Nature of hydrogen bonding of water molecules in aqueous solutions of glycerol by attenuated total reflection (ATR) infrared spectroscopy

Attenuated total reflection infrared (ATR-IR) spectroscopy was performed on glycerol/water solutions in order to gain a better understanding of the strong hydrogen bonding of glycerol as a humectant. The OH stretching band after eliminating the contribution of glycerol OH in the glycerol/water solutions was decomposed using three Gaussian components. With increasing glycerol concentrations up to 50 volume %, the decrease of the 3428 cm(-1) component (middle H-bond component) and the increase of the 3562 cm(-1) component (longer H-bond component) suggested the breaking of H bonds among water molecules. On the other hand, the 3242 cm(-1) component (shorter H-bond component) remained unchanged. It was expected that water molecules surrounding glycerol molecules are retained by strong H bonding between H atoms of water and O atoms in C-O of glycerol when aqueous solutions containing glycerol are introduced in human skin.     

Preparation of high performance films from poly(vinyl alcohol)/NaCl/H2O systems

The atactic poly(vinyl alcohol) (a-PVA) aqueous solutions with NaCl were cast to prepare films and then the NaCl in the films was removed. The films prepared by removing NaCl in water had a water-resistance property. The degree of crystallization of the films increased with an increase of the content of NaCl in the solutions up to 3 wt%. However, the melting temperature (222–225°C) was independent of the content of NaCl in the solutions. The draw ratio and Young's modulus of the films prepared from the solutions with 3 wt% NaCl were about 2.5 and 3 times than that of the films obtained from an aqueous solution. Namely, in case of the films obtained from a-PVA/H₂O/NaCl systems, both the drawability and mechanical properties as well as the degree of crystallization was higher than those for the film obtained from an aqueous a-PVA solution.     

A study on water adsorption onto microcrystalline cellulose by near-infrared spectroscopy with two-dimensional correlation spectroscopy and principal component analysis

Water adsorption onto microcrystalline cellulose (MCC) in the moisture content (M(c)) range of 0.2-13.4 wt % was investigated by near-infrared (NIR) spectroscopy. In order to distinguish heavily overlapping O-H stretching bands in the NIR region due to MCC and water, principal component analysis (PCA) and generalized two-dimensional correlation spectroscopy (2DCOS) were applied to the obtained spectra. The NIR spectra in four adsorption stages separated by PCA were analyzed by 2DCOS. For the low M(c) range of 0.2-3.1 wt %, a decrease in the free or weakly hydrogen-bonded (H-bonded) MCC OH band, increases in the H-bonded MCC OH bands, and increases in the adsorbed water OH bands are observed. These results suggest that the inter- and intrachain H-bonds of MCC are formed by monomeric water molecule adsorption. In the M(c) range of 3.8-7.1 wt %, spectral changes in the NIR spectra reveal that the aggregation of water molecules starts at the surface of MCC. For the high M(c) range of 8.1-13.4 wt %, the NIR results suggest that the formation of bulk water occurs. It is revealed from the present study that approximately 3-7 wt % of adsorbed water is responsible for the stabilization of the H-bond network in MCC at the cellulose-water surface.     

Transmittance Fourier transform infrared spectra of liquid water in the whole mid-infrared region: temperature dependence and structural analysis

Transmittance Fourier transform infrared (FT-IR) spectra of liquid water in the 4-80 degrees C temperature range are reported in the whole mid-infrared (MIR) region (4000-360 cm (-1)). The spectra were recorded by using a newly developed, home-made transmittance cell, working in light vacuum conditions (pressures of the order of 3-4 millibar). This permits the elimination of the aqueous vapor bands from the liquid spectra, particularly in the bending region, and the rapid collection of data without fluxing large amounts of nitrogen through the interferometer sample chamber. The temperature evolution of the OH stretching and HOH deformation bands is discussed in terms of Gaussian components analysis and a two-state model describing the equilibrium between different H-bond structures of liquid water. From this picture, structural and thermodynamic information about the hydrogen-bonding network of water is obtained.     

Corrosion behavior of AZ91 magnesium alloy in dilute NaCl solutions

The corrosion behavior of AZ91 magnesium alloy in dilute NaCl solutions was studied using electrochemical measurements, whereby a corrosion map in terms of electrode potential and chloride concentration [Cl⁻] was obtained. AZ91 alloy exhibited the corrosion and passivation zones in dilute NaCl solutions. The passivation zone became narrow with increasing [Cl⁻]. The values of open-circuit potential were in the passivation zone when the [Cl⁻] was less than 0.5 mol/L. XRD patterns showed the presence of the Mg(OH)₂, Mg₅(CO₃)₄(OH)₂·8H₂O and MgO phases in the corrosion product, whereas the latter two phases found in the passive film.     

