Hydrophobic Capillaries Research Articles

Application of polypropylene microfiltration membranes for separation of wastewater from car wash

In the final stage of washing the car is waxed and rinsed with demineralized water, however, at an initial stage reusing treated effluents as process water is possible. In the current work, the application of microfiltration (MF) polypropylene (PP) membranes for treatment of carwash wastewater was investigated. To compare the transport properties, more hydrophobic PTFE capillary membranes were also used. The examined process is restricted by the fouling phenomenon, which has been thoroughly studied by filtering both the synthetic and real wastewaters. The use of different types of foaming agents and hydrowaxes, allowed to found that the membranes fouling was caused not only by the impurities removed from the car, but also by the mixtures of commercial washing agents. As a result, the permeate flux was quickly reduced, to a level of 100–200 LHM for PP membrane and to 50–150 LHM for PTFE membrane (TMP = 0.05 MPa). Regardless of the degree of feed contamination, the clean permeate with turbidity of 0.2–0.8 NTU was obtained. In the case PTFE membrane, the permeate turbidity was at a level of 2–3 NTU. The tested wastewaters (5–100 NTU) contained the particles with the size in the range of 0.1–400 μm. The removal of larger particles by prefiltration was found to increase the membranes fouling. It has been noted that rinsing the modules with water was not effective. Nevertheless, the membranes were cleaned using alkaline solutions (pH = 11.5–12.0) used at the car wash station to remove insects and to wash the wheel. This procedure was less effective for PTFE membranes, which experienced significantly greater irreversible fouling. It has been shown that the PP membranes used, in addition to removing turbidity, ensured the retention of Escherichia coli in almost 100%.

Experimental validation of a coupling concept for drop formation and growth onto porous materials by high-resolution X-ray imaging technique

Droplets formed on the hydrophobic surface of a porous medium exposed to a cross-flowing gas stream have a strong influence on the mass, momentum, and energy exchange across the porous interface, being of importance in several physical systems and engineering applications, like fuel cells. However, the fluid displacement front is highly complex at the pore-scale, since it is characterized by the surface wettability and a contact angle variation along the triple line. Furthermore, the droplet formation is affected by the pore geometry and the surface wettability. These result in a challenging multi-phase scenario with controversial literature, and few studies consider the detailed mechanism of droplet formation on the surface of the porous medium. In this work, two multi-scale simulations for the emerging water droplet from a single hydrophobic capillary pore opening into the gas phase are validated by a benchmark experiment with the help of a high-resolution X-ray imaging technique to characterize the droplet growing. A three-domain approach (gaseous free flow, interface and porous medium, FIP) was compared with a two-domain approach (based on a free-flow and the porous medium, FP). Whereas the three-domain approach introduces two sets of coupling conditions, one for the free flow-interface and one for the interface-porous medium, the two-domain approach introduces only one set of coupling connections for describing the interaction between the domains. In both approaches, droplet formation and growth alter the coupling conditions between the domains. While the FIP approach treats the porous medium as a continuous matter, it is resolved discretely with the help of a pore network in the FP approach. Both approaches show good agreements with the experimental observations and high correspondences for the drop volume, radii and contact angle evolution. The proposed models provide a base for future developments and help to gain a better insight about the impact of the droplet formation on the interface in a coupled free flow-porous medium system.

Generation and characterization of air micro-bubbles in highly hydrophobic capillaries.

The generation of air microbubbles in microfluidic systems or in capillaries could be of great interest for transportation (single cell analysis, organite transportation) or for liquid compartmentation. The physicochemical characterization of air bubbles and a better understanding of the process leading to bubble generation during electrophoresis is also interesting in a theoretical point of view. In this work, the generation of microbubbles on hydrophobic Glaco™ coated capillaries has been studied in water-based electrolyte. Air bubbles were generated at the detection window and the required experimental parameters for microbubbles generation have been identified. Generated bubbles migrated against the electroosmotic flow, as would do strongly negatively charged solutes, under constant electric field. They have been characterized in terms of dimensions, electrophoretic mobility, and apparent charge.

