Yuhui Ao

Improvement of the thermal conductivity and friction performance of poly(ether ether ketone)/carbon fiber laminates by addition of graphene

Poly(ether ether ketone)/graphene/carbon fiber (PEEK/GE/CF) laminates with different weight percentages of GE were manufactured successfully through ball milling and hot-press processing. The effect of the GE on the morphology, thermal conductivity, friction performance, thermal and mechanical properties of composites was investigated. Scanning electron microscopy showed that the GE was uniformly distributed in matrix-rich regions. Thermal conductivity measurements demonstrated that addition of 0.7 wt% GE sharply improved the thermal conductivity of the laminates. Tribological tests revealed that the friction coefficient and wear rate rapidly decreased with the addition of GE. In the studied range, the friction reduction and wear resistance performance of PEEK/CF composites filled with 0.7 wt% GE is the most effective. Meanwhile, the obtained PEEK/GE/CF laminates also possessed excellent mechanical and thermal properties. Thus, graphene-reinforced PEEK/CF composites possessed better overall properties than conventional PEEK/CF composites.

Improving the interfacial properties of carbon fibers/vinyl ester composites by vinyl functionalization on the carbon fiber surface

A novel “coupling agent” N-(4-amino-phenyl)-2-methyl-acrylamide (APMA) was synthesized to efficiently enhance interfacial interactions between the carbon fiber (CFs) and vinyl ester resin (VE). Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) were employed to characterize functional groups and chemical compositions of a carbon fiber surface, which indicated that the vinyl groups of APMA were grafted successfully on the surface of the CFs. Four different treatments of CFs (pristine CFs, carboxylic-CFs, acrylamide-CFs and APMA-CFs) were used to prepare the CF-reinforced VE composites. The mechanical properties were analysed and a micro-droplet test was performed to investigate the enhancement effect of the coupling agent on the interfacial strength of the composites. Scanning electron microscopy (SEM) showed that APMA-CFs were uniformly distributed throughout the matrix, and no open ring holes were found at the cross-section of the composites; furthermore, after micro-droplet test, some matrix was still attached to the debonded CF surface. As a result, APMA functionalized CFs improved the flexural strength of the APMA-CF/VE composites by 19.4%, and significantly improved the interfacial shear strength between APMA-CFs and VE by 90.53%.

Molecular engineering of organic chromophores and polymers for enhanced bulk second-order optical nonlinearity

Second-order nonlinear optical (NLO) materials have been investigated for decades driven by the application requirements of electro-optic modulators for optical communication, optical switches, sensors, terahertz generation and detection. The prominent advantages of organic NLO materials are ultra-fast response and structural versatility, which gives the materials large NLO activity, good processability and other necessary properties for specific applications via suitable molecular engineering. In this review, historic and recent studies of organic dipolar chromophores in acentric alignment affording macroscopic anisotropy are overviewed. In particular, recent marked progress in the development of acentric bulky materials, including isolating chromophores to prevent centrosymmetric alignment, is focused on. We also review fascinating methods for the ordered alignment of chromophores, which include supramolecular interaction, light fields, electric fields and so on. It is hoped that better chromophore molecular structures and film construction techniques can be devised using suitable NLO films to achieve higher performances in optoelectronic devices.

Crosslinking network structure effects on particle coagulation in the emulsion polymerization of styrene in methanol solution

This work is an extension of previous research results reported by our team (Colloid Polym Sci 292:519–525; 1347–1353), where how to control particle size distribution by adjusting particle coagulation has been investigated. There is limitation in previous studies, that is, the particles taking part in coagulation only possess a linear structure. However, the crosslinking network structure is necessary to many fields, such as rubber and plastic modifier. Thus, it is very significant to investigate the effect of the crosslinking network structure on particle coagulation for understanding the nature of particle coagulation and controlling particle size distribution. In this manuscript, dihydrodicyclopentadienyl acrylate (DCPA) is chosen as a crosslinker to copolymerize with styrene to promote particle structure shift from the linear to the crosslinking network structure and to investigate further the coagulation behavior of the particles with the crosslinking network structure. Experimental results are explained by the collision frequency of particles and stability dependence of the particle structure.

Enhanced tribological performance of PEEK/SCF/PTFE hybrid composites by graphene

Polyetheretherketone (PEEK)/short carbon fiber (SCF)/polytetrafluoroethylene (PTFE)/graphene (GE) composites (PSPGE) with different weight fractions of GE were prepared successfully. The effect of GE on the tribological behavior of PEEK composites was investigated under different applied pressures, sliding speeds and temperatures. Characterization results revealed that the tribological performance was improved with the increase of GE loading, and 2.0 wt% GE filled PEEK/SCF/PTFE composites had the lowest friction coefficient and wear rate. The PSPGE exhibited excellent lubrication and wear resistance efficiency especially under harsh conditions. Moreover, the improved thermal conductivity of the PSPGE composites allowed friction heat to be transferred and further increased the wear resistance. Thus, this newly developed novel PSP2.0GE composite could be applied to many new fields as an advanced friction material.

