar to those of the bare PI fiber.

Preparation and characterization of polyimide/ladder like polysiloxane hybrid films

Co-reporter:Yuzhong Feng, Shengli Qi, Zhanpeng Wu, Xiaodong Wang, Xiaoping Yang, Dezhen Wu

Materials Letters 2010 Volume 64(Issue 24) pp:2710-2713

Publication Date(Web):31 December 2010

DOI:10.1016/j.matlet.2010.08.067

Novel polyimide (PI)/ladder like polyphenylsilsesquioxane (PPSQ) hybrid films was prepared. PI was made from poly(amide acid) of 4, 4′’-diaminodiphenylether and pyromellitic dianhydride. PPSQ was prepared from phenyltrimethoxysilane through sol–gel process. The chemical structure of PPSQ was characterized by Fourier transform infrared and nuclear magnetic resonance. The coefficients of thermal expansion for the hybrid films decrease with the increasing content of PPSQ. The thermal and mechanical properties of the hybrid films were essentially similar to the neat PI.

Formation and characterization of cobalt oxide layers on polyimide films via surface modification and ion-exchange technique

Co-reporter:Shuxiang Mu, Zhanpeng Wu, Yue Wang, Shengli Qi, Xiaoping Yang, Dezhen Wu

Thin Solid Films 2010 Volume 518(Issue 15) pp:4175-4182

Publication Date(Web):31 May 2010

DOI:10.1016/j.tsf.2009.12.004

Polyimide (PI) films with thin cobalt oxide (Co3O4) layers on both film sides have been prepared via a surface modification and ion-exchange technique. The method works by hydrolyzing the PI film surfaces in aqueous potassium hydroxide solution and incorporating Co2+ into the hydrolyzed layers of PI film via subsequent ion exchange, and followed by thermal treatment in ambient atmosphere. The PI composite films were characterized by Attenuated total reflection-Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffractions, scanning electron microscopy, transmission electron microscopy and thermogravimetric analyses, as well as surface resistance and mechanical measurements. By varying the absorbed cobalt ion content, a series of PI/Co3O4 composite films with insulative to semiconductive surfaces were obtained. The room temperature surface resistances of the semiconductive composite films reached to about 107 Ω. The Co3O4 particle formed on PI film surfaces was in the range of 10–40 nm. The final composite films maintained the essential mechanical properties and thermal stability of the pristine PI films. The adhesion between surface Co3O4 layers and PI matrix was acceptable.

Directly ultraviolet photochemical deposition of silver nanoparticles on silica spheres: Preparation and characterization

Co-reporter:Ning Luo, Lixin Mao, Lizhong Jiang, Jiayu Zhan, Zhanpeng Wu, Dezhen Wu

Materials Letters 2009 Volume 63(Issue 1) pp:154-156

Publication Date(Web):15 January 2009

DOI:10.1016/j.matlet.2008.09.033

A simple method was developed to directly deposit silver nanoparticles on the surface of silica spheres. The photochemical reduction was carried out by ultraviolet irradiation in air atmosphere at room temperature. The [Ag(NH3)2]+was reduced to silver atoms upon ultraviolet irradiation. Silver atoms subsequently deposited on the surface of silica spheres and agglomerated into silver nanoparticles. Silica spheres with silver nanoparticles of different size and density can be simply controlled by adjusting the UV-light irradiation time. The silver nanoparticles deposited on silica spheres were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, and field emission scanning electron microscopy.

The chemistry involved in the loading of silver(I) into poly(amic acid) via ion exchange: A metal-ion-induced crosslinking behavior

Co-reporter:Shengli Qi, Zhanpeng Wu, Dezhen Wu, Wantai Yang, Riguang Jin

Polymer 2009 50(3) pp: 845-854

Publication Date(Web):

DOI:10.1016/j.polymer.2008.12.010

Preparation and characterization of polyimide/silica/silver composite films

Co-reporter:Ning Luo;Zhanpeng Wu;Nanxiang Mou

Frontiers of Chemical Science and Engineering 2008 Volume 2( Issue 3) pp:291-295

Publication Date(Web):2008 September

DOI:10.1007/s11705-008-0059-3

Polyimide/silica/silver hybrid films were prepared by the sol-gel method combined with in situ single-stage self-metallization technique. The structure of polyimide films in the thermal curing process and the influence of silica content on the migration and aggregation of silver particles to the surface of hybrid films were investigated. The hybrid films were characterized by transmission electron microscopy, dynamic mechanical thermal analysis, Fourier transform infrared spectroscopy, ultraviolet visible spectroscopy and mechanical measurements. The results indicated that there was no degradation of the polyimide matrix after the formation of silica and silver particles. Silica acted as the nucleus for the silver particles. With increasing silica content, more and more silver particles were kept in the hybrid films instead of being migrated onto the surface of the hybrid films and the reflections of hybrid films decreased gradually.