CuSO4 chromogenic tracing for migration and crystallization of salt solution in porous materials

The migration and crystallization of CuSO4 solution characterized by color change property on the surface of glass of hydrophobic property, capillaries and porous resin materials were observed online in real time. The research results indicated that under the condition of stable environment, crystals generated by CuSO4 droplets were relatively complete, and crystals would also easily be accumulated both inside and outside of the capillaries, in particularly, the crystal morphology inside the capillaries altered along with the change of solution state. Meanwhile, there were parabolic migration and crystallization of the salt solution in the porous material samples, and the samples with saturated salt solution had a wide range of crystal areas when the salt solution had been completely crystallized in the porous samples, while the crystal belt in the interior samples was produced with less salt solution. In this paper, the parabola with opposite direction in the process of salt solution migration and crystallization, as well as the distribution of whitespace and crystal belt were found for the first time.

Effect of mixing on mass transfer characterization in continuous slugs and dispersed droplets in biphasic slug flow microreactors

The mass transfer of slug flow, a widely applied flow pattern in microreactors, is still difficult to predict mainly due to the competing nature between convection and diffusion. This work focused on the influence of the mixing mechanism on the mass transfer performance under gas–liquid and liquid–liquid slug flow, in both continuous slugs and dispersed droplets. Colorimetric study with the resazurin oxidation system was implemented, where the mass transfer resistance was constantly located in the aqueous phase. In the hydrophilic glass microreactor, the convection featured by intensive internal circulation and/or inter-slug leakage flow dominated diffusion, leading to nearly-constant kLa along the channel under given flow rates. However, in the hydrophobic PTFE capillary, the stagnant region constituted a significant share in the aqueous droplet, indicating the prominent role of diffusion against convection therein. As a result, kLa values decreased along the main channel length in fixed operating conditions. Accordingly, prediction models were respectively correlated depending on mixing mechanisms. Moreover, mass transfer contributions from the bubble and droplet formation stages were also investigated. This work is expected to shed light on judicious process design and reliable predictions in microreactor operations.

β-Cyclodextrin covalent organic framework–modified organic polymer monolith as a stationary phase for combined hydrophilic and hydrophobic aqueous capillary electrochromatographic separation of small molecules

Aβ-Cyclodextrin covalent organic framework (β-CD COF) was successfully prepared under ambienttemperature with a mild chemistry strategy from heptakis(6-amino-6-deoxy)-β-cyclodextrin and terephthalaldehyde. It was embedded into the poly[(glycidyl methacrylate)-co-(ethylene dimethacrylate)] [poly(GMA-co-EDMA)] monolith and served as the β-CD COF material-incorporated monolith. The synthetic materials were characterized by field emission scanning electron microscopy, energy-dispersive X-ray mapping analysis, transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and N2 adsorption-desorption isotherm. The β-CD COF material-incorporated monolith achieved baseline separation in capillary electrochromatographic separationof three amides, three amino acids, three nucleosides, four aromatic acids, and three positional isomers (withresolutionvalues of three amides, 1.75 and 1.54; three amino acids, 5.24 and 1.75; three nucleosides, 2.56 and 1.77; four aromatic acids, 6.96, 2.74, and 1.64; three positional isomers, 1.61 and 1.50). In comparison with the original monolith, the β-CD COF material-incorporated monolith shows significantly enhanced resolution for mixed molecules. The effect ofpH and concentration of buffer and applied voltage were discussed in detail. The fabricated monolith showed good stability and reproducibility (relative standard deviation (RSD) < 6.9%). Molecular modeling illuminated the interactions between the small molecules and stationary phase, and provided a sufficient theoretical basis for experimental data. Graphical abstract Schematic presentation of the preparation of β-cyclodextrin covalent organic framework (β-CD COF) material-incorporated organic polymer monolith for separating the amides, amino acids, nucleosides, aromatic acids, and positional isomers. β-CD COF materials were synthesized and incorporated into the monolith as the stationary phase. Then, the incorporated monolith was applied in the capillary electrochromatography system for separating small molecules.

Insight into the pressure-induced displacement mechanism for selecting efficient nanofluids in various capillaries

A pressure-induced displacement mechanism in hydrophobic and hydrophilic capillaries.

