Preparation and characteristics of composite films with functionalized graphene/polyimide

Polyimide (PI) has the inherent defect of poor intrinsic thermal conductivity and cannot meet the increasing demand for rapid heat dissipation in the thermal management introduction. To improve the thermal conductivity of PI, in this study, thick sheet graphene-ionic liquid (TSG-IL) functionalized graphene has been prepared by a one-step ultrasonic-chemical method. Under the action of mechanical force, IL is successfully modified on the surface of TSG, and TSG is peeled to some extent. TSG-IL/PI has been prepared the typical method of solution casting followed by thermal imidization. The structure, morphology, thermal conductivity, and mechanical properties of the composites are evaluated by Fourier-transform infrared spectroscopy, x-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy, and Hot Disk thermal conductivity tests. When the amount of TSG-IL is 0.3 wt%, the thermal conductivity of TSG-IL/PI (0.18 W·m⁻¹·k⁻¹) than pure PI and TSG (ultrasonication)/PI increased by 50.0% and 28.6%, respectively. Moreover, it can maintain good mechanical properties, and its tensile strength (121.5 MPa) is 6.5% and 3.5% higher than that of pure PI and TSG (ultrasonication)/PI, respectively. The potential for application in the preparation of composites with high-thermal conductivity is promising.     

Preparation of polyimide/siloxane‐functionalized graphene oxide composite films with high mechanical properties and thermal stability via in situ polymerization

An effective approach to prepare polyimide/siloxane‐functionalized graphene oxide composite films is reported. The siloxane‐functionalized graphene oxide was obtained by treating graphene oxide (GO) with 1,3‐bis(3‐aminopropyl)‐1,1,3,3‐tetra‐methyldisiloxane (DSX) to obtain DSX‐GO nanosheets, which provided a starting platform for in situ fabrication of the composites by grafting polyimide (PI) chains at the reactive sites of functional DSX‐GO nanosheets. DSX‐GO bonded with the PI matrix through amide linkage to form PI‐DSX‐GO films, in which DSX‐GO exhibited excellent dispersibility and compatibility. It is demonstrated that the obvious reinforcing effect of GO to PI in mechanical properties and thermal stability for PI‐DSX‐GO is obtained. The tensile strength of a composite film containing 1.0 wt% DSX‐GO was 2.8 times greater than that of neat PI films, and Young's modulus was 6.3 times than that of neat PI films. Furthermore, the decomposition temperature of the composite for 5% weight loss was approximately 30 °C higher than that of neat PI films. © 2015 Society of Chemical Industry     

Kevlar oligomer functionalized graphene for polymer composites

Kevlar oligomer functionalized graphene (FGS) was prepared by simple grafting of amino-terminated Kevlar oligomer on graphene oxide (GO) followed by reducing with hydrazine hydrate. The incorporation of FGS shows pronounced effect on the host polymers. High-level reinforcement of both PMMA and PI is observed with low content of FGS (≤0.2 wt %), in this lower loading range, the tensile modulus and strength of composites increase almost linearly as a function of the adding amount of FGS. But no further improvement is obtained as the content of FGS further increased (>0.2 wt %). The mechanism under the reinforcement effect against the FGS loadings is discussed based on the morphological characterizations of the composites. The thermal properties of the composites were also investigated. The glass transition temperature and thermal stability of PMMA were dramatically increased even with the addition of only a small amount of FGS.     

Polyimide nanohybrid films with electrochemically functionalized graphene

Graphite was functionalized electrochemically in a potassium fluoride solution and used to prepare polyimide (PI)/graphene nanohybrid films. The as‐made electrochemically fluorinated graphene (EFG) was used to prepare nanohybrid films with colorless PI, which was synthesized from 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride and bis(trifluoromethyl) benzidine by in situ polymerization. The surface functionalization of graphite was characterized by powder XRD, TEM with energy dispersive X‐ray spectroscopy elemental mapping, X‐ray photoelectron spectroscopy, Raman spectroscopy, and TGA. The microstructure of the films was characterized by Fourier transform IR spectroscopy, XRD and SEM. The film properties were measured using a universal testing machine, TGA, dynamic mechanical analysis, four‐point probe, UV–visible spectroscopy and water contact angle analysis. EFG improved the tensile strength and modulus of the nanohybrid films by 20% and 50%, respectively. The glass transition temperature and electrical conductivity of the nanohybrid films were 12 °C and nine orders of magnitude higher than those of the neat PI film, respectively. The nanohybrid film maintained 80% optical transmittance even after the addition of 0.1 wt% EFG. © 2019 Society of Chemical Industry     

