Solvent treatment inducing ultralong cycle stability poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) fibers as binding-free electrodes for supercapacitors

As one kind of conducting polymer composite, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) has been widely used as an electrode for energy storage and conversion devices because of its optical transmittance, flexibility, and high electrical conductivity etc. Here, we prepared binding-free PEDOT:PSS fibers (PFs) electrodes with high capacitive performance for supercapacitors via a facile method followed by various solvent treatments. Dimethyl sulfoxide (DMSO)-treated electrodes displayed a better specific capacitance (C_s) of 202 F/g at 0.5 A/g with higher elongation at break, flexibility, and conductivity of 140.7 S/cm, compared to those of pristine PEDOT:PSS materials. More importantly, the DMSO-treated fibers possessed improved stability, which retained 105% of the initial C_s after 22 000 long cycles at 10 A/g. It is believed that the fabricated PFs will be promising organic electrodes for portable supercapacitors and other flexible electronic devices in the near future.     

OPPC预绞式耐张线夹处光纤温度研究

针对光纤复合架空相线(OPPC)预绞式耐张线夹处光纤温度对OPPC使用寿命影响的问题,文章提出在耐张线夹处加装一根截面相等的分流线的方案,并采用光纤测温法对3种试验规格的OPPC(630/45、400/50、185/30)进行“电流-温升”试验。试验结果表明,未加装分流线时,当非耐张线夹处OPPC表面温度为设计要求的70℃时,此处光纤温度小于80℃,而3种规格的OPPC耐张线夹处内部光纤温度均大于95℃,超过了公认的85℃的光纤最高安全运行温度;在加装分流线后,耐张线夹处光纤温度降至85℃以下,避免了长期的高温环境加速光纤涂层的老化而失去对光纤的保护,保证了OPPC的30年设计寿命。     

Scalable optical fiber reactor for photocatalytic H2 production: Addressing scattering issues

Scattering is one of the main challenges in scaling up photocatalytic water splitting using the most prevalent powder catalysts. This can be overcome by decoupling the reaction medium from light transmission, as in the case of optical fibers. Here we explore utilizing optical fibers coated with 5 wt% CuO supported on TiO₂ for photocatlytic H₂ production from water-methanol mixtures. CuO/TiO₂ is a well studied photo catalyst in which photoreduced Cu species are known to act as sensitizers for inducing visible light activity. Lower activity of sequentially coated systems indicates that appropriate interfaces of active Cu and TiO₂ with water are desirable. The scalability of such optical fiber-based systems along with potential in non-potable turbid water media are demonstrated. Maximum activity of 22 μmoles of H₂ in 8 h was obtained with 50 mg of catalyst coated on optical fibers, which increases linearly with increase in fiber numbers, whereas, drastic reduction in activity is observed in powder catalyst upon increasing the catalyst quantity. A one-to-one comparison of 700 mg of catalyst in powder form and coated on optical fibers indicates more than one order enhancement in activity in the optical fiber based system. In addition, ∼70% retention in activity in highly turbid non-potable water was observed as compared to powdered system which shows complete reduction in the activity by 99.99%.     

Fabrication of porous titanium dioxide fibers and their photocatalytic activity for hydrogen evolution

TiO₂ semiconductor is one of the important photocatalysts for solar light conversion. The challenge is how to improve their efficiency. Creation of porous structures on/in the fibers could favor them a higher surface area as compared to the conventional solid counterparts, which thus could make the achievement for the desired high efficiency. In present work, we report the fabrication of porous TiO₂ fibers with high purity via electrospinning of butyl titanate (TBOT) and polyvinylpyrrolidone (PVP) combined with the subsequent calcination in air. It is found that the TBOT content in the spinning solution plays a profound effect on the growth of the fibers, enabling the synthesis of porous TiO₂ fibers with tunable structures and high purity. The photocatalytic activity for hydrogen evolution of the as-fabricated TiO₂ nanostrcutres has been investigated, suggesting that porous TiO₂ nanomaterials with a high purity and well-defined one-dimensional fiber shape could be an excellent candidate to be utilized as the photocatalyst for hydrogen evolution.     

The use of plastic optical fibers in photocatalysis of trichloroethylene

In this study, plastic optical fibers (POFs) were considered as light-transmitting media and substrates for the potential use in photocatalytic environmental purification system and the performance of POFs was also compared with that of quartz optical fibers (QOFs). After the characteristic of POFs in terms of light transmittance was determined in the beginning, detailed investigation was further conducted through the photocatalytic degradation of trichloroethylene. It is concluded that the use of POFs is preferred to QOFs since the advantages such as ease of handling, lower cost, relatively reasonable light attenuation at the wavelength of near 400 nm can be obtained.     

