Low Hydrophobic Surface Research Articles

Lateral Drop Rebound on a Hydrophobic and Chemically Heterogeneous Surface.

In this paper, the process of a drop rebounding from a hydrophobic and chemically heterogeneous surface is investigated using the multiphase lattice Boltzmann method. The bounce behavior of drops is dependent on the degree of hydrophobicity and heterogeneity of the surface. When the surface is homogeneous, the drop rebounds vertically and the height increases with the enhancement of the surface hydrophobicity. For the heterogeneous surface with two different hydrophobic parts, the drop rebounds laterally toward the lower hydrophobic side. Because the high hydrophobic side exerts the stronger unbalanced Young's force on the contact line compared with the low hydrophobic side, the difference of the forces results in the asymmetrical rebound. A phase diagram displays the rebound numbers of a drop impacting on the various chemically homogeneous and heterogeneous surfaces. A simply quantitative estimation is made to predict the rebound heights and flying times through the contact angles of the surface. This work promotes the understanding of the rebound mechanism of a drop impacting on a chemically heterogeneous surface and provides a guiding strategy for the precise control of the lateral behavior of rebounding drops by hydrophobic and heterogeneous surfaces.

Molecular Dynamics Study on Proton Transport in Supported Nafion Ionomer Thin Films on Lennard-Jones Walls

The catalyst layer, one of the components of membrane electrode assembly in polymer electrolyte fuel cells, was modeled by molecular dynamics methods, and proton transport in ionomer thin films was simulated to elucidate the effect of surface wetting interaction on the ionomer thin film morphology and proton transport property. Ionomer thin film properties are considered to be affected by the surface property of supported carbon due to their nano-scale thickness (4-10 nm thick). One of the surface properties is surface wetting interaction basically attributed to the physical or chemical property of surfaces.In this study, modeled Nafion thin films with 4 nm and 10 nm thick were generated on the two ideal LJ smooth surfaces which have different strength of interactions to focus on the effect of the surface wetting interaction on the ionomer thin film morphology and proton transport. Protons exist as hydronium ions in ionomer thin films for chemical stability and are transported by the two transport mechanisms which are the vehicle mechanism (just move as hydronium ions) and the Grotthuss mechanism called proton hopping. It is common that proton transport model is restricted to only the vehicle mechanism when using classical molecular dynamics method, however, our proton transport model includes the Grotthuss mechanism by using aTS-EVB method (anharmonic two-state empirical valence bond method) in order to make proton transport model more reproducible.From the analysis in the ionomer thin films with 4 nm thick, surface wetting interaction was found to affect the orientation of sulfonic group near the surface. The orientation is well-ordered on the higher hydrophobic surface, and the sulfonic groups point to the gas phase direction, while it is randomly distributed on the lower hydrophobic surface, which make differences in the water cluster connectivity and size in ionomer thin films between the two surfaces. Proton transport property was evaluated by the self-diffusion coefficient. The proton self-diffusion coefficient in ionomer thin films was indicated to be improved on higher hydrophobic surface probably because higher hydrophobic surface makes ideal water cluster structures for proton transport in ionomer thin films.As compared to the ionomers with the different film thickness, the proton self-diffusion coefficient in ionomer thin films on higher hydrophobic surface was indicated to decrease in the increase of the film thickness, while that on lower hydrophobic surface was indicated to increase slightly. This result is expected to come from the confinement and interface effects which can be remarkable when the thickness decrease. The ionomer morphology on higher hydrophobic surface has advantages for proton transport probably thanks to the effects as observed in the ionomer with 4 nm thick, while that on lower hydrophobic surfaces has disadvantage. Since the effects can be weaker with the increase in the film thickness, the proton self-diffusion coefficient in ionomer thin films on higher hydrophobic surface was found to decrease with the increase in the film thickness, while that on lower hydrophobic surface was found to increase slightly.

Deviation of sliding drops at a chemical step.

The motion of partially wetting liquid drops in contact with a solid surface is strongly affected by contact angle hysteresis and interfacial pinning. However, the majority of models proposed for drops sliding over chemical surface patterns consistently neglect the difference between advancing and receding contact angles. In this article, we present a joint experimental and numerical study of the interaction of gravity-driven drops with a chemical step formed at the junction between a hydrophilic and a hydrophobic region. It demonstrates the strong impact of a contact angle hysteresis contrast on the motion of drops at a linear chemical step. Surprisingly, the smallest driving force required to drag the drop across the step onto the lower hydrophobic surface is not observed at a right angle of incidence. Our model reveals that the non-monotonous response of this passive drop 'filter' is solely due to the higher advancing contact angle on the lower surface, and creates an instance where drop motion is affected by dissipation at the contact line rather than by surface energy.

