Direction Of Fiber Axis Research Articles

Poly‐l‐Lactic Acid/Graphene Electrospun Composite Nanofibers for Wearable Sensors

Piezoelectric organic films as flexible and wearable pressure sensors are ideal materials for manufacturing of electronic skin. Poly‐l‐lactic acid (PLLA)/graphene composite nanofibers are fabricated by electrospinning. The relative crystallinity of the PLLA/graphene electrospun composite nanofibers increases from 9% to 30%. The d14 value of sample K0.1 (d14 = 9.02 pC N−1) increases by 2048% compared with sample K0 (d14 = 0.42 pC N−1). Piezoelectric bioelectronic skin is fabricated using the PLLA/graphene electrospun nanofiber mat, polyester fabric, and poly(dimethylsiloxane) (PDMS). The maximum open‐circuit voltage (Voc) and short‐circuit current (Isc) of the wearable sensors are 184.6 V and 10.8 μA. The response generated by touching the bioelectronic skin can be converted to a digital signal. The piezoelectric bioelectronic skin is used to monitor the pulse of the human body. Based on the results, a pulse of 76 beats min−1 is calculated, which coincides with the normal human heart rate interval (60–100 beats min−1). The addition of graphene influences the fiber diameters, thermal stability, relative crystallinity, and the piezoelectric properties along the fiber axial direction (d14) of PLLA. This small, flexible sensor, which can achieve high sensitivity, can be used for physiological and health care monitoring phonetic recognition.

Electromagnetic and thermal analysis of a multilayer CFRP panel struck by lightning with the FDTD method

The transient distribution of heat generated in a 16‐layer carbon fiber‐reinforced plastic (CFRP) panel, in which a lightning current with a magnitude of 3 kA, a rise time of 6.4 µs, and a time to half‐peak value of 69 µs is injected, has been computed. Each layer of the CFRP panel has a fiber axis direction of 45, 90, −45, or 0° and, therefore, has anisotropic electrical and thermal conductivities. This multilayer CFRP panel has been represented with a conductivity matrix consisting of off‐diagonal elements in the finite‐difference time domain (FDTD) simulation. The heat is computed, on the basis of FDTD‐computed conduction current densities, using a discretized heat equation. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Preparation of carboxylic graphene oxide-composited polypyrrole conduits and their effect on sciatic nerve repair under electrical stimulation.

Carboxylic graphene oxide-composited polypyrrole/poly-l-lactic acid (C-GO/PPy/PLLA) films were fabricated by electrochemical deposition of C-GO-composited PPy on PLLA fibers-film, and their conductivity and tensile strength (∼4.6 S/cm and 26.4 MPa, respectively) were stably remained after the immersion of 4 weeks, due to the hydrogen bond interaction between graphene oxide's carboxylic groups and pyrrole's imino groups. Their specific surface areas of ∼57.5 m2 /g and pore volume of ∼0.02 cm3 /g were significantly larger than those of PPy/PLLA films, due to the addition of C-GO nanosheets. Then, C-GO/PPy/PLLA conducting conduit with 2 mm inner diameter was prepared to bridge 10 mm sciatic nerve defect of rats, and the direction of fiber-axis in the conduit was the same as the conduit central axis. Electrical stimulation (ES) of 1 V and 20 Hz through the conducting conduit was exerted on the defect site. The results of in vivo electrophysiological and histological evaluation indicated that, the sciatic nerve defect could be repaired in C-GO/PPy/PLLA conduit, moreover the re-innervated gastrocnemius muscle and nerve conduction in C-GO/PPy/PLLA conduit & ES group were obviously better than the conduit without ES group. The results of transmission electron microscope analysis also demonstrated that the mean thickness of myelin sheath and diameter of axon in C-GO/PPy/PLLA conduit & ES group were significantly larger than those without ES, suggesting that the repair efficiency of ES & conduit group was closer to that of autograft group. These results indicated the great potential of C-GO/PPy/PLLA with the in vivo ES in the application of sciatic nerve repair.

