Thermal,spectral, magnetic and biologic characterization of new Ni(II), Cu(II) and Zn(II) complexes with a hexaazamacrocyclic ligand bearing ketopyridine moieties

Five types of fibrous assemblies, namely, polyester, wool, cashmere, kapok, and goose down, were tested for their heat-insulating properties in the natural state using the apparatus developed by the authors. The influences of bulk density, fiber type, fiber arrangements, and compression on the heat-insulating properties of the fibrous assemblies was examined systematically. The results show that kapok assembly with low bulk density, goose down assembly with high bulk density and the randomly arranged fibrous assembly demonstrated the best heat-insulating property; however, considering practical use and the influence of compression, kapok assembly and fibrous assemblies arranged in the form of fiber balls exhibited the most stable and optimum heat-insulating property. The Daryabeigi heat-transfer model that considers fiber contact and scattering effect was used to calculate the heat-insulating properties of the five fibrous assemblies. A similar model was developed by Fanworth, which neglected the fiber and the scattering effect. Comparison of the two models showed that the Daryabeigi model was more accurate in predicting the heat-insulating properties of fibrous assemblies.     

Sound absorption behavior of electrospun polyacrylonitrile nanofibrous membranes

The acoustical damping property of electrospun polyacrylonitrile(PAN) nanofibrous membranes with different thicknesses and porosities was investigated.The sound absorption coefficients were measured using the impedance tube instrument based on ISO 10534-2:1998(E).Results indicate that the first resonance absorption frequency of nanofibrous membranes shifts to the lower frequency with the increase of the back cavity or the thickness of membranes.Moreover,the sound absorption performance of the perforated panel can be greatly improved by combination with a thin layer of PAN nanofibrous membrane.Traditional acoustical damping materials(foam,fiber) coated with nanofibrous membranes have better acoustical performance in the low and medium frequency range than that of acoustical materials alone.All of the results demonstrate the PAN nanofibrous membrane is a suitable candidate for noise reduction.     

SOUND ABSORPTION BEHAVIOR OF ELECTROSPUN POLYACRYLONITRILE NANOFIBROUS MEMBRANES

The acoustical damping property of electrospun polyacrylonitrile(PAN) nanofibrous membranes with different thicknesses and porosities was investigated.The sound absorption coefficients were measured using the impedance tube instrument based on ISO 10534-2:1998(E).Results indicate that the first resonance absorption frequency of nanofibrous membranes shifts to the lower frequency with the increase of the back cavity or the thickness of membranes.Moreover,the sound absorption performance of the perforated ...     

聚合物阻尼材料的吸音系数研究

不同聚合物材料具有不同的吸声特征吸收峰,这对于研究聚合物材料的阻尼性能及其应用都有一定的意义。本文利用驻波管吸音系数测试仪测量了聚氧乙烯(PVC)聚合物材料在不同温度及频率下的吸系数,得到了不同频率下吸音系数和温度的关系图,与理论计算得到的谱图拟合较好,进一步的     

FACILE FABRICATION OF LARGE SCALE MICROTUBES WITH A NATURAL TEMPLATE—KAPOK FIBER

<正>A newly natural fine template,kapok fiber,for microtube preparation was reported.Large scale microtubes with high length/diameter ratio and controllable wall thickness and morphology have been successfully fabricated with this template.It is a wildly available,low-cost,environmental friendly and fine structured natural template for microtubes.Its thin wall thickness is only about 1-2μm that means the whole template material is tiny and easy for removing.Even there is any residue the amount can be ignored.When the template is covered with a shell component,hollow structured microtube could be obtained by removing the thin inner template,and its shape could be the same as that of the original template (positive copy of the template's shape).The products have high length/diameter ratio and uniform tubular structure.By further modifying the fabricating methods,facile fabrication not only exists for polypyrrole(PPy) in electrochemical deposition,but also for many other organic and inorganic materials.The surface morphology and wall thickness of the resultant microtubes can be easily modulated by controlling the processing conditions.This natural fiber is predicted to be a fine template for fabricating large scale microtubes with large cavity and high length/diameter ratio.     