Optical properties of polymeric materials for concentrator photovoltaic systems

As part of our research on materials for concentrator photovoltaics (CPV), we are evaluating the optical properties and solar radiation durability of a number of polymeric materials with potential in CPV applications. For optical materials in imaging or non-imaging optical systems, detailed knowledge of the wavelength-dependent complex index of refraction is important for system design and performance, yet optical properties for many polymeric systems are not available in the literature. Here we report the index of refraction, optical absorbance, haze, and Urbach edge analysis results of various polymers of interest for CPV systems. These values were derived from ellipsometry and from using a VUV-VASE and transmission based absorbance spectroscopy on thick film samples.Fluoropolymers such as poly(tetrafluoroethylene-co-hexafluoropropylene) (Teflon^® FEP), poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether) (Teflon^® PFA) and poly(ethylene-co-tetrafluoroethylene) (Teflon^® ETFE Film) have desirable optical and physical properties for optical applications in CPV. Ethylene backbone polymers such as polyvinylbutyral (PVB) sheet (e.g., DuPont^TM PV5200), and ethylene co-polymers such as poly(ethylene-co-vinyl acetate) (EVA) (e.g., DuPont^TM Elvax^® PV1400), and poly(ethylene-co-methacrylic acid metal salt) ionomer sheet (e.g., DuPont^TM PV5300) have applications as encapsulants in crystalline silicon (c-Si) and other flat plate PV applications. These materials are available with both a wide variety of polymer compositions and additive packages which affect their optical properties such as the UV absorption edge. Even materials such as DuPont’s Kapton^® polyimide films, which are used behind the PV cell for their electrically insulating properties, have optical requirements, and we have also characterized these materials.The detailed optical properties of these materials will be useful in the design of the geometrical optics of a CPV system and optimization of the system’s optical throughput. This information will also provide insights into the system’s optical absorption. This is important, for example in the UV, where this absorption can impact the radiation durability of the materials.     

Preparation and electrochromic properties of spin self-assembled polyelectrolyte multilayer films composed of PEDOT:PSS and PAH

Polyelectrolyte multilayer films composed of a polycation (poly(allylamine hydrochloride) PAH) and a polyanion (poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) PEDOT:PSS) were prepared by a spin self-assembly method, and their electrochemical and electrochromic properties were investigated. The change in the surface charge and the optical absorption spectra of the multilayer films revealed that sequential deposition of polyelectrolyte was successfully achieved during the spin self-assembly. The electrochromic properties of 20-bilayered PAH/PEDOT:PSS were also investigated. The response time for the coloring and bleaching processes was 6.2 and 2.5 s, respectively, and the coloration efficiency was 199.3 cm²/C. These results indicate that a spin self-assembly process could be a viable alternative for the fabrication of electrochromic devices.     

Reversible hydrogen storage in electrospun polyaniline fibers

Due to its many physisorption sites as well as chemisorption sites, polyaniline (PANI) has been investigated for hydrogen storage purposes. The PANI was produced in house via traditional chemical synthesis methods and then electrospun to produce fibers. These PANI fibers were investigated and compared with standard bulk PANI and found to be stable up to 150 °C. When investigating PANI fibers, using PCT measurements, it was found that a reversible hydrogen storage capacity of ∼3–10 wt.% could be obtained at different temperatures. Hydrogen kinetic sorption measurements in prolonged cycles (up to 66 cycles) reveal an uptake and release of >6–10 wt.% on these PANI materials. The importance of the type of measurement is discussed as to its effect on the morphology and structure of the PANI nanofibers. The surface morphologies before and after hydrogen sorption on these PANI fibers encompass significant changes in the microstructure (nanofibrallar swelling effect). Detailed chemical and physical characterization of the PANI fibers is reported as part of this work.     

Optical fibers and solar power generation

A study of the potential use of optical fibers for solar thermal power generation is presented. The main performance characteristics (numerical aperture and attenuation) and typical costs of currently available fibers are discussed. Several approaches to the application of fibers are presented, for centralized (tower, central receiver) and distributed (dish–engine) systems. The overall system design-point efficiency and overall system cost are estimated. A scaling relation between system size and the cost of the fiber component is identified, which severely limits the applicability of fibers to small systems only. The overall system cost for centralized systems is found to be higher than the currently competitive range, even under optimistic assumptions of mass production of major components. A significant reduction in fiber cost is required before the use of fibers for centralized solar power generation can become competitive. In distributed generation using dish/engine systems, however, the use of fibers does achieve competitive performance and costs, comparable to the costs for conventional dish systems.     