Hydrophobic ceramic capillary membranes for versatile virus filtration

In this study, we present hydrophobic yttria-stabilized zirconia capillary membranes conditioned for virus filtration. These macroporous ceramic filters (d50 = 150 nm) efficiently extract viruses regardless of their surface charge with high throughput rates. For hydrophobic functionalization of the ceramic membranes we used two different silanes, n-hexyltriethoxysilane (HTS, C6-chain) and n-octyltriethoxysilane (OTS, C8-chain), in three different molarities. The virus retention of the membranes is tested in dead-end mode by intracapillary virus feeding using two small bacteriophages as model species: MS2 and PhiX174. Virus retention increases most strongly for hydrophobic capillaries functionalized with 0.05 M OTS, showing a virtually complete retention with log-reduction values (LRVs) of ~ 9 for both bacteriophages compared to the non-functionalized membrane with LRVs of 0.3 ± 0.1 for MS2 and 3.4 ± 0.2 for PhiX174. The functionalized membranes allow a high membrane flux of ~ 150 L/(m2hbar), with throughput rates up to ~ 400 L/(m2 h) while maintaining high filtration efficiency. Even under varying feed conditions using only mono- or divalent salt ions or pH values ranging from 3 to 9, retention capacities of the capillary membranes are high. Accordingly, such hydrophobic ceramic membranes offer a versatile alternative to conventional polymeric membranes for virus removal with greatly improved membrane flux.

Apply surface wettability gradient to non-wetting capillary: A simulation study on spontaneous droplet flow

The present work simulates a concept about how to drive droplet flowing through non-wetting (hydrophobic) capillaries without any external force by using many-body dissipative particle dynamics. By decorating the capillary segments with wettability gradients, a droplet with proper radius can be absorbed by the non-wetting capillaries and then constantly flow through the capillary. The simulation results show the droplet can keep flowing through the whole capillaries under certain wettability gradients and the flow velocity also depends on the degree of the wettability gradients. The average wettability of the whole capillary is also essential for the continuous flowing, higher non-wetting capillaries can still keep the flowing with low wettability gradients due to less surface adhesion. A strategy on how to achieve longer flow pathway is also presented. It is also find that unbalanced uptake of droplet via lateral heterogeneous surfaces cannot stir the inside flow of the droplet. The simulation results could inspire the new design of microfluidics in which the transportation of droplet is an important aspect.

Cation capture and overcharging of a hydrophobized quartz surface in concentrated potassium chloride solutions

The paper presents experimental data indicating interesting new phenomena related to overcharging of a hydrophobic surface in concentrated potassium chloride solutions. We attribute these data to cation complexation and capture of the cations by the hydrophobic surface. The analysis of the mechanism of the detected phenomena is based on capillary electrokinetic and wettability studies and confirmed by SEM data and XPS spectra. It was found that cation capture/complexation takes prolonged time, being associated with hydrolysis of Si-O bonds in hydrophobic molecules and affected by salt concentration. In addition, the time necessary for reversal of the sign of ζ-potential when solutions with lower salt concentrations are pumped through the hydrophobic capillary is much longer than that required to simply replace the solution inside the capillary.

Microgravity spreading of water spheres on hydrophobic capillary plates

We create nearly perfect centimetric spheres of water by splitting a cavity consisting of two metal hemispheres coated with a hydrophobic paint and under-filled with liquid, while releasing the apparatus in free-fall. A high-speed camera captures how water spread on hydrophobic aluminum and polycarbonate plates perforated with cylindrical capillaries. We compare observations at the ZARM drop tower in Bremen with Lattice-Boltzmann numerical simulations of Frank, Perre and Li for the inertial phase of imbibition.

Development of a single-cell X-ray fluorescence flow cytometer.

An X-ray fluorescence flow cytometer that can determine the total metal content of single cells has been developed. Capillary action or pressure was used to load cells into hydrophilic or hydrophobic capillaries, respectively. Once loaded, the cells were transported at a fixed vertical velocity past a focused X-ray beam. X-ray fluorescence was then used to determine the mass of metal in each cell. By making single-cell measurements, the population heterogeneity for metals in the µM to mM concentration range on fL sample volumes can be directly measured, a measurement that is difficult using most analytical methods. This approach has been used to determine the metal composition of 936 individual bovine red blood cells (bRBC), 31 individual 3T3 mouse fibroblasts (NIH3T3) and 18 Saccharomyces cerevisiae (yeast) cells with an average measurement frequency of ∼4 cells min(-1). These data show evidence for surprisingly broad metal distributions. Details of the device design, data analysis and opportunities for further sensitivity improvement are described.