纤维集合体内液体浸润的统计力学模型

采用Ising模型研究液体在纤维集合体内的浸润过程.假定纤维之间、纤维和液体之间的相互作用以van der Waals力为主,则纤维与液体之间的粘附能和液体内部的内聚能均可用Lifshitz理论计算（表面张力所作的功也被考虑在内）.该模型结合Monte Carlo 方法可用于模拟纤维集合体内液体浸润过程.模拟结果与芯吸实验相吻合,表明这一方法适用于液体在纤维集合体内浸润过程的研究.通过改变初始条件,该模型可进一步模拟液体在更加复杂的纤维结构内的浸润过程.     

Melt crystallization of polypropylene: Effect of contact with fiber substrates

The isothermal crystallization of isotactic polypropylene at different temperatures in the presence of fibrous substrates has been investigated. It is shown that preferential transcrystalline growth occurs at the fiber surface and that changes in nucleation density in the bulk material adjacent to the fibers also occur, the extent of which is dependent on temperature and fiber volume fraction. The effects are discussed in terms of the diffusion of heterogeneities in the bulk due to interaction and the adsorption on the fibers.     

Bio-based polybenzoxazine composites for oil-water separation,sound absorption and corrosion resistance applications

In the present work, an attempt has been made to develop bio-based composites using cardanol and eugenol based benzoxazine matrices with bio-silica as well as natural fibrous materials (coir felt, kapok fabric, jute felt and rice husk) as reinforcements. The bio-composites developed were studied for different applications viz., dielectric, water repellent, oil-water separation, sound-absorption including corrosion resistance use. Among the bio-silica reinforced benzoxazine composites, 7 wt% bio-silica reinforced cardanol composites possesses the highest value of water contact angle (147°) and the lowest value of dielectric constant (2.0) than those of other bio-silica reinforced composites. Further, the cotton fabric was coated with cardanol and eugenol based polybenzoxazines separately, whose values of water contact angles are found to be 159° and 157° with oil-water separation efficiency as 96% and 95% respectively. Furthermore, the cardanol based benzoxazine was separately reinforced with jute felt, coir felt, kapok fabric and rice-husk. The corresponding sound absorption efficiency was found to increase in the following order, Neat polybenzoxazine < rice husk < coir felt < kapok fabric < jute felt. Data resulted from corrosion studies, it was noticed that the mild steel specimen coated with bio-based benzoxazine matrices and bio-silica reinforced benzoxazine composites coated specimens exhibit an excellent resistance to corrosion. Data resulted from different studies, it is suggested that the cardanol and eugenol based bio-composites can be considered as an effective materials for microelectronics insulation, water repellent, oil-water separation, sound absorption and corrosion resistant applications.     

Light Electrospun Polyvinylpyrrolidone Blanket for Low Frequencies Sound Absorption

Light polymeric soundproofing materials(density = 63 kg/m~3) of interest for the transportation industry were fabricated through electrospinning. Blankets of electrospun polyvinylpyrrolidone(average fiber diameter =(1.6 ± 0.5) or(2.8 ± 0.5) μm) were obtained by stacking disks of electrospun mats. The sound absorption coefficients were measured using the impedance tube instrument based on ASTM E1050 and ISO 10534-2. For a given set of disks(from a minimum of 6) the sound absorption coefficient changed with the frequency(in the range 200–1600 Hz) following a bell shape curve with a maximum(where the coefficient is greater than 0.9) that shifts to lower frequencies at higher piled disks number and greater fiber diameter. This work showed that electrospinning produced sound absorbers with reduced thickness(2–3 cm) and excellent sound-absorption properties in the low and medium frequency range.     

