Improving the adhesion between a aqueous PU and a polyamide fibre with silane

Glycidoxypropyltrimethoxysilane (GPS) and γ-aminopropyltrimethoxysilane (APS) were used to modify the surface chemistry of polyamide fibre. The surface chemistry was characterised using X-ray photoelectron spectroscopy. The silanol functional group was designed to be introduced on the surface of polyamide fibre to increase its chemical activity by N-alkylation of GPS and hydrolysis of APS, and to improve the poor interfacial adhesion between a polyamide 66 fibre and an aqueous polyurethane polymer adhesive. The microbond test was used to measure the interfacial shear strength between the waterborne PU adhesive and the polyamide fibre. It has been found that APS hydrolysis and GPS-alkylated fibre surface can be used to improve the interfacial adhesion of polyamide fibre to PU. The IFSS can be improved by N-alkylation of GPS from 5.0 to 8.4?MPa. After water immersion at 50?°C for 48?h, then drying, the IFSS increased to 8.8?MPa due to the plasticisation of PU in water. Better interfacial adhesion was also observed by the hydrolysis of APS, but not significantly improved by this method due to the relatively weak hydrogen bond at the interface between APS and polyamide fibre.     

Fabrication of an intelligent superhydrophobic surface based on ZnO nanorod arrays with switchable adhesion property

The superhydrophobic ZnO surface possessing water adhesive reversibility is fabricated by a facile method. The as-prepared surface is low adhesive; however, after being irradiated by UV light through a photomask, it becomes highly adhesive. A water droplet can suspend on the irradiated surface. Further annealing the irradiated surface, water droplets can roll on the surface again. Reversible transition between the high adhesive pinning state and low adhesive rolling state can be realized simply by UV illumination and heat treatment alternately. The adhesion transition is attributed to the adsorption/desorption of surface hydroxyl groups and the organic chains rearrangement on the top surfaces of ZnO.     

Atmospheric effects on the adhesion and friction between non-hydrogenated diamond-like carbon (DLC) coating and aluminum - A first principles investigation

Experimentally, non-hydrogenated DLC coatings were tested against 319 Al alloy in the nitrogen, hydrogen, dry air (0% RH), and ambient air (40% RH) environments using a vacuum pin-on-disc tribometer. The average coefficient of friction (COF) and the material transfer changed dramatically depending on the test environment. Density functional theory (DFT) calculations were performed to investigate the interaction of diamond surface, to represent non-hydrogenated DLC, with N₂, H₂, and H₂O molecules. These calculations suggested that hydrogen and water would dissociate and be chemically adsorbed at a diamond surface whereas the dissociation of nitrogen is very unlikely to happen. Therefore, the diamond/DLC surface is passivated by -H termination in hydrogen and by -OH termination in water vapor, but not passivated in nitrogen. The calculated work of separation for Al with non-passivated and reacted diamond surfaces indicated the same tendency of adhesive transfer as observed in the pin-on-disc tests. The calculated work of separation at the interfaces formed after material transfer has the same trend with the measured COF. Therefore, DFT calculations successfully explained the atmospheric dependency of the tribological behavior of non-hydrogenated DLC coatings.     

电解质溶液的太赫兹透射特性研究

许多生物大分子的振动和转动能级都在太赫兹波段,且太赫兹波具有光子能量低,峰值功率高的特点,因此用太赫兹技术进行检测,能够从很大程度上保证生物分子不被破坏.然而,大部分的生物分子只有在水溶液中才能保持其生物活性,且水是极性分子,对太赫兹波有强烈的吸收,因此使用常规的太赫兹技术检测水溶液中生物样品的特性存在一定困难.设计了...     

Predictions of dynamic behavior under pressure for two scenarios to explain water anomalies

Using Monte Carlo simulations and mean field calculations for a cell model of water we find a dynamic crossover in the orientational correlation time tau from non-Arrhenius behavior at high temperatures to Arrhenius behavior at low temperatures. This dynamic crossover is independent of whether water at very low temperature is characterized by a "liquid-liquid critical point" or by the "singularity-free" scenario. We relate tau to fluctuations of hydrogen bond network and show that the crossover found for tau for both scenarios is a consequence of the sharp change in the average number of hydrogen bonds at the temperature of the specific heat maximum. We find that the effect of pressure on the dynamics is strikingly different in the two scenarios, offering means to distinguish between them.     