Effects of crosslinking agents on the physical properties of polyimide/amino‐functionalized graphene oxide hybrid films

The effects of crosslinking agents (crosslinkers) on polyimide (PI)/graphene oxide (GO) hybrid films were extensively investigated. The surface of GO was modified with amino groups using 4‐aminobenzylamine to improve compatibility with pyromellitic dianhydride/4,4′‐oxydianiline PI, and two kinds of crosslinkers were used: tris(4‐aminophenyl)amine and 1,3,5‐triazine‐2,4,6‐triamine (melamine). The mechanical, thermal and optical properties of the PI hybrid films were investigated. In particular, the transparency and physical properties of the PI hybrid films containing amino‐functionalized GO with homogeneous dispersion were improved. As the content of the crosslinker increased, a crosslinking network was formed between the PI chains, and the stiffness of the hybrid films was increased. The glass transition temperature, heat resistance and mechanical properties were also enhanced. The PI hybrids prepared with a rigid crosslinker exhibited higher optical transparency due to the reduction of the intermolecular charge transfer interactions with increasing interchain spacing between the PI chains. © 2018 Society of Chemical Industry     

Transparent polyimide nanocomposites with improved moisture barrier using graphene

A facile technique was developed to improve the water barrier properties of transparent polyimide (PI) films. Transparent and organo‐soluble PI films were synthesized from an alicyclic tetracarboxylic dianhydride (bicyclo[2.2.2]oct‐7‐ene‐2,3,5,6‐tetracarboxylic dianhydride) and an aromatic diamine (3,4′‐oxydianiline) in a co‐solvent of dimethylacetamide (DMAc) and γ‐butyrolactone via a one‐step process. Thermally reduced graphene (RG) was then blended with the PI in DMAc solution to fabricate PI/RG nanocomposite films without the addition of coupling agent. With the incorporation of only 0.1 wt% highly exfoliated RG in the PI matrix, the resultant PI/RG‐0.1 nanocomposite exhibited a superior barrier to moisture and retained high transmittance in the visible light region. The surface of PI/RG was more hydrophobic than that of pure PI and simultaneously the water vapor transmission rate was significantly reduced to 13 g m^?2 day^?1 for the PI/RG‐0.1 nanocomposite compared to 181 g m^?2 day^?1 for pure PI. Notably, the PI/RG‐0.1 nanocomposite also exhibited favorable thermal stability with a lower coefficient of thermal expansion and a higher thermal degradation temperature compared to pure PI. The easy processing of PI solution and RG nanosheets, the good orientation of RG in PI and the excellent barrier and thermal properties of PI/RG make the transparent PI nanocomposite films potential substrate materials in flexible electronic applications .     

In situ preparation of transparent polyimide nanocomposite with a small load of graphene oxide

Polyimide (PI) nanocomposites with 4,4′‐bisphenol A dianhydride, 4,4′‐oxydiphthalic anhydride, and diaminodiphenyl methane (MDA) as comonomers and functionalized with graphene oxide (GO), were prepared by in situ polymerization. Only a small amount of GO (0.03–0.12 wt %) is added to improve the mechanical properties of PI and to avoid a substantial decrease of PI transparence. The nanocomposites are characterized by FTIR, X‐ray diffraction, thermogravimetric analysis, transmission electron microscope, tensile test, and UV‐vis spectroscopy. It is demonstrated that the PI/GO composite films possess transmittance of above 80% at wavelengths of 500–800 nm when the GO content is under 0.12 wt %, while the stress intensity and Young's modulus are improved by 29 and 25%, respectively. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Enhancement of physical properties of electroactive polyimide nanocomposites by addition of graphene nanosheets

