Electrospinning of polystyrene/dicyanopyrazine-linked porphyrin nanofibers

We have fabricated fluorescing polystyrene/dicyanopyrazine-linked porphyrin (PS/4-TDCPP) nanofibers using the electrospinning technique. UV-vis spectroscopy shows a strong Soret band and two relatively weak Q bands from the PS/4-TDCPP films and fibers, and reveals that the 4-TDCPP molecules are homogeneously dispersed in the films and fibers. Scanning electron microscopy (SEM) reveals the effect of solvent and collecting distance on the morphology of the electro-spun PS/4-TDCPP fibers. Fibers spun from a 50% dimethlyformamide (DMF), 50% methylethylketone (MEK) solution have ultra-fine structures with an average diameter of 300 nm. In the case of fibers from pure DMF and DMF:MEK (1:3) solutions, beads are formed along the length of the fibers. Variation of the collecting distance from 20 to 30 cm does not induce significant differences in the morphology of the electro-spun PS/4-TDCPP fibers. However, at a collecting distance of 15 cm, many beads are formed along the fibers. Acid-sensing capability of the PS/4-TDCPP fibers is demonstrated by fluorescence microscopy.     

Nanofiber deposition by electroblowing of PVA (polyvinyl alcohol)

Electrospinning provides a relatively versatile method of creating a variety of ultrathin nanofibers. One of the well known problems in electrospinning is low productivity. To increase the inherently low productivity in electrospinning, an assembly of multi-needles has been widely introduced. This process may be enhanced by introducing the electroblowing process that combines air blowing and electrospinning. In this study, the effect of electroblowing on web deposition was explored via the simultaneous and separate application of two forces: an electrostatic force and an air blowing-induced shear force, which are adjusted by the applied voltage and the air blowing pressure, respectively. The image filtering technology was used to evaluate the web deposition. The application of the shear force significantly affected the web deposition, especially at low voltage.     

Electrospun polyvinyl alcohol/chitosan composite nanofibers involving Au nanoparticles and their in vitro release properties

Au nanoparticles (Au NPs) containing polyvinyl alcohol (PVA)/chitosan (CS) composite nanofibers were successfully prepared by a simple and effective method called electrospinning. Au NPs were firstly synthesized under a mild condition with CS as the reducing agent and stabilizer, followed by being mixed with PVA solution and then the resulting fibers were fabricated. The research indicated that Au NPs were indeed doped into the as-prepared fibers and the composite fibers well preserved Au NPs' unique optical characteristics. Additionally, with the adjustment of the weight ratios between PVA and CS, the diameter distribution and the morphology of the nanofibers were largely changed. In vitro drug release experiments demonstrated that the drug release rate can be conveniently controlled by changing the crosslink time.     

Effect of dopant concentration on the electrical properties of polyvinyl alcohol (PVA)

The real part of the dielectric constant () of pure and doped polyvinyl alcohol (PVA) with 1, 2 and 3 wt% vanadate was measured as a function of temperature and frequency. () decreases with increasing frequency due to a rapid variation of the field accompanied with the applied frequency as well as the disordering of the segmental parts of the polymer chain. The vanadate effects appear in a form of increasing the crystallinity in the sample leading to a decrease in (), except in the case of 2 wt% vanadate in which () is drastically increased. The d.c. conductivity for the vanadate doped PVA is measured as a function of temperature. The values of the activation energy as obtained from the experimental data give information about the presence of more than one conduction mechanism as well as the useful applications of PVA, especially in the field of electronics. © 1998 Kluwer Academic Publishers     

Biodegradation of phenol by Pseudomonas putida immobilized in polyvinyl alcohol (PVA) gel

Batch experiments were carried out to evaluate the biodegradation of phenol by Pseudomonas putida immobilized in polyvinyl alcohol (PVA) gel pellets in a bubble column bioreactor at different conditions. The bacteria were activated and gradually acclimatized to high concentrations of phenol of up to 300 mg/l. The experimental results indicated that the biodegradation capabilities of P. putida are highly affected by temperature, pH, initial phenol concentration and the abundance of the biomass. The biodegradation rate is optimized at 30 degrees C, a pH of 7 and phenol concentration of 75 mg/l. Higher phenol concentrations inhibited the biomass and reduced the biodegradation rate. At high phenol concentration, the PVA particle size was found to have negligible effect on the biodegradation rate. However, for low concentrations, the biodegradation rate increased slightly with decreasing particle size. Other contaminants such heavy metals and sulfates showed no effect on the biodegradation process. Modeling of the biodegradation of phenol indicated that the Haldane inhibitory model gave better fit of the experimental data than the Monod model, which ignores the inhibitory effects of phenol.     

