Fabrication of superhydrophobic electrospun polyimide nanofibers modified with polydopamine and polytetrafluoroethylene nanoparticles for oil–water separation

The oil–water separation technologies of removing oil pollutants from water in an efficient and economical way is a challenge. The current methods used for oil–water separation suffer many shortcomings, including a low separation efficiency, complex separation equipment, high operation costs, and secondary pollution. In this study, we fabricated a highly flexible, high-intensity, quite stable superhydrophobic and superoleophilic polyimide (PI) nanofibrous membranes, which are much more efficient and cost efficient for oil–water separation by modifying the membranes with a polydopamine (PDA) solution and polytetrafluoroethylene (PTFE) dispersion. The fabricated membrane (PDA–PTFE–PI) possesses both the high tensile stress of PI and the superhydrophobic and superlipophilic properties of the PDA–PTFE coating. The modified membrane could separate various oil–water mixtures efficiently at a high flux (6000 L·m⁻²·h⁻¹) and an extremely high efficiency (>99%). Furthermore, even when the membrane was under an extremely hostile environment (with an ultrahigh temperature, strong acidity, or strong basicity), it still remained quickly stable with a good separation efficiency and recyclability after 10 cycles. We anticipate that our study will provide a new technology for the highly efficient mass production of oil–water mixture management. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47638.     

Preparation and characterization of electrospun polyurethane–polypyrrole nanofibers and films

Polyurethane (PU)–polypyrrole (PPy) composite films and nanofibers were successfully prepared for the purpose of combining the properties of PU and PPy. Pyrrole (Py) monomer was polymerized and dispersed uniformly throughout the PU matrix by means of oxidative polymerization with cerium(IV) [ceric ammonium nitrate Ce(IV)] in dimethylformamide. Films and nanofibers were prepared with this solution. The effects of the PPy content on the thermal, mechanical, dielectric, and morphological properties of the composites were investigated with differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), Fourier transform infrared (FTIR)–attenuated total reflection (ATR) spectroscopy, dielectric spectrometry, and scanning electron microscopy. The Young's modulus and glass-transition temperatures of the composites exhibited an increasing trend with increases in the initially added amount of Py. The electrical conductivities of the composite films and nanofibers increased. The crystallinity of the composites were followed with DSC, the mechanical properties were followed with DMA, and the spectroscopic results were followed with FTIR–ATR spectroscopy. In the composite films, a new absorption band located at about 1650 cm⁻¹ appeared, and its intensity improved with the addition of Py. The studied composites show potential for promising applications in advanced electronic devices. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis of carbon–silica core–shell nanofibers from a dispersion of fluorinated carbon nanofibers in solvated polysiloxane

Carbon–silica core–shell fibers (which unusually consist of carbon nanofibers coated with silica) were synthesized using a two-step process. First, fluorination of carbon nanofibers (CNFs) allows their homogenous dispersion into a polysiloxane matrix. A longlife dispersion of nanofibers in solvated polysiloxane has been prepared. Second, the polysiloxane/fluorinated carbon was thermally treated in air until 700 °C. Defluorination and conversion of polysiloxane into silica occur and result in carbon–silica core–shell fibers. The thermal treatment of the polysiloxane/carbon and the resulting silica/carbon–silica core–shell nanostructures were investigated using solid state nuclear magnetic resonance using ¹⁹F, ¹³C ¹H, and ²⁹Si nuclei, X-ray diffraction, Raman spectroscopy, scanning and transmission electron microscopies.     

Preparation of PVDF/PVP core–shell nanofibers mats via homogeneous electrospinning

The polyvinylpyrrolidone (PVP)/poly(vinylidene fluoride) (PVDF) core–shell nanofiber mats with superhydrophobic surface have been prepared via electrospinning its homogeneous blending solutions, and the formation of the core–shell structure was achieved by the thermal induced phase separation assisted with the low surface tension of PVDF. The electrospinnability of the blending solutions was also investigated by varying the blending ratio of the PVP and PVDF, and it enhanced with the increase of PVP content. SEM and TEM results showed that the fibers size was varied in the range of 100 nm–600 nm with smooth surface and core–shell structure. The composition of the shell layer was determined by the XPS analysis, and further confirmed by water contact angle (WCA) testing. As the fraction of PVDF exceeding PVP in the electrospinning solutions, the nanofiber mats showed superhydrophobic property with the WCA above 120°. It indicated that the PVDF was concentrated in the shell layer of the fibers. X-Ray diffraction (XRD) and attenuated total reflection infrared spectroscopy (ATR-IR) analysis indicated that the PVDF was aggregated with the β-phase crystallite as dominant crystallite. The nanofiber mats with the gas breathability and watertightness ability due to the porous structure and superhydrophobic would be potential applied in wound healing.     

