These results were found to agree with what was reported by Marand et al.
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With the addition of 0. The yield stress decreased from 5.
However, with the addition of 0. The mechanical properties of porous membranes depend to a great extent on the average pore size, porosity, and pore size distribution of the membranes. For porous composite membranes with identical matrix and fillers, processing conditions and filler content, their mechanical properties are anticipated to be better for membranes with smaller pore size and porosity [ 8 ].
In Figure 5 , the higher tensile behavior of the pristine PS membrane is mainly due to its lower porosity. The exceptionally high aspect ratio, in addition to the high strength and stiffness, make CNTs a potential candidate as a reinforcement for polymer materials. More specifically, the presence of carboxylic groups on the surface of CCNTs offered multiple sites for hydrogen bonding between these groups and sulfonic groups of PS improving the membranes mechanical properties.
All the curves show similar post-yield strain-hardening slope. When the temperature rises, the distance between the polymer structural units increases due to thermal agitation and in consequence, interaction forces decrease, which implies a degradation of mechanical properties. Therefore, the increased temperature had limited effect on the motion of polymer chains, resulting in similar fracture strains for the membranes at higher temperatures. This reason may also be used to explain the less changed post-yield strain-hardening slopes for both membranes with increasing temperatures.
In addition, drying of the membranes during heating by continuous air circulation in the environmental chamber is another likely reason for the less changed fracture strain with increasing temperature for both membranes. In order to measure the fracture strain of dried membranes, tensile tests were also conducted at room temperature under the same crosshead speed. It was found that the elongation at fracture of dried pristine PS membranes was 0. Therefore, drying of the membranes by the environmental chamber had an important effect on the fracture strain of the membranes in our investigated range.
The results indicated that the incorporation of CNTs into the polymer matrix significantly enhances the performance of the fabricated nanocomposite membranes and must be controlled carefully to achieve the optimum results. This means that more thorough work must be conducted in order to have a better understanding of the relationship between the membrane structure and its properties. Conceptualization, M. K and M. National Center for Biotechnology Information , U.
Journal List Membranes Basel v. Membranes Basel. Published online Nov Yehia M. Johnson , 3 Muataz A. Atieh , 1 and Marwan K. Find articles by Yehia M. Find articles by Viktor Kochkodan. Daniel J. Muataz A. Find articles by Muataz A. Marwan K. Author information Article notes Copyright and License information Disclaimer. Received Oct 2; Accepted Nov 7. Abstract In this work, novel polysulphone PS porous membranes for water desalination, incorporated with commercial and produced carbon nanotubes CNT , were fabricated and analyzed.
Keywords: membranes, atomic force microscopy, mechanical properties, water desalination. Introduction Global fresh water scarcity and pollution is becoming one of the most critical issues due to rapid economic development and population growth. Experimental 2.
Table 1 Main properties of commercial and produced CNTs. Open in a separate window. Results and Discussion 3. Figure 1. Figure 2. Figure 3. Figure 4.
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Figure 5. Figure 6. Figure 7. Author Contributions Conceptualization, M. Funding This research received no external funding. Conflicts of Interest The authors declare no conflict of interest. References 1. Elimelech M. The future of seawater desalination: Energy, technology, and the environment. Kayvani Fard A. Kochkodan V. Then topics such as surface modification by graft polymerization and macromolecule immobilization, biomimetic surfaces, enzyme immobilization, molecular recognition, and nanostructured surfaces are discussed.
This book provides a unique synthesis of the knowledge of the role of surface chemistry and physics in membrane science. Customer Reviews Average Review. See All Customer Reviews. Shop Textbooks. Add to Wishlist. USD Besides, they suffer from the limits of low efficiency and high operation cost. In fact, the separation of water-in-oil emulsions also becomes available if the pore size of a hydrophobic-oleophilic membrane is rationally designed to be smaller than the emulsified water droplets 15 , The oil adhered on the material surfaces are generally difficult to be removed, which makes a washing process necessary and leads to unavoidable wastes of oils, cleaning fluids and the materials themselves.
Besides, water normally has higher density than oil, which tends to settle below oil and then forms a barrier layer above the materials for oil permeation or adsorption. Recently, considerable attention has been focused on the underwater oil-repellency of fish scales Studies reveal that superhydrophilic materials such as fish scales can trap abundant water on their rough surfaces.
These membranes showed high separation efficiency and low oil fouling. Moreover, a recent breakthrough was achieved by Tuteja and co-workers 31 , According to the permeation theory 33 , membrane pores with large size can reduce the flow resistance of water and facilitate water permeation, hence enabling the membranes with gravity-driven filtration and high flux.
It means the height of the liquid column that the membranes can support is lower than several centimeters, limiting their practical applications. The as-prepared membranes are superhydrophilic, underwater superoleophobic, and antifouling to oils. The hydrophilic CaCO 3 coating was deposited on the membrane pore surface through photoinitiated grafting of PAA and then followed by an alternate soaking process Figure 1 shows typical SEM images of the mineral-coated membranes.