Improvement of interfacial strength and thermal stability of carbon fiber composites by directly grafting unique particles: functionalized mesoporous silicas

A facile process was used to introduce vinyl functionalized mesoporous silicas onto a carbon fiber to improve the interfacial strength of composites. The characterization of successfully grafted vinyl groups on mesoporous silicas was determined by Fourier transform infrared (FTIR) and X-ray diffraction (XRD). The morphology of the vinyl functionalized mesoporous silicas uniformly distributed on the surface of carbon fiber was characterized by scanning electron microscopy (SEM), which indicated that the homogeneous dispersion of vinyl functionalized mesoporous silicas on a fiber may benefit the interfacial adhesion of matrix. Interfacial shear strength and thermal stability of the composites were improved by increasing the vinyl functionalized mesoporous silicas. This effect arose from the fact that functionalized mesoporous silicas serve as a “rivet joint” produced from chemical bonding and physical interlocking among the mesoporous silicas, carbon fiber and matrix. Notably, introduction of functional mesoporous silicas may be applied for fabricating high performance, multifunctional carbon fiber composites.

Facile synthesis of benzothiadiazole-based chromophores for enhanced performance of second-order nonlinear optical materials

Novel benzothiadiazole-based second-order nonlinear optical (NLO) chromophores with different push–pull structures were developed. Incorporation of benzothiadiazole (BTD) as a bridge for improving the electro-optic (EO) coefficient (r33) of bulky materials has not been well investigated, despite its extensive application in other photonic materials as electron acceptor. NMR and MS have been used to characterize the structure of synthesized chromophores 5–7. Optical properties have been investigated by UV-vis spectra. Density functional theory calculations have been used to calculate the first-order hyperpolarizability (β) of chromophores r1, 5a, 7a and 5b. Moreover, the poling results of guest–host EO polymers, 5a/PC and 5b/PC, afforded good r33 values of 67 pm V−1 and 45 pm V−1, respectively. All the results demonstrated an improvement in both micro- and macroscopic nonlinearity after incorporation of BTD into chromophores.

Preparation of carbon nanotube/copper/carbon fiber hierarchical composites by electrophoretic deposition for enhanced thermal conductivity and interfacial properties

A facile electrophoretic deposition method was proposed to deposit copper (Cu) and carbon nanotubes (CNTs) on the surface of carbon fiber (CF) to improve the thermal conductivity and interfacial properties of carbon fiber-reinforced polymer (CFRP) composites. Surface morphologies, crystallographic properties, thermal conductivity, interlaminar shear strength (ILSS) and element distribution of the composites were characterized by scanning electron microscopy (SEM), X-ray diffraction, thermal constant analysis, short-beam bending tests and SEM energy-dispersive X-ray diffractometer (SEM–EDX), respectively. The results indicate that the presence of Cu and CNTs generated networks and bridges with each other, which produced continuous heat conduction pathways and significantly enhanced both the specific surface area and roughness of the fiber surface. These pathways obviously promoted an improvement in the thermal and interfacial properties. The thermal conductivity and ILSS of the CNTs–Cu–CF/epoxy composites increased by 292 and 39.5%, respectively, compared with CF/epoxy composites. Therefore, this method is anticipated to be utilized in the future fabrication of multifunctional CFRP composites.

Tribological performance and thermal conductivity of graphene–Fe3O4/poly(phenol-formaldehyde resin) hybrid reinforced carbon fiber composites

Poly(phenol-formaldehyde resin)/carbon fiber composites with different ratios of graphene–Fe3O4 were manufactured through a molding press process. Fe3O4 was introduced into the graphene to avoid recombination of the layers. The effects of the amount of added graphene–Fe3O4 on the morphology, thermal conductivity, friction performance and thermal properties of the composites were investigated via scanning electron microscopy, thermal constants analysis, tribology and thermogravimetric tests. Scanning electron microscopy confirmed the enhanced friction surface of the composites and the combination of the resin with the fibers. The thermal conductivity measurements showed that the best results were achieved with 2.0 wt% graphene–Fe3O4. The friction coefficient and wear rate also decreased with the addition of graphene–Fe3O4 based on the tribological results.

Two new molybdates based on ∞[MonO3n+1]2− units (n = 11, 4) with proton conduction under ionothermal

Two new hybrid organic–inorganic molybdates have been synthesized under ionothermal conditions, namely (H4C3N2(C6H4N)2N2C3H4)2/∞[Mo11O34]·H2O (1), and (H6C5N(CH2)3NC5H6)1/∞[Mo4O13] (2), which were based on layered and chained ∞[MonO3n+1]2− (n = 11, 4) blocks and two different sizes of organoammonium dications bis-(4-imidazol-1-yl-phenyl)-diazene and 1,3-di-(4-pyridyl)-propane (+HL1H+ and +HL2H+), respectively. The 2/∞[Mo11O34]2− and 1/∞[Mo4O13]2− units in 1 and 2 are unprecedented members of the ∞[MonO3n+1]2− family with the new n value extended to 11 and 4, whose structure is similar with the ∞[MoO3] slabs in α-MoO3. Single crystal X-ray analysis shows that the ∞[MonO3n+1]2− layers and chains in 1 and 2 are pillared in the three-dimensional (3D) networks by the organic dications, while the two connections at the organic–inorganic interface are similar. At the same time, the different ∞[MonO3n+1]2− blocks (n = 11, 4) in hybrid organic–inorganic layered and chained molybdate materials are clearly evidenced by the efficient Raman spectroscopy. Moreover, the electrochemical impedance spectroscopy (EIS) measurements of 1 show a high conductivity (2.3 × 10−4 S cm−1 at 75 °C and 90% relative humidity), with an activation energy of 0.45 eV for proton conduction. The mechanism of proton conduction for this molybdate material is proved to be Vehicular mechanism.