Strain hardening behavior of lightweight hybrid polyvinyl alcohol (PVA) fiber reinforced cement composites

Experimental results on the strain hardening and multiple cracking behaviors of polyvinyl alcohol (PVA) fiber reinforced cementitious composites under bending are reported in this paper. Different hybrid combinations of PVA fibers with different lengths and volume fractions are considered to reinforce the mortar matrix. Among different hybrid combinations, the composite containing 2% thicker PVA fibers of 12 mm length and 1% thinner PVA fibers of 6 mm length and the composite containing 2% thicker PVA fibers of 24 mm length and 1% thinner PVA fibers of 6 mm length showed the best performance in terms of highest ultimate load, largest CMOD (crack mouth opening displacement) at peak load and multiple cracking behavior. The effects of four types of light weight sands on the strain hardening and multiple cracking behavior of hybrid fiber composites are also evaluated in this study. It has been observed that the ultimate load and CMOD at peak load for all light weight hybrid fiber composites are almost the same irrespective of volume fractions of light weight sand. The composites containing finer light weight sands exhibited higher ultimate load than those containing coarser light weight sands. It is also observed that the hybrid fiber composite containing normal silica sand exhibited higher ultimate load than the composites with light weight sands.     

聚乙二醇改性纳米纤维素/聚乙烯醇复合水凝胶的制备及性能

通过酸碱处理和机械研磨结合的方法制备纳米纤维素(CNFs),并利用冻融循环法分别制备了聚乙烯醇(PVA)和纳米纤维素/聚乙烯醇(CNFs/PVA)复合水凝胶,以及聚乙二醇(PEG)改性PVA和CNFs/PVA复合水凝胶。考察不同配方下复合水凝胶的微观形貌变化,并对复合水凝胶的溶胀性能、压缩强度及热稳定性能进行研究。结果表明,CNFs与PEG对PVA水凝胶的微观形貌均有改善作用,加入PEG后形成的PEG/PVA凝胶产生明显的三维网络结构。当PEG与CNFs同时加入到PVA凝胶后形成的CNFs-PEG/PVA凝胶具有均匀的互穿孔洞结构,此时复合水凝胶的孔隙率最高((67.5±4.3)%),溶胀度最好(980%),且压缩强度较PVA水凝胶也有所提升。PEG对复合凝胶的热稳定性无影响,而加入CNFs后,CNFs-PEG/PVA复合凝胶的初始热分解温度从235℃上升至300℃,显著提高了PVA凝胶的热稳定性。     

Electrospun single-walled carbon nanotube/polyvinyl alcohol composite nanofibers: structure-property relationships

Polyvinyl alcohol (PVA) nanofibers and single-walled carbon nanotube (SWNT)/PVA composite nanofibers have been produced by electrospinning. An apparent increase in the PVA crystallinity with a concomitant change in its main crystalline phase and a reduction in the crystalline domain size were observed in the SWNT/PVA composite nanofibers, indicating the occurrence of a SWNT-induced nucleation crystallization of the PVA phase. Both the pure PVA and SWNT/PVA composite nanofibers were subjected to the following post-electrospinning treatments: (i) soaking in methanol to increase the PVA crystallinity, and (ii) cross-linking with glutaric dialdehyde to control the PVA morphology. Effects of the PVA morphology on the tensile properties of the resultant electrospun nanofibers were examined. Dynamic mechanical thermal analyses of both pure PVA and SWNT/PVA composite electrospun nanofibers indicated that SWNT-polymer interaction facilitated the formation of crystalline domains, which can be further enhanced by soaking the nanofiber in methanol and/or cross-linking the polymer with glutaric dialdehyde.     

磷虾蛋白/海藻酸钠/聚乙烯醇复合纳米纤维的制备及表征

以磷虾蛋白(AKP)、海藻酸钠(SA)、聚乙烯醇(PVA)为纺丝原料,通过静电纺丝制备AKP/SA/PVA复合纳米纤维,系统研究了纺丝液浓度和纺丝电压对纤维形貌的影响。通过FT-IR分析复合纤维的结构,结果表明SA与AKP间存在化学反应,而与PVA是物理共混,通过红外的二阶导数和拟合分峰研究共混纤维间的氢键作用,结果表明氢键的类型及含量与纤维构成有关。通过DSC和TGA测试纳米纤维的热性能,表明纤维在250℃左右开始熔融并伴随着分解。     

Electrospinning of CeO2-ZnO composite nanofibers and their photocatalytic property

