The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Taishung Chung - One of the best experts on this subject based on the ideXlab platform.
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pvdf hollow fibers with novel sandwich structure and superior wetting resistance for vacuum membrane distillation
Desalination, 2017Co-Authors: Jia Zuo, Taishung ChungAbstract:Abstract PVDF hollow fiber membranes with a unique sandwich structure and superior wetting resistance have been designed for vacuum membrane distillation (VMD) of seawater desalination in this study. The sandwich structure consists of two sponge-like inner and outer porous layers and a thin middle layer full of small-size Macrovoids. The sponge-like structure in the two porous layers is specially designed because it enhances the mechanical strength of hollow fibers with high wetting resistance. This structure is derived from the spinodal liquid-liquid decomposition during phase inversion. Meanwhile, the middle layer of Macrovoids is beneficial for VMD flux because they perform as highways for water transport. Comparing to the large size Macrovoids, the small-size Macrovoids in PVDF hollow fibers are preferred for VMD applications because they would not significantly reduce the membrane mechanical strength. As a result, the newly developed membranes possess impressively high liquid entry pressures (LEPs) of > 3 bar. This study may provide valuable guidelines in designing next generation PVDF hollow fiber membranes for practical VMD applications.
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dual layer pvdf ptfe composite hollow fibers with a thin macrovoid free selective layer for water production via membrane distillation
Chemical Engineering Journal, 2011Co-Authors: May May Teoh, Taishung ChungAbstract:Abstract In this study, the polyvinylidene fluoride (PVDF)/polytetrafluoroethylene (PTFE) composite is used to fabricate hollow fiber membranes for seawater desalination via direct contact membrane distillation (DCMD) application. The incorporation of PTFE particles in the formulated dope solution can efficiently suppress the formation of Macrovoids and enhance the outer surface hydrophobicity. Dual-layer hollow fibers with a desirable macrovoid-free morphology and a relatively thin (13 ± 2 μm) outer-layer can be obtained via blending 30 wt% of PTFE particles in the outer-layer dope. The resultant dual-layer hollow fiber (DL-30) displays a moderately high contact angle of 114.5° and porosity of 81.5%. Compared to the single-layer hollow fiber with 30 wt% (SL-30) PFTE particles, the DL-30 fiber exhibits a flux enhancement of approximately 24% that is contributed to the reduction in inner-layer mass transfer resistance. Dual layer membrane configuration with a lower wall thickness as well as larger outer and inner diameters provides even higher water vapor transport is potentially suitable for desalination. Both single- and dual-layer PVDF/PTFE hollow fiber membranes reveal good long-term stability of up to 100 h of continuous testing. By utilizing the state-of-the-art dual-layer spinning technology, hollow fiber membranes with better performance (i.e. enhanced flux) and morphology (i.e. macrovoid-free) can be tailored.
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molecular design of the morphology and pore size of pvdf hollow fiber membranes for ethanol water separation employing the modified pore flow concept
Journal of Membrane Science, 2011Co-Authors: Panu Sukitpaneenit, Taishung ChungAbstract:In this study, we have established the fundamental science and engineering of fabricating poly(vinylidene fluoride) (PVDF) asymmetric hollow fiber membranes for ethanol–water separation and elucidated the complicated relationship among membrane morphology, pore size, pore size distribution and separation performance using the concept of the modified pore-flow model proposed in our previous work. The variation of bore-fluid composition, air-gap distance and take-up speed results in membranes with various morphologies ranging from large-finger-like macrovoid to nearly perfect macrovoid-free structures. Interestingly, an increase in air-gap distance or take-up speed not only effectively suppress the formation of Macrovoids but also results in the reduction of membrane pore size and the narrowing of pore size distribution, hence leading to the enhancement of membrane performance. The permeation flux is found to be mainly controlled by the overall porosity and the contribution of large pore sizes of the membrane, while the selectivity or separation factor is greatly determined by membrane pore size and pore size distribution, which is consistent with the modified pore-flow model proposed in our previous works. The newly developed PVDF asymmetric hollow fiber membranes demonstrates remarkable high fluxes of 3500–8800 g m−2 h−1 and reasonable ethanol–water separation factors of 5–8 compared to existing polymeric-based pervaporation membranes.
