Highly porous solid-phase microextraction fiber coating based on poly(ethylene glycol)-modified ormosils synthesized by sol-gel technology

The preparation and characteristics of solid-phase microextraction (SPME) fibers coated with Carbowax 20M ormosil (organically modified silica) are described here. Raw fused silica fibers were coated with Carbowax 20M-modified silica using sol-gel process. Scanning electron micrographs of fibers revealed a highly porous, sponge-like coating with an average thickness of (8 +/- 1) microm. The sol-gel Carbowax fibers were compared to commercial fibers coated with 100 microm polydimethylsiloxane (PDMS) and 65 microm Carbowax-divinylbenzene (DVB). Shorter equilibrium times were possible with the sol-gel Carbowax fiber: for headspace extraction of the test analytes, they ranged from less than 3 min for benzene to 15 min for o-xylene. Extraction efficiencies of the sol-gel Carbowax fiber were superior to those of conventional fibers: for o-xylene, the extracted masses were 230 and 540% of that obtained with 100 microm PDMS and 65 microm Carbowax-DVB fibers, respectively.     

Generation of electrospray from a solution predeposited on optical fibers coiled with a platinum wire

This study examines the feasibility of generating electrospray directly from the tip of two optical fibers bound together with Teflon tape. This approach does not require a capillary and syringe pump. The electrospray source is simply constructed by coiling the two optical fibers with a platinum (Pt) wire. The optical fibers extend beyond the Pt coil for approximately 1 cm. The sample solution is predeposited on the Pt coil by a micropipette. As the high voltage required for electrospray is applied to the coil, the sample solution moves along the grooves between the two optical fibers. A stable electrospray is subsequently generated at the tip of the fibers. The mass spectra of insulin, lysozyme, and ubiquitin are exactly the same as those obtained by conventional electrospray using a capillary and syringe pump. Rapid determination of the active ingredient in a tablet by this technique is demonstrated.     

Evaluation of headspace solid-phase microextraction for analysis of phosphine residues in wheat

In headspace (HS) analysis, a fumigant is released from a commodity into a gas-tight container by grinding, heating, or microwaves. A new technique uses HS-solid-phase microextraction (SPME) for additional preconcentration of fumigant. HS-SPME was tested for detection of phosphine (PH3), chosen for examination because of its wide use on stored commodities. PH3 was applied to 50 g wheat in separate 250 mL sealed flasks, which were equipped either with a septum for conventional HS analysis or with one of four HS-SPME fibers [100 microm polydimethylsiloxane (PDMS), 85 microm carboxen (CAR)/PDMS, 75 microm CAR/PDMS, and 65 pm PDMS/divinylbenzene (DVB)]. The wheat was heated at 45 degrees C for 20 min. In conventional HS analysis, a gaseous aliquot (80 pL) was taken from the HS and injected into the GC instrument. In the HS-SPME procedure, the fiber was removed from the HS and exposed in the heated injection port of the GC instrument. In all cases, PH3 was determined under the same chromatographic conditions with a GC pulsed flame photometric detector. In a comparison of the efficacy of the fibers, the bipolar fibers (CAR/PDMS and PDMS/DVB) contained more PH3 than the aliquot in the conventional HS analysis; larger size bipolar fibers extracted PH3 more efficiently than smaller fibers (e.g., 85 > 75 > 65 microm). The nonpolar fiber (PDMS) contained no PH3. Four fortification levels of PH3 on wheat were tested: 0.01, 0.05, 0.1, and 0.3 microg/g. The response of each bipolar fiber increased with the fortification levels, but the conventional HS analysis detected no fumigant at the lowest fortification level of 0.01 mg/g. Under the conditions of the validation study, the LOD was in the range of 0.005-0.01 ng PH3/g wheat.     

Field air analysis with SPME device

Solid-phase microextraction (SPME) devices were used for a wide scope of air-monitoring including field sampling and analysis of volatile organic compounds (VOCs), formaldehyde, and particulate matter (PM) in air. Grab (instantaneous) and time-weighted average (TWA) sampling were accomplished using exposed and retracted SPME fibers, respectively. Sampling time varied from 1 to 75 min, followed by analysis with a gas chromatograph (GC). A portable GC equipped with unique, in-series detectors: photoionization (PID), flame ionization (FID), and dry electrolytic conductivity (DELCD), provided almost real-time analysis and speciation for common VOCs during an indoor air quality surveys. Indoor air samples collected with SPME devices were compared with those collected using conventional National Institute for Occupational Safety and Health (NIOSH) methods. Air concentrations measured with the SPME device were as low as 700 parts-per-trillion (ppt) for semi-volatile organic compounds. SPME methodology proved to be more sensitive than conventional methods, and provided a simple approach for fast, cost-effective sampling and analysis of common VOCs in indoor air. SPME technology combined with fast portable GC reduced the sampling and analysis time to less than 15 min. The configuration offered the conveniences of immediate on-site monitoring and decision making, that are not possible with conventional methods. In addition, SPME fibers were applied to sampling of particulate matter in diesel engine exhaust. Linear uptake and particulate build-up on the fiber were observed. Preliminary research suggests that SPME fibers could also be applied to sampling of airborne particulate matter.     

