An experimental and numerical study of droplet spreading and imbibition on microporous membranes

The battery separator plays a key role in determining the capacity of the battery. Since separator performance mainly depends on the pore size of membrane, development of a technique for the fabrication of the membrane having controlled pore size is essential in producing a highly functional battery separator. In this study, microporous membranes having the desired pore size were produced via thermally‐induced phase separation (TIPS) process. Control of the phase boundaries of polymer‐diluent blends is the main concern in manipulating pore size in TIPS process, because pore size mainly depends on the temperature gap between phase separation temperature of the blend and the crystallization temperature of polymer. Microporous membranes having controlled pore size were produced from polyethylene (PE)/dioctyl phthalate (DOP) blends, PE/isoparaffin blends, and polymer/diluent‐mixture ternary blends, that is, PE/(DOP/isoparaffin) blends. PE/DOP binary blends and PE/(DOP/isoparaffin) ternary blends exhibited typical upper critical solution temperature (UCST) type phase behavior, while PE formed a homogeneous mixture with isoparaffin above the crystallization temperature of PE. When the mixing ratio of polymer and diluent‐mixture was fixed, the phase separation temperature of PE/diluent‐mixture blend first increased with increasing DOP content in the diluent‐mixture, went through a maximum centered at about 80 wt % DOP and then decreased. Furthermore, the phase separation temperatures of the PE/diluent‐mixture blends were always higher than that of the PE/DOP blend when diluent‐mixture contained more than or equal to 20 wt % of DOP. Average pore size of microporous membrane prepared from PE/DOP blend and that prepared from PE/isoparaffin blend were 0.17 and 0.07 μm, respectively. However, average pore size of microporous membrane prepared from ternary blends was varied from 0.07 to 0.5 μm by controlling diluent mixing ratio. To understand the phase behavior of ternary blend, phase instability of the ternary mixture was also explored. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2025–2034, 2006

Surface modification of microporous polyurethane membrane with poly(ethylene glycol) to develop a novel membrane

Chemical valves based on poly(4-vinylpyridine)-filled microporous membranes

Study on pore size distributions of microporous polymer membranes having different physical architecture using capillary flow porometry

Microporous polyethylene (PE) membranes having a controlled pore size were produced via the thermally induced phase separation process by manipulation of the phase boundary of the PE/diluent blend and process conditions. The phase boundary of the PE blend, caused by upper critical solution temperature type phase behavior, was controlled by the use of a diluent mixture, that is, an isoparaffin/soybean oil mixture. The phase‐separation temperature of the PE/soybean oil blend was always higher than that of the PE/isoparaffin blend. In PE/(isoparaffin/soybean oil) ternary blends, the phase‐separation temperature of the ternary blend rapidly increased with increasing soybean oil content in the diluent mixture. Furthermore, the phase‐separation temperatures of ternary blends were always higher than that of the PE/soybean oil blend, regardless of the blend compositions, when the diluent mixture contained more than 50 wt % soybean oil. The observed phase behavior of the ternary blends was analyzed with interaction energy densities calculated with the Flory–Huggins theory and ternary stability conditions. The growth of droplets caused by both coalescence and the Oswald ripening process was observed after the onset of phase separation. As the blends became less stable, the droplet growth rate increased, and larger equilibrium droplets were formed. Microporous membranes with the desired pore structure could be prepared by control of the phase boundary and the variation of processing conditions such as the quenching depth, annealing time, and cooling rate. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Role of polyethylene glycol in formation and structure of regenerated cellulose microporous membrane

Beneficial effects of wettability altering surfactants in oil-wet fractured reservoirs

Effect of extraction and drying on the structure of microporous polyethylene membranes prepared via thermally induced phase separation

In membrane hybrid liver support devices (HLSDs) using isolated hepatocytes where oxygen is transported only by diffusion to the cells, about 15-40% of the cell mass is likely to be in direct contact with the semipermeable membranes used as immunoselective barriers: quantitative effects of membrane surface properties on the kinetics of hepatocyte metabolic reactions may also affect HLSD performance. In this paper, we report our investigation of the effects of surface morphology of two microporous commercial membranes on the kinetics of oxygen consumption and ammonia elimination by primary hepatocytes in adhesion culture. Isolated rat hepatocytes were cultured on polypropylene microporous membranes with different surface roughness and pore size in a continuous-flow bioreactor whose fluid dynamics was optimized for the kinetic characterization of liver cell metabolic reactions. Collagencoatcd membranes were used as the reference substratum. Hepatocyte adhesion was not significantly affected by membrane surface morphology. The rates of the investigated reactions increased with ammonia concentration according to saturation kinetics: the values of kinetic parameters Vmax and KM increased as cells were cultured on the membrane with the greatest membrane surface roughness and pore size. For the reaction of oxygen consumption, Vmax increased from 0.066 to 0.1 pmol h-1 per cell as surface roughness increased from 70 to 370 nm. For the kinetics of ammonia elimination, KM increased from 0.23 to 0.32 mM and Vmax increased from 1.49 to 1.79 pmol h-1 per cell with membrane surface roughness increasing from 70 to 370 nm. Cells cultured on collagen-coated membranes consistently yielded the highest reaction rates. The Vmax values of 0.18 and 2.84 pmol h-1 per cell for oxygen consumption and ammonia elimination, respectively, suggest that cell functions are also affected by the chemical nature of the substratum.

