Enhanced surface free energy of polyimide fibers by alkali treatment and its interfacial adhesion behavior to epoxy resins

In this article, polyimide (PI) fibers were modified by alkali treatment, and PI fiber-reinforced epoxy composites were fabricated. The effects of different alkali treatment times on the surface properties of the PI fibers and the adhesion behaviors of PI fiber/epoxy composites were studied. The surface morphologies, chemical compositions, mechanical properties, and surface free energy of the PI fibers were characterized by atomic force microscopy, X-ray photoelectron spectroscopy, single-fiber tensile strength analysis, and dynamic contact angle analysis, respectively. The results show that alkali treatment plays an important role in the improvement of the surface free energy and the wettability of PI fibers. We also found that, after the 3 min, 30 °C, 20 wt% NaOH solution treatment, the fibers possessed good mechanical properties and surface activities, and the interlaminar shear strength of the composites increased to 64.52 MPa, indicating good interfacial adhesion properties.     

Processing and characterization of α-elastin electrospun membranes

Elastin isolated from fresh bovine ligaments was dissolved in a mixture of 1,1,1,3,3,3-Hexafluoro-2-propanol and water were electrospun into fiber membranes under different processing conditions. Fiber mats of randomly and aligned fibers were obtained with fixed and rotating ground collectors and fibrils were composed by thin ribbons whose width depends on electrospinning conditions; fibrils with 721 nm up to 2.12 μm width were achieved. After cross-linking with glutaraldehyde, α-elastin can uptake as much as 1700 % of PBS solution and a slight increase on fiber thickness was observed. The glass transition temperature of electrospun fiber mats was found to occur at ～80 °C. Moreover, α-Elastin showed to be a perfect elastomeric material, and no mechanical hysteresis was found in cycle mechanical measurements. The elastic modulus obtained for random and aligned fibers mats in a PBS solution was 330±10 kPa and 732±165 kPa, respectively. Finally, the electrospinning and cross-linking process does not inhibit MC-3T3-E1 cell adhesion. Cell culture results showed good cell adhesion and proliferation in the cross-linked elastin fiber mats.     

Predicting Polymorphism of Electrospun Polyvinylidene Fluoride Membranes by Their Morphologies

Although electrospinning of polyvinylidene fluoride (PVDF) has been studied for more than 10 years, the crystalline phase differentiation of the electrospun mats is still normally through the combination of different characterization techniques, and the relationship between polymorphism and morphology of the fibers in electrospun PVDF membranes has never been reported. Here, we show their close relationships by conducting room-temperature electrospinning experiments on various polymer/solvent systems. The electrospun membranes full of bead-free fibers have a very high fraction of β-phase, F(β), over 90%, and high orientation, whereas the membranes comprising beads and/or a large number of beaded fibers most often result in a low fraction of β-phase (F(β) normally below 50%) and low orientation. On the other hand, electrospun membranes consisting of both bead-free fibers and a very limited number of beaded fibers showed a medium high fraction of β-phase, F(β) more than 70% but less than 90%. These findings suggest the feasibility of intuitively predicting the crystalline phase of electrospun PVDF membranes directly by their morphologies, which is obviously simple, inexpensive and convenient for future investigations.     

Synthesis,characterization and mechanical properties of nylon–silver composite nanofibers prepared by electrospinning

Silver (Ag) nanoparticles (∼3 nm) were synthesized using silver nitrate as the starting precursor, ethylene glycol as solvent and poly (N-vinylpyrrolidone) (PVP) introduced as a capping agent. These nano-Ag particles were reinforced in nylon matrix by electrospinning of nylon-6/Ag solution in 2,2,2-trifluoroethanol and composite nanofibrous membranes were synthesized. The effects of solution concentration and relative humidity (RH) on the resultant fibrous membranes were studied. Scanning electron microscopy and Transmission electron microscopy was used to study the size and morphology of the fibers. It was observed that concentration and RH could be used to modulate the fiber diameter. Tensile test was used to evaluate the mechanical property of these electrospun composite membranes. The composite membranes showed higher strength (approx. 2–3 times increase in strength) compare to as synthesized nylon fibers.     

