Structural and water diffusion of poly(acryl amide)/poly(vinyl alcohol) blend films: Experiment and molecular dynamics simulations

To study the effects of composition ratios and temperature on the diffusion of water molecules in PVA/PAM blend films, five simulation models of PVA/PAM with ten water molecules at different composition ratios (4/0, 3/1, 2/2, 1/3, 0/4) were constructed and simulated by using a molecular dynamics (MD) simulation. The diffusion behavior of water molecules in blends were investigated from the aspects of the diffusion coefficient, free volume, pair correlation function (PCF) and trajectories of water molecules, respectively. And the hydrophilicity of blend composite was studied based on the contact angle and equilibrium water content (EWC) of the blend films. The simulation results show that the diffusion coefficient of water molecules and fractional free volume (FFV) of blend membranes increase with the addition of PAM, and a higher temperature can also improve the diffusion of water molecules. Additionally, the analysis of PCFs reveals the main reason why the diffusion coefficient of water in blend system increases with the addition of PAM. The measurement results of contact angle and EWC of blend films indicate that the hydrophilicity of blend films decreases with the addition of PAM, but the EWC of blends increases with the addition of PAM.     

An experimental study of convective heat transfer in silicon microchannels with different surface conditions

An experimental investigation has been performed on the laminar convective heat transfer and pressure drop of water in 13 different trapezoidal silicon microchannels. It is found that the values of Nusselt number and apparent friction constant depend greatly on different geometric parameters. The laminar Nusselt number and apparent friction constant increase with the increase of surface roughness and surface hydrophilic property. These increases become more obvious at larger Reynolds numbers. The experimental results also show that the Nusselt number increases almost linearly with the Reynolds number at low Reynolds numbers (Re<100), but increases slowly at a Reynolds number greater than 100. Based on 168 experimental data points, dimensionless correlations for the Nusselt number and the apparent friction constant are obtained for the flow of water in trapezoidal microchannels having different geometric parameters, surface roughnesses and surface hydrophilic properties. Finally, an evaluation of heat flux per pumping power and per temperature difference is given for the microchannels used in this experiment.     

Enhancement of visible light-induced hydrophilicity on nitrogen and sulfur-codoped TiO2 thin films

We fabricated N, S-codoped, N-doped, S-doped TiO₂ anatase thin films by a radio-frequency (RF) sputtering method and evaluated the photoelectrochemical and photoinduced hydrophilic activities. The N, S-codoped TiO₂ thin film showed obviously higher activities than either the N-doped or S-doped TiO₂ under visible light irradiation. The photoinduced hydrophilic activity of the N, S-codoped TiO₂ was also greater than that of the undoped TiO₂ even under fluorescent light bulb, which contained both visible and UV lights. The high activities of the N, S-codoped TiO₂ could be attributed to the hybridization of the introduced N 2p and S 3p, which was supported by the results of ab initio calculations.     

Characterization of metal (Ba, Al, Si, V, and W)-incorporated TiO2 and toluene photodecomposition in the presence of H2O

This study focused on toluene photodecomposition in the presence of H₂O over metal (Ba, Al, Si, V, and W)-incorporated TiO₂. The nanometer-sized, metal-TiO₂ photocatalyst samples, including Ba²⁺, Al³⁺, Si⁴⁺, V⁵⁺, and W⁶⁺ ions, were prepared by using the solvothermal method. The X-ray photoelectron spectroscopy (XPS) results showed that the Ti-OH peak, which indicates hydrophilicity, increased with increasing Al and Si ion components but decreased with increasing Ba, V, and W ion components. The contact angles were distributed over the range of 0–10° on almost all films (200-nm thick) after irradiation for 2 h, and in particular approached 0° on the Al-TiO₂ and Si-TiO₂ nanometer-sized films after just 30 min. The toluene (100 ppm) photodecomposition in the continuous system increased in the order of Al-TiO₂>Si-TiO₂>pure TiO₂>W-TiO₂>Ba-TiO₂>V-TiO₂, and the maximum toluene conversion rate achieved was 45% over Al-TiO₂ film after 120 min. The toluene conversion remarkably increased; however, over all photocatalysts, with H₂O addition during the toluene photo-decomposed reaction, and in particular, the conversion reached up to 90% after 120 min over Al-TiO₂ and Si-TiO₂ with increased hydrophilicity. After photoreaction for 24 h, minimal carbon was deposited on the photocatalyst under both reaction conditions, with and without H₂O addition, although the deposited carbon amounts were smaller for the former. These results confirmed that the hydrophilicity of the photocatalyst had a greater effect on toluene decomposition, while the photocatalytic deactivation could be retarded by H₂O supplementation during toluene decomposition.     

Hydrophilicity and photocatalysis of Ti1−xVxO2 films prepared by sol-gel method

Ti_1−xV_xO₂ films were prepared by sol-gel dip-coating method. To study the effects of vanadium incorporation on the self-cleaning properties of TiO₂ film, the crystallization behavior and surface morphology of Ti_1−xV_xO₂ films were investigated by an X-ray diffraction (XRD) analysis and an Atomic force microscope (AFM) respectively. The band-gap E_g of Ti_1−xV_xO₂ was determined by optical transmission spectra. Hydrophilicity and photocatalysis of Ti_1−xV_xO₂ films were characterized. The results showed that Ti_1−xV_xO₂ films had super-hydrophilicity and greater photocatalysis under day light illumination when x = 0.1-0.2. An optimal photocatalytic activity was obtained when x = 0.15. Moreover, Ti_0.85V_0.15O₂ films were proven to have excellent photocatalysis and hydrophilicity in visible region simultaneously, which made the application of Ti_0.85V_0.15O₂ film as self-cleaning and anti-fogging material practical under everyday condition.     