Multi-electron transfer reactions and exciton interactions in fibrous porphyrin and metalloporphyrin assemblies

Non-covalent porphyrin and metalloporphyrin fibers of bimolecular thinness in bulk aqueous media are compared with the well-known H- and J-aggregates of cyanines. The J-aggregates of cyanines fluoresce and are useful as photographic sensitizers. The J-aggregates of porphyrins show light-induced charge separation and the corresponding metal complexes produce stable radical dimers. The distance between the metalloporphyrin centers is calculated from circular dichroism spectra to be 8 Å in the J-aggregates and about 4 Å in the H-aggregates. Multi-electron reactions of the fibers in the ground and excited states can therefore occur in the fibrous porphyrin assemblies. In amphiphilic tetraphenylporphyrins (“octopus porphyrin”), on the other hand, the porphyrin–porphyrin distance is much larger and the fiber dissolves electron-accepting compounds, e.g. quinones, which also allow for multiple charge separation within such a fiber.     

Continuous In Situ Oil Recovery From Oil/Water Mixture with Natural Kapok Fiber and External Pumping

An oil recovery system composed of an oil capture module packed kapok fibers and a vacuum pump was developed for continuous oil recovery from artificial oil/water (O/W) mixture. The mechanism of porous hydrophobic–oleophilic kapok fiber layer (KFL) for O/W separation was analyzed, and a physical model for continuous oil recovery process was established. The oil recovery performance, which was evaluated by oil recovery rate (ORR, %) and oil enrichment rate (OER, %), depended on turbulence intensity of O/W mixture, driving pressure, KFL porosity and thickness, initial oil content of O/W mixture, and oil viscosity. Owing to the well oil selectivity of kapok, the oil content of the permeate was above 95.0% when the initial oil content of the O/W mixture was between 6.0% and 8.0%. The system was capable of collecting low viscosity oil efficiently.     

Nanoaerosol Filtration with Fine-Fiber Polydisperse Filters

The self-consistent theory of nanoaerosol filtration has been considered at small Peclet numbers. It has been shown that, at Pe < 1, it is necessary to consider the deposition of particles simultaneously on thePe < entire ensemble of fibers. Only at can the filtration efficiency be found from the collection efficiencies calculated separately for each fiber. The self-consistent theory has been used to estimate the efficiencies of filtration with polydisperse fibrous filters. The penetrations of particles through filters with different variances of the functions of fiber length distribution over fiber radii have been compared at a constant packing density or a constant total length of all fibers. It has been shown that, at a constant packing density, a rise in the variance leads to a decrease in the filtration efficiency, while, at a constant total fiber length, the efficiency is almost independent of the width of the distribution function.     

Study on radiative heat transfer property of fiber assemblies using FTIR

Radiative heat transfer could be a significant contribution to the total heat transfer within the highly porous materials. This article reports on the use of a conventional instrument, viz. Fourier transform infrared (FTIR) spectroscopy, for the characterization of radiative heat properties of fiber assemblies with low bulk densities. Experimental measurements on spectral transmission with FTIR were performed on five types of fiber assemblies commonly used for insulating materials. From the measurements, radiative heat conductivity was determined by calculating extinction coefficient using Beer’s Law and applying the diffusion approximation approach. Bulk density, fiber arrangement, and temperature influences to radiative heat transfer were discussed. Results show that radiative heat conductivity decreases with bulk density and that of the random arranged fiber assemblies shows lower radiative heat conductivity than the random ball and parallel arranged fiber assemblies. Radiative heat conductivity is proportional to the cubic temperature. The existing theoretical model was modified by comparing theoretical and experimental radiative heat conductivity results.     

Hydrodynamically induced formation of cellulose fibers. I. Observations on the formation of cellulose fibers from stirred solutions

Like synthetic polymers, a natural polymer such as cellulose may crystallize in fibrous form from stirred solutions. In the present work, it is demonstrated that cellulose fibers can be formed by precipitation from dimethyl sulfoxide/paraformaldehyde solutions by two methods that involve different mechanisms of fiber formation, viz., (A) precipitation of cellulose by addition of nonsolvent to the stirred cellulose solution, and (B) precipitation of cellulose by coagulation of droplets of cellulose solution in a stirred precipitant. Both processes yield fibers with properties depending on the stirring speed and the coagulant strength. The molecular orientation and tensile strength of the fibers produced by method A was low, but increased with the stirring speed, while some fibers formed by method B reached extremely high orientation, depending on the thickness of the fibers. The two mechanisms of fiber formation are discussed on the basis of the experimental observations.     