Electrospinning of Poly(Hydroxybutyrate-co-hydroxyvalerate) Fibrous Scaffolds for Tissue Engineering Applications: Effects of Electrospinning Parameters and Solution Properties

Electrospinning, a technology capable of fabricating ultrafine fibers (microfibers and nanofibers), has been investigated by various research groups for the production of fibrous biopolymer membranes for potential medical applications. In this study, poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV), a natural, biocompatible, and biodegradable polymer, was successfully electrospun to form nonwoven fibrous mats. The effects of different electrospinning parameters (solution feeding rate, applied voltage, working distance and needle size) and polymer solution properties (concentration, viscosity and conductivity) on fiber diameter and morphology were systematically studied and causes for these effects are discussed. The formation of beaded fibers was investigated and the mechanism presented. It was shown that by varying electrospinning parameters within the processing window that was determined in this study, the diameter of electrospun PHBV fibers could be adjusted from a few hundred nanometers to a few microns, which are in the desirable range for constructing “biomimicking” fibrous scaffolds for tissue engineering applications.     

Nanofiber membrane based on ionic liquids as high-performance polymer electrolyte for sodium electrochemical device

Composite nanofibrous electrolyte membranes (CFEM) of poly(vinylidene fluoride-hexafluoropropylene) P(VdF-HFP)-1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF₄) and its NaSCN are electrospun as nanofibrous membranes. Scanning electron microscope (SEM) images clearly inform that electrospun CFEM and CFEM–NaSCN with average fiber diameters of 50–200 nm have interconnected multifibrous layers with ultrafine porous structures. They exhibited a high uptake of the electrolyte solution (370–880 %). The polymer electrolytes have decreased crystalline, which is advantage to the increase in ionic conductivity. In addition, polymer electrolytes also are prepared by swelling nanofibre into blend of sodium salt and BMIMBF₄. CFEM obtained 15 % BMIMBF₄ exhibited higher ionic conductivity maximum of 5.6?×?10^?5 S cm^?1 at room temperature, and the conductive model of CFEM–NaSCN electrolyte answer for Arrhenius function. CFEM–NaSCN electrolyte showed a high electrochemical window of above 4.5 V, which is higher than electrospun pure P(VdF-HFP) without BMIMBF₄ or BMIMBF₄–NaSCN. With these improved performance characteristics, CFEM electrolyte and CFEM–NaSCN electrolyte will be found its suitability as polymer electrolyte for high-performance rechargeable batteries and super capacitor.     

Preparation of TiO<Subscript>2</Subscript>-loaded electrospun fibers of polylactide/poly(vinylpyrrolidone) blends for use as catalysts in epoxidation of unsaturated oils

Nanofibers of polylactide (PLA)/poly(vinylpyrrolidone) (PVP) blends, loaded with TiO₂ nanoparticles, have been prepared by an electrospinning method. The electrospun fiber mats were characterized by ATR-FTIR, X-ray diffraction (XRD), SEM, EDX, and UV-visible spectroscopy to examine structures, functional groups, crystallinity, surface morphology, and UV absorptivity. It is clearly observed that TiO₂ particles are embedded on the filaments. All PLA-based spun fibers are completely amorphous in nature. The surface morphology of those blended with PVP is smoother and more uniform than the corresponding samples without PVP. Neat PLA fibers show a UV absorption band at around 200 nm, whereas the fibers loaded with TiO₂ nanoparticles show an additional absorption band covering the 200–380-nm region. Photo-degradation of the fiber samples are conducted in phosphate buffer solution (PBS) under UVA light. The results indicate that the PVP component dissolves into the PBS solution, and the PLA matrix degrades as a function of time. The fibers are then applied as a catalytic system for epoxidation of unsaturated sunflower oil (SFO), for use as additives or plasticizers for biopolymers, employing a performic acid oxidizing agent. The fibers, especially those containing PVP, can effectively enhance the epoxidation yield of oils with a slow rate of undesirable side reactions, which break ester bonds of triglycerides to generate free fatty acids.     

Banana fiber strands–reinforced polymer matrix composites

Banana fiber (BF)-reinforced low-density polyethylene (LDPE) unidirectional composites were fabricated by the compression molding process with 40 wt% fiber loading. The fibers were modified with methylacrylate (MA) mixed with methanol (MeOH) along with 2% benzyl peroxide under thermal curing method at different temperatures (50–90 °C) for different curing times (10–50 min) in order to have better compatibility with the matrix. The effect of fiber surface modification on the mechanical properties (tensile and impact properties) of the composites were evaluated. Monomer concentration, curing temperature, and curing time were optimized in terms of polymer loading and mechanical properties. The mechanical properties were found to be improved based on the improved interaction between the reinforcement and the matrix. Optimized BFs were again treated with 2–5 wt% starch solutions and composites made of 4% starch treated BF showed the highest mechanical properties than that of MA treated composites. Scanning electron microscopy (SEM) was performed to get an insight into the morphology of the composites. Water uptake and soil degradation test of the composites were also investigated.     