Mechanically strong and electrically stable polypyrrole paper using high molecular weight sulfonated alkaline lignin as a dispersant and dopant

Flexible and conductive polypyrrole (PPy) paper shows the potential use in electromagnetic shielding, antistatic packaging, and electrochemical materials due to its low cost and facile manufacturing procedure. However, the poor mechanical strength and relatively low electrical stability of PPy paper is still challenging. In this study, we use horseradish peroxidase polymerized sulfonated alkaline lignin (HSAL) as a dispersant and dopant for PPy and demonstrate mechanically strong and electrically stable PPy paper by a combination of multiple impregnations and in-situ polymerization. The abundant sulfonic, carboxyl, and phenolic hydroxyl groups of HSAL could significantly improve the interfacial interaction between cellulose fibers and PPy. Meanwhile, its high molecular weight facilitated the uniform distribution of pyrrole along the fiber axial direction during in-situ polymerization. As a result, the resulting PPy paper exhibits enhanced mechanical properties and electrical stability, as well as high conductivity (24.84 S cm−1). More significantly, we investigated the influences of the dosage of HSAL and the cycles of multilayer impregnations on the electrical and mechanical properties of PPy paper. This work sheds light on the design and fabrication of flexible and conductive PPy paper with superior mechanical robustness and stable electrical performance.

Preparation and Properties of High-performance Polyimide Copolymer Fibers Derived from 5-Amino-2-(2-hydroxy-5-aminobenzene)-benzoxazole

A series of polyamic acid copolymers (co-PAAs) with para-hydroxyl groups was synthesized using two diamine monomers, namely p-phenylenediamine (p-PDA) and 5-amino-2-(2-hydroxy-5-aminobenzene)-benzoxazole (m-pHBOA), of different molar ratios through copolymerization with 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) in N,N-dimethyacetamine (DMAc). The co-PAA solutions were used to fabricate fibers by dry-jet wet spinning, and thermal imidization was conducted to obtain polyimide copolymer (co-PI) fibers. The effects of the m-pHBOA moiety on molecular packing and physical properties of the prepared fibers were investigated. Fourier transform infrared (FTIR) spectroscopic results confirmed that intra/intermolecular hydrogen bonds originated from the hydroxyl group and the nitrogen atom of the benzoxazole group and/or the hydroxyl group and the oxygen atom of the carbonyl group of cyclic imide. As-prepared PI fibers displayed homogenous and smooth surface and uniform diameter. The glass transition temperatures (Tgs) of PI fibers were within 311−337 °C. The polyimide fibers showed 5% weight loss temperature (T5%) at above 510 °C in air. Two-dimensional wide-angle X-ray diffraction (WXRD) patterns indicated that the homo-PI and co-PI fibers presented regularly arranged polymer chains along the fiber axial direction. The ordered molecular packing along the transversal direction was destroyed by introducing the m-pHBOA moiety. Moreover, the crystallinity and orientation factors increased with increasing draw ratio. Small-angle X-ray scattering (SAXS) results showed that it is beneficial to reduce defects in the fibers by increasing the draw ratio. The resultant PI fibers exhibited excellent mechanical properties with fracture strength and initial modulus of 2.48 and 89.73 GPa, respectively, when the molar ratio of p-PDA/m-pHBOA was 5/5 and the draw ratio was 3.0.

Numerical and Experimental Characterization of Radiation Mode of 45° Tilted Fiber Grating

In this paper, we have numerically and experimentally investigated the radiation mode of 45° tilted fiber grating (45° TFG). By introducing the axial distributions into the volume current method, we have established a three-dimensional theoretical model to analyze spatial distributions of the radiation mode of 45° TFG, and measured the radiation mode spatial distributions in experiment. Both numerical and experimental results show that the radiation mode of 45° TFG exhibits an exponential reduction along the fiber axial direction, and a quasi-Gaussian profile along the radial direction of fiber. Additionally, we have also measured the detailed polarization-dependent azimuthal intensity distributions of radiation modes of both s- and p-polarized core modes. The degree of polarization of radiation mode is around 99.886%, which is independent of the length and the polarization extinction ratio of the grating. Moreover, for the first time, we have experimentally observed a very weak p-polarized component existing in the radiation mode, which has matched well with the simulation results.