正渗透过程参数对渗透性能的影响

正渗透是新的非热能驱动膜过程。采用界面聚合的方法制备了中空纤维复合膜。以Na2SO4、MgSO4、NaCl和Mg-Cl2水溶液作为驱动液进行了正渗透实验。实验表明,正渗透通量随着驱动液浓度的增加而增加,其中Na2SO4、MgCl2水溶液的渗透通量大于MgSO4、NaCl水溶液的。驱动液中无机盐向原水中扩散的渗透速率随无机盐浓度的增加而增加,且MgCl2>NaCl>Na2SO4>MgSO4。原水流速对正渗透通量的影响极小,而驱动液流速对正渗透通量的影响较大。     

Effect of fillers on the degradation of automotive epoxy adhesives in aqueous solutions

Absorption of water in epoxy adhesives containing different types of fillers was studied after immersion in distilled water and in NaCl solutions during several periods of time. The amount of water uptake in the adhesives was found to increase with the concentration of water-soluble fillers incorporated in the adhesive matrix. The water absorption behaviour of the adhesives investigated was found to be non-Fickian. Owing to reverse osmosis, the amount of water absorbed in the adhesives decreases with the concentration of the bulk NaCl solution.     

Sugar interaction with metals in aqueous solution: indirect determination from infrared and direct determination from nuclear magnetic resonance spectroscopy

In this article, mid-infrared Fourier transform (Mid-FT-IR) and carbon thirteen nuclear magnetic resonance (13C NMR) spectroscopy have been used to determine possible interactions between sucrose and various alkali or alkaline earth metals in aqueous solution. In the presence of these metals, significant shifts in the absorption bands of sucrose were noted by mid-FT-IR coupled with principal component analysis (PCA). These shifts were explained on the basis of weakening of the H-bond network between sucrose and water and possible interactions between sucrose and the metal ion. Factorial maps were established and the spectral patterns obtained show that these interactions vary according to the nature of the metal ion. 13C NMR analysis showed that the carbon atoms of sucrose undergo shielding or deshielding in the presence of metal ions in aqueous solutions. Two factors were invoked to account for the variation of chemical shifts: the rupture of hydrogen bonds due to hydration of the metal ion and the possible coordination of the metal ion to the oxygen atoms of sucrose.     

New Oral Dosage Form for Elderly Patients. III. Stability of Trichlormethiazide in Silk Fibroin Gel and Various Sugar Solutions

The hydrolysis of trichlormethiazide (TCM) in silk fibroin gel (SFG) prepared in various sugar solutions (such as ribose, fructose, mannose, and glucose solutions) was determined. The hydrolysis rate of TCM differed with the variety of sugars utilized in this study; that is, it decreased in the following order: ribose > fructose > mannose > glucose. To investigate the relationship between the hydrolysis rate of TCM and the physicochemical properties of the sugar molecule, the amount of unfrozen water of sugar molecules was calculated from differential scanning calorimetry (DSC). The amount of unfrozen water increased with an increase in the number of the equatorial OH groups n(e–OH) per sugar molecule that are able to hydrate favorably to the surrounding water molecules. The hydrolysis rate constant decreased with increase in n(e–OH); glucose, having a large n(e–OH) in this study could effectively stabilize TCM.     

An investigation into the structure of aqueous NaCl electrolyte solutions under magnetic fields

Molecular dynamics simulations are performed to investigate the effects of magnetic fields with intensities of 1–10 T on aqueous NaCl electrolyte solutions at 298 K. The simulations employ the F3C (flexible three centered) water model and investigate electrolyte solutions with both low (1 M) and high (5 M) NaCl concentrations. The results show that the self-diffusion coefficient of the water molecules decreases in a low-concentration solution as the magnetic field intensity is increased, but increases in a high-concentration solution. The magnetic field enhances the mobility of the Na⁺ and Cl⁻ ions in both low- and high-concentration solutions. The average number of hydrogen bonds increases when the magnetic field is applied to pure water or to a solution with a low NaCl concentration, but decreases in a solution with a high-concentration. The results show that the enhanced mobility of the ions under a magnetic field causes serious damage to the hydrogen bond network in the high-concentration solution. Conversely, in the low-concentration solution, the structural behavior is dominated by the properties of the water molecules, and hence the hydrogen bonding ability is enhanced as the magnetic field is increased.     