Formation of uniform PVDF fibers under ultrasound exposure in presence of anionic surfactant

Polyvinylidene fluoride (PVDF) was electrospun into fibrous membranes from its solutions in mixture of dimethylformamide (DMF) and acetone with and without an anionic fluorosurfactant. The results indicate that PVDF fibers contain a number of beads at any solvents compositions and solution concentrations. Addition of the surfactant does not affect considerably the morphology of fibers, however it helps to decrease the surface tension of the solution and reduce the beading of fibers. The most important factor affecting the fiber morphology is sonication. Sonication of the spinning solution promotes the formation of perfect, uniform, thin and cylindrical PVDF nanofibers without any beading.     

Poly(ɛ-caprolactone) Electrospun Scaffolds Filled with Nanoparticles. Production and Optimization According to Taguchi's Methodology

Polycaprolactone (PCL) scaffolds were produced by electrospinning. Polymeric solutions in a mix of dichloromethane (DCM) and dimethylformamide were electrospun to form fibers in the sub-micron range. Physical properties of the PCL solutions were characterized with respect to density, viscosity, conductivity and surface tension. Processing was optimized following Taguchi's methodology to select the set of processing parameters that resulted in producing fibers with the smallest diameters, minimum number of defects and with the narrowest distribution of fiber diameter. Morphology of electrospun fibers was qualitatively and quantitatively analyzed for the different sets of processing parameters. The optimum conditions found to electrospun PCL were used to process PCL solutions containing nanoparticles of hydroxyapatite (HA) or bioactive glass (BG). Bioactivity of nanocomposite electrospun membranes in simulated body fluid (SBF) was analyzed and biological response was tested by assessing proliferation and viability of MT3C3-E1 preosteoblasts cultured on PCL and its nanocomposite membranes.     

Controlled growth of standing Ag nanorod arrays on bare Si substrate using glancing angle deposition for self-cleaning applications

A facile approach to manipulate the hydrophobicity of surface by controlled growth of standing Ag nanorod arrays is presented. Instead of following the complicated conventional method of the template-assisted growth, the morphology or particularly average diameter and number density (nanorods cm^?2) of nanorods were controlled on bare Si substrate by simply varying the deposition rate during glancing angle deposition. The contact angle measurements showed that the evolution of Ag nanorods reduces the surface energy and makes an increment in the apparent water contact angle compared to the plain Ag thin film. The contact angle was found to increase for the Ag nanorod samples grown at lower deposition rates. Interestingly, the morphology of the nanorod arrays grown at very low deposition rate (1.2 Å?sec^?1) results in a self-cleaning superhydrophobic surface of contact angle about 157° and a small roll-off angle about 5°. The observed improvement in hydrophobicity with change in the morphology of nanorod arrays is explained as the effect of reduction in solid fraction within the framework of Cassie–Baxter model. These self-cleaning Ag nanorod arrays could have a significant impact in wide range of applications such as anti-icing coatings, sensors and solar panels.     

Fabrication and Optimization of Poly(vinyl alcohol)/Zirconium Acetate Electrospun Nanofibers Using Taguchi Experimental Design

This paper presents an investigation regarding poly(vinyl alcohol)/zirconium acetate (organic–inorganic) (PVA/Zrace) nanofibers prepared by electrospinning which could be used as a precursor for fabricating ceramic metal oxide nanofibers. The effect of some processing variables, including polymer solution concentration, tip to collector distance and applied voltage of electrospinning, and the amount of Zrace and their interactions, on the diameter of the nanofibers were studied. Taguchi experimental design and a statistical analysis (ANOVA) were employed and the relationship between experimental conditions and yield levels determined. It was concluded that to obtain a narrow diameter distribution as well as maximum fiber fineness, a polymer concentration of 10 wt%, tip to collector distance of 18 cm and applied voltage of 20 kV variables were the optimum. Furthermore, it was also concluded that the ratio of Zrace (6 g) to PVA solution (10% wt) played an important role for achieving the minimum fiber diameter. Under these optimum conditions, the diameters of the electrospun composite fibers ranged from 86 nm to 381 nm with a diameter average of 193 nm. The experiments were done with Qualitek-4 software with “smaller is better” as the quality characteristics. The optimized conditions showed an improvement in the fibers diameter distribution and the average fibers diameter showed good resemblance with the result predicted using the Taguchi method and the Qualitek-4 software. The ANOVA results showed that all factors had significant effects on the fibers diameter and distribution, but the effect of PVA concentration and zirconium acetate were more significant than the other factors.     