Pumping of confined water in carbon nanotubes by rotation-translation coupling

Bidirectional single file water transport in a carbon nanotube is known to occur in "bursts" in short nanotubes. Here we show that in long carbon nanotubes, when the orientation of the water molecules is maintained along one direction, a net water transport along that direction can be attained due to coupling between rotational and translational motions. The rotations of the water molecules are correlated more with the translation of the neighboring water molecule with the acceptor oxygen than the neighbor with the donor hydrogen. This mechanism can be used to pump water through nanotubes.     

Diffusion studies in porous media with the "inside-out" technique

Diffusion measurements of water in a glass beads porous media were carried out by the "One-Sided Access" sensor. An approach to determine the long time mean square displacement of hydrogen molecules by measuring the ratio of stimulated echo to primary echo in a three pulse sequence in the presence of permanent static field gradient is analysed. The difference between the apparent diffusion coefficient in a pure water sample and in water/glass beads mixtures becomes visible.     

High-temperature dynamic behavior in bulk liquid water: A molecular dynamics simulation study using the OPC and TIP4P-Ew potentials

Classical molecular dynamics simulations were performed to study the high-temperature (above 300 K) dynamic behavior of bulk water, specifically the behavior of the diffusion coefficient, hydrogen bond, and nearest-neighbor lifetimes. Two water potentials were compared: the recently proposed “globally optimal” point charge (OPC) model and the well-known TIP4P-Ew model. By considering the Arrhenius plots of the computed inverse diffusion coefficient and rotational relaxation constants, a crossover from Vogel–Fulcher–Tammann behavior to a linear trend with increasing temperature was detected at T* ≈ 309 and T* ≈ 285 K for the OPC and TIP4P-Ew models, respectively. Experimentally, the crossover point was previously observed at T* ± 315–5 K. We also verified that for the coefficient of thermal expansion α _P (T, P), the isobaric α _P (T) curves cross at about the same T* as in the experiment. The lifetimes of water hydrogen bonds and of the nearest neighbors were evaluated and were found to cross near T*, where the lifetimes are about 1 ps. For T < T*, hydrogen bonds persist longer than nearest neighbors, suggesting that the hydrogen bonding network dominates the water structure at T < T*, whereas for T > T*, water behaves more like a simple liquid. The fact that T* falls within the biologically relevant temperature range is a strong motivation for further analysis of the phenomenon and its possible consequences for biomolecular systems.     

Fixation of nitrogen with cavitation

The sonochemical fixation of nitrogen to ammonia was investigated by sonolysis of liquids with nitrogen/hydrogen gas mixtures passing through them. The maximum rate (4 nmol min-1 W-1) was found in water irradiated with 900 kHz ultrasound with gas of a mole fraction 0.6 of nitrogen and the lowest temperature (278 K). Some traces of ammonia were found in the absence of external hydrogen gas, as hydrogen atoms are also formed in sonolysis of water. Thermodynamic calculations indicate that some ammonia formation should occur at the "hot spot" temperatures present in collapsing cavities. The decrease in the rate with bulk temperature suggests that kinetics, rather than thermodynamics, is the limiting condition for sonochemical synthesis of ammonia. Ammonia can be produced in organic media, but at a lower rate. A substantial portion of the ammonia in the experiments with alkanes exited with the sparging gas and was trapped in a dilute HCl solution.     

Structures of high and low density amorphous ice by neutron diffraction

Neutron diffraction with isotope substitution is used to determine the structures of high (HDA) and low (LDA) density amorphous ice. Both "phases" are fully hydrogen bonded, tetrahedral networks, with local order similarities between LDA and ice Ih, and HDA and liquid water. Moving from HDA, through liquid water and LDA to ice Ih, the second shell radial order increases at the expense of spatial order. This is linked to a fifth first neighbor "interstitial" that restricts the orientations of first shell waters. This "lynch pin" molecule which keeps the HDA structure intact has implications for the nature of the HDA-LDA transition that bear on the current metastable water debate.     