钢芯铝绞线的铝线在NaCl溶液中的腐蚀行为

钢芯铝绞线正常运行温度达80℃,受到环境中盐离子的严重腐蚀。采用Tafel直线外推法、电化学阻抗谱法及加速腐蚀试验法,研究了钢芯铝绞线的铝线在不同浓度NaCl溶液中的腐蚀行为,利用SEM和XRD等表征了其腐蚀表面状态及产物形貌。结果表明:随着NaCl浓度的升高,铝线的自腐蚀电位负移,极化电阻变小,腐蚀速率增大,当NaCl为70 mg/L时腐蚀速率急剧增加,是10 mg/L NaCl时的40倍;腐蚀产物及钢芯表面镀锌层可抑制铝线的腐蚀,铝线腐蚀后的表面出现大量的"麻点"及腐蚀坑,白色的腐蚀产物主要由Zn0.64Al0.36(OH)2(CO3)0.18.0.86H2O组成。     

AM60镁合金在侵蚀性溶液中的电化学阻抗分形(英文)

研究了AM60镁合金在0.1 mol/L NaCl,Na2SO4和饱和Mg(OH)2溶液中浸泡96小时的电化学阻抗谱(Electrochemical impedance spectroscopy,EIS)行为。溶液中含有Cl-时,阻抗谱呈现高中频两个容抗弧和低频感抗成分,且低频感抗组分在浸泡36小时后消失。AM60浸泡在Na2SO4溶液中具有类似的电化学阻抗行为,区别在于低频弛豫过程和容抗大小。相比于Cl-离子,SO42-离子具有相对较弱的腐蚀进攻能力。在饱和Mg(OH)2溶液中,由于Mg(OH)2弱水解有效抑制了阴阳极反应(极化曲线结果),EIS谱图仅有中高频两个容抗弧,没有对应孔核形成和消失的低频感抗行为。由于高频容抗弧对应AM60原表面的双电层信息,其弥散系数n、分形维数DE可以获取腐蚀过程中的细节信息。阻抗分形维数DE随时间的变化曲线结果表明Cl-具有最强的腐蚀进攻性,同时也具有再钝化效应,以修复由于Cl-进攻形成的孔核。SO42-离子腐蚀进攻性相对较弱,且没有再钝化现象。饱和Mg(OH)2溶液中DE的增加主要是由于不溶性Mg(OH)2沉积吸附在镁合金表面,增加表面的粗糙度。     

Geometric confinement governs the rupture strength of H-bond assemblies at a critical length scale

The ultrastructure of protein materials such as spider silk, muscle tissue, or amyloid fibers consists primarily of beta-sheets structures, composed of hierarchical assemblies of H-bonds. Despite the weakness of H-bond interactions, which have intermolecular bonds 100 to 1000 times weaker than those in ceramics or metals, these materials combine exceptional strength, robustness, and resilience. We discover that the rupture strength of H-bond assemblies is governed by geometric confinement effects, suggesting that clusters of at most 3-4 H-bonds break concurrently, even under uniform shear loading of a much larger number of H-bonds. This universally valid result leads to an intrinsic strength limitation that suggests that shorter strands with less H-bonds achieve the highest shear strength at a critical length scale. The hypothesis is confirmed by direct large-scale full-atomistic MD simulation studies of beta-sheet structures in explicit solvent. Our finding explains how the intrinsic strength limitation of H-bonds can be overcome by the formation of a nanocomposite structure of H-bond clusters, thereby enabling the formation of larger and much stronger beta-sheet structures. Our results explain recent experimental proteomics data, suggesting a correlation between the shear strength and the prevalence of beta-strand lengths in biology.     

Fabrication and formation mechanism of hollow MgO particles by pulsed excimer laser ablation of Mg in liquid

We report on the formation of hollow MgO particles by excimer laser ablation of bulk Mg in water and aqueous solutions of sodium dodecyl sulfate (SDS) and sodium citrate (SC). Lamellar nanostructures of Mg(OH)(2) also formed in water, but the formation could be avoided by the addition of SDS or SC. Laser ablation produced not only Mg species that were oxidized into MgO and Mg(OH)(2) in water, but also cavitation bubbles. The bubble interfaces trapped the MgO nanoparticles to decrease the surface free energy of the system, finally resulting in hollow particles.     