Verbesserte Hydrophilie von Hohlfasermembranen mittels funktionalisierter Trennschicht für die Ultrafiltration

Dual layer hollow fiber membranes, based on poly(ether sulfone), were fabricated to achieve hydrophilic membranes with improved fouling resistance. A new triblock copolymer, consisting of two hydrophilic poly(ethylene oxide) blocks and an inner poly(ether sulfone) block, was chosen for the functionalization of the inner layer. The most promising membrane of this study was characterized by an improved hydrophilicity, and a performance in the ultrafiltration studies of 2000 L m⁻²h⁻¹bar⁻¹ and retention of 100 kDa.     

Vapor/gas separation through carbon molecular sieve membranes: Experimental and theoretical investigation

The separation of H₂O vapor from (hydrogen-rich) gaseous streams is a topic of increasing interest in the context of CO₂ valorisation, where the in situ water removal increases product yield and catalyst stability. In this work, composite alumina carbon molecular sieve membranes (Al-CMSM) were prepared from phenolic resin solutions loaded with hydrophilic boehmite (γ-AlO(OH)) nanosheets (0.4–1.4 wt. % in solution) which partially transform to γ-Al₂O₃ nanosheets upon thermal decomposition of the resin, improving the hydrophilicity and thus the adsorption-diffusion contribution of the H₂O permeation. The γ-Al₂O₃ nanosheets showed no influence on the pore size distribution of the membranes in the range of micropores, but they increased the membrane hydrophilicity. In addition, the use of boehmite in the resin solution causes an increase in the viscosity and thus an increase in the carbon layers thickness deposited on the porous α-Al₂O₃ support (from 1 to 3.3 μm). Furthermore, the alumina sheets introduce defects in the carbon matrix, increasing the tortuosity of the active layer, as concluded via phenomenological modelling and parametric fitting of the experimental results. As a consequence, the water permeability exhibits a maximum (1.3?10^?6 mol?s^?1 Pa^?1 m^?1 at 150 °C) with boehmite/alumina content of ca. 0.8 wt. %, as the combined effects of increasing hydrophilicity (which favour H₂O permeability) and increasing thickness and tortuosity (which hamper permeability) upon increasing boehmite loading. Similarly, the H₂O/gas perm-selectivity is optimum at 1.2 wt. % boehmite loading. We further investigated the H₂O permeation mechanism by modelling the mono- and multi-layer adsorption and capillary condensation of water in microporous media, which result as the main transport mechanisms in the explored conditions.     

Hybrid plasma bonding of germanium and glass wafers at low temperature

Hybrid plasma bonding (i.e., sequentially plasma activation followed by anodic bonding) has been demonstrated for germanium and glass wafers for the first time. Void-free interface with high bonding strength has been observed at 200 °C. This improved quality is attributed to reduced surface roughness and increased hydrophilicity of sequentially activated germanium and glass. Three layers caused by reactions of OH molecules between the highly reactive surfaces after plasma activation and opposite migration of cations and anions are observed across the interface.     

Thermoplastic starch modified with polyurethane microparticles: Effects of hydrophilicity of polyurethane prepolymer

It is important to chemically modify starch in an effective way. In this study, a series of polyurethane prepolymers (PUP) using 2,2‐dimethylol propionic acid (DMPA) as hydrophilic chain extender was synthesized and then used to modify starch by intensive mixing to obtain modified thermoplastic starch (TPS). The structure and properties of the modified TPS were investigated. The results showed that the elongation at break of the modified TPS increased from 5.4 to 9.8% with the content of PUP in modified TPS increasing from 10 to 20%, suggesting the PUP played an important role in the enhancement of the flexibility of the modified TPS sheet. The reaction ratio of PUP used for preparing the modified TPS was 98.5 ± 0.03%, indicating the modification was conducted efficiently because the multifunctional groups of polyurethane microparticles dramatically improved the reaction probability of the PUP modifier. The modified TPS prepared with PUP by adding DMPA showed increasing viscosity and decreasing contact angle due to the hydrophilicity of DMPA.     

Performance of RC and PES ultrafiltration membranes in filtration of pulp mill process waters

Issues of fouling and effective cleaning limit the adoption of UF in pulp and paper mill applications. The choice of an optimal membrane for a specific filtration application is a challenging task due to the fact that fouling is a complex phenomenon. This study compares regenerated cellulose (RC) and polyethersulphone (PES) membranes in UF of two chemithermomechanical pulp mill process waters. The process waters originated from hardwood and softwood pulping. Based on their flux recovery, PES membranes sustained greater fouling than RC membranes even though the hydrophobicity of RC membranes was increased remarkably by adsorptive fouling. The process water affected the performance of the membranes. The membrane characteristics were more important in determining fouling when softwood process water was used than when hardwood process water was used. Hydrophilicity and morphology of the membranes were seen to have a clear influence on fouling.