Solar light transmission of polymer optical fibers

Light transfer (10 m) has been shown in recent experiments that used large-core optical fibers. Theoretical models are not extensive, however, and a further correlation between the theory and experiments has not been given. In this paper, straight and bent fiber subsystem models are introduced with skew and meridional rays to predict the light transmission of POFs (plastic optical fibers). Such fibers have been realized, for example, in HSL (hybrid solar lighting) systems. The purpose of this paper is to combine the straight and bent fiber subsystems to estimate the light transmission of HSL systems. It is shown that meridional rays, for which the optical-loss parameters were estimated, better represent the experimental results compared to skew rays (±5.3% vs ±24.7% of %-difference). Model predictions were compared with the results of a commercial software. Sensitivity analysis on the subsystems indicated the most-to-least significant parameters in light transmission.     

白腐菌对染料废水脱色的研究

白腐菌利用其分泌的特殊降解酶系或其它机制能将各种合成染料彻底降解为CO2和H2O,并具有良好的脱色效果。实验采用白腐菌为黄孢原毛平革菌,分别研究了不同废水浓度、不同染料废水投加时间、不同染料废水pH值、振荡等条件对模拟染料废水的脱色效果的影响。     

Effect of strong base addition to hole-collecting buffer layer in polymer solar cells

We report a brief study on the effect of strong base addition to the hole-collecting buffer layer [poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)] on the performance of polymer solar cells made using blend films of poly(3-hexylthiophene) and soluble fullerene. A concentrated aqueous solution of sodium hydroxide (NaOH) was added to the PEDOT:PSS solution to decrease its acidity. The optical absorption spectra of modified buffer layers were measured to investigate the influence of NaOH addition on the spectral shape, while the surface of modified buffer layers was examined using atomic force microscopy. Results showed that the acidity of PEDOT:PSS solutions was remarkably reduced by adding the NaOH solution. However, the performance of solar cells was slightly degraded, which has been attributed to the decreased charge transportability as evidenced from the dark current-voltage characteristics.     

Analytical Monte Carlo Ray Tracing simulation of radiative heat transfer through bimodal fibrous insulations with translucent fibers

In this study, a Monte Carlo Ray Tracing (MCRT) simulation technique is developed to study steady-state radiative heat transfer through fibrous insulation materials. The simulations are conducted in 3-D disordered virtual fibrous media with unimodal and/or bimodal fiber diameter distributions consisting of fibers whose surfaces are specularly reflective, and are translucent to Infrared (IR) radiation. Scattering within the realm of geometric optics is incorporated into our MCRT simulations using Snell’s Law for ray refraction. Fibers’ optical properties are obtained from Fresnel’s law and Beer’s law based on the refractive index of the material. Two different treatments of “high” and “low” conductivities are considered for the fibers and their effects are discussed. Our results indicate that heat flux through a fibrous medium with translucent fibers decreases with increasing packing fraction of the fibers. It was observed that IR transmittance through the media increases with increasing through-plane orientation of the fibers, but is independent of their in-plane orientations. It was also found that fiber orientation has generally a negligible effect on the temperature profile across the media’s thickness. However, for the case of high-conductivity fibers, increasing fibers’ through-plane orientation tends to flatten the temperature profile. The results obtained from simulating bimodal fibrous structures indicate that increasing the fiber-diameter dissimilarity, or the mass fraction of the coarse fibers, slightly increases the radiation transmittance through the media, and accordingly reduces the temperature gradient across the thickness. Our simulation results are compared with those from the two-flux model and good agreement is observed.     

Preparation of a low proton resistance PBI/PTFE composite membrane

We present a method for fabrication of poly(benzimidazole)/porous poly(tetra fluorocarbon) (PTFE) composite membranes. A coupling agent containing perfluorocarbon sulfonic acid ionomer is used as an interface between PTFE and poly(benzimidazole) (PBI), which contained –NH groups. The porous PTFE substrate was impregnated with a diluted PFSI coupling agent solution. The optimum concentration of the coupling agent solution was that the concentration of coupling agent was just high enough to cover the surface of the fibers of the porous PTFE substrate membranes. The PBI solutions were then fabricated onto the PTFE membranes containing the coupling agent to prepare the proton exchange composite membranes. The PBI/PTFE composite membrane had a film thickness of ∼22 μm and thus a lower proton resistance than a PBI membrane with a film thickness of ∼100 μm. The PEMFC single cell tests showed that PBI/PTFE composite membrane had a better performance than PBI.     