Non-axially aligned ZrB2-SiC/ZrB2-SiC-graphene short fibrous monolithic ceramics with isotropic in-plane properties

Although axially aligned fibrous monolithic ceramics have superior mechanical properties in ceramic fiber axial direction, the obvious anisotropy in physical and chemical properties of fibrous monolithic ceramics predetermine the significant on-axis and off-axis discrepancy. The existing ZrB2-based fibrous monolithic ceramics were all arranged by axially aligned ceramic fibers. Non-axially aligned ZrB2-SiC/ZrB2-SiC-graphene short fibrous monolithic ceramics with isotropic in-plane properties were fabricated by hot pressing of disorderly-arranged short ZrB2-SiC/ZrB2-SiC-graphene fibers to overcome in-plane anisotropy of the ZrB2-based fibrous monolithic ceramics. ZrB2-SiC/ZrB2-SiC-graphene short fibrous monolithic ceramics have remarkable increase in fracture toughness, critical crack size and work of fracture compared with ZrB2-SiC ceramics. The toughening mechanism of ZrB2-SiC/ZrB2-SiC-graphene short fibrous monolithic ceramics include macroscopic toughening of crack deflection, crack branching, interface friction and ZrB2-SiC cell extraction, and microscopic toughening of graphene bridging and pull-out.

High-performance polyimide copolymer fibers derived from 5-anino-2-(2-hydroxy-4-aminobenzene)-benzoxazole: Preparation, structure and properties

A series of high-performance polyimide copolymer (co-PI) fibers containing phenylenebenzoxazole moiety with one hydroxyl group are synthesized based on the copolymerization of 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA) with two diamine monomers, namely, p-phenylenediamine (p-PDA) and 5-anino-2-(2-hydroxy-4-aminobenzene)-benzoxazole (p-mHBOA), through a two-step method. The molar ratio of p-PDA/p-mHBOA varies from 10/0 to 0/10. Influences of the p-mHBOA moieties on the thermal stability, crystal structure, crystal orientation, microvoid morphology, and mechanical properties are systemically investigated. Fourier transform infrared results confirm that intra/inter molecular hydrogen bonds come from the OH group and nitrogen atom of the benzoxazole group and/or OH group and the oxygen atom of the carbonyl group of cyclic imide. The glass transition temperatures (Tgs) of co-PI fibers are in the range of 290 °C–325 °C. The prepared fibers show excellent thermal stabilities, and their T5% is within 528 °C–542 °C in air. Two-dimensional wide-angle X-ray diffraction spectra indicate that homo-PI and co-PI fibers present a regularly arranged polymer chains along the fiber axial direction. Moreover, the ordered molecular packing along the transversal direction of fibers is destroyed by the copolymerization. Small-angle X-ray scattering results show that co-PI fibers with optimal mechanical properties exhibit the shortest average length (L) and the smallest radius (R¯) of microvoids. When the p-mHBOA/p-PDA molar ratio is 5/5, the fracture strength and initial modulus can reach approximately 30.31 cN/dtex (4.40 GPa) and 894.88 cN/dtex (129.8 GPa), respectively. The relationship between structure and mechanical properties is also discussed.

Macro-polyolefin fiber pull-out behaviour from HPC matrix: evaluation of type of surface treatment

In this paper, the effect of different surface treatment of a smooth Polyolefin macro-fibre (macro-PO) on the pull-out behaviour from high performance cementitious (HPC) matrix is investigated. The macro-PO fibres were treated in the way that grooves provided in longitudinal and transverse directions on the surface. A latex surface treatment also used for macro-PO to evaluate frictional interaction between the fibre and matrix. The details of pull-out test results were compared with un-treated macro-PO to determine the effectiveness of different surface treatment on load-bearing capacity during pulling-out process. From the results of pull-out test it was found that treatment of fibres with mechanical modification in fibre axis direction can increase the bonding strength and the energy absorption capacity during pull-out.

