Scaling resistance by fluoro-treatments: the importance of wetting states

Abstract

Membrane distillation is a thermally driven separation process using hydrophobic, porous membranes. Among various problems faced by membrane distillation, scaling remains an unresolved challenge in treating streams of high salinity....

Stability of Superhydrophobicity and Structure of PVDF Membranes Treated by Vacuum Oxygen Plasma and Organofluorosilanisation

“…A WCA higher than that of the pristine PVDF (119.4 ± 1.7°) was obtained for all the tested plasma-treated membranes, with an overall mean value of 153.3°, showing that the modification procedure with the oxygen plasma activation proposed in this work was suitable to obtain superhydrophobic PVDF membranes. As observed by other authors [ 19 , 72 ], droplets placed on the membranes for the WCA measurements easily rolled off the surface in most of plasma-treated membranes, which is an essential condition for superhydrophobic and self-cleaning surfaces.…”

“…Only a few works evaluating a membrane modification procedure with plasma activation followed by grafting of FASs can be found in the literature. In a similar approach to this work, Liu et al [ 19 ] activated a PVDF membrane with oxygen plasma at 50 W for 1 min, followed by grafting of the FAS 1H,1H,2H,2H-perfluorodecyltriethoxysilane, achieving a WCA of 162.0 ± 2.3° in membrane surfaces with a pillar surface structure. The higher WCA reported in that work could be ascribed to the higher fluorine chain length of the modifying agent used [ 39 ] and the high initial WCA of the pristine membrane (155.3 ± 1.7°) [ 19 ].…”

“…Afterwards, the coupons were placed on a metal holder and then coated with a fine layer of Au/Pd by sputtering in vacuum for 45 s. The surface and cross-section morphology, thickness and chemical composition were analysed. The surface porosity of the membranes was measured from the surface FESEM images by using ImageJ software [ 19 , 60 , 71 ]. The average membrane thickness and surface porosity were measured in at least six separate locations on the membrane, and the chemical composition was determined at a minimum of three locations on the surface using the standard deviation as a measure of the associated error.…”

“…Therefore, the useful lifetime of the membrane can decline considerably, and the operational cost would rise [ 15 , 16 , 17 ]. Up to now, these issues are not completely resolved, hindering the large-scale application of membrane technology in areas such as the desalination of seawater or methane recovery from anaerobic effluents [ 18 , 19 ].…”

“…In this regard, superhydrophobic membranes with a water contact angle (WCA) higher than or equal to 150° [ 22 ] have been reported to significantly mitigate the wetting, which was attributed to the low contact area between the liquid phase and the membrane [ 23 , 24 ]. Additionally, superhydrophobicity has been related to the improvement in the self-cleaning properties of the membrane surface [ 12 , 19 ]. Thus, membrane surface functionalisation has been applied to increase its hydrophobicity at the surface level, whilst the bulk properties remain unchanged [ 25 ] by means of the addition of new hydrophobic functional groups, such as siloxanes and fluoroalkyls [ 26 , 27 ].…”