Water as the Pore Former in the Synthesis of Hydrophobic PVDF Flat Sheet Membranes for Use in Membrane Distillation

Although PVDF flat sheet membranes have been widely tested in MD, their synthesis and modifications currently require increased use of green and inexpensive materials. In this study, flat sheet PVDF membranes were synthesized using phase inversion and water as the pore former. Remarkably, the water added in the casting solution improved the membrane pore sizes; where the maximum pore size was 0.58 µm. Also, the incorporation of f-SiO2NPs in the membrane matrix considerably enhanced the membrane hydrophobicity. Specifically, the membrane contact angles increased from 96° to 153°. Additionally, other parameters investigated were mechanical strength and liquid entry pressure (LEP). The maximum recorded values were 2.26 MPa and 239 kPa, respectively. The modified membranes (i.e., using water as the pore former and f-SiO2NPs) were the most efficient, showing maximum salt rejection of 99.9% and water flux of 11.6 LMH; thus, indicating their capability to be used as efficient materials for the recovery of high purity water in MD.

A Fractal Model of Hydraulic Conductivity for Saturated Frozen Soil

In cold regions, hydraulic conductivity is a critical parameter for determining the water flow in frozen soil. Previous studies have shown that hydraulic conductivity hinges on the pore structure, which is often depicted as the pore size and porosity. However, these two parameters do not sufficiently represent the pore structure. To enhance the characterization ability of the pore structure, this study introduced fractal theory to investigate the influence of pore structure on hydraulic conductivity. In this study, the pores were conceptualized as a bundle of tortuous capillaries with different radii and the cumulative pore size distribution of the capillaries was considered to satisfy the fractal law. Using the Hagen-Poiseuille equation, a fractal capillary bundle model of hydraulic conductivity for saturated frozen soil was developed. The model validity was evaluated using experimental data and by comparison with previous models. The results showed that the model performed well for frozen soil. The model showed that hydraulic conductivity was related to the maximum pore size, pore size dimension, porosity and tortuosity. Of all these parameters, pore size played a key role in affecting hydraulic conductivity. The pore size dimension was found to decrease linearly with temperature, the maximum pore size decreased with temperature and the tortuosity increased with temperature. The model could be used to predict the hydraulic conductivity of frozen soil, revealing the mechanism of change in hydraulic conductivity with temperature. In addition, the pore size distribution was approximately estimated using the soil freezing curve, making this method could be an alternative to the mercury intrusion test, which has difficult maneuverability and high costs. Darcy’s law is valid in saturated frozen silt, clayed silt and clay, but may not be valid in saturated frozen sand and unsaturated frozen soil.

Pore size fractal dimension for characterizing Au/TiO2 catalyst

The quality and assessment of a catalyst can be documented in detail by the application of pore size. This research aims to calculate fractal dimension from the relationship among pore size, maximum pore size and wetting phase saturation and to confirm it by the fractal dimension derived from the relationship among the ratio between surface area per unit pore volume, entry surface area per unit pore volume and wetting phase saturation. In this research, pore size was measured on Au/TiO2 using Brunauer–Emmett–Teller (BET) surface area. Two equations for calculating the fractal dimensions have been employed. The first one describes the functional relationship between wetting phase saturation, pore size, maximum pore size and fractal dimension. The second equation implies to the wetting phase saturation as a function of surface area per unit pore volume, entry surface area per unit pore volume and the fractal dimension. Two procedures for obtaining the fractal dimension have been utilized. The first procedure was done by plotting the logarithm of the ratio between pore size and maximum pore size versus logarithm wetting phase saturation. The positive slope of the first procedure = 3 − Df (fractal dimension). The second procedure for obtaining the fractal dimension was determined by plotting the logarithm of the ratio between surface area per unit pore volume, entry surface area per unit pore volume versus the logarithm of wetting phase saturation. The negative slope of the second procedure = Df − 3. It was found that the plasma + thermally treated Au/TiO2 has the highest fractal dimension value owing to possibility of having holes and channels. The results also show similarity between pore size fractal dimension and surface area per unit pore volume fractal dimension. In our case, as conclusions, the higher the fractal dimension, the better the catalytic activity.

ANALYSIS OF INFLUENCE OF ACTIVATOR CONCENTRATION ON CHARACTERISTICS OF ACTIVATED CARBON FROM KETAPANG SHELL (Terminalia Catappa) BASED ON IMAGE PROCESSING METHOD

Activated carbon from ketapang shell (Terminalia Catappa) has been successfully synthesized usingdehydration-carbonization method. Activated carbon was conducted by immersing with sulphuric acid andfollowed by carbonization at 600oC for 2 hours. Pore characteristics were determined using imageprocessingmethods of activated carbon micrographs based on parameters of area and caliper length. Fromthe area approximation method obtained that the maximum pore size estimate was 5,69 μm at activatorconcentration 3% while the minimum was 4,88 μm at activator concentration 11% activator concentrationrespectively. At the other hands, caliper length approximation method obtained estimation of maximum poresize that was equal to 9,09 μm at activator concentration 3% and its minimum that was equal to 7,35 μm atactivator concentration 7%. The porosity of the activated carbon from ketapang shell increased with theincrease of sulfuric acid concentration and the highest value reached 24.96%.

Ab initio and classical simulations of the temperature dependence of zeolite pore sizes

Maximum pore size (pore size + vibrational amplitude), which is roughly independent of temperature, predicts zeolite pore size for bulky molecules.

A FRACTAL APPROACH TO SPONTANEOUS IMBIBITION HEIGHT IN NATURAL POROUS MEDIA

Spontaneous imbibition of wetting liquids in porous media is of great importance in many fields. In this paper, an analytical model for characterizing spontaneous imbibition height versus time in natural porous media was derived using fractal approach. The average imbibition height in porous media is in terms of porosity, fractal dimensions, maximum pore size and viscosity, surface tension and liquid–solid interactions. The developed model is consistent with previous results and is tested against available experimental data showing fair agreements.

Study on Pore Structure of Multi-Layered Spunbonded Nonwovens

In this study, three kinds of single-layered spunbonded nonwovens with different specifications were prepared as materials. The relation between layer number and pore structure (morphology characteristics, pore size and pore distribution, and Solid Volume Fraction) was studied. The results show that mean pore size decreases as layer number increases and the degree tends to be gentle. But the change law of maximum pore size is not obvious. Furthermore, pore size distribution of single-layered or two-layered nonwovens is concentrated and further increase in layer number doesnt have obvious effects on it . Air permeability reduces when the layer number increases and the variation trend accords with that of mean pore size.

PREDICTION OF MAXIMUM PORE SIZE OF POROUS MEDIA BASED ON FRACTAL GEOMETRY

The macroscopic transport properties of porous media have received steadily attention in science and engineering areas in the past decades. It has been shown that the maximum pore size in a porous medium plays the crucial role in determination of transport properties such as flow resistance, permeability, thermal conductivity and electrical conductivity, etc. In this study, two models for predicting the maximum pore size in porous media based on fractal geometry are presented. The present analytical expressions may be used to calculate the maximum pore size from porosity and permeability data, as well as from liquid properties, structure parameters of media and imbibition coefficient data, respectively. Predicted maximum pore sizes by the proposed models show good agreement with the available experimental results.