“…This was because the omniphobicity of the PVDF-FAS-60 membrane prevented complete penetration of saline feed solution with surfactants into the porous membrane structure. It should be noted that the highest SDS concentration resisted by our omniphobic membrane is comparable or higher than that reported in prior work with particle-incorporated, hierarchically structured omniphobic membranes 23,24,27–29 , indicating that a monolithic membrane with reentrant texture is sufficient to achieve omniphobicity in MD desalination.Fig. 2Membrane distillation (MD) performance of different PVDF membranes.…”
Section: Resultssupporting
confidence: 61%
“…3). A thorough literature search indicates a similar phenomenon—omniphobic MD membranes with higher wetting resistance typically possess lower water vapor permeability compared to hydrophobic MD membranes with lower wetting resistance (see Supplementary Table 2) 13,16,24–26,28,29,50,51 . This phenomenon is intriguing because wetting resistance (an inverse measure of ease of liquid permeation) and water vapor permeability (a measure of ease of water vapor permeation) are distinct properties.…”
Section: Resultsmentioning
confidence: 96%
“…Omniphobic membranes are typically fabricated by combining reentrant texture and materials of low solid surface energy 17–22 . To date, the fabrication of omniphobic membranes involves complex and/or time-consuming processes, which typically require incorporation of micro- or nano-sized particles onto the membrane surface to create a hierarchical surface texture 13,16,23–29 . Also, the unintended environmental and health impacts of such particles, especially those with nano-scale sizes, continue to be an active area of research 30–32 .…”
Omniphobic membranes are attractive for membrane distillation (MD) because of their superior wetting resistance. However, a design framework for MD membrane remains incomplete, due to the complexity of omniphobic membrane fabrication and the lack of fundamental relationship between wetting resistance and water vapor permeability. Here we present a particle-free approach that enables rapid fabrication of monolithic omniphobic membranes for MD desalination. Our monolithic omniphobic membranes display excellent wetting resistance and water purification performance in MD desalination of hypersaline feedwater containing surfactants. We identify that a trade-off exists between wetting resistance and water vapor permeability of our monolithic MD membranes. Utilizing membranes with tunable wetting resistance and permeability, we elucidate the underlying mechanism of such trade-off. We envision that our fabrication method as well as the mechanistic insight into the wetting resistance-vapor permeability trade-off will pave the way for smart design of MD membranes in diverse water purification applications.
“…This was because the omniphobicity of the PVDF-FAS-60 membrane prevented complete penetration of saline feed solution with surfactants into the porous membrane structure. It should be noted that the highest SDS concentration resisted by our omniphobic membrane is comparable or higher than that reported in prior work with particle-incorporated, hierarchically structured omniphobic membranes 23,24,27–29 , indicating that a monolithic membrane with reentrant texture is sufficient to achieve omniphobicity in MD desalination.Fig. 2Membrane distillation (MD) performance of different PVDF membranes.…”
Section: Resultssupporting
confidence: 61%
“…3). A thorough literature search indicates a similar phenomenon—omniphobic MD membranes with higher wetting resistance typically possess lower water vapor permeability compared to hydrophobic MD membranes with lower wetting resistance (see Supplementary Table 2) 13,16,24–26,28,29,50,51 . This phenomenon is intriguing because wetting resistance (an inverse measure of ease of liquid permeation) and water vapor permeability (a measure of ease of water vapor permeation) are distinct properties.…”
Section: Resultsmentioning
confidence: 96%
“…Omniphobic membranes are typically fabricated by combining reentrant texture and materials of low solid surface energy 17–22 . To date, the fabrication of omniphobic membranes involves complex and/or time-consuming processes, which typically require incorporation of micro- or nano-sized particles onto the membrane surface to create a hierarchical surface texture 13,16,23–29 . Also, the unintended environmental and health impacts of such particles, especially those with nano-scale sizes, continue to be an active area of research 30–32 .…”
Omniphobic membranes are attractive for membrane distillation (MD) because of their superior wetting resistance. However, a design framework for MD membrane remains incomplete, due to the complexity of omniphobic membrane fabrication and the lack of fundamental relationship between wetting resistance and water vapor permeability. Here we present a particle-free approach that enables rapid fabrication of monolithic omniphobic membranes for MD desalination. Our monolithic omniphobic membranes display excellent wetting resistance and water purification performance in MD desalination of hypersaline feedwater containing surfactants. We identify that a trade-off exists between wetting resistance and water vapor permeability of our monolithic MD membranes. Utilizing membranes with tunable wetting resistance and permeability, we elucidate the underlying mechanism of such trade-off. We envision that our fabrication method as well as the mechanistic insight into the wetting resistance-vapor permeability trade-off will pave the way for smart design of MD membranes in diverse water purification applications.
