Self-Diffusion in Confined Water: A Comparison between the Dynamics of Supercooled Water in Hydrophobic Carbon Nanotubes and Hydrophilic Porous Silica

Confined liquids are model systems for the study of the metastable supercooled state, especially for bulk water, in which the onset of crystallization below 230 K hinders the application of experimental techniques. Nevertheless, in addition to suppressing crystallization, confinement at the nanoscale drastically alters the properties of water. Evidently, the behavior of confined water depends critically on the nature of the confining environment and the interactions of confined water molecules with the confining matrix. A comparative study of the dynamics of water under hydrophobic and hydrophilic confinement could therefore help to clarify the underlying interactions. As we demonstrate in this work using a few representative results from the relevant literature, the accurate assessment of the translational mobility of water molecules, especially in the supercooled state, can unmistakably distinguish between the hydrophilic and hydrophobic nature of the confining environments. Among the numerous experimental methods currently available, we selected nuclear magnetic resonance (NMR) in a field gradient, which directly measures the macroscopic translational self-diffusion coefficient, and quasi-elastic neutron scattering (QENS), which can determine the microscopic translational dynamics of the water molecules. Dielectric relaxation, which probes the re-orientational degrees of freedom, are also discussed.     

亲、疏水性功能单体对聚丙烯酸酯乳液聚合的影响研究

以OP-10和SDS为乳化剂,采用预乳化半连续种子乳液聚合工艺制备聚丙烯酸酯乳液。加入亲水单体丙烯酸(AA)、丙烯酸羟乙酯(HEA)和疏水单体丙烯酸长链烷基酯(V)为功能单体,研究了的亲、疏水性功能单体及配比对乳液粘度、表面能、耐水性及涂膜吸水率的影响。结果表明,采用m(AA)∶m(HEA)∶m(V)=1.25∶2∶5得到的丙烯酸酯多元共聚乳液各项性能较佳,此时乳液转化率可达99.91%,乳胶膜吸水率仅为15.21%,表面能为46.3143 J/m2,胶膜浸水脱落时间≥96 h。     

Effects of the Quantity and Structure of Hydrophobes on the Properties of Hydrophobically Modified Alginates in Aqueous Solutions

Summary Alginate is an important polysaccharide with applications in food industry, cosmetics and pharmacy. In this study, three hydrophobically modified alginates with different amount of various hydrophobic groups have been synthesized. Rheology and turbidity measurements have been carried out on polymer solutions in the concentration regime 0.005–2.0 wt %. The rheological results indicate that the introduction of hydrophobic groups induce the formation of intra- or intermolecular associations in the aqueous solutions depending on the polymer concentration and the hydrophobicity. The concentration dependency of the viscosity exhibit different power-law behaviors depending on the concentration regime and the hydrophobic modification. This has been scrutinized in view of theoretical scaling laws presented in the literature.     

内掺硅烷乳液憎水剂对混凝土性能的影响

通过强度测试、水化热实验、热重分析、毛细吸水实验以及压汞实验研究了内掺硅烷乳液憎水剂对混凝土强度以及毛细吸水性能的影响规律及其机理.结果表明:高掺量硅烷乳液一定程度上抑制水泥水化,从而导致混凝土早龄期抗压强度和劈裂抗拉强度下降以及28 d养护后水泥净浆试块中毛细孔的体积增大.毛细吸水实验表明:28 d龄期混凝土毛细吸水...     

疏水性沸石分子筛的特性及表面改性研究

介绍了疏水性沸石分子筛的疏水机理、吸附特性和表面改性技术 ,探讨了这一技术用于二氧化碳控制技术的发展前景     

Characterization and Reshaping of a Large and Hydrophobic Nucleophile Pocket in Lipases/Acyltransferases