基于硒化镓纳米片填充的空芯光纤超高二次谐波增强

与传统的光学晶体相比,全光纤功能器件由于和光纤系统的天然兼容性,被认为是下一代集成光学的重要研究方向,吸引了人们的广泛关注。然而,由于二氧化硅固有的中心反演对称性质,光纤中的二阶非线性光学过程仍有待探索,这在可调谐超快激光、全光信号处理、成像和光通信等商业全光纤非线性光学应用中具有重要意义。因此,我们提出了一种新的溶液填充方法,可有效地将具有高非线性的硒化镓纳米片直接沉积在长度达半米的空芯光纤(HCF)的内孔壁上。此外,采用制备的硒化镓纳米片-空芯光纤(GaSe-HCF)作为光频率转换器,其二次谐波(SHG)比嵌入MoS₂的HCF和普通HCF分别提高了2个数量级和3个数量级。我们的研究成果将拓展其它非线性材料在全光纤高端非线性光学和光电子学中的应用,并提供新的制备思路。     

Study of dye diffusion in fibers by laser scanning confocal microscopy

The diffusion of a fluorescent dye in nylon 66 fibers was studied by using a laser scanning confocal microscope (LSCM) and by a conventional method. The diffusion coefficients were determined by both methods and they were in close agreement. The study of dye diffusion in fibers by LSCM is simple, quick and also able to provide high resolution images of fiber cross-sections and 3D images of the dye distribution in fibers. To our knowledge this is the first report of using a LSCM to study dye diffusion in polymeric fibers.     

Segmental and chain orientational behavior of spandex fibers

The internal structure and orientation behavior of two series of spandex fibers, which were made with different spinning methods and different soft and hard segment types, were studied by FTIR (Fourier Transform Infrared Spectroscopy), polarizing light microscopy, and Instron. The orientation behavior of hard and soft segments was studied with FTIR and those of polymeric chains with polarizing miscroscopy while the fibers were being stretched by the mechanical stretcher. The orientation behavior of dry-spun fibers was observed to be very different from that of the melt-spun fibers, which may be explained in terms of the internal structural difference such as the degree of phase separation and mechanical stability of the hard domains between the two types of fibers. In general, the dry-spun fibers showed better elastic recovery property than the melt-spun fibers. Since the polymer for the dry-spun fibers was synthesized with ethylene diamine as a chain extender resulting in the urea groups in the hard segments, it forms more stable hard domain due to the high cohesion energy between the urea groups. The change of the birefringence values during the cyclic deformation was studied with the polarizing light microscopy. The birefringence behaviors of the two dry-spun fibers were similar, whereas there was a noticeable difference between the two melt-spun fibers. The difference was explained in terms of the effect of crosslinking agent in one of the melt-spun fibers, which can stabilize the hard domain structure against the external stress. Mechanical hysteresis values measured gave results consistent with those of FTIR and birefringence measurements. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1821–1832, 1997     

Solid Phase Microextraction Fibers Coated with Sol-gel Aminopropylsilica/polydimethylsiloxane: Development and Its Application to Screening of Beer Headspace

The preparation and applicability of solid phase microextraction (SPME) fibers coated with a sol-gel organically modified silica based on 3-aminopropyltrimethoxysilane and polydimethylsiloxane (APTMS/PDMS) are described here. Micrographs of the coated fibers revealed a rugous surface; the thickness of the coating was estimated to be less than 30 microm. The APTMS/PDMS fibers were tested with synthetic samples and compared to commercial fibers for headspace SPME analysis of beer. Extraction and desorption using the APTMS/PDMS fibers were faster, which is typical for sol-gel SPME fibers. For polar and semi-polar compounds on beer headspace, the extraction efficiencies of the APTMS/PDMS fiber were superior to those of conventional fibers. The APTMS/PDMS fiber was found to be capable of extracting a broad range of analytes, including highly polar acidic species such as organic acids.     