It can be seen that a rough coating is formed on the smooth surface of PAA-grafted membrane Figure S1. The coating distributes conformally and the porous structure is mostly retained for the prepared membrane. The enlarged view of membrane Figure 1b indicates that the coating is composed of CaCO 3 nanoparticles with size in Additionally, Ca element EDX mapping of the membrane cross-section further confirms that the mineral coating distributes evenly throughout the membrane Figure 1c,d.
The dense spots below the lower dash line originate from the bottom surface of the membrane. Our previous work has proved that the mineral-coated membranes are superhydrophilic Figure S3 Figure 2a shows the wetting behavior of 1,2-dichloroethane DCE on the membranes prepared with different mineral-coating cycles. As is well-known, the wettability of a surface is mainly governed by its chemical composition and roughness 6 , 7 , 35 , MPPM possesses porous structure with certain roughness.
After being grafted with PAA, a hydrophilic layer is introduced onto the membrane pore surface and helps to trap water into the membrane. The trapped water decreases the contact area between the membrane surface and the oil droplet, leading to a dramatic increase in oleophobicity. However, this PAA-grafted membrane surface still suffers from high oil-adhesion. The sliding angle SA is found to be Inset photographs show that the oil-adhesion declines after mineral-coating.
The membranes exhibit stable superoleophobicity.
After being mineral-coated, these drawbacks can be totally overcome. The roughness of the membrane surface is greatly increased and the contact area between the membrane surface and the oil droplet is decreased. As a result, oil-adhesion of the membrane declines gradually with increasing the mineral-coating cycles Figure 2a. The SA is only 2.
Surface Engineering of Polymer Membranes
To verify it, the optimal as-prepared membranes were pre-wetted with water and then immersed into DCE for a certain time. In addition to DCE, the membranes are also highly repulsive to other organic solvents and oils, including hexadecane, petroleum ether, gasoline and diesel. Figure 2c shows the underwater wetting behavior of various oils. Therefore, the optimal as-prepared membranes were used in the following studies unless otherwise specified. In view of the contrary wettability of water and oil on the mineral-coated membranes, it is reasonable to expect that these two liquids will have different permeabilities towards the membranes.
As shown in Figure S4 , a mixture of DCE and water was poured onto the membrane sample which was mounted in a dead-end cell. The sole driving force used for separation is the gravity of the mixture. The oil rejection ratio is higher than No visible oil was observed in the filtrate.
However, the external trans-membrane pressure also has the risk of exceeding the oil breakthrough pressure. In this case the oil is forced to permeate through the membranes, decreasing the separation efficiency quickly. We measured the pressure of various oils for the mineral-coated membranes. To the best of our knowledge, these values are 2—3 orders of magnitude greater than those of reported separation materials with similar superoleophobicity. On the other hand, the stable hydrated mineral layer offers a robust oil-repellent interface high OCA , further increasing the oil-flow resistance.
Theoretical P breakthrough range was calculated based on this equation Table S1. The results are consistent with the experimental values Figure 3c. Membrane-based technology is of particular interest among the existing methods for emulsion separation, since it integrates demulsification and separation into a single unit 15 , 16 , 31 , In order to improve oil rejection, ultrafiltration membranes are commonly preferred because their pore size is smaller than the emulsified oil droplets 37 , 38 , However, common ultrafiltration membranes have drawbacks such as low permeate flux and poor resistance to oil fouling, due to their small pore size, low porosity and oleophilic membrane surface.
Given that the mineral-coated membranes are superoleophobic and have relatively larger pores microfiltration membrane , we systematically studied their separation performances for oil-in-water emulsions. Diesel was utilized as the target oil for preparing oil-in-water emulsions. As mentioned above, the mineral-coated membranes have high breakthrough pressure for diesel. Therefore, the separation experiments were carried out under a series of external pressures in a dead-end filtration mode.
Figure S7 shows the dependence of permeation flux on trans-membrane pressure for emulsions with different oil contents. The water flux increases linearly with increasing the external pressure, but decreases dramatically with the oil content. This decrease is attributed to the increasing content of emulsified oil droplets and the high rejection of the membranes. Since oil can not penetrate through the membranes below their breakthrough pressure, the rejected emulsified oil reduces the contact area between the membrane surface and the water phase.
As a result, the available pores for water permeation are decreased, leading to the decline of water flux. In addition, a repeating separation experiment was performed on the mineral-coated membranes to further study their separation efficiency and recyclability. As shown in Figure 4a , the filtration process includes three cycles. In each cycle, pure water and oil-in-water emulsion were sequentially filtered through the membranes. During the interval of different cycles, the membranes were simply rinsed with pure water.
The gradual decline of flux during emulsion separation is ascribed to the oil droplet accumulation above the membrane surface.
Surface Engineering of Polymer Membranes | Zhi-Kang Xu | Springer
Moreover, the membranes are highly resistant to oil fouling. The slight decrease of flux is due to the mineral loss when a large amount of water flows through the membranes. Although CaCO 3 is added to the water during filtration, the concentration of enriched Ca in water is still much lower than the value recommended by World Health Organization for soft water or safe drinking water In addition to diesel, the coated membranes can effectively separate emulsions composed by a range of oils such as DCE, gasoline, etc Figure 4b.
The filtration contains three cycles and every cycle includes two steps: water filtration and emulsion filtration.