Electroactive polyimide (EPI) nanocomposites with amino‐capped aniline trimer and 4′‐(4,4′‐isopropylidene‐diphenoxy)bis(phthalic anhydride) as monomers, and functionalized with carboxyl‐graphene nanosheets, were prepared by thermal imidization. The as‐prepared electroactive polyimide/graphene nanocomposite (EPGN) materials were then characterized by Fourier transform infrared spectroscopy and transmission electron microscopy. In situ monitoring of the redox behavior of the as‐prepared EPGN materials was performed by cyclic voltammetry studies. The effects of material composition on the mechanical, thermal, thermal transport, dielectric and molecular barrier properties of EPGN membranes were investigated by dynamic mechanical analysis, TGA, DSC, the transient plane source technique, LCR meter and gas permeability analyzer, respectively. It should be noted that all the properties of the EPGN membranes were found to improve substantially over those of non‐electroactive polyimide and EPI. For example, upon loading of 1 wt% graphene, EPGN membranes were found to have an increase of over 20%, 5%, 65% and 20% in mechanical strength, thermal stability, thermal conductivity and dielectric constant, respectively, and a reduction of over 20% in gas permeability. © 2013 Society of Chemical Industry     

Enhanced thermal conductivity and dimensional stability of flexible polyimide nanocomposite film by addition of functionalized graphene oxide

Polyimide (PI) nanocomposites with both enhanced thermal conductivity and dimensional stability were achieved by incorporating glycidyl methacrylate‐grafted graphene oxide (g‐GO) in the PI matrix. The PI/g‐GO nanocomposites exhibited linear enhancement in thermal conductivity when the amount of incorporated g‐GO was less than 10 wt%. With the addition of 10 wt% of g‐GO to PI (PI/g‐GO‐10), the thermal conductivity increased to 0.81 W m^?1 K^?1 compared to 0.13 W m^?1 K^?1 for pure PI. Moreover, the PI/g‐GO‐10 composite exhibited a low coefficient of thermal expansion (CTE) of 29 ppm °C^?1. The values of CTE and thermal conductivity continuously decreased and increased, respectively, as the g‐GO content increased to 20 wt%. Combined with excellent thermal stability and high mechanical strength, the highly thermally conducting PI/g‐GO‐10 nanocomposite is a potential substrate material for modern flexible printed circuits requiring efficient heat transfer capability.     

Preparation of electrospun nanofibers of carbon nanotube/polycaprolactone nanocomposite

Multiwalled carbon nanotube/polycaprolactone nanocomposites (MWNT/PCL) were prepared by in situ polymerization, whereby functionalized MWNTs (F-MWNTs) and unfunctionalized MWNTs (P-MWNTs) were used as reinforcing materials. The F-MWNTs were functionalized by Friedel-Crafts acylation, which introduced the aromatic amine (COC₆H₄-NH₂) groups on the side wall. The F-MWNTs were chemically bonded with the PCL chains in the F-MWNT/PCL, as indicated by the appearance of the amide II group in the FT-IR spectrum. The TGA thermograms showed that the F-MWNT/PCL had better thermal stability than PCL and P-MWNT/PCL. The PCL and the nanocomposite nanofibers were prepared by an electrospinning technique. The nanocomposites that contain more than 2 wt% of MWNTs were not able to be electrospun. The bead of the F-MWNT/PCL nanofiber was formed less than that of the P-MWNT/PCL. The nanocomposite nanofibers showed a relatively broader diameter than the pure PCL nanofibers. The MWNTs were embedded within the nanofibers and were well oriented along the axes of the electrospun nanofibers, as confirmed by transmission electron microscopy.     

Intercalated structure of polypropylene/in situ polymerization-modified talc composites via melt compounding

Talc was modified with methyl methacrylate (MMA) or butyl acrylate (BA) via in situ polymerization. The talc/isotactic polypropylene (PP) composites with nano-sized intercalated structure were formed by melt compounding of PP with the modified talc. The results showed that the talc layers were partially delaminated, aligned along the flow direction, and uniformly dispersed in the PP matrix. The thickness of the PMMA-modified talc layers in the PP matrix was in the range 80-240 nm, while the PBA-modified talc was even thinner. PMMA or PBA macromolecules attached on the surface of talc layers hindered the crystallization of the PP component. Moreover, the aligned pristine talc layers promoted the orientation of the PP crystals. However, the extent of PP crystal orientation decreased in the presence of PMMA or PBA-modified talc.     

