The sharkskin-mimetic, patterned TFC RO membranes exhibited superior biofouling resistance compared to conventional and simple patterned membranes.

We report on a unique, facile and scalable fabrication technique, dual-layer slot coating (DSC) for high performance polyamide (PA) thin film composite (TFC) reverse osmosis (RO) membranes. DSC allows the simultaneous and continuous spreading of two reactive monomer solutions to create an unsupported PA layer via in situ polymerization, which is then adhered onto a porous support to form a membrane. DSC facilitates the characterization of the PA layer structure by easily isolating it. The DSC-assembled PA layer exhibits a thinner and smoother structure with a more wettable and less negatively charged surface than the one prepared via conventional interfacial polymerization (IP), which was attributed to the uniformly expedited amine (MPD) diffusion at the bulk liquid interface during film formation. As a result, DSC enables the formation of an extremely thin (∼9 nm) and dense PA layer using a very low MPD concentration, which is not feasible by conventional IP. Importantly, the DSC-assembled membrane shows an excellent water flux and NaCl rejection, exceeding both IP control and commercial RO membranes. The DSC technique will open a new paradigm for the fabrication of TFC membranes with strong commercial potential due to its simplicity, scalability and high performance.

This study investigates the crosslinking dynamics and swelling properties of pH-responsive poly(ethylene glycol) (PEG)/poly(acrylic acid) (PAA) interpenetrating polymer network (IPN) hydrogels. These hydrogels feature denser crosslinked networks compared to PEG single network (SN) hydrogels. Fabrication involved a two-step UV curing process: First, forming PEG-SN hydrogels using poly(ethylene glycol) diacrylate (PEGDA) through UV-induced free radical polymerization and crosslinking reactions, then immersing them in PAA solutions with two different molar ratios of acrylic acid (AA) monomer and poly(ethylene glycol) dimethacrylate (PEGDMA) crosslinker. A subsequent UV curing step created PAA networks within the pre-fabricated PEG hydrogels. The incorporation of AA with ionizable functional groups imparted pH sensitivity to the hydrogels, allowing the swelling ratio to respond to environmental pH changes. Rheological analysis showed that PEG/PAA IPN hydrogels had a higher storage modulus (G′) than PEG-SN hydrogels, with PEG/PAA-IPN5 exhibiting the highest modulus. Thermal analysis via thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) indicated increased thermal stability for PEG/PAA-IPN5 compared to PEG/PAA-IPN1, due to higher crosslinking density from increased PEGDMA content. Consistent with the storage modulus trend, PEG/PAA-IPN hydrogels demonstrated superior mechanical properties compared to PEG-SN hydrogels. The tighter network structure led to reduced water uptake and a higher gel modulus in swollen IPN hydrogels, attributed to the increased density of active network strands. Below the pKa (4.3) of acrylic acid, hydrogen bonds between PEG and PAA chains caused the IPN hydrogels to contract. Above the pKa, ionization of PAA chains induced electrostatic repulsion and osmotic forces, increasing water absorption. Adjusting the crosslinking density of the PAA network enabled fine-tuning of the IPN hydrogels’ properties, allowing comprehensive comparison of single network and IPN characteristics.