Lipases/acyltransferases, such as CpLIP2 from Candida parapsilosis and CduLAc from Candida dubliniensis, catalyze acyl transfer preferentially over hydrolysis if a suitable nucleophile is present, even in a medium with a high thermodynamic activity of water (a_W). These enzymes are related to CAL‐A from Moesziomyces antarcticus, which, in comparison, displays a lower acyl transfer ability. The 3D structures of wild types and mutants of CAL‐A, CpLIP2, and CduLAc revealed differences in size and hydrophobicity of a large pocket located under the catalytic triad. The kinetic behavior of site‐directed mutants confirmed the role of this pocket in competition between methanol and water as the nucleophile acceptor for the deacylation step. The mutations provided a better understanding of key structural determinants for variable levels of acyltransferase ability observed and supported the existence of a complex network of nucleophile interactions within the enzymes. The shape and size of the possible nucleophile pocket identified also suggested that multiple binding sites could exist, which supported the hypothesis of non‐overlapping leaving and accepting nucleophile binding sites.     

On Liquid Water Isothermic Segregation in a Medium of Highly Elastic Hydrophobic Polymers Such as Polymethyl Methacrylate

Abstract

Deglassifying the films of plasticized polymethyl methacrylate (PMMA) in heated water causes the spontaneous segregation of water drops of micrometer and larger radius. This process which is accompanied by a change in the film size is impossible in structureless hydrophobia systems. The phenomenon indicates a structural organization of polymer chains, which are responsible for adsorption of a certain amount of molecular water by hydrophobic PMMA. From a thermodynamic standpoint, “structural hydrophily” is of entropic nature and is provided by the micropore generation caused by fluctuations. The micropores are stabilized through the capture of water molecules. When the polymer transforms to the highly elastic state, zones of a dynamically active microporous sponge are formed with the participation of moisture. In these zones, the fluctuation results in the formation and destruction of hydrophobic slits, which ensure the appearance of the water interlayers and drops of critical size that merge into the stable water phase. A thermodynamic model of the process is considered.     

改性聚丙烯酰胺水溶液的疏水缔合性质

合成了一种疏水缔合水溶性聚丙烯酰胺共聚物，使用荧光光谱法并结合紫外及流变性实验，对制备的疏水缔合水溶性聚丙烯酰胺共聚物在水溶液中形成疏水微区、超分子聚集体及空间网络结构进行了研究，并用扫描电子显微镜证实了溶液中网络结构的存在．     

疏水型阳离子水性聚氨酯的合成与性能研究

以甲苯二异氰酸酯,聚酯、聚醚混合多元醇为基本原料,N-甲基二乙醇胺(MDEA)为亲水扩链剂,羟丙基聚二甲基硅氧烷、单硬酯酸甘油酯为改性剂,通过醋酸中和反应制备出疏水型自乳化阳离子水性聚氨酯乳液;研究了改性剂用量、R值(体系中—NCO和—OH的物质的量比)、MDEA含量和中和度对乳液耐水性的影响。结果表明:羟丙基聚二甲基硅氧烷和单硬酯酸甘油酯加入到聚氨酯体系中,均能显著提高聚氨酯的耐水性;胶膜吸水率随MDEA含量增加呈先降低后升高的趋势;当中和度小于100%时,胶膜吸水率随中和度的增大而减小;当中和度大于100%时,中和度对胶膜吸水率无明显影响。     

Rheological Behaviour of Poly (Acrylamide-G-Propylene Oxide) Solutions: Effect of Hydrophobic Content,Temperature and Salt Addition

Abstract

The viscosity of hydrophobically modified polyacrylamide was investigated as a function of polymer concentration in aqueous and in salt solutions, and also as a function of temperature. The graft copolymers were constituted of polyacrylamide backbone and different amount of hydrophobic polypropylene oxide) graft chains. Measurements of intrinsic viscosities have been performed by using a Contraves low-shear LS-40 rheometer. From these results, a dependence of the intrinsic viscosity of the polymer solution with the molecular weight was observed, where an increase of the latter resulted in higher intrinsic viscosity. In this case, the effect of the molecular weight was more emphasized than the effect caused by the slightly different degrees of hydrophobic incorporation. When enhancing the temperature, it was not verified a significant change on the reduced viscosities of the copolymer solutions and the graft chain length was also observed.     