Liquid surface tension and refractive index sensor based on a tilted fiber Bragg grating

A refractive index (RI) and liquid surface tension (ST) (at the level of 10−3 N) measurement system has been proposed by using a 1.80-cm-long, 8°-tilted fiber Bragg grating (TFBG). When the TFBG is pulled up from the liquid into the air at a fixed height (corresponding to a fixed contact angle between the fiber and the liquid), the ST acting upon the TFBG depends on the length of the TFBG covered with the liquid film along the fiber axis direction. The liquid film covering the grating results in the shifts of the resonant cladding modes of the TFBG. For the liquid with an RI in the range from 1.3341 to 1.4415, its RI and ST can be obtained through the measurements of shifts in the resonant wavelengths of the cutoff mode and changes in the intensities of the resonant wavelength dips in the TFBG spectrum by using the known ST and RI of water as a reference.

Optical spectral sweep comb liquid flow rate sensor.

In microfluidic chip applications, the flow rate plays an important role. Here we propose a simple liquid flow rate sensor by using a tilted fiber Bragg grating (TFBG) as the sensing element. As the water flows in the vicinity of the TFBG along the fiber axis direction, the TFBG's spectrum changes due to its contact with water. By comparing the time-swept spectra of the TFBG in water to that of the TFBG with water flowing over it, a spectral sweep comb was formed, and the flow rate can be detected by selecting a suitable sweeping frequency. The proposed sensor has a high Q-value of over 17,000 for the lower rate and a large detectable range from 0.0058mm/s to 3.2mm/s. And the calculated corresponding lower detectable flow rate of 0.03nL/s is 3 orders magnitude better than that of the current fiber flowmeter. Meanwhile, the proposed sensor has the temperature self-compensation function for the variation of the external temperature. We believe that this simple configuration will open a research direction of the TFBG-deriving theory and configuration for lower flow rate measurements for microfluidic chip applications.

Characterization of macromolecular orientation in κ-carrageenan fibers using polarized Fourier-transform infrared spectroscopy

In the current study, polarized infrared (IR) microspectroscopy was employed to characterize the macromolecular orientation in wet-spun and stretched κ-carrageenan fibers. The fibers were shown to be well oriented by X-ray diffraction, suggesting that the κ-carrageenan molecules were generally aligned along the fiber axis direction. Longitudinal fiber pieces of about 10 μm thick were obtained by focused ion beam (FIB) micromilling. The fiber pieces were examined by polarized IR in transmission mode. Several bands, including those characteristic of κ-carrageenan at 845 and 930 cm−1, were polarization-dependent, demonstrating polarized IR as a useful tool to evaluate macromolecular orientation in carrageenan fibers. Band assignments were discussed by considering the general alignment of molecules and the polarization dependence of vibration modes, and our results agreed well with band assignments from previous reports.

Observation of the Interface between Resin and Carbon Fiber by Scanning Transmission X-ray Microscopy

The sub-micron spatial distribution of chemical states of carbon fiber (CF) and the interface between CF and resin must affect physical properties of carbon-fiber-reinforced plastic (CFRP). In order to evaluate scanning transmission X-ray microscopy (STXM) techniques for application to the chemical-state analysis of CFRP, we performed STXM measurements near C K-edge energies. The results of the spectral deconvolution analysis suggest the presence of another phase at the interface of CF and resin, which may be a coating layer. In addition, the preferred orientation of the stuck of graphene sheets to the fiber axis direction of CF was observed by using linear polarized X-ray beams.

Dynamic Transverse Debonding of a Single Fiber

By integrating a Kolsky tension bar along with a high-speed x-ray phase contrast imaging method and a high speed optical camera, high strain rate debonding processes of an opaque composite composed of a single S-2 fiber and SC-15 epoxy resin is recorded in real time and analyzed. Specifically, imaging of transverse debonding initiation and progression along with debonding loads are obtained and then compared to quasi-static debonding loads in this research. The dynamic loading direction was perpendicular to the fiber axial direction. The dynamic tensile loading history as the debonding initiated and propagated was recorded using a piezoelectric load cell. The initial debonding crack speed was also measured. Quasi-static experiments were also completed as a basis of comparison. It is shown that the debonding loads under dynamic and quasi-static loading conditions are similar. The fracture surfaces from the dynamically debonded samples were subsequently examined by scanning electron microscopy.