核-壳结构壳聚糖/聚乙烯醇-聚碳酸亚丙酯超细纤维的制备

利用同轴电纺丝技术制备出具有核-壳结构的壳聚糖/聚乙烯醇-聚碳酸亚丙酯电纺丝纤维,考察了溶剂复配对成纤的影响,采用扫描电镜和透射电镜对纤维的形貌、结构、直径分布等进行了探索,并在优化的工艺条件下,将羟基磷灰石负载在内层结构中.研究表明,采用氯仿/N,N-二甲基甲酰胺(1/1)复配溶剂可有效避免聚合物溶液在喷丝口处的凝结现象.同单纺纤维相比,核壳结构的纤维直径分布较宽,纤维壳层和核层界限清晰;红外谱图分析证明羟基磷灰石可负载在纤维的核结构中.     

Axial X-ray scattering on high-performance polymeric fibers

High-temperature polymers were spum from liquid-crystalline solutions into fibers of superior thermal stability and mechanical properties. Fibers of two extended-chain polymers poly(p-phenyleneterephthalamide), PPTA, and poly-2,5-benzoxazole, ABPBO, as well as a rod-like polymer poly(p-phenylenebenzobisoxazole), PBO, were examined by axial x-ray scattering. Both wide-angle scattering and small-angle scattering were performed with CuKα radiation aiming along the fiber axis (c-axis) for structural information on the a-b lattice plane. In addition to previously reported lattice structure, the PPTA fibers (Kevlar® 29, 49, and 149) showed strong [004] and a [022] reflections suggesting that segments of the PPTA molecules were transverse to the fiber axis. This unique fiber structure is more prominent and the void content is less for the PPTA fibers with higher tensile modulus, (i.e., Kevlar® 149 > Kevlar® 49 > Kevlar® 29). Similar measurements on thermally annealed ABPBO and PBO fibers showed no [00l], [h0l], or [0kl] reflection indicative of a truly uniaxial molecular orientation. Evidence of microfibrillar order was discovered for the Kevlar® fibers and the ABPBO fiber. Results of conventional x-ray scattering on these fibers were compared and reconciled. © 1994 John Wiley & Sons, Inc.     

Effect of the Micronization of Pulp Fibers on the Properties of Green Composites

Green composites, composed of bio-based matrices and natural fibers, are a sustainable alternative for composites based on conventional thermoplastics and glass fibers. In this work, micronized bleached Eucalyptus kraft pulp (BEKP) fibers were used as reinforcement in biopolymeric matrices, namely poly(lactic acid) (PLA) and poly(hydroxybutyrate) (PHB). The influence of the load and aspect ratio of the mechanically treated microfibers on the morphology, water uptake, melt flowability, and mechanical and thermal properties of the green composites were investigated. Increasing fiber loads raised the tensile and flexural moduli as well as the tensile strength of the composites, while decreasing their elongation at the break and melt flow rate. The reduced aspect ratio of the micronized fibers (in the range from 11.0 to 28.9) improved their embedment in the matrices, particularly for PHB, leading to superior mechanical performance and lower water uptake when compared with the composites with non-micronized pulp fibers. The overall results show that micronization is a simple and sustainable alternative for conventional chemical treatments in the manufacturing of entirely bio-based composites.     

Preparation and application of the sol-gel-derived acrylate/silicone co-polymer coatings for headspace solid-phase microextraction of 2-chloroethyl ethyl sulfide in soil

Three types of novel acrylate/silicone co-polymer coatings, including co-poly(methyl acrylate/hydroxy-terminated silicone oil) (MA/OH-TSO), co-poly(methyl methacrylate/OH-TSO) (MMA/OH-TSO) and co-poly(butyl methacrylate/OH-TSO) (BMA/OH-TSO), were prepared for the first time by sol-gel method and cross-linking technology and subsequently applied to headspace solid-phase microextraction (HS-SPME) of 2-chloroethyl ethyl sulfide (CEES), a surrogate of mustard, in soil. The underlying mechanisms of the coating process were discussed and confirmed by IR spectra. The selectivity of the three types of sol-gel-derived acrylate/silicone coated fibers was studied, and the BMA/OH-TSO coated fibers exhibited the highest extraction ability to CEES. The concentration of BMA and OH-TSO in sol solution was optimized, and the BMA/OH-TSO (3:1)-coated fibers possessed the highest extraction efficiency. Compared with commercially available polyacrylate (PA) fiber, the sol-gel-derived BMA/OH-TSO (3:1) fibers showed much higher extraction efficiency to CEES. Therefore, the BMA/OH-TSO (3:1)-coated fibers were chosen for the analysis of CEES in soil matrix. The reproducibility of coating preparation was satisfactory, with the RSD 2.39% within batch and 3.52% between batches, respectively. The coatings proved to be quite stable at high temperature (to 350 degrees C) and in different solvents (organic or inorganic), thus their lifetimes (to 150 times) are longer than conventional fibers. Extraction parameters, such as the volume of water added to the soil, extraction temperature and time, and the ionic strength were optimized. The linearity was from 0.1 to 10 microg/g, the limit of detection (LOD) was 2.7 ng/g, and the RSD was 2.19%. The recovery of CEES was 88.06% in agriculture soil, 92.61% in red clay, and 101.95% in sandy soil, respectively.     