Mass Diffusion in a Hydrophobic Membrane Humidification/Dehumidification Process: the Effects of Membrane Characteristics

Abstract

Humidification and dehumidification are common processes in air conditioning industry. In this study, a new technique‐the hydrophobic membrane based air humidification and dehumidification are investigated. The effects of membrane characteristics on moisture exchange effectiveness of the system are studied. A two‐dimensional transient model which takes into account the combined mechanisms of Knudsen flow and ordinary diffusion in membrane pores is proposed and validated. Four membranes, 2 hydrophobic treated Nylon and 2 PVDF, are used in the test to validate the model. Then the effects of variations of membrane properties on the system performance and membrane to total resistance ratio, are evaluated. A dimensionless Number of Transfer Units (NTU) can be summarized to govern the moisture exchange performance. Following, a correlation has been obtained to reflect the relations between the moisture exchange effectiveness and the Number of Transfer Units.     

Temperature-Induced Change of Water Structure in Aqueous Solutions of Some Kosmotropic and Chaotropic Salts

The hydrogen bond structure of water was examined by comparing the temperature dependent OH-stretching bands of water and aqueous NaClO₄, KClO₄, Na₂SO₄, and K₂SO₄ solutions. Results called attention to the role of cations on top of the importance of anions determining the emerging structure of a multi-layered system consisting single water rings or multi-ring water-clusters.     

分子动力学模拟研究盐离子对十二烷基硫酸钠胶束溶液中亲水亲油协调机制的影响

The presence of salt has a profound effect on the size, shape and structure of sodium dodecyl sulfate (SDS) micelles. There have been a great number of experiments on SDS micelles in the presence and absence of salt to study this complex problem. Unfortunately, it is not clear yet how electrolyte ions influence the structure of micelles. By describing the compromise between dominant mechanisms, a simplified atomic model of SDS in presence of salt has been developed and the molecular dynamics (MD) simulations of two series of systems with different concentrations of salt and charges of ion have been performed. Polydispersity of micelle size is founded at relatively high concentration of SDS and low charge of cation. Although the counter-ion pairs with head groups are formed, the transition of micelle shape is not observed because the charge of cation is not enough to neutralize the polar of micelle surface.     

Influences of Ligand Structure and pH on the Adsorption with Hydrophobic Charge Induction Adsorbents: A Case Study of Antibody IgY

The adsorption behaviors of hydrophobic charge induction chromatography (HCIC) adsorbents with different functional ligands were investigated with immunoglobulin of egg yolk (IgY) as a model antibody. The adsorption isotherm and retention behavior in the column were studied, and the influences of the ligand structure and the pH on the adsorption were discussed. The results indicated that the pI of the target protein and pKa of HCIC ligand are the important parameter to determine the maximum adsorption pH of HCIC adsorbent, and high adsorption of IgY was found at pH 5 for all five adsorbents tested. Some differences could be found for different HCIC adsorbents, and the ligand structure influenced pH effect on the binding/elution of target protein. 2-mercapto-1-methyl-imidazole (MMI) ligand with a sulfone group showed a high adsorption capacity and strong pH-sensitivity, which would be more suitable for antibody purification. Moreover, the retention experiments indicated that IgY could be efficiently eluted from the adsorbents with 4-mercapto-ethyl-pyridine (MEP) or MMI as the ligand at acid conditions, while 2-mercapto-benzimidazole (MBI) ligand showed some difficulties on the elution. The retention study would help in defining not only the effective pH of elution for a given protein but also the elution efficiency of a given adsorbent.     

氨基聚硅氧烷接枝改性纤维素膜对其结构和性能的影响

采用氢氧化锂/尿素/水溶液作为溶剂,通过冷冻-解冻配置稳定的纤维素溶液并制备纤维素膜.利用高碘酸钠选择性氧化纤维素葡萄糖单元临近的两个羟基制备出二醛纤维素,然后用氨基聚硅氧烷对其进行改性制备出憎水性复合纤维素膜.通过傅立叶红外光谱仪、扫描电镜、热重分析、接触角测定和溶胀率测定等表征氧化纤维素和憎水性复合纤维素的结构和性能.研究了不同质量分数的高碘酸溶液对纤维素的氧化程度以及对纤维素膜的结构的影响,通过改变氨基聚硅氧烷的摩尔浓度来制备不同接枝度的憎水性复合纤维素.结果表明,二醛纤维素具有很强的反应活性,改性纤维素膜的憎水性得到明显提高.在纤维素改性及功能化材料制备的研究中,较强的反应活性使其可以应用在更多的领域.     