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grafting thermally labile molecules on cross linkable polyimide to design membrane materials for natural gas purification and co2 capture
Energy and Environmental Science, 2011Co-Authors: Youchang Xiao, Taishung ChungAbstract:A novel strategy to design molecularly the cavity size and free volume of flexible polyimide materials via thermal treatment of rigid and cross-linkable polyimides grafted with thermal liable side beta-cyclodextrin (CD) molecules is demonstrated in this study. The spaces occupied by the labile groups may become microvoids after low-temperature thermal degradation while the rigid polyimide backbone prevails. The thermal induced cross-linking reaction among polyimide chains may create ultra-fine micro-pores that integrally connect with microvoids. As a result, the thermally cured membranes fabricated from dense polyimide precursors show gas separation performance surpassing the trade-off lines, with tough and flexible mechanical properties. Thermal annealing at 425 °C produces polyimide membranes with the best CO2 permeability of 4016 Barrer with reasonable gas pair selectivity.
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micelle like Macrovoids in mixed matrix pvdf ptfe hollow fiber membranes
Journal of Membrane Science, 2009Co-Authors: May May Teoh, Taishung ChungAbstract:Abstract Unique ‘micelle-like’ Macrovoids have been observed for the first time in the polyvinylidene fluoride-polytetrafluoroethylene (PVDF-PTFE) hollow fiber membranes. FESEM results show that the incorporation of 30 and 40 wt% PTFE particles (
Rong Wang - One of the best experts on this subject based on the ideXlab platform.
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explorations of delamination and irregular structure in poly amide imide polyethersulfone dual layer hollow fiber membranes
Journal of Membrane Science, 2012Co-Authors: Laurentia Setiawan, William B Krantz, Rong WangAbstract:Abstract Dual layer hollow fiber membranes have become increasingly attractive due to their many benefits made possible by one-step fabrication using the non-solvent induced phase inversion method. Obtaining a good lamination between the two layers as well as a regular morphology are critical to make a usable hollow fiber membrane. This study aims to explore the mechanism of the lamination/delamination phenomenon and regular/irregular morphology that can occur in the fabrication of dual layer hollow fiber membrane. Simultaneous extrusion of poly(amide-imide) and polyethersulfone (PES) dope solutions was carried out by using a triple orifice spinneret. Thermodynamic properties and phase separation kinetics of the polymer dopes as well as various spinning parameters were carefully tailored in order to investigate the evolution of the membrane morphology and structure. A series of experiments have confirmed that when the external coagulant, water, has a higher diffusion rate in the outer layer than in the inner layer, the outer layer tends to expand to form large Macrovoids and to hold more water at the interface. As a result, the accumulated water probably impedes the adhesion of the two layers, leading to a delamination of two layers. On the other hand, if water has a slower penetration rate through the outer layer dope than the inner layer dope, a good adhesion between these two layers is expected. Under this scenario, since Macrovoids formed in the inner layer may lead to the expansion of the inner layer, a distortion of the finger-like structure/Macrovoids in the inner and an irregularity of the inner contour may occur. This study provides a solid foundation to develop superior dual layer hollow fiber membranes with an inter-penetrating dual layer structure.
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effects of additives and coagulant temperature on fabrication of high performance pvdf pluronic f127 blend hollow fiber membranes via nonsolvent induced phase separation
Chinese Journal of Chemical Engineering, 2012Co-Authors: Rong WangAbstract:Poly(vinylidene fluoride) (PVDF) has become one of the most popular materials for membrane prepara- tion via nonsolvent induced phase separation (NIPS) process. In this study, an amphiphilic block copolymer, Plu- ronic F127, has been used as both a pore-former and a surface-modifier in the fabrication of PVDF hollow fiber membranes to enhance the membrane permeability and hydrophilicity. The effects of 2nd additive and coagulant temperature on the formation of PVDF/Pluronic F127 membranes have also been investigated. The as-spun hollow fibers were characterized in terms of cross-sectional morphology, pure water permeation (PWP), relative molecular mass cut-off (MWCO), membrane chemistry, and hydrophilicity. It was observed that the addition of Pluronic F127 significantly increased the PWP of as-spun fibers, while the membrane contact angle was reduced. However, the size of Macrovoids in the membranes was undesirably large. The addition of a 2nd additive, including lithium chlo- ride (LiCl) and water, or an increase in coagulant temperature was found to effectively suppress the macrovoid for- mation in the Pluronic-containing membranes. In addition, the use of LiCl as a 2nd additive also further enhanced the PWP and hydrophilicity of the membranes, while the surface pore size became smaller. PVDF hollow fiber with a PWP as high as 2530 L·m −2 ·h −1 ·MPa −1 , a MWCO of 53000 and a contact angle of 71° was successfully fabricated with 3% (by mass) of Pluronic F127 and 3% (by mass) of LiCl at a coagulant temperature of 25 °C, which shows better performance as compared with most of PVDF hollow fiber membranes made by NIPS method. Keywords amphiphilic block copolymer, pore forming, surface modifying, additive, poly(vinylidene fluoride), hollow fiber membrane