CeO₂-ZnO composite nanofibers were fabricated via the electrospinning technique using zinc acetate and cerium nitrate as the precursors, poly(vinylpyrrolidone) as the fiber template, and 2:1(v/v) ethanol/water mixtures as the co-solvent, followed by thermal treatment at 600 °C for 3 h. Various characterization methods were employed to investigate the morphologies and structures of the nanofibers. The calcined composite nanofibers showed a continuous line feature with an average diameter of 46 nm composed of 15 ± 3 nm CeO₂ and ZnO nanoparticles. Photocatalytic activity experiments showed that the Rhodamine B was almost completely decomposed when it was catalyzed by CeO₂-ZnO nanofibers within 3 h, while only 17.4% and 82.3% were decomposed under catalysis by CeO₂ and ZnO nanofibers respectively. Such CeO₂-ZnO composite nanofibers could have potential applications in the treatment of organic-polluted water.     

Eco-friendly polyvinyl alcohol (PVA)/bamboo charcoal (BC) nanocomposites with superior mechanical and thermal properties

Carbon-based nanofillers, such as carbon nanotubes (CNTs) and graphene sheets are considered as effective nanoreinforcements due to their unique structures and material performance. However, the utilisation of such nanofillers can be hindered owing to a high level of nanotoxicity via human inhalation and high material cost for CNTs, as well as the tendency to form agglomerates of graphene sheets in polymer matrices. Bamboo charcoals (BCs) are eco-friendly and sustainable carbon-based particles, which possess good affinity with polyvinyl alcohol (PVA), one of popular water soluble biopolymers, to achieve excellent properties of PVA/BC nanocomposites. In particular, porous structures of BC particles enable polymeric molecules to easily penetrate with the strong internal bonding. In this study, fully eco-friendly PVA/BC nanocomposite films were successfully fabricated using a simple solution casting method to achieve the high dispersibility of BCs. With the inclusion of only 3 wt% BCs, tensile modulus and tensile strength of PVA/BC nanocomposite films were enhanced by 70.2 and 71.6%, respectively, when compared with those of PVA films. Better thermal stability is manifested for resulting nanocomposite films as opposed to that of pristine PVA, which is evidenced by the maximum increase of 17.8% in the decomposition temperature at the weight loss of 80%. It is anticipated that BCs can compete against conventional carbon-based nanofillers with a great potential to be developed into eco-friendly nanocomposites used for thin-film packaging application.     

静电纺丝法制备PVP/PVDF复合微/纳米纤维

研究了不同条件下聚乙烯吡咯烷酮/聚偏氟乙烯(PVP/PVDF)的N,N-二甲基乙酰胺(DMAc)溶液的静电纺丝.采用扫描电镜(sEM)观察不同条件下制备的PVP/PVDF复合微/纳米纤维的微观形貌,并利用傅立叶变换红外光谱分析(FT-IR)纤维结构特征.结果表明,当PVP:PVDF为6:4时,制得的PVP/PVDF复合微/纳米纤维较好.     

Effect of the PVA (polyvinyl alcohol) concentration on the optical properties of Eu-doped YAG phosphors

The influence of the polyvinyl alcohol (PVA) concentration on the synthesis and structural, morphological and optical properties of Y₃Al₅O₁₃: Eu (Eu-doped YAG) was systematically investigated in this work. The final concentration of PVA in the preparation step influenced the crystallite size and also the degree of particle agglomeration in Eu-doped YAG phosphors. X-ray excited optical luminescence (XEOL) emission spectra results indicated typical Eu³⁺ emission lines and an abnormally intense ⁵D₀ → ⁷F₄. The intensity parameters Ω₂ and Ω₄ were calculated and indicated the PVA concentration affects the ratio Ω₂:Ω₄. X-ray absorption spectroscopy (XAS) results showed Eu valence did not change and the symmetry around the Eu³⁺ is influenced by the PVA concentration. XEOL-XAS showed the luminescence increases as a function of energy.     

Property-based design: optimization and characterization of polyvinyl alcohol (PVA) hydrogel and PVA-matrix composite for artificial cornea

Each approach for artificial cornea design is toward the same goal: to develop a material that best mimics the important properties of natural cornea. Accordingly, the selection and optimization of corneal substitute should be based on their physicochemical properties. In this study, three types of polyvinyl alcohol (PVA) hydrogels with different polymerization degree (PVA1799, PVA2499 and PVA2699) were prepared by freeze-thawing techniques. After characterization in terms of transparency, water content, water contact angle, mechanical property, root-mean-square roughness and protein adsorption behavior, the optimized PVA2499 hydrogel with similar properties of natural cornea was selected as a matrix material for artificial cornea. Based on this, a biomimetic artificial cornea was fabricated with core-and-skirt structure: a transparent PVA hydrogel core, surrounding by a ringed PVA-matrix composite skirt that composed of graphite, Fe-doped nano hydroxyapatite (n-Fe-HA) and PVA hydrogel. Different ratio of graphite/n-Fe-HA can tune the skirt color from dark brown to light brown, which well simulates the iris color of Oriental eyes. Moreover, morphologic and mechanical examination showed that an integrated core-and-skirt artificial cornea was formed from an interpenetrating polymer network, no phase separation appeared on the interface between the core and the skirt.     