Effects of Water Content on the Properties of Sodium Aluminosilicate Glasses

Sodium aluminosilicate glasses of the general formula 25Na₂O. x Al₂O₃.(75 – x )SiO₂ were prepared with a range of hydroxyl contents. Both the glass transformation and isokom temperatures decrease as the hydroxyl content increases. The magnitude of the decrease in each property is a function of the alumina content of the glass, with the largest effects occurring for the glass containing 25 mol% Al₂O₃. The magnitude of the effect of water as a function of alumina content reflects the decrease in the concentration of nonbridging oxygens in the glass with increasing Al₂O₃ content, since the effect of the terminal hydroxyl species on the connectivity of the glass is enhanced by the elimination of nonbridging oxygens. The results indicate that the large effect of water content on the properties of these glasses must be considered when discussing the role of alumina in glasses.     

亲水单体对聚氨酯丙烯酸复合乳液性能的影响

采用种子乳液聚合法,以甲苯二异氰酸酯(TDI)、聚醚二元醇(N210)、二羟甲基丙酸(DMPA)和甲基丙烯酸甲酯(MMA)为主要原料合成了聚氨酯丙烯酸(PUA)复合乳液。考察了DMPA对PUA乳液的制备和性能的影响;确定了DMPA的添加工艺及中和度。发现随DMPA添加量增加,PUA乳液的外观变好,乳液粒径变小,乳液黏度增大,乳液凝胶量降低,稳定性变好。随DMPA添加量增大,PUA乳液涂膜的吸水率增大,涂膜的耐水性越差。综合得到w(DMPA)=7 5%,采用后添加DMPA的工艺,且DMPA的中和度90%～100%,可得到性能优异的PUA复合乳液。     

组织结构对三维机织物的吸水导湿性能影响

以差动毛细效应为基础,细旦丙纶和黏胶长丝为原料,设计织造了正交结构、角联锁结构和多层接结结构的三维机织物,并对各织物的吸水导湿性能进行测试分析。结果表明:正交结构三维机织物的吸水导湿性能最优。     

In situ XAFS Studies on the Effects of the Hydrophobic–Hydrophilic Properties of Ti-Beta Zeolites in the Photocatalytic Reduction of CO2 with H2O

The photocatalytic reduction of CO₂ with H₂O to produce CH₄ and CH₃OH was found to proceed in the gas phase at 323 K with different reactivities and selectivities on hydrophilic Ti-Beta(OH) and hydrophobic Ti-Beta(F) zeolites prepared in the OH^– and F^– media, respectively. In situ XAFS measurements have revealed that these differences are attributed to the differences in the affinity for the adsorption of H₂O molecules on the highly dispersed tetrahedrally coordinated titanium oxide species depending on the hydrophobic–hydrophilic properties of zeolites.     

Specific Ion Effects of Salt Solutions on Colloidal Properties of Octadecylamine Hydrochloride

Flotation continues to be a major technique for the production of potash from low grade, complex systems containing a variety of ores and ions. The specific ion effects on the behavior of the flotation collector in the KCl flotation system becomes important to the interpretation of the flotation mechanism. In this work, specific ion effects on the turbidity, surface tension and aggregation behavior of the common collector in KCl flotation, octadecylamine hydrochloride (ODA), have been investigated. The results from turbidity and surface tension studies of ODA solutions show that both cations and anions can affect the colloidal properties of ODA. Molecular dynamics simulations show that the binding that energy barrier between ODA headgroups and anions is principally responsible for the specific anion effect of γ _CAC of ODA solutions. In addition, the ion effect on the ODA aggregation particle size was also studied by using transmission electron micrographs (TEM) and dynamic light scattering. The data reveal that the presence of salt ions can induce the formation of larger ODA colloidal particles, on which the cation effect is more significant. This work provides detailed information of specific ion effect on colloidal properties of ODA, which may promote a further understanding of the flotation mechanism and help to improve the flotation of KCl from brine sources.