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effect of polyethylene glycol peg as an additive on the fabrication of polyvinylidene fluoride co hexafluropropylene pvdf hfp asymmetric microporous hollow fiber membranes
Journal of Membrane Science, 2011Co-Authors: Sunee Wongchitphimon, Rong Wang, Ratana Jiraratananon, Lei Shi, Chun Heng LohAbstract:Abstract Polyvinylidene fluoride- co -hexafluropropylene (PVDF-HFP) has received much attention recently as a promising membrane material for membrane contactor application. A systematic study has been carried out to investigate the effects of polyethylene glycol (PEG) with different molecular weights and different loadings as an additive on the fabrication of PVDF-HFP asymmetric microporous hollow fiber membranes. Moreover, the synergetic effects of coagulation temperature and the second additive (lithium chloride: LiCl) with PEG are also evaluated. Experiments revealed that the addition of PEG into the PVDF-HFP/NMP solution resulted in the system thermodynamically less stable in reaction with water, promoting rapid phase demixing in the phase inversion process. When the same 3 wt% PEG was added into the dope solution, the dimension of finger-like Macrovoids of the resultant membrane increased in parallel with the increase of PEG molecular weight from 200 to 600 and 6000 kDa, and pure water permeability (PWP) also increased accordingly. An increase in PWP was also observed when PEG-200 loading in the dope solution was increased from 3 to 5 and 10 wt%, corresponding to the morphology change of resultant membranes. As a synergetic effect of coagulation temperature with PEG, the finger-like pores occurred in the membrane at room temperature expanded to much larger Macrovoids using 10 °C water as the coagulant, and the big finger-like pores almost disappeared when the coagulation bath temperature was increased to 40 °C because of delayed phase demixing. The big macrovoid size can also be suppressed by adding the second small molecule additive, LiCl, due to its strong interactions with NMP and PVDF-HFP to delay the dope precipitation. The irregular inner contour of the membrane can be eliminated by the increase of coagulation bath temperature to 40 °C. The hollow fiber membrane made by a dope of PVDF-HFP/PEG-6000/LiCl/NMP (15/3/3/79 in weight) using 40 °C water as the coagulant exhibited a high PWP of 117 L/m 2 h atm and reasonably good MWCO of 150 kDa. An improvement has been made in the current work as compared to previous PVDF-HFP hollow fiber membranes reported in literatures.
Santi Kulprathipanja - One of the best experts on this subject based on the ideXlab platform.
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fabrication of matrimid polyethersulfone dual layer hollow fiber membranes for gas separation
Journal of Membrane Science, 2004Co-Authors: Lan Ying Jiang, Taishung Chung, Chun Cao, Santi KulprathipanjaAbstract:Abstract We have developed almost defect-free Matrimid/polyethersulfone (PES) dual-layer hollow fibers with an ultra-thin outer layer of about 10 × 10−6 m (10 μm), studied the effects of spinneret and coagulant temperatures and dope flow rates on membrane morphology and separation performance, and highlighted the process similarities and differences between single-layer and dual-layer hollow fiber fabrications. The compositions of the outer and inner layer dopes were 26.2/58.8/15.0 (in wt.%) Matrimid/NMP/methanol and 36/51.2/12.8 (in wt.%) PES/NMP/ethanol, respectively. It is found that 25 °C for both spinneret and coagulant is a better condition, and the fibers thus spun exhibit an O2/N2 selectivity of 6.26 which is within the 87% of the intrinsic value and a calculated apparent dense-layer thickness of about 2886 × 10−10 m (2886 A). These dual-layer membranes also have impressive CO2/CH4 selectivity of around 40 in mixed gas tests. The scanning electron microscopy (SEM) studies show that low coagulant temperatures produce dual-layer hollow fibers with an overall thicker thickness and tighter interfacial structure which may result in a higher substructure resistance and decrease the permeance and selectivity simultaneously. The elemental analysis of the interface skins confirms that a faster inter-layer diffusion occurs when the fibers are spun at higher spinneret temperatures. Experimental results also reveal that the separation performance of dual-layer hollow fiber membranes is extremely sensitive to the outer layer dope flow rate, and the inner layer dope flow rate also has some influence. SEM pictures indicate that the macrovoid formation in dual-layer asymmetric hollow fiber membranes is quite similar to that in single-layer ones. It appears that Macrovoids observed in this study likely start from local stress imbalance and weak points.
Loredana De Bartolo - One of the best experts on this subject based on the ideXlab platform.