Equilibrium and kinetics of wetting hydrophobic microporous membrane in sodium dodecyl benzene sulphonate and diethanolamine aqueous solutions

AbstractLiquid penetrations into hydrophobic capillaries are controlled by the adsorption and diffusion of the solute in the vicinity of the moving meniscus. The wetting process of microporous hydrophobic polyvinylidenefluoride (PVDF) and polytetrafluoroethylene (PTFE) membrane was investigated in both sodium dodecyl benzene sulphonate (SDBS) and diethanolamine (DEA) aqueous solutions. The experimental results revealed that wetting both the PVDF and PTFE membranes in SDBS solutions at high concentrations proceeded in two stages: rapid wetting and slow wetting, but this transition in the wetting rate was not observed during the membrane wetting at low SDBS concentration and in DEA solutions. The membrane wetting process was accelerated by increasing the solution temperature.

Effect of top soil wettability on water evaporation and plant growth

In general, agricultural soil surfaces being hydrophilic in nature get easily wetted by water. The water beneath the soil moves through capillary effect and comes to the surface of the soil and thereafter evaporates into the surrounding air due to atmospheric conditions such as sunlight, wind current, temperature and relative humidity. To lower the water loss from soil, an experiment was designed in which a layer of hydrophobic soil was laid on the surface of ordinary hydrophilic soil. This technique strikingly decreased loss of water from the soil. The results indicated that the evaporation rate significantly decreased and 90% of water was retained in the soil in 83h by the hydrophobic layer of 2cm thickness. A theoretical calculation based on diffusion of water vapour (gas phase) through hydrophobic capillaries provide a meaningful explanation of experimental results. A greater retention of water in the soil by this approach can promote the growth of plants, which was confirmed by growing chick pea (Cicer arietinum) plants and it was found that the length of roots, height of shoot, number of branches, number of leaves, number of secondary roots, biomass etc. were significantly increased upon covering the surface with hydrophobic soil in comparison to uncovered ordinary hydrophilic soil of identical depth. Such approach can also decrease the water consumption by the plants particularly grown indoors in residential premises, green houses and poly-houses etc. and also can be very useful to prevent water loss and enhance growth of vegetation in semi-arid regions.

Three-fluid membrane contactors for improving the energy efficiency of refrigeration and air-handling systems

This paper concerns an innovative three-fluid membrane contactor able to exchange both sensible heat and latent heat with the process air. A condensing/evaporating refrigerant (first fluid) exchanges heat with a second fluid (water/liquid desiccant) flowing over the outer surface of hydrophobic membrane capillaries, inside which the process air flows (third fluid). In this study, bench tests were carried out with either distilled water or saturated KCOOH solution as the desiccant. Water at a controlled temperature was used to simulate the refrigerant-phase change across the component. A theoretical model of the component yielded predictions that displayed good agreement with the experimental results. Ways of improving the enthalpy effectiveness of the component are discussed, as are applications in refrigeration plants and hybrid air-conditioning systems (vapour-compression cycles plus liquid desiccants). This new component raises very interesting applicative opportunities; though fairly compact, it can improve the energy efficiency of refrigeration and air-handling systems.

An extension of Miller scaling to scale sorptivity by contact angle

[1] This study sheds light on the limitations of using [(cos θ)½] to scale sorptivity by contact angle while reaffirming its scaling by geometrical Miller scaling factor (λ½). The sorptivity for uniform and nonuniform (wavy) capillary tubes was determined by a mathematical model that includes the effect of inertia and dynamic contact angle. Given that real porous media are preferably represented by a bundle of nonuniform rather than uniform capillary tubes, the relationship between sorptivity and contact angle was examined for different combinations of contact angles and capillary tube degrees of waviness. A general relationship of S = f [cos θ)β] (with β ≤ ½) was found. The deviation of β from ½ (associated with uniform capillary tubes) increased with contact angle and capillary waviness increase. Zero sorptivity was obtained even for wettable capillaries, θ < 90°, a phenomenon that has been generally associated with hydrophobic capillaries (θ ≥ 90°). Contact angle and nonuniform pore structure had a synergistic effect on sorptivity. Capillary nonuniformity per se diminished sorptivity but its synergy with contact angle markedly magnified this reduction. Thus, following the sorptivity impact on finger width, it is rational to assume that larger-than-zero contact angles are involved in the formation of narrow fingers with an abrupt change between the inner wet and surrounding dry areas.