FDTD Simulation of Lightning Current in a CFRP Panel: Comparison of the Use of Conductivity Matrix Approach With That of Triangular Prism Cells

The transient distribution of lightning current, which flows in a multilayer carbon-fiber-reinforced plastic (CFRP) material of aircraft, has been studied using the finite-difference time-domain (FDTD) method. Each layer of the multilayer CFRP panel has a fiber direction of 45°, 90°, –45° or 0°, and, therefore, has an anisotropic conductivity: the conductivity is high in the fiber axial direction and low in other directions. It is impossible to represent such an anisotropic layered panel using the FDTD method with common rectangular prism or cubic cells. In this letter, two approaches are employed: one is the application of conductivity matrix having off-diagonal elements and the other is the application of triangular-prism cells. The transient distribution of the magnetic field over the surface of the CFRP panel, computed with the former approach, is compared with that computed with the latter approach. Also, the results are compared with the corresponding measured ones.

Electrospinning in Situ Synthesis of Graphene-Doped Porous Copper Indium Disulfide/Carbon Composite Nanofibers for Highly Efficient Counter Electrode in Dye-Sensitized Solar Cells

Porous graphene-doped copper indium disulfide/carbon (p-GN@CuInS2/C) composite nanofibers were fabricated via electrospinning, in situ synthesis, and carbonization. A polyacrylonitrile (PAN) solution containing graphene oxide nanosheets, copper dichloride (CuCl2), indium trichloride (InCl3), and thiourea (Tu.) in a mixed solvent of N,N-dimethylformamide/trichloromethane (DMF/CF) was used as the precursor solution for electrospinning. The resulting porous GN@CuInS2/C nanofibers were 107±24nm in diameter, and graphene nanosheets anchored with chalcopyrite CuInS2 nanocrystals 7–12nm in diameter were overlapped and embedded in the carbon matrix, aligning along the fiber axial direction. The Brunauer–Emmett–Teller (BET) surface area of the p-GN@CuInS2/C composite nanofibers was 795m2/g, with a total pore volume of 0.71cm3/g. These values were significantly larger than those of the sample without graphene and CuInS2/C nanofibers. A dye-sensitized solar cell (DSSC) assembled using the p-GN@CuInS2/C nanofibers as the counter electrode (CE) delivered a photoelectric conversion efficiency of 7.23%, which was higher than the efficiencies of DSSCs assembled using the samples without graphene (6.48%) and with the CuInS2/C nanofibers (5.45%). It was also much higher than that of the DSSC with a Pt CE (6.34%). The excellent photoelectric performance of the p-GN@CuInS2/C CE was attributed to its special hierarchical porous structure, which facilitated permeation of the liquid electrolytes and provided additional active catalytic sites for the oxidation reaction of the electrolytic (I−/I3−). The doping of reduced graphene oxide (RGO) resulted in the well-dispersed growth of CuInS2 nanocrystals in the carbon nanofibers, which further increased the number of active catalytic sites and promoted electron and ion transfer.

Mineralization of Calcium Carbonate on Multifunctional Peptide Assembly Acting as Mineral Source Supplier and Template

Crystal phase and morphology of biominerals may be precisely regulated by controlled nucleation and selective crystal growth through biomineralization on organic templates such as a protein. We herein propose new control factors of selective crystal growth by the biomineralization process. In this study, a designed β-sheet Ac-VHVEVS-CONH2 peptide was used as a multifunctional template that acted as mineral source supplier and having crystal phase control ability of calcium carbonate (CaCO3) during a self-supplied mineralization. The peptides formed three-dimensional nanofiber networks composed of assembled bilayer β-sheets. The assembly hydrolyzed urea molecules to one carbonate anion and two ammonium cations owing to a charge relay effect between His and Ser residues under mild conditions. CaCO3 was selectively mineralized on the peptide assembly using the generated carbonate anions on the template. Morphology of the obtained CaCO3 was fiber-like structure, similar to that of the peptide template. The mineralized CaCO3 on the peptide template had aragonite phase. This implies that CaCO3 nuclei, generated using the carbonate anions produced by the hydrolysis of urea on the surface of the peptide assembly, preferentially grew into aragonite phase, the growth axis of which aligned parallel to the direction of the β-sheet fiber axis.