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Double porous poly (Ɛ-caprolactone)/chitosan membrane scaffolds as niches for human mesenchymal stem cells
Colloids and Surfaces B: Biointerfaces, 2019Co-Authors: Pritam Das, Jean-françois Lahitte, Simona Salerno, Jean-christophe Remigy, Patrice Bacchin, Loredana De BartoloAbstract:In this paper, we developed membrane scaffolds to mimic the biochemical and biophysical properties of human mesenchymal stem cell (hMSC) niches to help direct self-renewal and proliferation providing to cells all necessary chemical, mechanical and topographical cues. The strategy was to create three-dimensional membrane scaffolds with double porosity, able to promote the mass transfer of nutrients and to entrap cells. We developed poly (Ɛ-caprolactone) (PCL)/chitosan (CHT) blend membranes consisting of double porous morphology: (i) surface Macrovoids (big pores) which could be easily accessible for hMSCs invasion and proliferation; (ii) interconnected microporous network to transfer essential nutrients, oxygen, growth factors between the Macrovoids and throughout the scaffolds. We varied the mean macrovoid size, effective surface area and surface morphology by varying the PCL/CHT blend composition (100/0, 90/10, 80/20, 70/30). Membranes exhibited Macrovoids connected with each other through a microporous network; Macrovoids size increased by increasing the CHT wt%. Cells adhered on the surfaces of PCL/CHT 100/0 and PCL/CHT 90/10 membranes, that are characterized by a high effective surface area and small Macrovoids while PCL/CHT 80/20 and PCL/CHT 70/30 membranes with large Macrovoids and low effective surface area entrapped cells inside Macrovoids. The scaffolds were able to create a permissive environment for hMSC adhesion and invasion promoting viability and metabolism, which are important for the maintenance of cell integrity. We found a relationship between hMSCs proliferation and oxygen uptake rate with surface mean macrovoid size and effective surface area. The Macrovoids enabled the cell invasion into the membrane and the microporosity ensured an adequate diffusive mass transfer of nutrients and metabolites, which are essential for the long-term maintenance of cell viability and functions.
William J Koros - One of the best experts on this subject based on the ideXlab platform.
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Macrovoids in hybrid organic inorganic hollow fiber membranes
Industrial & Engineering Chemistry Research, 2009Co-Authors: Shabbir Husain, William J KorosAbstract:Large, characteristically tear- or finger-shaped voids found in polymer hollow fiber membranes, termed Macrovoids, have been known since the early development of asymmetric membranes. These voids are undesirable as they decrease the mechanical integrity of the hollow fiber membrane, limiting the use of high pressure feeds for separations. Moreover, if such Macrovoids penetrate the selective layer they become and even more serious problem for membrane performance. With current membrane technology moving toward a mixed-matrix hybrid format with inorganic and carbon molecular sieves embedded in a polymer matrix, additional complications caused by the presence of particulates within the spinning dope toward the formation of Macrovoids must be considered. While numerous hypotheses have been suggested regarding the formation of Macrovoids formed in polymer-only membranes, no mention so far has been made of such Macrovoids initiated in hollow fiber membranes by particles present in the spinning dope. This paper ...
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phase separation vitrification and the manifestation of Macrovoids in polymeric asymmetric membranes
Journal of Membrane Science, 1996Co-Authors: Scott A Mckelvey, William J KorosAbstract:Nonsolvent-induced precipitation processes may generate an asymmetric morphology from an initially single-phase homogeneous polymer solution. In these processes, mass transfer induces phase separation and subsequent vitrification eliminates further reorganization of a polymer-rich phase. Kinetics is responsible for trapping specific morphologies and can be influenced by local composition, temperature, applied stress, and preexisting nuclei. Focusing only on the influence of composition changes, the growth of a preformed hypothetical nucleus in a metastable region is considered during rapid phase separation induced by an advancing front that is rich in nonsolvent for the dissolved polymer. Expansion of the preformed nucleus can be promoted by osmotically-generated forces arising from a net volumetric accumulation of fluid in the nucleus. Growth of the nucleus is opposed by the vitrification of the polymer-rich matrix surrounding the nucleus. The process described produces structures, typically referred to as Macrovoids, which are undesirable features and tend to reduce the mechanical strength of the membrane. Thus, the balance between the local volumetric rate of solvent-nonsolvent exchange compared to the vitrification rate are key factors in the growth or suppression of Macrovoids. This process may be controlled by altering the initial dope composition, the nature of the various additives, and the rates of mass transfer (specifically across the nucleus wall), by imposing temperature gradients or by altering the external quench bath composition.