Femtosecond laser machining of electrospun membranes

We demonstrate that a femtosecond laser can be used to machine arbitrary patterns and pattern arrays into free-standing electrospun polycaprolactone (PCL) membranes. We also examine the influence of various laser irradiation settings on the final microstructure of electrospun membranes. A beam fluence of 0.6 J/cm² is used to ablate holes in 100 μm thick PCL membranes. The machined holes have an average diameter of 436 μm and a center-to-center spacing of 1000 μm. Based on these results, the femtosecond ablation of electrospun membranes shows great potential for fabricating a variety of functional tissue scaffolds. This technique will advance scaffold design by providing the ability to rapidly tailor surface morphology, while minimizing and controlling the deformation of the electrospun fibers.     

Preparation of graphene-glass fiber-resin composites and its electromagnetic shielding performance

The surface of the glass fiber (GF) was modified by silane coupling agent (KH550) and bovine serum albumin (BSA), and then the graphene oxide (GO) was coated onto the modified surface of the glass fiber. Followed by a reduction reaction, the reduced graphene oxide (RGO) coated on glass fiber was obtained. Finally, the reduced graphene oxide-glass fibers (RGO-GF) were combined with unsaturated resins. The interfacial morphology of reduced graphene oxide-glass fibers was investigated by scanning electron microscopy (SEM). The structure of the materials was analyzed by Fourier transform infrared spectroscopy (FT-IR). The crystal phases of the material were identified by X - ray diffraction (XRD). The mechanical properties and electromagnetic shielding effectiveness of the sample were tested. The results showed that the interface between glass fibers and graphene binds more closely after the glass fibers was treated by KH550. The tensile strength of the RGO-GF composites reached 85.05 MPa. Compared with the GF composites, it increased by 51.4% when the glass fibers content was 30%. The shielding effectiveness of the composites reached 21.3 dB at the frequency range of 8.2–12.4 GHz (x-band). Therefore, by coating the surface with reduced graphene oxide, the glass fibers can make a great shielding effect on the electromagnetic wave.     

Wettability Improvement of Poly (Butylene Terephthalate) Nanofibrous Mats Prepared via Electrospinning by Blending With Regenerated Silk Fibroin

Poly (butylene terephthalate) (PBT)/regenerated silk fibroin (RSF) blend electrospun nanofibrous mats were manufactured to combine the excellent mechanical behavior of PBT with the extraordinary hydrophilic property of RSF. A 1:1 mixture of trifluoroacetic acid (TFA) and dichloromethane (DCM) was adopted as the solvents for PBT and RSF with 20% (w/v) PBT and 16 wt% RSF solutions being mixed in various proportions for electrospinning. The morphology, crystallization, Fourier transform infrared (FTIR) spectra, surface roughness, contact angle, and wetting time of the electrospun blended materials were studied. When the weight ratio of RSF was larger than 50%, a water drop on the surface of the electrospun mat was completely permeated within 300 s or less. Besides the chemical influence of the amino and carboxy groups in RSF, the physical characteristics of the RSF in the blend electrospun mats, such as random coil structure, lower crystallinity, rougher surface than PBT, etc., were a partial reason for the improvement of wettability. The blend nanofibrous mats may be especially applicable in biomedical fields.     

Multipoint contact modeling of nanoparticle manipulation on rough surface

In this paper, the atomic force microscopy (AFM)-based 2-D pushing of nano/microparticles investigated on rough substrate by assuming a multipoint contact model. First, a new contact model was extracted and presented based on the geometrical profiles of Rumpf, Rabinovich and George models and the contact mechanics theories of JKR and Schwartz, to model the adhesion forces and the deformations in the multipoint contact of rough surfaces. The geometry of a rough surface was defined by two main parameters of asperity height (size of roughness) and asperity wavelength (compactness of asperities distribution). Then, the dynamic behaviors of nano/microparticles with radiuses in range of 50–500 nm studied during their pushing on rough substrate with a hexagonal or square arrangement of asperities. Dynamic behavior of particles were simulated and compared by assuming multipoint and single-point contact schemes. The simulation results show that the assumption of multipoint contact has a considerable influence on determining the critical manipulation force. Additionally, the assumption of smooth surfaces or single-point contact leads to large error in the obtained results. According to the results of previous research, it anticipated that a particles with the radius less than about 550 nm start to slide on smooth substrate; but by using multipoint contact model, the predicted behavior changed, and particles with radii of smaller than 400 nm begin to slide on rough substrate for different height of asperities, at first.     

