Abstract
Membrane surface patterning is one approach used to mitigate fouling. This study used a combination of flux decline measurements and visualization experiments to evaluate the effectiveness of a microscale herringbone pattern for reducing protein fouling on polyvinylidene fluoride (PVDF) ultrafiltration membranes. Thermal embossing with woven mesh stamps was used for the first time to pattern membranes. Embossing process parameters were studied to identify conditions replicating the mesh patterns with high fidelity and to determine their effect on membrane permeability. Permeability increased or remained constant when patterning at low pressure (≤4.4 MPa) as a result of increased effective surface area; whereas permeability decreased at higher pressures due to surface pore-sealing of the membrane active layer upon compression. Flux decline measurements with dilute protein solutions showed monotonic decreases over time, with lower rates for patterned membranes than as-received membranes. These data were analyzed by the Hermia model to follow the transient nature of fouling. Confocal laser scanning microscopy (CLSM) provided complementary, quantitative, spatiotemporal information about protein deposition on as-received and patterned membrane surfaces. CLSM provided a greater level of detail for the early (pre-monolayer) stage of fouling than could be deduced from flux decline measurements. Images show that the protein immediately started to accumulate rapidly on the membranes, likely due to favorable hydrophobic interactions between the PVDF and protein, followed by decreasing rates of fouling with time as protein accumulated on the membrane surface. The knowledge generated in this study can be used to design membranes that inhibit fouling or otherwise direct foulants to deposit selectively in regions that minimize loss of flux.
Highlights
Membrane biofouling occurs when biomass deposits form on a membrane surface or within its pores [1]
The aims of this study were to evaluate the efficacy of using woven mesh fabric for patterning ultrafiltration membranes and to combine flux decline measurements and visualization experiments to elucidate the mechanism(s) of protein fouling on the resulting microscale herringbone patterned membranes
Using Confocal laser scanning microscopy (CLSM) imaging in this study provided a greater level of detail for the early stage fouling than could be deduced from flux decline measurements; it revealed high rates of initial fouling due to protein adsorption and demonstrated that this rate was different for as-received and patterned membranes
Summary
Membrane biofouling occurs when biomass deposits form on a membrane surface or within its pores [1]. Biofouling impairs membrane performance by increasing the masstransfer resistance for fluid transport through the membrane, which increases operating costs [2,3,4] Preventing it is the main objective of this and numerous other studies. Modifying membrane surfaces with ordered patterns of micro- and nanoscale features can alter shear-stress profiles in ways that mitigate fouling [15,16,17] The effects of such microscale features as shark skin mimics [18], pyramids [2,19] and line and groove patterns [20,21] on protein fouling have been studied, and results show the positive influence of patterning on decreasing the rate of fouling. Realizing these benefits through the commercial adoption of patterning will depend in part on the development of efficient, cost-effective manufacturing approaches
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