Liquid–liquid slug flow separation in a slit shaped micro device

As micro reactors are more and more used in research and production, the need for micro work-up facilities like separators for organic and aqueous slug flow is growing. Numerous examples of these capillary force based separators are presented in literature. The disadvantage of these devices is that at higher flow rates, the hydraulic pressure exceeds the capillary pressure which results in breakthrough. In this paper we present a micro separator for liquid–liquid slug flow with hydrophobic and hydrophilic rectangular capillaries (height: 0.1–2mm, length: 5mm and width: 10mm) to prevent this. The narrow height of the capillary provides a large capillary pressure and the large width a low hydraulic pressure. Separation efficiencies of 99.5% for flow rates of 30–50mlmin−1 are obtained. The ratio between the capillary pressure and the hydraulic pressure is a good predictor of the separation efficiency and must have the value 2 or higher to prevent breakthrough.

Droplet-based Extraction of Hepatitis B Virus DNA in a Capillary

A novel capillary droplet-based DNA-extraction method was developed, using the principle of water-in-oil droplet formation in a highly hydrophobic polytetrafluoroethylene capillary. By sequentially introducing droplets containing a sample or reagents, all the steps related to Hepatitis B virus DNA extraction from blood, including sample injection, DNA binding, magnetic bead rinsing, and DNA elution were continuously implemented in the capillary. Experimental results showed that Proteinase K lysis and elevated elution temperature facilitated higher extraction efficiency. Under optimized conditions, an extraction was completed within 25 min with microliter level consumption of the sample or reagent. The droplet-based method achieved an extraction efficiency of about 60%, which was comparable to that of conventional methods, with the relative standard deviation of extraction efficiency for the droplet-based method being relatively higher. In summary, the herein-developed droplet-based DNA-extraction method is simple, fast, and economic, thus having the potential to be integrated into a micro-total analysis system for nucleic acids.

Non-Dispersive Solvent Extraction and Stripping of Neodymium (III) using a Hollow Fiber Contactor with TODGA as the Extractant

Membrane based non-dispersive solvent extraction (NDSX) of Nd(III) from aqueous nitric acid medium was carried out using a commercial liquid-liquid extraction system consisting of an extra-flow hollow fiber module with about 10,000 microporous hydrophobic polypropylene capillaries with an effective surface area of 1.4 m2. The NDSX operation was carried out by pumping about 1 g/L Nd(III) solutions at a fixed nitric acid concentration of 3.57 M through the tube side and organic solvent (tetra-n-octyl-3-oxapentane-diamide (TODGA) in normal paraffin hydrocarbon (NPH)) through the shell side of the hollow fiber capillaries. NDSX studies were performed under different hydrodynamic conditions and the overall mass transfer was evaluated under counter-current flow conditions. Conditions for quantitative extraction and stripping were also identified. Reproducibility of the results from multiple runs was found to be excellent after five different identical runs.

Transport of thorium from nitric acid solution by non-dispersive solvent extraction using a hollow fibre contactor

Membrane based non-dispersive solvent extraction (NDSX) of Th(IV) from aqueous nitric acid medium was carried out using di-n-hexyl octanamide (DHOA) in normal paraffin hydrocarbon (NPH) using a commercial hollow fiber module containing microporous hydrophobic polypropylene capillaries. The NDSX operation was carried out with pumping various concentrations of nitric acid (1–6 M) containing Th(IV) through the tube side and organic extractant (usually 1.1 M DHOA in NPH) through the shell side of the hollow fibre capillaries at aqueous and organic phase flow rates of 3.5 mL/s and 4.5 mL/s, respectively. Extraction studies were performed under different hydrodynamics conditions and the overall mass transfer was evaluated under cuonter-current flow condition. The percentage NDSX of Th(IV) increased with the increase in the extractant concentration (from 0.1 M DHOA to 1.1 M DHOA) as well as with nitric acid concentration (from 1 M to 6 M). Stripping studies were carried out using both distilled water as well as oxalic acid as the strippant. The possibility of the separation of U from Th was also evaluated.