聚（丙烯酸-CO-丙烯酰胺）／腐殖酸钠／高岭土复合高吸水性树脂的制备及溶胀行为

以N,N′-亚甲基双丙烯酰胺为交联剂、过硫酸铵为引发剂,采用水溶液聚合法合成了聚(丙烯酸-co-丙烯酰胺)/腐殖酸钠/高岭土多功能复合高吸水性树脂。研究了腐殖酸钠和高岭土含量对吸水倍率的影响,同时考察了该树脂的吸水速率及溶液pH值和不同阴阳离子对吸水倍率的影响。结果表明,在腐殖酸钠∶高岭土=2∶3(质量比)时树脂具有最高的吸水倍率,其吸蒸馏水和0.9%(质量分数)NaCl溶液分别达到450 g/g和39 g/g。     

Factors governing the Pu(IV) speciation in solutions

After storage of Pu(IV) hydroxide for more than 4 months, ～90% of this compound polymerizes, the remainder (～ 10%) being weakly polymerized Pu(IV). In 0.01 M NaCl solutions (pH ～4–10) being in equilibrium with mixed or polymeric Pu(OH)₄ (decantates), plutonium is mainly in the form of highly polymerized colloidal particles of molecular weight exceeding 100 kDa. Therefore, the Pu concentration in the solutions prepared by decantation or centrifugation of decanted solutions can range from 10^?4 to 10^?7 M. The content of weakly polymerized Pu in solutions varies from 10^?7 to 10^?9 M and depends on pH of the solution in the range 4–6. This dependence is virtually absent at pH 6–10.     

A simple method for fabricating single-crystalline Fe nanowires

This work reports a simple and environmental friendly approach for the fabrication of Fe nanowires under normal pressure and low temperature in the absence of any inorganic or organic templates, substrate, surfactant, external field or magnetic field. This approach involved the production of Fe(OH)₃/NaCl by mechanically milling a mixture of Fe(OH)₃ and NaCl, and the reduction of Fe(OH)₃/NaCl to Fe nanowires. The as-prepared product (Fe/NaCl) and the Fe nanowires obtained by dissolving the NaCl from Fe/NaCl were characterized using transmission electron microscopy, X-ray diffraction and vibrating sample magnetometer. The results showed that the Fe nanowires are about 10-100 nm in diameter and 8-16 μm in length and their saturation magnetization (M_s) and coercivity (H_c) values are 145 emu/g and 206 Oe, respectively.     

Dynamics of Changes in the Infrared Spectrum of Distilled and Heavy Water upon Exposure to an Electron Beam of Nanosecond Duration

The absorption spectra of distilled and heavy water upon exposure to an electron beam of nanosecond duration are investigated. The changes in the absorption spectrum of distilled water after exposure to an electron beam are that the absorption band of valence vibrations of the OH groups becomes broadened, the amplitude of the valence asymmetric band increases, and a shift of the absorption maximums toward shorter wavelength frequencies and an increase in the amplitudes with insignificant band broadening are observed for absorption bands comprised of the sum of deformation and libration vibrations of water molecules and the deformation band of water. The changes in the absorption spectrum of heavy water after its irradiation with an electron beam consist in that the band of valence vibrations of the OH groups of the H₂O and HDO molecules is broadened, while the absorption band of the OH overtones of the deformation vibrations of the HDO molecule becomes stronger and the absorption range is preserved. A shift of the absorption maximum toward higher frequencies is observed for the deformation vibrations of the H₂O and HDO molecules of heavy water, and the maximum of deformation vibrations of the D₂O molecules remains unchanged.     

An optical technique forin situ density determination in electrolyte solutions under hydrothermal conditions

We report on a technique which determines the density of hydrothermal solutions through the relationship between density and refractive index given by the Lorentz Lorenz equation. An optical cell is described which allows the refractive index of fluids to be measured at temperatures up to 823 K and pressures up to 1200 bar. The validity of the Lorentz-Lorenz equation is demonstrated for pure water and water/NaCl solutions. New experimental results are presented for the density of water/NaNO₃ solutions at high temperature and pressure. The use of density data to derive other properties such as compressibility, thermal expansion coefficient, and apparent molar volume is demonstrated.     

PAA-Na/PVA半互穿网络水凝胶的离子强度及pH敏感性

采用水溶液聚合法制备了聚丙烯酸钠(PAA-Na)/聚乙烯醇(PVA)半互穿网络水凝胶,研究了水凝胶在不同pH溶液、不同浓度NaCl与CaCl2溶液中的溶胀行为,结果表明,溶胀比随丙烯酸含量增大而增加,在碱性溶液中的溶胀度明显高于酸性溶液,溶胀平衡凝胶在酸性及碱性条件下均出现收缩,在pH=2和pH=12溶液中反复交换时,表现出可逆溶胀-退溶胀性能,具有较好的pH敏感性,凝胶在不同浓度NaCl与CaCl2溶液中溶胀性表明,溶液的离子强度及阳离子的电荷数对凝胶溶胀行为有较大影响。