Progress in low‐loss and high‐bandwidth plastic optical fibers

Plastic optical fibers (POFs) are highly promising transmission media for future home networking.In comparison to glass optical fibers (GOFs), which are commonly used in core and metropolitan networks, POFs offer many advantages such as great flexibility and easy handling. This review begins with the basic concepts of optical fibers and moves on to the early history of loss reduction in POFs. What drastically changed the status of POFs in the communications field was a graded‐index technology that improved the bandwidth to over 1 gigabits per second. However, even after the loss and bandwidth were enhanced to their limits, the performances of POFs were insufficient for market demand when using conventional optical polymer materials such as poly(methyl methacrylate). Recently, this problem has been solved by several lines of material research using fluorinated polymers. As a result, high‐speed optical home networking by POFs has become more realistic. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Efficient Use of Carbon Fibers as Heating Elements for Curing of Epoxy Matrix Composites

The aim of this study is to achieve a fully cured thermoset matrix that is heated by a direct electric current passing through the reinforcement fibers i.e., the Joule heating effect. Two types of fibers were used as heating elements for curing the epoxy resins. Kanthal resistance fibers were used as reference heating elements and subsequently, they were replaced by a Torayca Carbon Tow of the same radius. The specimens were cured by the heat produced by a direct electric current passing through the fibers and achieving temperatures of 50 °C and 70 °C. Specimens cured in a conventional oven were also manufactured, to compare the resistance heating method to the conventional one. Next, all specimens were mechanically characterized in a quasi-static three-point bending mode of loading and experimental results were compared to derive useful conclusions concerning the applicability of the technique to polymer/composite materials mass production. Finally, a preliminary economical study concerning power consumption needed for the application of both the traditional oven curing and the carbon fibers heating elements use for the manufacturing of the same amounts of materials is presented, showing a maximum financial benefit that can be achieved, on the order of 68%.     

Symmetric and helical growth of polyacetylene fibers over a single copper crystal derived from copper tartrate decomposition

[reaction: see text] Helical polyacetylene fibers with absolutely symmetric structures were prepared by polymerization of acetylene using copper tartrate as a catalyst. There were always only two coiled polyacetylene fibers grown on a single copper nanocrystal. The two coiled fibers had absolutely opposite helical senses but were identical in cycle number, coil diameter, coil length, coil pitch, and fiber diameter.     

Nano‐emulsion use for the synthesis of polyaniline nano‐grains or nano‐fibers

We report that nano‐emulsions can be creatively used as a morphology selective synthesis method to prepare not only nano‐grains but also nano‐fibers with high selectivity. Synthesis of the two different morphological materials was demonstrated using polyaniline synthesis as a model case. Polyaniline nano‐grains were synthesized from aniline molecules in nano‐size aqueous droplets as polymerization sites whose droplets were generated by inverse water‐in‐oil nano‐emulsion use, and polyaniline nano‐fibers were synthesized from aniline in aqueous nano‐dimensional channels as polymerization sites whose channels were generated by direct oil‐in‐water nano‐emulsion use containing high population of oil droplets. Using the approaches, we successfully synthesized nano‐fibers of 60 nm diameter with 0.5 µm length and also nano‐grains having diameter of 60–80 nm. The two different polymerization sites of nano‐scale dimension were made by changing the ratio among surfactant, aqueous aniline/HCl solution, and oil, i.e. organic solvent. We found the nano‐fibers synthesized from the channels formed by the direct oil‐in‐water nano‐emulsion have higher bulk electrical conductivity than the nano‐grains which were synthesized from the droplets formed by the inverse water‐in‐oil emulsion. We also found that the emulsion use allows us to use a room temperature synthesis unlike conventional synthesis methods which require to use ice bath temperature. Physical properties of both nano‐fibers and nano‐grains synthesized were characterized by Fourier transform infrared (FTIR), UV–Vis spectra, scanning electron microscopy (SEM), and four probes conductivity measurement. Copyright © 2009 John Wiley & Sons, Ltd.     

