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This paper presents a full set of numerical methods for predicting the effective thermal conductivity of natural fibrous materials accurately, which includes a random generation-growth method for generating micro morphology of natural fibrous materials based on existing statistical macroscopic geometrical characteristics and a highly efficient lattice Boltzmann algorithm for solving the energy transport equations through the fibrous material with the multiphase conjugate heat transfer effect considered. Using the present method, the effective thermal conductivity of random fibrous materials is analyzed for different parameters. The simulation results indicate that the fiber orientation angle limit will cause the material effective thermal conductivity to be anisotropic and a smaller orientation angle leads to a stronger anisotropy. The effective thermal conductivity of fibrous material increases with the fiber length and approach a stable value when the fiber tends to be infinite long. The effective thermal conductivity increases with the porosity of material at a super-linear rate and differs for different fiber location distribution functions. (c) 2006 Elsevier Masson SAS. All rights reserved.

Triazole compounds are important organic systems with excellent electronic properties, which have diagnostic potential in the fields of organic electronics and organic photovoltaics. The important photophysical nature of these systems is the transformation between the enol and keto forms after excited-state proton transfer. In this study, the IR vibrational spectrum, ESIPT mechanism, and excited-state decay dynamics of 2,2′-(1-phenyl-1H-1,2,4-triazole-3,5-diyl)diphenol (ExPh) were explored using electronic structure calculations and non-adiabatic dynamics simulations. Two S1/S0 conical intersections with distinct proton transfer (ESIPT-I and ESIPT-II) involved were obtained. The associated two-dimensional S1 minimum-energy potential energy surface indicated that the dynamical roles of these two S1/S0 conical intersections in the S1 excited-state decay were quite different. The ESIPT-I reaction was more favorable to occur than the ESIPT-II process. Our dynamics simulations supported this hypothesis with the whole trajectories decaying to the ground state via the S1S0-1 conical intersection, which involved the ESIPT-I process. The ESIPT-Involved efficient deactivation pathway could be partially responsible for the decrease in fluorescence emission. These results and ESIPT mechanisms are helpful for understanding the decay pathways of similar systems. [ABSTRACT FROM AUTHOR]

It is challenging to predict the frequency property of a nonlinear vibration system conveniently and efficiently. Especially, an invalid or physically irrelevant result might be obtained by some advanced methods. Therefore, predicting the frequency lacks an expedient and efficient method. This challenge is addressed by developing a straightforward and effective frequency formulation that reliably predicts the frequency-amplitude relationship. This study provides a one-step approach which can fast determine the periodic properties of any conservative oscillators and also provides a reference for other similar studies [ABSTRACT FROM AUTHOR]

As a new preparation process of nanofibers, electrospinning technology developed by bionic spider spinning can further improve the molecular structure and mechanical properties of nanofibers, and obtain nanofibers and base membrane products with better mechanical properties. The spider spinning needs minimal energy consumption though it has a very long liquid transport tube. Because spider silk has high mechanical properties and wide industrial applications, so a kind of new biomimetic electrospinning technology which harnessed a very long spiral-needle was proposed. Then poly(lactic acid)PLA/graphite oxide(GO)/dopamine (DA) nanofiber membrane was fabricated by the new biomimetic electrospinning technology. The results showed that compared with the pure PLA nanofiber membranes, the average pore size of PLA/GO porous nanofiber membranes decreased, the total number of pores increased, and the fracture strength and elongation at break increased. At the same time, the spun nanofibers were also more uniform. The pore size distribution of nanofiber was more dense after adding DA, and the fracture strength and elongation at break of nanofiber increased, while the nanofiber was also more even. After adding DA, the fracture strength was greatly increased and the elongation at break was similar to that of pure PLA nanofiber. The nanofiber membrane was obtained after oxidative polymerization of DA into poly(dopamine) (PDA), a layer of nanofiber membrane was attached to the surface of nanofiber. The performance of PLA/GO/PDA nanofiber membranes prepared based on PLA/GO/DA nanofiber membranes was superior to that of PLA/GO/PDA nanofiber membranes prepared based on PLA/GO nanofiber membranes, and its adsorption rate after 24 h was as high as 98.81%. [ABSTRACT FROM AUTHOR]