Optimization of a thermal manufacturing process: Drawing of optical fibers

The optimization of thermal systems and processes has received much less attention than their simulation and often lags behind optimization in other engineering areas. This paper considers the optimization of the important thermal manufacturing process involved in the drawing of optical fibers. Despite the importance of optical fibers and the need to enhance product quality and reduce costs, very little work has been done on the optimization of the process. The main aspects that arise in the optimization of such thermal processes are considered in detail in order to formulate an appropriate objective function and to determine the existence of optimal conditions. Using validated numerical models to simulate the thermal transport processes that govern the characteristics of the fiber and the production rate, the study investigates the relevant parametric space and obtains the domain in which the process is physically feasible. This is followed by an attempt to narrow the feasible region and focus on the domain that could lead to optimization. Employing standard optimization techniques, optimal conditions are determined for typical operating parameters. The study thus provides a basis for choosing optimal design conditions and for more detailed investigations on the feasibility and optimization of this complicated and important process.     

Optical Measurement of Void Fraction and Bubble Size Distributions in a Microchannel

An optical measurement system was developed to investigate gas-liquid two-phase flow characteristics in a circular microchannel of 100 μ m diameter. By using multiple optical fibers and infrared photodiodes, void fraction, gas and liquid plug lengths, and their velocities were measured successfully. The probes responded to the passage of gas and liquid phases through the microchannel adequately so that the time-average void fraction could be obtained from the time fraction for each phase. Also, by cross-correlating the signals from two neighboring probes, the interface velocity representing gas plug velocity or ring-film propagation velocity depending on the flow pattern could be computed. Within the ranges of superficial gas and liquid velocities covered in the experiments (j _L = 0.2～0.4 m/s and j _G = 0～5 m/s), the gas plug length was found to increase with the increasing superficial gas velocity, but the liquid plug length was found to decrease sharply as the superficial gas velocity was increased; thus, the total length of the gas-liquid plug unit decreased with the superficial gas velocity.     

Electrospun phase change fibers based on polyethylene glycol/cellulose acetate blends

Ultrafine phase change fibers based on polyethylene glycol (PEG)/cellulose acetate (CA) blends in which PEG acts as a model phase change material (PCM) and CA acts as a supporting material, were successfully prepared via electrospinning. The effect of PEG content on the morphology, crystalline properties, phase change behaviors and tensile properties of the composite fibers was studied systematically by field-emission scanning electron microscopy (FE-SEM), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and a tensile tester, respectively. The SEM observation indicates that maximum PEG content in the fibers could reach up to 70 wt%, and the morphology and average diameter of the composite fibers vary with PEG content. Thermal analysis results show that the latent heats of the phase change fibers increase with the increasing of PEG content in the fibers, and the PEG/CA fibers with high enthalpies have a good capability to regulate their interior temperature as the ambient temperature alters. Therefore, the developed phase change fibers have enormous applicable potentials in thermal energy storage and temperature regulation.     

Numerical study on the dopant concentration and refractive index profile evolution in an optical fiber manufacturing process

The index of refraction is an important property of optical fibers, since it directly affects the bandwidth and optical loss during information transmission. The refractive index is governed by the dopant concentration distribution across the fiber cross section, which is strongly influenced by the processing conditions. An understanding of the effects of process parameters on the dopant concentration profile evolution is important to design the drawing process for tailored refractive index and optical transmission characteristics. Although the heat and momentum transport in optical fiber drawing have been studied extensively, little has been reported in the open literature on dopant concentration and index of refraction profile development during processing. This paper presents a two-dimensional numerical analysis on the flow, heat and mass transfer phenomena involved in the drawing and cooling process of glass optical fibers using a finite difference approach based on primitive variables. The effects of several important parameters are investigated in terms of nondimensional groups, including: fiber draw speed, inert gas velocity, furnace dimensions, gas properties, and dopant properties on the flow, temperature and dopant concentration distribution.     

Numerical simulation of the Czochralski growth process of oxide crystals with a relatively thin optical thickness

For the single crystal growth of an oxide, the global analysis of heat transfer in the inductively heated Czochralski (CZ) furnace was carried out to investigate the effect of optical properties of crystal on the CZ crystal growth process. Here, the finite volume method (FVM) was used as the radiative transfer model to solve the radiative transfer equation, and consequently the crystal with a relatively thin optical thickness (∼0.01) could be accounted for. As a result, it was found that the melt/crystal interface becomes more convex toward the melt for a small crystal rotational Reynolds number as the optical thickness of the crystal, κ_s, decreases, although its dependence is slight for κ_s < 0.1. In addition, the critical Reynolds number, at which the interface inversion occurs, decreases with the optical thickness of the crystal.     

Using fiber optics to tap the sun's power

This paper discusses a solar energy collection system in which optical fibers are used to transport energy from a single-stage and a double-stage, three-dimensional Compound Parabolic Concentrator (CPC). After developing a thermo-mathematical model for the assembly of CPC and fibers, numerical simulations are used to optimize the system design. The modules filled with plastic and glass are shown to perform considerably better than those filled with air. A two-stage system performs better than a single-stage module. CPC surface reflectance improves the yield but an increase in fiber length decreases the performance.