“…[18,25,32] The majority of the methods introduced for the fabrication of omniphobic domains on membrane surfaces are multi-step and time-consuming, making them very challenging to scale up. [33][34][35][36][37][38][39][40][41] Additionally, to achieve the desired surface topographies, in most of the reported approaches, nanoparticles and nanomaterials have been employed. The potential health and environmental hazards of using these particles, which is an active area of research in membrane science, [42,43] makes the large scale application of the proposed methods less attractive.…”
Creating reentrant structures on flexible and porous substrates is a significant challenge for the scalable fabrication of omniphobic membranes. The design of such membranes requires control over the surface topography and chemistry of the interfacial domains. Here, a continuous bottom-up method, based on initiated chemical vapor deposition (iCVD), is developed to enable the fabrication of flexible omniphobic membranes. The developed membranes hinder the intrusion of droplets of low surface energy liquids (e.g., ethanol) colliding with the surface at a velocity of about 2 m/s. The stable wetting resistance of the membranes allows for the desalination of low surface energy synthetic and municipal wastewater streams.
“…Development of desalination techniques with a higher permeate flux has been conducted for improved seawater desalination system [ 6 , 7 ]. Despite major advances in developing membrane materials on distillation performance [ 8 , 9 , 10 ] and pressure driven membrane separation processes are still facing the problems of the temperature polarization effect [ 11 , 12 ]. Previous studies in improving the permeate flux enhancement by incorporating proper flow alteration configurations such as filament [ 13 , 14 , 15 ], roughened surface [ 16 ] and eddy promoter [ 17 ] into the flow channel of DCMD modules to boost the turbulence intensity were also investigated.…”
Two geometric shape turbulence promoters (circular and square of same areas) of different array patterns using three-dimensional (3D) printing technology were designed for direct contact membrane distillation (DCMD) modules in the present study. The DCMD device was performed at middle temperature operation (about 45 °C to 60 °C) of hot inlet saline water associated with a constant temperature of inlet cold stream. Attempts to reduce the disadvantageous temperature polarization effect were made inserting the 3D turbulence promoters to promote both the mass and heat transfer characteristics in improving pure water productivity. The additive manufacturing 3D turbulence promoters acting as eddy promoters could not only strengthen the membrane stability by preventing vibration but also enhance the permeate flux with lessening temperature polarization effect. Therefore, the 3D turbulence promoters were individually inserted into the flow channel of the DCMD device to create vortices in the flow stream and increase turbulent intensity. The modeling equations for predicting the permeate flux in DCMD modules by inserting the manufacturing 3D turbulence promoter were investigated theoretically and experimentally. The effects of the operating conditions under various geometric shapes and array patterns of turbulence promoters on the permeate flux with hot inlet saline temperatures and flow rates as parameters were studied. The distributions of the fluid velocities were examined using computational fluid dynamics (CFD). Experimental study has demonstrated a great potential to significantly accomplish permeate flux enhancement in such new design of the DCMD system. The permeate flux enhancement for the DCMD module by inserting 3D turbulence promoters in the flow channel could provide a maximum relative increment of up to 61.7% as compared to that in the empty channel device. The temperature polarization coefficient (τtemp) was found in this study for various geometric shapes and flow patterns. A larger τtemp value (the less thermal resistance) was achieved in the countercurrent-flow operation than that in the concurrent-flow operation. An optimal design of the module with inserting turbulence promoters was also delineated when considering both permeate flux enhancement and energy utilization effectiveness.
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