In this paper, we combine electrospinning with laminar flow theory to verify the influence of the spinning needle length on the internal structure of PVDF (polyvinylidene fluoride) nanofibers. The long spinning needle is referred as a reference like long ducts in the body of spiders. We also discussed the effect of different needle length on the micro-morphology, mechanical properties, electrical properties, porosity, and hydrophobic properties of PVDF nanofiber membranes. The results showed that when the needle length increased, more PVDF macromolecular chains will have sufficient time to be straightened and aligned, resulting in an increasingly ordered internal structure of the prepared PVDF nanofibers. The different length of the long needle has a certain influence on the morphology, mechanical properties, electrical properties, porosity, and hydrophobic properties of PVDF nanofiber membrane obtained by electrospinning. The more ordered the internal structure of nanofibers, the worse the membrane's mechanical properties, but the lower its electrical resistivity. [ABSTRACT FROM AUTHOR]

Electrospinning is a powerful method for fabricating micro/nano fibers that can be applied to various fields. Composite materials with nanoscale structure can show more excellent properties than their conventional partners. Here, we reported hierarchical structured nanofibers with beads and spheres by double needle electrospinning with an auxiliary airflow. Two different spinning solutions with different concentrations were placed into different syringes. The action of airflow was able to make the two differently morphological nanofibers mixed together evenly. The results showed that the obtained nanofiber membrane has a good hierarchical structure with different morphologies. [ABSTRACT FROM AUTHOR]

Nano or micro-scale particles are considered as a zero-dimensional material, and their shape is difficult to control. Here the costal-like microparticles are formed, and the existence criterion of crystal-like low dimensional materials is established. The hydrothermal method is used to fabricate copper-1, 3, 5-phenyltricarboxylate (Cu-BTC) microparticles, which have a regular geometric shape with regular triangle, quadrangle and hexagon. The benzene ring and carboxyls (--COOH) attached to the benzene ring form two basic molecular structures of [ Cu3 [(BTC)2]n, which play an essential role in the constmction of a threedimensional crystal-like structure. [ABSTRACT FROM AUTHOR]

Biodegradable and efficient filtration membrane is essential to practical oil–water separation. Herein, we fabricated highly porous membrane induced by the humidity. The resulting poly(lactic acid) fiber membrane exhibits superhydrophobicity due to more trapped air by the increased roughness of fiber at the relative humidity of 80%. Meanwhile, the increased humidity favors to the membrane porosity improvement from 81 ± 3.3% to 92 ± 4.1% with the humidity change from 40% to 80%. The superhydrophobicity company with the increased membrane porosity makes the functional poly(lactic acid) membrane with enhanced flux for practical oil–water separation. [ABSTRACT FROM AUTHOR]

The study of oil sorbents with high oil sorption capacity is of great significance for oil–water separation, especially for oil spillage on seawater. In this work, we report polysulfone, poly(lactic acid), and polysulfone/poly(lactic acid) nanoporous fibrous mats prepared by one-step electrospinning process used as oil sorbents for oil–water separation. The morphology, porous structure, oleophilicity and hydrophobicity, oil sorption capacity, and oil retention of these nanoporous fibrous mats are investigated in detail. It is noticeable that the motor oil and linseed oil sorption capacity of polysulfone and polysulfone/poly(lactic acid) fibrous mats have little difference, but the motor oil sorption capacity (147.8 g g−1) of polysulfone is approximately 2.95 times as much as that (50.1 g g−1) of poly(lactic acid). The linseed oil sorption capacity (131.3 g g−1) is approximately 3.74 times than that (34.6 g g−1) of poly(lactic acid). Besides, they all exhibit quick oil sorption speed and high buoyancy. It is suggested that polysulfone and polysulfone/poly(lactic acid) nanoporous fibrous mats have a better oil sorption capacity than poly(lactic acid) nanoporous fibrous mat, which is contributed to volume expansion, highly micrometer porous structure among fibers, and specific surface area of fiber. [ABSTRACT FROM AUTHOR]

A novel catalyst, TiO2 nanotubes ( TiO2 NTs) composite decorated by CuO and CeO2 particles, was prepared by a simple and cost-effective method. The TiO2 NTs were fabricated by the hydrothermal method, and CuO and CeO2 particles loaded onto TiO2 NTs (CuO/CeO2 @ TiO2 NTs) were prepared by the water bath heating method. The CuO/CeO2 @ TiO2 NTs were investigated and characterized by transmission electron microscope ( TEM), energy dispersive spectrometer ( EDS), photoluminescence (PL), X-ray diffractometer ( XRD) and ultraviolet-visible light diifuse reflectance spectrum (UV-Vis DRS). Both the p-n heterojunction formed at the p-CuO and n-TiO2 interfaces and the highly induced electron transfer of CeO2 can greatly promote the separation of elections-holes. Therefore, CuO/CeO2 @ TiO2 NTs show enhanced absorption and have potential applications in photocatalysis. [ABSTRACT FROM AUTHOR]