Superparamagnetic polyimide/γ-Fe2O3 nanocomposite films: Preparation and characterization

Co-reporter:Jiayu Zhan, Guofeng Tian, Lizhong Jiang, Zhanpeng Wu, Dezhen Wu, Xiaoping Yang, Riguang Jin

Thin Solid Films 2008 Volume 516(Issue 18) pp:6315-6320

Publication Date(Web):31 July 2008

DOI:10.1016/j.tsf.2007.12.090

Polyimide/γ-Fe2O3 nanocomposite films with superparamagnetic behavior have been prepared by thermal curing of the magnetite (Fe3O4) nanoparticles-containing poly(amic acid) (PAA) derived from pyromellitic dianhydride (PMDA) and 4,4’-oxydianiline (4,4’-ODA) in N,N-dimethylacetamide (DMAc). To improve the dispersion of the doped nanoparticles, the amine-functionalized Fe3O4 nanoparticles reacted with the PMDA dianhydride in DMAc firstly, and then polymerization was carried out by adding 4,4’-ODA and then PMDA to form the PAA-grafted magnetic particles. Thermal treatment of the Fe3O4-doped precursor film converted the PAA into its final polyimide form with concomitant transformation of Fe3O4 into γ-Fe2O3, yielding a polyimide film with superparamagnetic behavior. The distribution of nanoparticles in the polymer matrix was investigated by transmission electron microscopy and field emission scanning electron microscopy. The nanoparticles and composite films were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, magnetic and mechanical measurement.

Preparation of ultra-fine polyimide fibers containing silver nanoparticles via in situ technique

Co-reporter:Qian Zhang, Dezhen Wu, Shengli Qi, Zhanpeng Wu, Xiaoping Yang, Riguang Jin

Materials Letters 2007 Volume 61(19–20) pp:4027-4030

Publication Date(Web):August 2007

DOI:10.1016/j.matlet.2007.01.011

Ultra-fine polyimide fibers containing silver nanoparticles were prepared by electrospinning from poly(amic acid)/(trifluoroacetylacetonoto)silver(I) (PAA/AgTFA) solution. Thermal curing of the silver(I)-containing fibers led to cycloimidization of the poly(amic acid) into polyimide with concomitant silver(I) reduction. The polyimide–silver fibers were characterized by FT-IR, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The average diameters of silver nanoparticles and ultra-fine PI fibers electrospun from solutions with different amounts of AgTFA were studied, and the crystal structure of silver nanoparticles was also presented.

Preparation of silver quantum dots embedded water-soluble silica/PAAc hybrid nanoparticles and their bactericidal activity

Co-reporter:Lizhong Jiang, Wencai Wang, Dezhen Wu, Jiayu Zhan, Qin Wang, Zhanpeng Wu, Riguang Jin

Materials Chemistry and Physics 2007 Volume 104(2–3) pp:230-234

Publication Date(Web):15 August 2007

DOI:10.1016/j.matchemphys.2007.03.023

Silver quantum dots (QDs) embedded silica/PAAc hybrid nanoparticles were prepared by copolymerization of acrylic acid (AAc) onto γ-Methacryloxypropyltrimethoxysilane (MPS) modified silica nanoparticles followed by reduction of the immobilized Ag+ ions to metallic Ag. The prepared hybrid nanoparticles were characterized using X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The hybrid nanoparticles dispersed well in aqueous media and showed effective bactericidal activities. The results suggest that the hybrid nanoparticles have potential application as a water-soluble agent in many fields.

Effects of water on the preparation, morphology, and properties of polyimide/silica nanocomposite films prepared by sol–gel process

Co-reporter:Lizhong Jiang;Dezhen Wu;Xiaowei Wei;Riguang Jin;Wencai Wang;Lizhong Jiang;Xiaowei Wei;Wencai Wang;Dezhen Wu;Riguang Jin

Journal of Applied Polymer Science 2007 Volume 104(Issue 3) pp:1579-1586

Publication Date(Web):26 FEB 2007

DOI:10.1002/app.25692

Polyimide/silica (PI/SiO₂) nanocomposite films with 10 wt % of silica content were prepared by sol–gel process under the conditions with and without additional water. The presence of additional water has great effect on the silica particle size and thus on the properties of the prepared PI/SiO₂ films. The results indicated that with additional water, the silica particles formed before the imidization of poly(amic acid) (PAA) and aggregated with the increasing of temperature and degree of the proceeding imidization process. For the nonaqueous process, the hydrolysis condensation reaction of tetraethoxysilane (TEOS) did not occur until the imidization of PAA took place, and no silica particles were found in the unimidized PAA films. The hydrolysis–condensation reaction of TEOS was initiated simultaneously by the trace water released from the imidization reaction, the self-catalysis mechanism of the approach provide a means of achieving uniformly dispersed silica particles formed in the PI matrix with particle size in the range of 30–70 nm. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1579–1586, 2007