Experimental and numerical analyses on the thermal conductive behaviors of carbon fiber/epoxy plain woven composites

The thermal conductive behaviors of carbon fiber/epoxy plain woven composites along in-plane and out-of-plane (thickness) directions were reported in this paper. The thermal conductivities of the plain woven composites were tested with a self-designed thermal chamber under different temperatures. The multi-scale finite element analyses (FEA) were used to investigate the thermal conductive behaviors of plain woven composites. From the comparisons of the thermal conductive behaviors between the plain woven composites and unidirectional (UD) lamina, the effect of the plain woven preform structure on the thermal conduction was further explained. It was found that the thermal conductivity along fiber axial direction is greater than that along its radial direction, and the thermal conductivities of plain woven composites fall in between those of 0° UD lamina (upper bound) and those of 90° UD lamina (lower bound). The temperature distributions and heat flux transferring pathways are mainly along the yarns’ orientation directions. In addition, a simplified unit-cell model was developed to decompose the plain woven unit-cell into the combinations of several UD laminas. The experimental thermal conductivities showed a good agreement with those of FEA. The simplified unit-cell model manifests the feasibility for predicting the thermal conductivity of complex textile structure composites from the UD laminas.

Tensile and interfacial properties of polyacrylonitrile-based carbon fiber after different cryogenic treated condition

Abstract Polyacrylonitrile-based carbon fibers are cryogenically conditioned both through a low cooling rate and a quench rate to explore the effects of cryogenic treatments on properties and micro-structures of carbon fibers. The internal structure, tensile properties and surface morphologies of the fiber are investigated. Increase in crystallinity and tighter packing of molecules of the fiber after the cryogenic treatments are observed regardless the cooling rate. After slow cooling cryogenic treatment, the inter-planar distance increases in the fiber axial direction and decreases in the fiber radial direction, resulting in 3% shrinkage of fiber diameter and extension in fiber axial direction. Scanning electron microscopy and atomic force microscopy analysis show slightly wider and deeper rill-like folds and 41% roughness increase for the fiber surfaces, leading to an increase in interfacial shear strength between the fiber and epoxy by 30.2%. In contrast, after sharp cooling cryogenic treatment, no obvious change is detected in inter-planar distance, fiber diameter, surface morphology and interfacial shear strength with epoxy. The bimodal additive Weibull distributions of tensile strengths for the cryogenic treated fibers show an increase of the bimodality parameter α and a decrease in scale parameter σ indicating higher probability of extrinsic defects but no significant mechanical degradation of the fiber after cryogenic treatments.

Structure and electrochemistry comparison of electrospun porous carbon nanofibers for capacitive deionization

The porous carbon nanofibers, PCNFPMMA and PCNFPS with different pore configuration, were prepared by electrospinning polyacrylonitrile (PAN) blending with the sacrificial polymers polystyrene (PS) and polymethyl methacrylate (PMMA) respectively, followed by carbonization. The pore structure and pore size of the obtained PCNFs can be tuned conveniently by altering the composition and content of the additives in the precursor solution. With PS as additive, the obtained PCNFPS consists mainly of non-interconnecting nanochannels along the fiber axis direction, with the specific surface area of 52.2m2/g. While with PMMA as additive the obtained PCNFPMMA possessed interconnecting micro-mesoporous structure with the specific surface area of 393.4m2/g. By using the porous carbon fibers as self-supporting electrode materials, the electrochemical double layer capacitance (EDLC) and impedance behavior were comparatively studied by cyclic voltammetry (CV), chronopotentiometry and electrochemical impedance spectroscopy (EIS), respectively. The PCNFPMMA presents excellent EDLC characteristic and CDI desalination performance, owing to its interconnecting micro-mesoporous structure. But the non-interconnecting nanochannel configuration in PCNFPS is unfavorable for ionic transportation, resulting in a lower specific capacity and lower desalination capacitance. Under the optimal blend ratio of polymers, PCNFPMMA has a salt removal rate of 0.21mg/g/min, much higher than that on PCNFPS (0.09mg/g/min).