Encasement of metallic cardiovascular stents with endothelial cell‐selective copolyetheresterurethane microfibers

Cardiovascular metallic stents established in clinical application are typically coated by a thin polymeric layer on the stent struts to improve hemocompatibility, whereby often a drug is added to the coating to inhibit neointimal hyperplasia. Besides such thin film coatings recently nano/microfiber coated stents are investigated, whereby the fibrous coating was applied circumferential on stents. Here, we explored whether a thin fibrous encasement of metallic stents with preferentially longitudinal aligned fibers and different local fiber densities can be achieved by electrospinning. An elastic degradable copolyetheresterurethane, which is reported to selectively enhance the adhesion of endothelial cells, while simultaneously rejecting smooth muscle cells, was utilized for stent coating. The fibrous stent encasements were microscopically assessed regarding their single fiber diameters, fiber covered area and fiber alignment at three characteristic stent regions before and after stent expansion. Stent coatings with thicknesses in the range from 30 to 50 µm were achieved via electrospinning with 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFP)‐based polymer solution, while a mixture of HFP and formic acid as solvent resulted in encasements with a thickness below 5 µm comprising submicron sized single fibers. All polymeric encasements were mechanically stable during expansion, whereby the fibers deposited on the struts remained their position. The observed changes in fiber density and diameter indicated diverse local deformation mechanisms of the microfibers at the different regions between the struts. Based on these results it can be anticipated that the presented fibrous encasement of stents might be a promising alternative to stents with polymeric strut coatings releasing anti‐proliferative drugs. Copyright © 2015 John Wiley & Sons, Ltd.     

Diffusion of cationic polyelectrolytes into cellulosic fibers

The penetration of cationic polyelectrolytes into anionic cellulosic fibers was evaluated with fluorescent imaging techniques in order to clarify the mechanism and time scales for the diffusion process. The bulk charge of the cellulosic fibers indirectly creates a driving force for diffusion into the porous fiber wall, which is entropic in nature due to a release of counterions as the polyelectrolyte adsorbs. The individual bulk charges in the fiber cell wall also interact with the diffusing polyelectrolyte, such that the polyelectrolyte diffuses to the first available charge and consequently adsorbs and remains fixed. Thus, subsequent polyelectrolyte chains must first diffuse through the adsorbed polyelectrolyte layer before adsorbing to the next available bulk charges. This behavior differs from earlier suggested diffusion mechanisms, by which polyelectrolytes were assumed to first adsorb to the outermost surface and then reptate into the pore structure. The time scales for polyelectrolyte diffusion were highly dependent on the flexibility of the chain, which was estimated from calculations of the persistence length. The persistence length ultimately depended on the charge density and electrolyte concentration. The charge density of the polyelectrolyte had a greater influence on the time scales for diffusion. High charge density polyelectrolytes were observed to diffuse on a time scale of months, whereas the diffusion of low charge density polyelectrolytes was measured on the order of hours. An influence of the chain length, that is, steric interactions due the persistence length of the polyelectrolyte and to the tortuosity of the porous structure of the fiber wall, could only be noted for low charge density polyelectrolytes. Increasing the electrolyte concentration increased the chain flexibility by screening the electrostatic contribution to the persistence length, in turn inducing a faster diffusion process. However, a significant change in the diffusion behavior was observed at high electrolyte concentrations, at which the interaction between the polyelectrolyte charges and the fiber charges was almost completely screened.     