Polytetrafluoroethylene (PTFE) micro-porous membranes were prepared from PTFE fine powder through extruding, rolling, and uniaxial longitudinally stretching. In contrast to conventional planar transverse stretching, a novel 3D mold design of non-planar transverse stretching process was employed in this study to produce micro-porous structure. The morphology, membrane thickness, mean pore size, and porosity of the PTFE membrane were investigated. The results show that the non-planar transverse stretched membranes exhibit more uniform average pore diameter with thinner membrane thickness. Morphological changes induced by planar and non-planar transverse stretching for pore characteristics were investigated. The stretching conditions, stretching temperature and rate, affect the stretched membrane. Increasing temperature facilitated the uniformity of pore size and uniformity of membrane thickness. Moreover, increase in stretching rate resulted in finer pore size and thinner membrane.

Pore sizes of microporous polymer membranes were determined by the calculation based on the gas permeability of porous media. The gas permeability coefficient K (given by J = K Δp/l, where J is the steady-state gas flux, Δp is the pressure, difference, and l = the thickness of a membrane) for porous membrane can be given generally by where K0 is the Knudsen permeability coefficient, η is the viscosity of the permeant gas, B0 is the geometric factor of a membrane, and Δp is the mean pressure of the gas on both sides of a membrane. From gas permeability measurements which yield the pressure dependence of gas permeability coefficient (expressed as above equation), the mean pore size of the porous membrane can be estimated as where M is the molecular weight of the permeant gas. The validity of this method was examined with various Millipore filters of which nominal pore sizes are known. It was confirmed that the method provided a simple and reliable means of estimating mean pore size of microporous membranes. The method was applied to investigate the influence of factors involved in preparation of microporous polysulfone membranes by coagulation procedure. It was found that the mean pore size of porous polysulfone membrane increases with (1) increasing with casting thickness, (2) increasing temperature of coagulation bath, and (3) decreasing concentration of polymer in casting solution (DMF as solvent). Water flux and water flux decline due to compaction are also examined as a faction of pore size, porosity, and the thickness of membranes.

We evaluated the filtration performance of microporous metal membranes fabricated by the rolling process. Metal wire meshes were rolled with thickness reduction ratios of 10, 20, and 30%. The pore size of the metal wire mesh membrane decreased with increasing rolling ratio, whereas the removal efficiency of the suspended solids and turbidity showed a very slight increase compared to that of an unrolled mesh membrane. The metal powder was dispersed on the surface of the rolled metal wire mesh membrane and bound with polyvinyl alcohol, then dried at 100°C for 1 h, and finally sintered at 1,000°C for 3 h. The mean pore size, suspended solids, and turbidity of the metal powder membrane at a rolling ratio of 30% were approximately 0.7 μm, 84% and 83%, respectively. Therefore, microporous metal membranes successfully fabricated by the rolling process were also sufficiently permeable filters.

Electro-osmosis at microporous membranes and the determination of zeta-potential

In this study, poly(ionic liquids/ N-isopropylacrylamide) (PIL/NIPAM) modified poly(ether sulfone) microporous membranes were prepared using a pore-filling method. Due to the anion-sensitive wettability of the PIL and the thermal-sensitive phase transformation of PNIPAM, the permeability of the modified membranes showed robust anion and thermal dual-responsive behaviors. In addition, the response temperature of the membranes could be adjusted precisely from 30 to 55 °C by anion exchange, which was attributed to the cooperative interaction of the PIL and PNIPAM. The switchable response temperature and the dual-responsive performances of the membranes were demonstrated by measuring the water fluxes under various conditions. The results indicated that the membrane permeabilities increased when exchanging the counteranions (CAs) from hydrophilic to hydrophobic ones; the thermal response behaviors were also obvious, and the sensitivity increased when increasing the hydrophobicity of the CA (the fluxes could be adjusted from 0 to 3800 mL/m2 mmHgh by controlling the temperature and CAs). At last, filtration tests were designed with the membranes, and the results indicated that by controlling the temperature and/or CA species, three different poly(ethylene glycol) molecules could be easily separated according to their molecule sizes in a single step.

Wellbore instability caused by the invasion of drilling fluids into formations remains a significant challenge in the application of oil-based drilling fluids (ODFs). In this study, carbon nanospheres (CNSs) were synthesized using glucose as the carbon source through a microwave-assisted method. The effects of the reaction temperature, carbon source concentration, and reaction time on the particle size of CNSs were systematically investigated. The results revealed that under optimal conditions, CNSs with an average particle size of 670 nm were successfully synthesized, exhibiting high sphericity and excellent dispersibility. CNSs demonstrated stable dispersion in mineral oil when lecithin was used as a dispersant. The plugging performance of CNSs in ODFs was evaluated through low-pressure filtration and high-temperature, high-pressure (HTHP) filtration tests. After aging at 180 °C for 16 h, the addition of 2% CNSs reduced the filtration volume from 10.6 mL to 2.5 mL on standard filter paper (average pore size: 3 μm) and from 8.5 mL to 1.6 mL on microporous membranes (average pore size: 0.5 μm). Additionally, the HTHP filtration volume decreased from 73 mL to 18 mL, and the permeability of the filter cake formed during HTHP filtration was reduced from 26.5 × 10−3 mD to 1.2 × 10−3 mD. Furthermore, CNSs improved the rheological properties and emulsion stability of ODFs. With excellent compatibility and applicability, CNSs offer a promising solution for enhancing the performance of oil-based drilling fluids.