Accelerating the graphitization process of polyimide by addition of graphene

In this article, a composite film from polyimide and thermally exfoliated graphene was prepared through in situ polymerization, and the weight percent of thermally exfoliated graphene with respect to the polyimide monomers was 5 wt %. The film was carbonized at 1000°C for 1 h and then heat‐treated at various temperatures up to 2100°C. For comparison, the corresponding pure polyimide film was also prepared and heat‐treated at the same condition. It was found that the addition of graphene could effectively prevent the polyimide film from shrinking in the direction parallel to the film surface during the heat treatment. Furthermore, the results of density, X‐ray diffraction, shrinkage in the direction perpendicular to the film surface and scanning electron microscopy revealed that the graphitization process of the polyimide could be accelerated by addition of graphene obviously. In view of the above phenomena, a reasonable explanation was presented. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41274.     

Preparation and electrochemical properties of polyaniline doped with benzenesulfonic functionalized multi-walled carbon nanotubes

Nanocomposite of benzenesulfonic functionalized multi-walled carbon nanotubes doped polyaniline (PANi/f-MWCNTs) was synthesized via a low-temperature in situ polymerization method. The PANi/f-MWCNTs composite has a thin film of PANi coating uniformly on the surface of the f-MWCNTs. The electrochemical results show that PANi/f-MWCNTs nanocomposite possesses good rate response, which could ascribe to the uniform structure and the better conductivity of composite as well as the in situ doping/de-doping process between the benzenesulfonic acid groups of f-MWCNTs and PANi chain. In addition, the composite also has better capacity and cyclability than PANi/p-MWCNTs composite. It could attribute to the presence of f-MWCNTs, which makes more electrolyte contact with PANi to participate in faradaic redox reactions and dopes with the PANi polymer chain through the benzenesulfonic acid groups to form stable polyemeraldine salts.     

Evaluation of a redox-initiated in situ hydrogel as vitreous substitute

Currently there is no material clinically available as a long-term vitreous substitute. In this study, an in-situ gelation system based on α-poly(ethylene glycol) methacrylate (α-PEG-MA) and a redox-initiated radical polymerization/crosslinking reaction was evaluated for this purpose. Ammonium persulfate (APS) and N,N,N′,N′-tetramethyl ethylene diamine (TMEDA) were used as initiators. The gelation time, rheological properties, reaction kinetics and swelling profiles were studied in detail and the system with 10 wt% of α-PEG-MA and 8 mM APS/TMEDA was chosen as the optimal material for in vivo studies. Using the rabbit as the animal model, we showed that the system did form a space-filling and transparent gel in the vitreous cavity, and the inflammation response could be controlled to an acceptable level.     

Comparison of In Situ Polymerization and Solution-Dispersion Techniques in the Preparation of Polyimide/Montmorillonite (MMT) Nanocomposites

In this paper, Polyimide/Montmorillonite Nanocomposites (PI/MMT NCs), based on aromatic diamine (4-Aminophenyl sulfone) (APS) and aromatic dianhydride (3,3',4,4'-benzophenonetetracarboxylic dianhydride) (BTDA) were prepared using in situ polymerization and solution-dispersion techniques. The prepared PI/MMT NCs films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). The XRD results showed that at the content of 1.0 wt % Organo Montmorillonite (OMMT) for two techniques and 3.0 wt % OMMT for the in situ polymerization technique, the OMMT was well-intercalated, exfoliated and dispersed into polyimide matrix. The OMMT agglomerated when its amount exceeded 10 wt % and 3.0 wt % for solution-dispersion and in situ polymerization techniques respectively. These results were confirmed by the TEM images of the prepared PI/MMT NCs. The TGA thermograms indicated that thermal stability of prepared PI/MMT NCs were increased with the increase of loading that, the effect is higher for the samples prepared by in situ polymerization technique.     