Effect of Fiber Treatment on Dimensional Stability and Chemical Resistance Properties of Hybrid Composites

In this work, oil palm empty fruit bunch (EFB) and jute fibers were treated by 2-hydroxy ethyl acrylate (2-HEA) to enhance interaction with the epoxy matrix in hybrid composites. Hybrid composites were fabricated by the hand lay-up technique by reinforcing chemical-treated oil palm EFB and jute fibers in an epoxy matrix. Physical (density, void content, water absorption, and thickness swelling) and chemical resistance properties of treated hybrid composites were characterized. Chemically treated oil palm EFB/jute fiber reinforced hybrid composites display better dimensional stability (water absorption and thickness swelling) and chemical resistance as compared to untreated hybrid composites.     

Effects of Multisolute Steric Interactions on Membrane Partition Coefficients

A key parameter in membrane and chromatographic separations is the partition coefficient, the equilibrium ratio of the solute concentration in a porous or fibrous material to that in bulk solution. The theoretical effects of solute size on partition coefficients in straight pores or randomly oriented fiber matrices have been investigated previously for very dilute solutions, where solute-solute interactions are negligible, and also for more concentrated solutions consisting of spherical solutes of uniform size. For concentrated solutions it has been found that steric and other repulsive interactions among solutes increase the partition coefficient above the dilute limit. To extend the results for porous or fibrous media to include concentrated mixtures of solutes with different sizes or shapes, we used an excluded volume approach. In this formulation, which describes steric interactions only, partition coefficients were computed by summing all volumes excluded to a solute molecule by virtue of its finite size, the finite size of other solutes, and the presence of fixed obstacles (pore walls or fibers). For a mixture of two spherical solutes, the addition of any second solute at finite concentration increased the partition coefficient of the first solute. That increase was sensitive to the size of the second solute; for a given volume fraction of the second solute, the smaller its radius, the larger the effect. When the total volume fraction of solutes was fixed, an increase in the amount of a second, smaller solute increased the partition coefficient of the first solute, whereas an increase in the amount of a second, larger solute had the opposite effect. Results were obtained also for oblate or prolate spheroidal solutes and for fibrous media containing fibers of different radii. For constant total fiber volume fraction, an increase in the amount of a second, smaller fiber decreased the partition coefficient of a spherical solute, whereas an increase in the amount of a second, larger fiber had the opposite effect. Overall, the theory suggests that the introduction of heterogeneities, whether as mixtures of solute sizes or mixtures of fiber sizes, may cause partition coefficients to differ markedly from those of uniform systems. Copyright 2000 Academic Press.     

Mechanical Properties and Dynamic Mechanical Analysis of Thermoplastic-Natural Fiber/Glass Reinforced Composites

The mechanical properties and dynamic behavior of thermoplastic composites based on polypropylene/glass fibers and polypropylene/natural fibers (i.e. kenaf, hemp, flax) are presented. A survey is given on some aspects, crucial for the use of these composites in structural and non-structural components such as their vibration-damping response, in relation to the composite compaction level and the manufacturing procedure. In order to investigate a wide vibration frequency range, including acoustic frequencies, different testing techniques, both with forced and free vibrations, were applied. A comparison between natural fiber and glass fiber reinforced laminates is presented. Compaction levels, allowing to obtain the best compromise between mechanical performance and damping response, are investigated.     

Effects of structural design including cellular structure precision controlling and sharp holes introducing on sound absorption behavior of polyimide foam

This paper aims to effectively improve acoustic property of polyimide foam (PIF) by regulating cellular structure of PIF on a large scale and introducing sharp hole structure simultaneously, adopting a special mold with split structure in a closed-mold foaming route. In this work, PIF with same split structure but different pore cell sizes, density, and windows opening rate were produced in the first time. Due to the stepwise transition principle, the impedance of the air acoustic medium and the acoustic material was well matched. In addition, the characterization results showed the effectively effects of microporous structure and split structure characteristics of PIF on the acoustical absorption coefficient. For PIF-4, sound absorption coefficient kept around 0.9 from 900 to 6300 Hz. Especially, the resonance sound absorption characteristics was basically eliminated, which ensured the high efficiency sound absorption behavior of PIF in the broadband range from 600 to 6300 Hz region.