Preparation, structure and properties of porous polyimide films via PAA/PU alloy

Co-reporter:Jiugui Liu;Lizhong Jiang;Jiayu Zhan;Dezhen Wu

Frontiers of Chemistry in China 2007 Volume 2( Issue 1) pp:13-16

Publication Date(Web):2007 March

DOI:10.1007/s11458-007-0003-y

A new route to porous polyimide (PI) films with pore sizes in the nanometer regime was developed. A polyamic acid (PAA)/polyurethane (PU) blend with PU as the disperse phase was first prepared via in situ polymerization of pyromellitic dianhydride and 4,4-oxydianiline in PU solutions. Porous PI films were obtained from PAA/PU films by thermolysis of PU at 360°C and imidization of PAA at 300°C, respectively. Fourier transform infrared spectroscopy and thermal gravimetric analysis were used to detect the imidization and thermolysis processes of PAA/PU blends under thermal treatment. The microporous structure of the PI films was observed by transmission electron microscopy. It was found that the size and content of pores increased with an increase in the PU mass fraction in the PAA/PU blend up to 20%. Because of the existence of nanopores, the dielectric constant of PI films decreased by a wide margin and was less than 2.0 at a PU mass fraction of 20%. It implies that this is an effective means to reduce the dielectric constant of PI, but it also causes the decrease of tensile strength and the rise of water absorption.

Preparation of highly reflective and conductive metallized polyimide films through surface modification: processing, morphology and properties

Co-reporter:Zhanpeng Wu, Dezhen Wu, Wantai Yang and Riguang Jin

Journal of Materials Chemistry A 2006 vol. 16(Issue 3) pp:310-316

Publication Date(Web):10 Nov 2005

DOI:10.1039/B509537A

Silvered polyimide films have been prepared by potassium hydroxide hydroxylation of polyimide film surfaces and incorporation of silver ions through subsequent ion exchange. Thermal curing not only recycloimidized the poly(amic acid) into polyimide, but also reduced silver ions into silver atoms and near-atomic silver clusters, which diffused and aggregated to give reflective and conductive surfaces without need of the addition of reducing agents. Films were characterized by X-ray photoelectron spectrometer, transmission electron microscopy, scanning electron microscopy and tapping mode atomic force microscopy. The thickness of the silvered layers and the reflectivity and conductivity of the silvered films can be controlled. By this method, the double-sided silvered polyimide films with excellent reflective (reflectivity > 97%) and conductive surfaces (surface resistivity = 0.02 Ω cm−2) could be easily fabricated. Their essential mechanical properties could be maintained, and the silver–polymer adhesion was outstanding.

Direct Ion Exchange Self-Metallization: A Novel and Efficient Route for the Preparation of Double-Surface-Silvered Polyimide Films

Co-reporter:Shengli Qi;Dezhen Wu;Zhanpeng Wu;Wantai Yang;Riguang Jin;Zongwu Bai

Macromolecular Rapid Communications 2006 Volume 27(Issue 5) pp:372-376

Publication Date(Web):21 FEB 2006

DOI:10.1002/marc.200500733

Summary: Silvered polyimide films have been fabricated by direct ion exchange of a damp-dry poly(amic acid) film with an aqueous silver solution such as silver nitrate. Thermal curing of the silver(I)-containing films under tension leads to cycloimidization of the poly(amic acid) into polyimide with a concomitant silver(I) reduction and aggregation at both film sides to give reflective and conductive double-surface-silvered polyimide films. The metallized films retain the essential properties of the parent polyimide.

Preparation of silvered polyimide films with reflective and electrically conductive surfaces using single-stage self-metallization techniques and factors affecting silver particles migration

Co-reporter:Zhanpeng Wu;Dezhen Wu;Teng Zhang;Lizhong Jiang;Wencai Wang;Riguang Jin

Journal of Applied Polymer Science 2006 Volume 102(Issue 3) pp:2218-2225

Publication Date(Web):23 AUG 2006

DOI:10.1002/app.24382

Reflective and surface conductive flexible polyimide (PI) films were prepared by the incorporation of silver(I) acetate and 1,1,1-trifluoro-2,4-pentanedione into a dimethylacetamide solution of several poly(amic acid)s which were prepared from dianhydrides and diamines. Thermal curing of the silver(I)-containing poly(amino acid)s precursor led to cycloimidization of the PI with silver(I) reduction and formation of a reflective and conductive silvered surface at about 13 wt % silver. Effects on silver particles migration and aggregation were discussed in this article. The results indicated that the PI structures with flexible chains and groups easily fabricate the silvered films, with both reflective and conductive characteristics. With the forced air condition, the evaporation rate of the solvent and water increases, which facilitates the migration of silver particles to give reflective and conductive silvered surfaces. Films were characterized by transmission electron microscopy, scanning electron microscopy, and tapping-mode atomic force microscopy. Electrical conductivity, reflectivity, and dynamic mechanical thermal analysis were performed on the metallized films. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2218–2225, 2006.