Preparation of functionalized graphene sheets by a low-temperature thermal exfoliation approach and their electrochemical supercapacitive behaviors

Two kinds of functionalized graphene sheets were produced by thermal exfoliation of graphite oxide. The first kind of functionalized graphene sheets was obtained by thermal exfoliation of graphite oxide at low temperature in air. The second kind was prepared by carbonization of the first kind of functionalized graphene sheets at higher temperature in N₂. Scanning electron microscopy images show that both two kinds of samples possess nanoporous structures. The results of N₂ adsorption-desorption analysis indicate that both of two kinds of samples have high BET surface areas. Moreover, the second kind of functionalized graphene sheets has a relatively higher BET surface area. The results of electrochemical tests is as follows: the specific capacitance values of the first kind of functionalized graphene sheets in aqueous KOH electrolyte are about 230 F g⁻¹; the specific capacitance values of the second kind of functionalized graphene sheets with higher BET surface areas are only about 100 F g⁻¹; however, compared with the first kind of functionalized graphene sheets, the second kind has a higher capacitance retention at large current density because of its good conductive behaviors; furthermore, in non-aqueous EC/DEC electrolyte, the specific capacitance values of the first kind sample and the second kind sample are about 73 F g⁻¹ and 36 F g⁻¹, respectively.     

High ionic transfer of a hyperbranched-network gel copolymer electrolyte for potential electric vehicle (EV) application

Hyperbranched network-based gel copolymer electrolytes are synthesized by in situ free radical polymerization. This research is separated into two parts: the first is an investigation of modified bismaleimide oligomer (MBMI) as a free volume additive, and the second investigates the salt concentration effect on high power application. A polymer electrolyte with MBMI additive provided more free volume space, and the ionic conductivity of gel copolymer electrolytes was measured as a function of the salt concentration of lithium hexafluorophosphate (LiPF₆). The highest ionic conductivity and the lowest activation energy of hyperbranched-network gel copolymer electrolytes were determined to be 7.72 × 10⁻³ S/cm at 23 °C and 5.41 kJ/mol, respectively. Furthermore, the MBMI additive and the optimal concentration of lithium salt increased the free space for carrier ions and contributed to increasing capacity and working voltage at a high rate discharge (8C). The reliability and cycling ability of lithium polymer batteries are as good as lithium ion batteries for potential electric vehicle (EV) application.     

Surface-catalyzed growth of poly(2-methoxyaniline) on gold

We report on catalytic growth of poly(2-methoxyaniline) on gold surface by in situ polymerization. The mechanism of catalysis and products of monomer oxidation are elucidated on the basis of complementary investigations including Raman and UV-Vis spectroscopy, surface plasmon resonance, electrospray ionization mass spectrometry, gel permeation chromatography as well as electrochemical and microscopic techniques.It was shown that chemical oxidation of 2-methoxyaniline in acidic medium results in formation of a linear trimer which is the only stable product yielded in the bulk of the solution. However, introduction of a gold substrate into the reaction mixture induces polymerization of monomers/oligomers and formation of a thin polymeric film on the surface. This catalytic activity of gold is associated with adsorption of trimeric species onto the metal. The oligomers, being in fully oxidized (quinoid) form in the solution, are reduced to radical cations after adsorption onto the gold substrate. Since the radical cations are significantly more reactive than fully oxidized species, the polymerization proceeds on the surface, while it is inhibited in the solution.     

The effect of synthesis procedure on the structure and properties of palladium/polycarbonate nanocomposites

In this paper, we compare two procedures for the synthesis of palladium (Pd)/polycarbonate (PC) nanocomposites as well as their morphological, optical, thermal and electrical properties. Pd nanoclusters were produced by the reduction of palladium chloride using a variation of Brust's method. Discrete Pd nanoclusters of ∼15 nm size were formed in the absence of PC in the reaction mixture (ex situ method) while agglomeration of Pd nanoclusters was noticed in the presence of PC in the reaction mixture (in situ method). Fourier transform infrared spectroscopy (FTIR) suggests nanoparticle-polymer interactions and polymer conformational changes in the in situ nanocomposite films. Even after having the same Pd content, the ex situ nanocomposites films were found to transmit more light than the in situ nanocomposites. The glass transition temperature (T_g), decreased by ∼16 °C for both the ex situ and in situ samples. Thermogravimetric analysis (TGA) indicated that the presence of Pd nanoclusters significantly improved the thermal stability of the nanocomposites, as evidenced by the enhanced onset of degradation by ∼20 °C and ∼40 °C for the in situ and ex situ nanocomposites, respectively. The electrical conductivity measurement shows a dramatic difference between these nanocomposites with a significantly higher value for the in situ nanocomposite (resistivity = 2.1 × 10⁵ Ωm) compared to the ex situ nanocomposite (resistivity = 7.2 × 10¹³ Ωm).