Structural evolution of β – iPP during uniaxial stretching studied by in–situ WAXS and SAXS

Polymorphism and crystal transition are of great significance for property mediation in polymer materials. Isotactic polypropylene (iPP) with β – crystal has been widely utilized for the preparation of high performance plastics or films. In the present work, the structural evolution of initially isotropic β – nucleated iPP (β – iPP) during uniaxial stretching at different temperatures was investigated by in–situ X – ray scattering using synchrotron radiation. The wide – angle X – ray scattering (WAXS) results confirmed that the β – crystal transformed either to the mesophase at lower temperature (30 °C) or to the α – crystal at higher temperature (60, 100 and 120 °C) during stretching. An interesting orientation of β – crystal with molecular chains perpendicular to the tensile direction was identified. As revealed by small – angle X – ray scattering (SAXS), cavitation took place in β – iPP stretched at temperatures lower than 120 °C. The size and shape of the cavities were observed by scanning electron microscope. A deformation mechanism of β – iPP combining the crystal transition, cavitation and orientation was proposed.     

Photocatalytic degradation of Rhodamine B dye using ZnO–SnO2 electrospun ceramic nanofibers

ZnO–SnO₂ nanofibers were fabricated by the electrospinning technique combined with calcination at 600 °C. Their structural and morphological properties were analyzed by X-ray diffraction and scanning/transmission electron microscopy, and their photocatalytic activity was investigated by the degradation of Rhodamine B (RhB) dye by visible light irradiation. UV–vis spectral data were used to estimate the photodegradation efficiency of the metal oxide nanocomposites. All the RhB dye samples were tested for six hours of degradation the highest efficiency being obtained for a molar ratio Sn/Zn of 0.030.     

Structural importance of Stone–Thrower–Wales defects in rolled and flat graphenes from surface-enhanced Raman scattering

We first survey the historical aspects of the term Stone–Thrower–Wales (STW) defect and its experimental identification. Physicochemical properties associated with the STW defect have been extensively investigated theoretically as well. However, it is difficult to verify the predicted properties by means of experiments. Here we demonstrate an experimental way to probe the vibrational properties of STW defects in single-wall carbon nanotubes (SWCNTs) using surface-enhanced Raman scattering (SERS). We also performed density functional theory calculations to support our interpretation of the SERS spectra. The characteristic fluctuations of peak intensities and frequencies are ascribed to dynamic motion of an STW defect in the hexagonal SWCNT lattice. The role of an STW defect at edges is also discussed in terms of its relevance to the stability and O₂ reactivity of flat and curved graphene structures.     

Structures and mechanical properties of electrospun cellulose nanofibers/poly(ε-caprolactone) composites

Poly(ε-caprolactone) (PCL) is one of the ecofriendly biodegradable polymers with excellent moldability but with rather low mechanical properties especially for the industrial and biomedical use. In this research, to overcome the problem, the two types of cellulose nanofibers, the cellulose acetate nanofibers (CA-NF) and the cellulose nanofibers (C-NF), were composited into PCL for the enhancement of the mechanical properties of PCL. CA-NF were prepared by electrospinning and converted into C-NF afterward by deacetylation. It was found that the Young's modulus of the CA-NF/PCL composite at the fiber concentration of 35 wt% significantly increased by ~3 times as compared with that of neat PCL, whereas C-NF/PCL of the same fiber concentration also increased by ~4.5 times. It was also found that the Young's moduli of CA-NF/PCL nearly reached the theoretical values calculated by the equation suggested by Tsai, but that the Young's moduli of C-NF/PCL could not reach the theoretical values. It indicates that CA-NF possessed better compatibility with PCL than C-NF, agreeing well with the fracture-surface analyses of the two composites by the scanning electron microscopy.     

Structural evolution of Fe–Y2O3–Ti powder during ball-milling and thermal treatment

Y₂O₃ dispersion is widely used in ceramics and steels strengthening. The improved performance results from very fine oxide particles being dispersed within the matrix by ball milling; however, during ball-milling and subsequent heat-treatment, the mechanism underpinning the evolution of Y₂O₃ and additive Ti remains uncertain. In this study ball-milling was performed on Fe+10% Y₂O₃+5%Ti powders for different times without adding a process control agent. Heat-treatment was then applied at 900 to 1200 °C. Then the powder after ball-milling and heat treatment was characterised, which showed that, with increased milling time, the average particle size increased while Fe and Y₂O₃ underwent an amorphous transition. After ball-milling for 30 h, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) both verified the generation of Y₂Ti₂O₇. In the subsequent heat-treatment, differential scanning calorimetry (DSC) showed that the amorphous Fe and Y₂O₃ had been transformed back to crystalline at 736.3 °C and 991.3 °C, respectively. With increased heating temperature, the Y₂O₃ content increased, while that of Y₂Ti₂O₇ remained stable throughout.     