New findings about the lipase acetylation of nanofibrillated cellulose using acetic anhydride as acyl donor

The acetylation efficiency of nanofibrillated cellulose (NFC) with acetic anhydride as acetyl donor was studied using lipase from Aspergillus niger in a mixture of dimethyl sulphoxide (DMSO) and phosphate buffer solution at ambient conditions and in supercritical carbon dioxide (scCO2). The chemical acetylation of NFC with comparable ester content was carried out for comparison. The ATR-FTIR, solid-state CP/MAS 13C NMR and DSC analyses revealed that, besides the enzyme-catalysed acetylation, predominantly appearing at the C-6 position of cellulose hydroxyls, a strong and stable acyl-enzyme intermediate attachment also occurred on the NFC via Maillard reaction. Enzymatic acetylation via attached acyl-enzyme complex on NFC yielded high hydophobicity (contact angle of 84±9°), whereas the chemical acetylation with comparable ester content resulted in a much lower hydrophobic surface with a contact angle of 33±3°. Finally, the adsorption capacity profiles of lysozyme and BSA proteins on native, chemically and enzymatically acetylated NFC as a function of the pH medium were determined.

Factors influencing the capillary separation of leukocytes from whole blood in a plastic-based microfluidic chip

Abstract This study describes some of the influencing factors, such as capillary action, static electricity and magnetic force, on the ability to separate living leukocytes from a single droplet of blood ( The chip was constructed from two substrate materials sandwiched together to form a micron-order gap (40 μm) with an upper hydrophilic (glass) surface and a lower hydrophobic (acrylic resin) surface. A blood sample flowed into the gap between the two substrates driven by the difference in surface tension between the two materials. Leukocytes adhered to the lower hydrophobic surface, whereas red corpuscles flowed toward the exit of the microfluidic device (this phenomenon is referred to as micro-flow). The separation rate of the red corpuscles was 91 ± 9% in a unit area of 0.1 mm2. Furthermore, we analyzed the change in the numbers of living leukocytes that could be collected after separation in the chip under different conditions. When SiO2 and iron composite particles, 10 μm in size, were added to the blood sample, leukocytes formed colonies containing two or three cells. The colonies could be moved freely on the x–y plane using a Nd magnet. When the upper board was charged by static electricity, the colonies adhered to the underneath of the upper board. Five or more colonies, as well as 10 or more individual leukocytes, were able to collect in a 0.1 mm2 area of the chip after micro-flow operation. Thus, the separation efficiency of a living cell colony containing Fe particles in a capillary chip is markedly influenced by magnetic and electrostatic forces.

Electrochemical synthesis of N 2O 5 by oxidation of N 2O 4 in nitric acid with PTFE membrane

Electrochemical synthesis of dinitrogen pentoxide (N 2O 5) by oxidation of dinitrogen tetroxide (N 2O 4) in a plate-and-frame electrolyzer was investigated. As the separator, different porous polytetrafluoroethylene (PTFE) membranes were tested in this process and the effects of hydrophilicity and of hydrophobicity on the electrolysis were discussed. The transport of N 2O 4 and water from catholyte to anolyte through membrane occurred in the electrolysis, especially at the end of the electrolysis. The water transport had a much more effect on the electrolysis than that of the N 2O 4 diffusion. The hydrophobic PTFE membranes had better performance on control of water transport from catholyte to anolyte than that of the hydrophilic ones. Hydrophobicity can increase the chemical yield of N 2O 5. The membranes with a low hydrophobic surface were preferred. All the hydrophobic PTFE membranes with low resistance have the specific energy of 1.1–1.5 kWh kg −1 N 2O 5. The current efficiency of 67.3–80.2% and chemical yield of 58.9–60.9% were achieved in production of N 2O 5. The technique of replacing the catholyte with fresh nitric acid can minimize the transport of N 2O 4 and water to a great extent, it can further improve the chemical yield and reduce the specific energy.