Effect of annealing temperature on optical and electrochemical properties of chitosan–ZnO nanostructure

Chitosan–ZnO nanostructures were prepared by chemical precipitation method using different concentration of zinc chloride and sodium hydroxide solutions. Nanorod-shaped grains with hexagonal structure for samples annealed at 300 °C and porous structure with amorphous morphology for samples annealed at 600 °C were revealed in SEM analysis. X-ray diffraction patterns confirmed the hexagonal phase ZnO with crystallite size found to be in the range of ~24.15–34.83 nm. Blue shift of UV–Vis absorption shows formation of nanocrystals/nanorods of ZnO with marginal increase in band gap. Photoluminescence spectra show that blue–green emission band at 380–580 nm. The chitosan–ZnO nanostructures used on surface of a glassy carbon electrode gives the oxidation peak potential at ~0.6 V. The electrical conductivity of chitosan–ZnO composites were observed at 2.1?×?10^?5 to 2.85?×?10^?5?S/m. The nanorods with high surface area and nontoxicity nature of chitosan–ZnO nanostructures observed in samples annealed at 300 °C were suitable as a potential material for biosensing.     

Compression of long-cavity Ti:sapphire oscillator pulses with large-mode-area photonic crystal fibers

Motivated by the pulse compression challenge of novel long-cavity, high-pulse-energy Ti:sapphire laser oscillators, we report on ~280 nm supercontinuum generation and 4.5-times compression of close to transform limited, high-energy oscillator pulses using different large-mode-area photonic crystal fibers and standard chirped mirrors. As input, we used pulses of a long-cavity Ti:sapphire oscillator with 190 nJ pulse energy, 70 fs pulse length and 3.6 MHz repetition rate. Compressed pulses at the fiber/compressor output had a duration of 15–18 fs with up to 100 nJ pulse energy representing as much as 53 % throughput for the fiber/chirped mirror system. Using transform-limited input pulses, we could use short fiber pieces and thus a simple, low-dispersion chirped mirror compressor comprised of one pair of mirrors.     

Icephobic performance on the aluminum foil-based micro-/nanostructured surface

The research of superhydrophobic materials has attracted many researchers' attention due to its application value and prospects.In order to expand the serviceable range,people have investigated various superhydrophobic materials.The simple and easy preparation method has become the focus for superhydrophobic materials.In this paper,we present a program for preparing a rough surface on an aluminum foil,which possesses excellent hydrophobic properties after the treatment with low surface energy materials at high vacuum.The resulting contact angle is larger than 160° and the droplet cannot freeze on the surface above-10 ℃.Meanwhile,the modified aluminum foil with the thickness of less than 100 μm can be used as an ideal flexible applied material for superhydrophobicity/anti-icing.     

The Abrasion Behavior and Mechanisms of a Superhydrophobic Surface Comprising Styrene Butadiene Rubber

The microprotuberances of superhydrophobic surfaces are easily destroyed during a friction cycle, resulting in invalidation of superhydrophobicity, because they are then loaded with pressure and shearing stress. Thus, the abrasion-resistance of superhydrophobic surfaces is the main barrier preventing their wide application. Elastic microprotuberances will be compressed and collapsed by elastic deformation to avoid being broken during a friction cycle, and the deformation will rebound to renew the original surface structure when the load is withdrawn. A superhydrophobic surface comprising styrene butadiene rubber (SBR) was fabricated via template replication in the research described here, with a water contact angle up to 160°. Friction testing was then used to characterize the abrasion resistance of the surface; the contact angle remained more than 139° even after being loaded with 4.4 KPa or 6.87 KPa and rubbed by a smooth metal surface at 18 cm/s for 10,000 times. Scanning electron microscopy was used to characterize the change of morphology before and after the friction testing and to explain the abrasion mechanism.