Correlation between processing conditions,microstructure and mechanical behavior in regenerated silkworm silk fibers

Regenerated silkworm fibers spun through a wet‐spinning process followed by an immersion postspinning drawing step show a work to fracture comparable with that of natural silkworm silk fibers in a wide range of spinning conditions. The mechanical behavior and microstructure of these high performance fibers have been characterized, and compared with those fibers produced through conventional spinning conditions. The comparison reveals that both sets of fibers share a common semicrystalline microstructure, but significant differences are apparent in the amorphous region. Besides, high performance fibers show a ground state and the possibility of tuning their tensile behavior. These properties are characteristic of spider silk and not of natural silkworm silk, despite both regenerated and natural silkworm silk share a common composition different from that of spider silk. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

连续SiC(Al)纤维的耐超高温性能及其机理

以有机金属聚合物聚铝碳硅烷为原料, 利用先驱体转化法制备出连续SiC(Al)纤维. 采用一系列分析测试对纤维的组成、结构以及耐超高温性能进行了表征, 通过与Nicalon纤维的比较, 对连续SiC(Al)纤维的耐超高温机理进行了研究. 结果表明, 连续SiC(Al)纤维具有优异的耐超高温性能,在1800 ℃氩气中处理1 h后, 纤维的强度保留率为80%左右; 元素分析和27Al MAS核磁共振等分析表明, 连续SiC(Al)纤维为近化学计量比的SiC纤维, 纤维中微量的铝元素以Al—O和Al—C键两种形式存在; 在超高温条件下, 两种不同存在形式的铝均能够抑制纤维中晶粒的长大. 纤维具有近化学计量比的组成和铝元素在高温条件下对于晶粒长大的抑制, 是连续SiC(Al)纤维具有优异耐超高温性能的原因.     

A PMMA composite as an optical diffuser in a liquid crystal display backlighting unit (BLU)

The effect of thermo-physical properties, relative humidity and stiffness on the warpage of a poly(methyl methacrylate) (PMMA) diffusing plate modified with glass fibers in a direct-lit backlight unit (BLU) of a liquid crystal display (LCD) was investigated. The warpage of the PMMA diffusing composites modified with a glass fiber were significantly reduced relative to that of a conventional PMMA diffusing plate. Luminance and scattering characteristics of the PMMA diffusing composites having 5, 10, 20 vol% of glass fibers were measured. Although the luminance of the composite was lowered as increasing the volume fractions of glass fibers in the PMMA composites, good brightness uniformity of the composites on a light source was obtained.     

Preparation of polybenzoxazole fibers via electrospinning and postspun thermal cyclization of polyhydroxyamide

Polybenzoxazole (PBO) fibers with a submicron diameter were successfully prepared by electrospinning its precursor, polyhydroxyamide (PHA), solutions to obtain the PHA fibers first, followed by appropriate thermal treatments for cyclization reaction. BisAPAF‐IC PHA with two different molecular weights (MWs) were synthesized from a low temperature polymerization of 2,2′‐bis(3‐amino‐4‐hydroxyphenyl) hexafluoropropane (BisAPAF) and isophthaloyl chloride (IC). Using dimethylacetamide (DMAc) and tetrahydrofuran (THF), solvent effects on the electrospinnability of PHA solutions were investigated. For balancing the solution properties, it was found that DMAc/THF mixture with a weight ratio of 1/9 was the best cosolvent to prepare smooth PHA fibers; uniform PHA fibers with a diameter of 325–720 nm were obtained by using 20 wt % PHA/(DMAc/THF) solutions. For a fixed PHA concentration, solutions with a lower MW of PHA yielded thinner electrospun fibers under the same electrospinning condition. After obtaining the electrospun BisAPAF‐IC PHA fibers, subsequent thermal cyclization up to 350 °C produced the corresponding thermally stable BisAPAF‐IC PBO fibers with a diameter of 305–645 nm. The structure of the precursor fibers and the fully cyclized fibers were characterized by FTIR. For the cyclized BisAPAF‐IC PBO fibers, thermogravimetric analysis showed a 5% weight loss temperature at 523 °C in nitrogen atmosphere. The interconnected fiber structure in the BisAPAF‐IC PBO fiber mats was irrelevant to the curing process, but resulted from the jet merging during the whipping process as revealed by the high speed camera images. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8159–8169, 2008