Frequency and temperature dependencies of a.c. conductivity of polyvinyl alcohol (PVA)-CoCl2 composites

The a.c. conductivity for polyvinyl alcohol (PVA)-CoCl₂ composites prepared by a casting method has been measured at different frequencies (0.1–10 kHz) in the temperature range 300–450 K. At constant temperature, the frequency dependence of a.c. conductivity, (), was found to fit the established equation () = A ^s quite well. On the other hand, the temperature dependence of a.c. conductivity suggested an electronic hopping conduction mechanism in a thermally assisted electric field. Various theoretical mechanisms have been discussed to clarify the conduction processes in these samples. The correlated barrier hopping (CBH) mechanism, proposed by Elliott, was found to be the most appropriate one.     

Synthesis of fluorescent PVA/polypyrrole-ZnO nanofibers

Electro spinning is a simple and efficient technique to produce polymer nanofibers. Here, we describe the preparation of electrospun PVA/PPy–ZnO fluorescent fibers and discuss their characterization by use of UV–Vis and Fourier transform infrared spectroscopies, and fluorescence and scanning electron microscopies. These hybrid organic–inorganic fibers exhibit a visible emission of 526 nm with a well-defined green color, as the ZnO–NPs fluorescence emission at 390 nm is quenched. The scanning electronic microscopy images reveal that the fibers present an average diameter of 324 nm and good surface quality. We have observed that their Ohmic behavior is light sensitive as the charge transport along the fibers is highly affected by UV illumination. Since this is a reversible effect, and a quick recovery of the electrical resistance original value occurs right after the incident UV light is turned off, we suggest that these organic–inorganic materials can find useful applications in the preparation of various polymer-based micro and nano optoelectronic devices, such as low-cost flexible photovoltaic devices and UV sensors.     

PEG/PVA复合物相变焓的影响因素研究

通过接枝共聚法制备了PEG/PVA复合高分子固-固相变材料,用DSC差示扫描量热法对其相变曲线进行了测试,讨论了影响PEG/PVA复合物相变焓的影响因素.结果表明,PVA含量、反应温度和反应时间都对复合物的相变焓有影响,且PVA含量对复合物相变焓值影响最大.     

Polylactic acid/cellulose whisker nanocomposites modified by polyvinyl alcohol

The aim of this study was to produce biodegradable polylactic acid/cellulose whisker nanocomposites by compounding extrusion and investigate the possibility to use polyvinyl alcohol to improve the dispersion of whiskers in the matrix. Two feeding methods of polyvinyl alcohol and cellulose nanowhiskers were used and evaluated, dry-mixing with polylactic acid prior extrusion or pumping as suspension directly into the extruder. Various microscopic techniques, tensile testing, and dynamic mechanical thermal analysis were used to study the structure and properties of the nanocomposites. Due to immiscibility of the polymers, phase separation occurred with a continuous polylactic acid phase and a discontinuous polyvinyl alcohol phase. The whiskers were primarily located in the polyvinyl alcohol phase and only a negligible amount was located in the polylactic acid phase. This inadequate dispersion of whiskers in the polylactic acid phase was probably the reason why no improvements in thermal properties were seen for the nanocomposites. The relative small improvements in tensile modulus, tensile strength, and elongation to break for the nanocomposites also indicated that it was principally the polyvinyl alcohol phase that was reinforced with whiskers but not the polylactic acid phase.     

聚乙烯醇/葡萄糖酸蒙脱土纳米复合材料的制备及表征

为了改善聚乙烯醇的力学强度、耐水性及耐热性,采用纳米葡萄糖酸蒙脱土对聚乙烯醇进行了物理复合改性,制备了聚乙烯醇/葡萄糖酸蒙脱土纳米复合材料.在机械搅拌与超声波震荡协同作用下,把纳米葡萄糖酸蒙脱土均匀预分散在甘油中,然后加入到聚乙烯醇乳液中,得到了聚乙烯醇/葡萄糖酸蒙脱土纳米复合薄膜.实验结果表明,当甘油用量为聚乙烯醇的...