Highly Efficient Antifouling Coating of Star-Shaped Block Copolymers with Variable Sizes of Hydrophobic Cores and Charge-Neutral Hydrophilic Arms

Abstract

Star-shaped block copolymers (SPs) have shown promise as antifouling coating materials on water purification membranes. The unique architectural design of these SPs, composed of covalently linked hydrophobic core and hydrophilic arms, offers the flexibility of tailoring the core and/or arm compositions to achieve properties on demand. Here, variable sizes of SPs with increasingly hydrophobic polystyrene cores (PSCs) and longer hydrophilic poly­(ethylene glycol) (PEG) arms were synthesized to evaluate their coatability on polysulfone ultrafiltration (PSF UF) membranes and to study the effect of the hydrophilic PEG arm lengths on the antifouling properties of SP-coated membranes. The oleophobicity evaluated from underwater hexadecane contact angle (CA) measurements of SP-coated membranes increased by approximately 3 times, leading to almost 7 times improvement in permeation flux during oil emulsion filtration. No flux recovery was observed for the pristine PSF membrane, whereas 100% flux recovery ratio (FRR) was achieved for SP-coated membranes. The filtration of bovine serum albumin (BSA) protein solution exhibited an improvement in the permeation flux by 2.7–8.9 times for SP-coated membranes. The FRR was only 64% for the pristine PSF membrane, as opposed to nearly 100% FRR for all SP-coated membranes. The stability of the SP coating was tested by rigorous washing with Tween 80 surfactant and three-cycle oil emulsion filtrations. Surfactant washing only removed the loosely bound extra layers of SP coating, leaving the surface-bound and pore-entrapped stable SP coating with remarkable antifouling properties. Since SP3 with the largest hydrophobic PSC showed much better performance, the effect of increasing its PEG arm length on the antifouling properties was studied further, and the largest size SP3 with the longest PEG arm was the optimum antifouling coating. This study provides insights into the design of block copolymer nanoarchitecture to develop antifouling surfaces of interest ranging from water purification to biomedical applications.

Antifouling Fibrous Membrane Enables High Efficiency and High-Flux Microfiltration for Water Treatment

“…High-concentration (50–1000 ppm) BSA solutions are commonly used for the evaluation of the antifouling properties of filtration membranes . Therefore, to further evaluate the antiprotein adhesion property of the membrane, 100 mg L –1 BSA solution was used as the feed solution.…”

“…It could be seen from Figure 6C, after 100 filtration cycles, the water flux of the composite membranes remained 41.89% for E. coli and 46.03% for S. aureus of their initial values, respectively, demonstrating High-concentration (50−1000 ppm) BSA solutions are commonly used for the evaluation of the antifouling properties of filtration membranes. 55 Therefore, to further evaluate the antiprotein adhesion property of the membrane, 100 mg L −1 BSA solution was used as the feed solution. The results are shown in Figure 7A and B.…”

Hybrid Star-Shaped Block Copolymers for Fabricating Fouling-Resistant Membranes

“…Among numerous physical and chemical modification processes, physical coating (i.e., adsorption) of hydrophilic material is found to be more efficient and feasible. − Linear polyelectrolytes are typically used as coating materials. − However, our recent reports demonstrate the advantages of branched amphiphiles, specifically the star-shaped block copolymers (SPs) composed of a hydrophobic cross-linked polystyrene (PS) core with extended hydrophilic polyethylene glycol (PEG) arms, over linear counterparts . Advantages include the enhanced hyper-brush structure of the SP and the homogeneity of the SP coating, providing a higher fouling barrier from a well-controlled nanoscale thin layer with minimal loss in water permeability.…”

“…The flexibility of tuning the structure, size, and properties of SPs enables us to achieve high mechanical stability of the coating. For instance, the mechanical stability can be increased by enhancing the hydrophobic interaction, by reducing the SPs solubility in aqueous solvents, − and by capturing SPs into pores and valleys of the membrane through a pressure-assisted coating …”

“…These complexities not only affect the cost and practical scale-up of the materials but also result in poor reproducibility. Finally, although larger size SPs with longer PS and PEG arms were shown to be more effective in fouling reduction, preparing a water processable larger SP than SP3 (i.e., star-shaped PS 87 - b -PPEGMA 115 block copolymer of d = 29.6 ± 4.6 nm, and 21 arms/SP) coating) was not possible …”