Use of novel carbon-nanofiber-doped carbon liquid crystals as suitable adsorbents for hydrogen storage

Over the last few years a number of groups have been exploring the possibilities and limitations associated with using adsorption on newly developed materials for the storage of hydrogen. Here we report the results of hydrogen adsorption investigations on a newly synthesized form of carbon nanofiber-doped carbon liquid crystals. This material shows a marked increase in specific surface area upon activation with water vapor, leading to activated samples that are capable of adsorbing hydrogen upto 3.5% by weight at 77.3 K, at moderate pressures. The possibility of higher adsorption (6.5 wt.%) in these materials is also discussed. PACS 68.43.-h; 68.43.De; 68.60.-p     

Rotational dynamics of Di-tert-butyl-nitroxide in normal and supercooled water: an electron paramagnetic resonance study

In order to obtain dynamical information on the water solvent, which is characterized by a strong anomalous behavior in its structural and transport properties especially in the supercooled region, low concentration di-tert-butyl-nitroxide (DTBN) aqueous solutions were studied by Electron Paramagnetic Resonance spectroscopy in the temperature range from 28 down to ?17°C. The accurate spectra reconstruction, achieved by a multi-parameters Monte Carlo fitting algorithm, allowed us to reliably extract some relevant spectral parameters of the spin probe, which were connected to the probe dynamics in the framework of the motional narrowing magnetic relaxation theory. The observed trend with the temperature showed however a significant deviation from what expected from the magnetic relaxation model. This anomalous behavior is discussed in terms of the influence upon the probe motion of solvent-induced local fluctuating structures which, very likely, are connected to the water hydrogen bond network dynamics.     

Folding and unfolding of an elastinlike oligopeptide: "inverse temperature transition," reentrance, and hydrogen-bond dynamics

The temperature-dependent behavior of a solvated oligopeptide, GVG(VPGVG), is investigated. Spectroscopic measurements, thermodynamic measurements, and molecular dynamics simulations find that this elastinlike octapeptide behaves as a two-state system that undergoes an "inverse temperature" folding transition and reentrant unfolding close to the boiling point of water. A molecular picture of these processes is presented, emphasizing changes in the dynamics of hydrogen bonding at the protein/water interface and peptide backbone librational entropy.     

Ultrasonic testing of anaerobic bonded joints

The paper deals with ultrasonic testing of adhesive joints between sheets of thickness greater than 1 mm, bonded by a "zero thickness" layer of anaerobic adhesive. In the case of equally thick sheets, interference phenomena can arise that make impossible the use of the "decay method" (a method previously developed by the authors for the case of non-zero adhesive thickness). Consequently an alternative method, termed "first peak", has been proposed. In order to evaluate the applicability of the two methods, a series of tests has been carried out on specimens having geometry suitable for both types of inspection. Also two different levels of surface roughness have been considered. The results allow for evaluating the defect detection capability of each method, accounting for the roughness effect, and give information on the suitable control procedures.     

Dynamics of supercooled confined water measured by deep inelastic neutron scattering

In this paper, we present the results of deep inelastic neutron scattering (DINS) measurements on supercooled water confined within the pores (average pore diameter ~ 20 Å) of a disordered hydrophilic silica matrix obtained through hydrolysis and polycondensation of the alkoxide precursor Tetra-Methyl-Ortho-Silicate via the sol-gel method. Experiments were performed at two temperatures (250 K and 210 K, i.e., before and after the putative liquid–liquid transition of supercooled confined water) on a “wet” sample with hydration h ~ 40% w/w, which is high enough to have water-filled pores but low enough to avoid water crystallization. A virtually “dry” sample at h ~ 7% was also investigated to measure the contribution of the silica matrix to the neutron scattering signal. As is well known, DINS measurements allow the determination of the mean kinetic energy and the momentum distribution of the hydrogen atoms in the system and therefore, allow researchers to probe the local structure of supercooled confined water. The main result obtained is that at 210 K the hydrogen mean kinetic energy is equal or even slightly higher than at 250 K. This is at odds with the predictions of a semiempirical harmonic model recently proposed to describe the temperature dependence of the kinetic energy of hydrogen in water. This is a new and very interesting result, which suggests that at 210 K, the water hydrogens experience a stiffer intermolecular potential than at 250 K. This is in agreement with the liquid–liquid transition hypothesis.     