Volumetric properties of polymer blends from Tao–Mason equation of state

The present study is an improvement of previous work (Yousefi and Karimi, Ionics 18:135–142, 17) concern to the assessment of the ability of the Tao–Mason equation of state to predict pressure–volume–temperature (PVT) of melting polymers. The present paper, focus on the modeling of volumetric properties of polymer blends based on melting temperature (T _m) and melting point density (ρ _m), as scaling constants. The calculation of second Virial coefficients (B ₂), effective van der Waals co-volume (b) and correction factor (α) are required for judgment about applicability of this model. The new correlations were used to predict the PVT behavior of polymer blends containing poly(propylene glycol) + poly(ethylene glycol) (PEG-200), poly(ethylene glycol) methyl ether(PEGME-350) + PEG-200, PEGME-350 + PEG-600, poly(2,6-dimethyl-1,4-phenylene oxide) + poly styrene(PS), and PS + poly(vinylmethylether) in different temperatures, pressures, and mole fractions. A collection of 5,397 data points has been examined for the aforementioned polymers in the temperature in the range of 298.15–605.05 K and pressures up to 200 MPa. The average absolute deviation between the calculated and experimental densities is of the order of 0.78 %.     

Self-assembly of silver–graphene hybrid on electrospun polyurethane nanofibers as flexible transparent conductive thin films

A method of integrating hybrid thin films of graphene nanosheets (GNSs) and silver nanoparticles (AgNps) by in situ chemical reduction to prepare transparent conductive films (TCFs) is studied. The surface functional groups of graphite oxide (GO) serve as nucleation sites of silver ions for adsorption of AgNps. To fabricate conductive films with high transmittance, polyurethane (PU) nanofibers are introduced to help construct two-dimensional conductive networks consisting of AgNps and GNSs (AgNps–GNSs). This method requires only a low percentage of conducting AgNps–GNSs covering the transparent substrate, thereby improving the transmittance. The flexible GNSs serve as nanoscale bridges between conductive AgNps and PU nanofibers, resulting in a highly flexible TCF. The optical transmittance can be further increased after melting the PU nanofibers at 100 °C. A fused film obtained after electrospinning (ES) a PU solution for 120 s and immersion in 0.05 wt.% AgNp–GNS (5:1) solution has a surface resistance of 150 Ω/sq and 85% light transmittance. Mechanical testing shows that AgNps–GNSs on flexible substrates yield excellent robustness. Thus, TCFs with a 3:1 ratio of AgNps:GNSs have high conductivity, good mechanical durability, and barely one order of magnitude increase of surface resistance when bent to an angle of 90°.     

Structural and textural evolution of nanocrystalline Mg–Al layered double hydroxides during mechanical treatment

Well-crystallized nanocrystalline Mg–Al layered double hydroxides (LDHs) were prepared by hydrothermal method and subjected to mechanical treatment to evaluate the structural and textural changes upon grinding. The powder samples were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field scanning electron microscopy (FESEM), and N₂ adsorption analysis. Grinding caused progressive reduction of crystallite size and structural degradation of the Mg–Al LDHs, resulting in a decrease in its crystallinity. The grinding products at various treatment times were mainly with micropores, resulting from the transformation of the original mesoporous structure, whereas the total pore volume of the milling samples gradually decreased with prolonged treatments. At shorter milling time (< 48 min), marked increases in surface area coupled with a severe reduction in crystallite size were observed. Delamination and fragmentation of the crystallites mainly occurred at this stage. At intermediate milling time (48 min to 72 min), the crystallite size approached a saturation value (ca.4.4 nm in the c axis direction), and the surface area reached a maximum value (about 117.0 m²g^− 1). Aggregations of the crystallites were clearly observed at this period. During the last milling stage (from 72 min to 240 min), heavy agglomeration contributed to the reduction in surface area, and the final grinding products were amorphous materials due to the complete destruction of the layer structure of the solids. The distribution, orientation, and aggregation degree of the Mg–Al LDH platelets during the mechanical process may be responsible for the textural evolution.     

Preparation and properties of core–shell silver/polyimide nanocomposites

A new series of core–shell structured silver/polyimide (PI) nanocomposites was prepared by in situ polymerization followed by the chemical imidization of poly(amic acid) (PAA, precursor of PI) at a low temperature. The TEM images showed that the silver cores of the nanocomposites were encapsulated with homogeneous shells with thickness of 4 and 8 nm at silver contents of 90 and 60 %, respectively. The shell thickness was controlled by varying the content of PAA. FTIR spectroscopic analysis indicated that the imide ring formation occurred after the chemical imidization. The Ag/PI nanocomposites showed excellent thermal stability and exhibited only 10 % weight loss at 300 °C in the air. Moreover, percolation was observed at silver weight fractions close to the critical value, and the maximum dielectric permittivity of the nanocomposites was 120, which is about 40 times higher than that of pristine PI.     

