Mechanically Strong and Multifunctional Polyimide Nanocomposites Using Amimophenyl Functionalized Graphene Nanosheets

We report an effective way to fabricate mechanically strong and multifunctional polyimide (PI) nanocomposites using aminophenyl functionalized graphene nanosheet (APGNS). APGNS was successfully obtained through a diazonium salt reaction. PI composites with different loading of APGNS were prepared by <i>in situ</i> polymerization. Both the mechanical and electrical properties of the APGNS/PI composites were significantly improved compared with those of pure PI due to the homogeneous dispersion of APGNS and the strong interfacial covalent bonds between APGNS and the PI matrix. The electrical conductivity of APGNS/PI (3:97 w/w) was 6.6 × 10^–2 S/m which was about 10¹¹ times higher than that of pure PI. Furthermore, the modulus of APGNS/PI was increased up to 16.5 GPa, which is approximately a 610% enhancement compared to that of pure PI, and tensile strength was increased from 75 to 138 MPa. The water vapor transmission rate of APGNS/PI composites (3:97 w/w) was reduced by about 74% compared to that of pure PI

Thiophene and Selenophene Donor–Acceptor Polyimides as Polymer Electrets for Nonvolatile Transistor Memory Devices

We report the nonvolatile memory characteristics of n-type <i><i>N,N</i></i>′-bis­(2-phenylethyl)­perylene-3,4:9,10-tetracarboxylic diimide (BPE-PTCDI) based organic field-effect transistors (OFET) using the polyimide electrets of poly­[2,5-bis­(4-aminophenylenesulfanyl)­selenophene–hexafluoroisopropylidenediphthalimide] (PI­(APSP-6FDA)), poly­[2,5-bis­(4-aminophenylenesulfanyl)­thiophene–hexafluoroisopropylidenediphthalimide] (PI­(APST-6FDA)), and poly­(4,4′-oxidianiline-4,4′-hexafluoroisopropylidenediphthalic anhydride) (PI­(ODA-6FDA)). Among those polymer electrets, the OFET memory device based on PI­(APSP-6FDA) with a strong electron-rich selenophene moiety exhibited the highest field-effect mobility and I_on/I_off current ratio of 10⁵ due to the formation of the large grain size of the BPE-PTCDI film. Furthermore, the device with PI­(APSP-6FDA) exhibited the largest memory window of 63 V because the highest HOMO energy level and largest electric filed facilitated the charges transferring from BPE-PTCDI and trapping in the PI electret. Moreover, the charge transfer from BPE-PTCDI to the PI­(APSP-6FDA) or PI­(APST-6FDA) electrets was more efficient than that of PI­(ODA-6FDA) due to the electron-donating heterocyclic ring. The nanowire device with PI­(APSP-6FDA) showed a relatively larger memory window of 82 V, compared to the thin film device. The present study suggested that the donor–acceptor polyimide electrets could enhance the capabilities for transferring and store the charges and have potential applications for advanced OFET memory devices

Grafting of Polyimide onto Chemically-Functionalized Graphene Nanosheets for Mechanically-Strong Barrier Membranes

A series of polyimide (PI) nanocomposite films with different loadings of aminophenyl functionalized graphene nanosheets (AP-rGO) was fabricated by in situ polymerization. AP-rGO, a multifunctional carbon nanofiller that can induce covalent bonding between graphene nanosheets and the PI matrix, was obtained through the combination of chemical reduction and surface modification. In addition, phenyl functionalized graphene nanosheets (P-rGO) were prepared by phenylhydrazine for reference nanocomposite films. Because of homogeneous dispersion of AP-rGO and the strong interfacial interaction between AP-rGO and the PI matrix, the resulting nanocomposite films that contained AP-rGO exhibited reinforcement effects of mechanical properties and oxygen barrier properties that were even better than those of pure PI and the reference nanocomposite films. In comparison to the tensile strength and tensile modules of pure PI, the composite films that contained AP-rGO with 3 wt % loading were increased by about 106% (262 MPa) and 52% (9.4 GPa), respectively. Furthermore, the oxygen permeabilities of the composites with 5 wt % filler content were significantly decreased, i.e., they were more than 99% less than the oxygen permeability of pure PI

Chemical Method for Improving Both the Electrical Conductivity and Mechanical Properties of Carbon Nanotube Yarn via Intramolecular Cross-Dehydrogenative Coupling

Chemical post-treatment of the carbon nanotube fiber (CNTF) was carried out via intramolecular cross-dehydrogenative coupling (ICDC) with FeCl₃ at room temperature. The Raman intensity ratio of the G band to the D band (<i>I</i>_G/<i>I</i>_D ratio) of CNT fiber increased from 2.3 to 4.6 after ICDC reaction. From the XPS measurements, the <i>A</i>_CC/<i>A</i>_C–C ratio of the CNT fiber increased from 3.6 to 4.8. It is of keen interest that both the electrical conductivity and tensile strength of CNT yarn improved to 3.5 × 10³ S/cm and 420 MPa, which is 180 and 200% higher than that of neat CNT yarn

Additive-Free Hollow-Structured Co₃O₄ Nanoparticle Li-Ion Battery: The Origins of Irreversible Capacity Loss

Origins of the irreversible capacity loss were addressed through probing changes in the electronic and structural properties of hollow-structured Co₃O₄ nanoparticles (NPs) during lithiation and delithiation using electrochemical Co₃O₄ transistor devices that function as a Co₃O₄ Li-ion battery. Additive-free Co₃O₄ NPs were assembled into a Li-ion battery, allowing us to isolate and explore the effects of the Co and Li₂O formation/decomposition conversion reactions on the electrical and structural degradation within Co₃O₄ NP films. NP films ranging between a single monolayer and multilayered film hundreds of nanometers thick prepared with blade-coating and electrophoretic deposition methods, respectively, were embedded in the transistor devices for <i>in situ</i> conduction measurements as a function of battery cycles. During battery operation, the electronic and structural properties of Co₃O₄ NP films in the bulk, Co₃O₄/electrolyte, and Co₃O₄/current collector interfaces were spatially mapped to address the origin of the initial irreversible capacity loss from the first lithiation process. Further, change in carrier injection/extraction between the current collector and the Co₃O₄ NPs was explored using a modified electrochemical transistor device with multiple voltage probes along the electrical channel