Hydrogen bonding, H-D exchange, and molecular mobility in thin water films on TiO2(110)

Hydrogen bonding, H-D exchange, and molecular mixing in water films on TiO2(110) have been studied using water electron-stimulated desorption. For T<70 K, films with different water isotopes adsorbed on the Ti4+ and bridging oxygen rows can be prepared. For T>70 K, H-D and molecular exchange between these "layers" occur with a distribution of activation energies and is surprisingly efficient. The results demonstrate that all the water molecules that are directly bound to TiO2(110) -- i.e., in the first and second monolayers -- are also hydrogen bonded to each other.     

A density functional theory and quantum theory of atoms in molecules study on hydrogen bonding interaction between paracetamol and water molecules

To consider the hydrogen bonding interactions between paracetamol and water molecules, probable complexes of paracetamol from three active sites (carbonyl oxygen atom, hydroxyl oxygen atom, and nitrogen atom) with H₂O molecule were formed. The optimized geometries and total energies have been obtained at the B3PW91/6-31+G(d, p) level of theory. Comparison of hydrogen bond lengths and the energies of complexes showed hydrogen bond that form between the oxygen atom of the carbonyl group and hydrogen atom is stronger than others. Moreover, an increase in the number of hydrogen bonds increases stability of paracetamol-water complexes. At the end, the QTAIM was applied to explain the nature of the hydrogen bonds and confirm the more stability by complexation.     

铵水间质子交换的再研究:不受扩散约束的化学交换

对铵盐水溶液中铵离子与水分子间的质子交换进行了再研究. 以核磁共振(NMR) 波谱学方法测定了不同pH值, 不同温度和含不同共存盐浓度的氯化铵水溶液中质子交换速率, 组分自扩散系数及NMR自旋晶格弛豫时间. 结果显示铵水间的质子交换并不受交换主体分子或离子自扩散的约束. 交换机理包括化学键和氢键的交换. 在溶液中, 水分子以氢键为桥 梁连接铵和其因水解而产生的碱性部分--氨. 在氢交换的过程中, 氨从水分子接受一个氢 成为铵, 同时另外一端的铵提供一个氢给水分子而变成氨, 或者一个氢从水分子转移到氨而同 时另外一个氢从铵转移到水. 在铵水质子交换的过程中没有净的电荷转移. 在低pH条件下, 由水解产生的氨的浓度降低, 亦即铵-水-氨复合物减少, 结果氢交换的可能性降低. 这解释了生物氢交换体系中的一种常见的在低pH值条件下氢交换变慢的现象.     

水分子链受限于单壁碳纳米管结构的密度泛函理论研究

本文采用第一性原理的密度泛函理论,主要以(6,6)Armchair型,(11,0)Zigzag型单壁碳纳米管为研究对象,研究了水分子链在碳纳米管内部吸附的稳定结构,以及结合能随其结构的变化.结果表明:当水分子链受限于碳纳米管内部时,引起碳纳米管直径收缩,这主要是由于水分子链与碳纳米管之间的氢键作用以及范德华弱相互作用所引起的.随着碳纳米管半径的增加,两种单体之间的结合能逐渐减小,但当碳纳米管半径增加至6.78时,其结合能又有所增加,这是由于在优化过程中,水分子链单体之间的氢键作用大于水分子链与碳纳米管之 关键词： 水分子链/单壁碳纳米管 密度泛函理论 结构稳定性     

Redox reaction of μ−O in water determined by the chemical shift

The chemical shift of ^–O in water, ice and in aqueous hydrogen peroxide (H₂O₂) was examined using ^–O resonance. Two distinct signals are obtained in water and ice. Using ⁺ resonance signal as a standard, the observed shiftsg are –7.0×10^–4 (signal A) and –12.1×10^–4 (signal B) respectively. The intensity of the two fractions are almost equivalent in water; however, in ice, the intensity of signal B decreases with increase of signal A. After the addition of hydrogen peroxide to the water signal B disappears, A increases, and the total amplitude is increased.