Bicomponent nanofibers from core–shell nozzle in gas jet spinning process

This work evaluates the use of a core–shell nozzle assembly in conjunction with gas jet spinning technique for production of bicomponent nanofibers from an immiscible polymer pair of polyvinylpyrrolidone (PVP) and poly(vinyl acetate) (PVAc) with three morphological forms—interpenetrating network (IPN), core–shell, and bilobal structurers—by varying the sets of miscible solvents offering different affinity for the polymers. Such fiber structures have strong potential in drug delivery and wound dressing applications. Solutions of PVP and PVAc in respective single solvents metered through a core–shell nozzle assembly meet at the exit of the nozzle and a liquid jet is initiated upon contact with a turbulent gas jet. The gas jet stretches the liquid jet into nanofibers. The results indicate that miscible solvent pairs with low affinity for one of the polymer component yield core–shell morphology with distinct polymer interfaces, while the miscible solvent pairs with high affinity for both polymers produce IPN morphology. Also, interchanging core and shell solutions does not alter the IPN morphology. Finally, bilobal nanofiber structures result from spinning of polymer solutions in miscible solvents with low affinity for the second polymer using a nonconcentric core–shell nozzle assembly. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48901.     

Processing–structure–property relationship in direct laser writing carbonization of polyimide

Direct laser writing carbonization (DLWc) of polyimide has recently emerged as a versatile method for facile fabrication of a variety of functional devices. Up-to-date, there is still a lack of comprehensive and in-depth experimental studies to understand the processing-structure–property relationship involved in this promising technique. With assistance of methylene blue adsorption as an in situ porous structure characterization method along with scanning electron microscopy, Raman scattering spectroscopy, X-ray photoelectron spectroscopy, and electrical property measurements, we systematically investigate the multiscale structure evolution and the electrical sheet resistance of the carbon lines fabricated by DLWc at varied laser processing conditions. The key processing parameters being investigated included: laser power (P), laser beam scanning speed (S), distance of laser beam waist to the surface of polyimide film (D), and their combined effect—the averaged areal laser energy density—(E). Quantitative relationships are established between these processing parameters and the specific surface area, the porosity, the degree of perfection of the layered carbon or graphitic basic structure units, as well as the electrical sheet resistance of the carbon lines created by DLWc. The comprehensive and quantitative processing-multiscale structure–electrical property relationships for DLWc established in this study expect to be useful for better understanding the complicated photo-thermally induced polyimide pyrolysis/carbonization process.     

Investigation of polyethylene–wax blends by CRYSTAF and SEC–FTIR

Summary Oxidized wax blends with respectively HDPE, LDPE and LLDPE were investigated using CRYSTAF and SEC–FTIR in order to determine the possibility and extent of co–crystallization of the wax with each of these polyethylenes. CRYSTAF shows very little or no co–crystallization of wax with HDPE and LDPE, while there is a strong indication of co–crystallization in the case of LLDPE. SEC-FTIR analyses show co–elution of wax with LLDPE, indicating some chemical interaction between the oxidized wax and LLDPE.     

Fabrication of shish–kebab structured poly(ε-caprolactone) electrospun nanofibers that mimic collagen fibrils: Effect of solvents and matrigel functionalization

Surface properties of tissue engineering scaffolds such as topography, hydrophilicity, and functional groups play a vital role in cell adhesion, migration, proliferation, and apoptosis. In this study, poly(ε-caprolactone) (PCL) shish–kebab scaffolds (PCL-SK), which feature a three-dimensional structure comprised of electrospun PCL nanofibers covered by periodic, self-induced PCL crystal lamellae on the surface, was created to mimic the nanotopography of native collagen fibrils in the extracellular matrix (ECM). Two different kinds of solvents used in creating kebabs on the shish were investigated by real-time observation. It was found that the solvent solubility directly affects the formation of kebabs: the lower the solubility of the solvent, the easier the formation of the kebabs on the surface of the electrospun nanofibers. In addition, matrigel was covalently immobilized on the surface of alkaline hydrolyzed PCL and PCL-SK scaffolds to enhance their hydrophilicity. This combined approach not only mimics the nanotopography of native collagen fibrils, but also simulates the surface features of collagen fibrils for cell growth. To investigate the viability of such scaffolds, HEF1 fibroblast cell assays were conducted and the results revealed that the nanotopography of the PCL-SK scaffolds facilitated cell adhesion and proliferation. The matrigel functionalization on PCL-SK scaffolds further enhanced cellular response, which suggested elevated biocompatibility and greater potential for tissue engineering applications.