Understanding the Role of Pattern Geometry on Nanofiltration Threshold Flux

Abstract

Colloidal fouling can be mitigated by membrane surface patterning. This contribution identifies the effect of different pattern geometries on fouling behavior. Nanoscale line-and-groove patterns with different feature sizes were applied by thermal embossing on commercial nanofiltration membranes. Threshold flux values of as-received, pressed, and patterned membranes were determined using constant flux, cross-flow filtration experiments. A previously derived combined intermediate pore blocking and cake filtration model was applied to the experimental data to determine threshold flux values. The threshold fluxes of all patterned membranes were higher than the as-received and pressed membranes. The pattern fraction ratio (PFR), defined as the quotient of line width and groove width, was used to analyze the relationship between threshold flux and pattern geometry quantitatively. Experimental work combined with computational fluid dynamics simulations showed that increasing the PFR leads to higher threshold flux. As the PFR increases, the percentage of vortex-forming area within the pattern grooves increases, and vortex-induced shielding increases. This study suggests that the PFR should be higher than 1 to produce patterned membranes with maximal threshold flux values. Knowledge generated in this study can be applied to other feature types to design patterned membranes for improved control over colloidal fouling.

Nanofiltration Membranes with Crumpled Polyamide Films: A Critical Review on Mechanisms, Performances, and Environmental Applications

“…One strategy is patterned membranes. Patterned membranes, often reported for fouling control, − typically involve fabrication methods such as phase separation micromolding, , thermal embossing/nanoimprinting, ,, and 3D printing. , Previous studies have constructed patterns such as grooved lines, ,, pillars, prism, and pyramid with dimensions ranging from tens of nanometers to hundreds of micrometers. These patterned membranes, when used as substrates, are expected to create aqueous/organic interfaces with regular/periodical morphological features.…”

Fouling Mitigation via Chaotic Advection in a Flat Membrane Module with a Patterned Surface

“…The above-mentioned studies on patterned membranes have revealed that the ratio between the pattern size and the length scale of other parameters such as particle size and channel height has a significant influence on fouling mitigation relying on the hydrodynamics of a feed fluid due to a specific membrane pattern. Computational fluid dynamics (CFD) simulations can be used to elucidate the influence of surface features on the hydrodynamics and concentration polarization near the membrane surfaces [ 35 , 36 ].…”

Studying Fluid Characteristics Atop Surface Patterned Membranes via Particle Image Velocimetry

“…Surface patterned membranes are a versatile platform that can overcome limitations of feed spacers, as well as promote separation performance and antifouling propensity of pressure-driven membranes in water treatment and desalination applications [1,2]. Membrane fouling and concentration polarization are among main obstacles that are challenging ultimate process efficiency, besides increasing energy demands and operation costs [3].…”

“…Additionally, alignment of surface microstructures with respect to feed flow direction was shown to influ-ence the desalination performance [7,11,13]. Nevertheless, recent publications have emphasized that such effects are substantially influenced by several operating parameters (e.g., pattern design, crossflow velocity and size of solutes) [2,4,6,7].…”