Layer-by-layer self-assembly of polyelectrolyte complexes and their multilayer films for pervaporation dehydration of isopropanol

Recent developments in polymeric nano-based separation membranes

Polymeric nanomaterials, which have tuneable chemical structures, versatile functionalities, and good compatibility with polymeric matrices, have attracted increasing interest from researchers for the construction of polymeric nano-based separation membranes. With their distinctive nanofeatures, polymeric nano-based membranes show great promise in overcoming bottlenecks in polymer membranes, namely, the trade-off between permeability and selectivity, low stability, and fouling issues. Accordingly, recent studies have focused on tuning the structures and tailoring the surface properties of polymeric nano-based membranes via exploitation of membrane fabrication techniques and surface modification strategies, with the objective of pushing the performance of polymeric nano-based membranes to a new level. In this review, first, the approaches for fabricating polymeric nano-based mixed matrix membranes and homogeneous membranes are summarized, such as surface coating, phase inversion, interfacial polymerization, and self-assembly methods. Next, the manipulation strategies of membrane surface properties, namely, the hydrophilicity/hydrophobicity, charge characteristics, and surface roughness, and interior microstructural properties, namely, the pore size and content, channel construction and regulation, are comprehensively discussed. Subsequently, the separation performances of liquid ions/molecules and gas molecules through polymeric nano-based membranes are systematically reported. Finally, we conclude this review with an overview of various unsolved scientific and technical challenges that are associated with new opportunities in the development of advanced polymeric nano-based membranes.

Review: Membrane Materials for the Removal of Water from Industrial Solvents by Pervaporation and Vapor Permeation

Organic solvents are widely used in a variety of industrial sectors. Reclaiming and reusing the solvents may be the most economically and environmentally beneficial option for managing spent solvents. Purifying the solvents to meet reuse specifications can be challenging. For hydrophilic solvents, water must be removed prior to reuse, yet many hydrophilic solvents form hard-to-separate azeotropic mixtures with water. Such mixtures make separation processes energy intensive and cause economic challenges. The membrane processes pervaporation (PV) and vapor permeation (VP) can be less energy intensive than distillation-based processes and have proven to be very effective in removing water from azeotropic mixtures. In PV/VP, separation is based on the solution-diffusion interaction between the dense permselective layer of the membrane and the solvent/water mixture. This review provides a state-of-the-science analysis of materials used as the selective layer(s) of PV/VP membranes in removing water from organic solvents. A variety of membrane materials, such as polymeric, inorganic, mixed matrix, and hybrid, have been reported in the literature. A small subset of these are commercially available and highlighted here: poly(vinyl alcohol), polyimides, amorphous perfluoro polymers, NaA zeolites, chabazite zeolites, T-type zeolites, and hybrid silicas. The typical performance characteristics and operating limits of these membranes are discussed. Solvents targeted by the U.S. Environmental Protection Agency for reclamation are emphasized and ten common solvents are chosen for analysis: acetonitrile, 1-butanol, N,N-dimethyl formamide, ethanol, methanol, methyl isobutyl ketone, methyl tert-butyl ether, tetrahydrofuran, acetone, and 2-propanol.

Porous Polyelectrolytes: The Interplay of Charge and Pores for New Functionalities

The past decade has witnessed rapid advances in porous polyelectrolytes and there is tremendous interest in their synthesis as well as their applications in environmental, energy, biomedicine, and catalysis technologies. Research on porous polyelectrolytes is motivated by the flexible choice of functional organic groups and processing technologies as well as the synergy of the charge and pores spanning length scales from individual polyelectrolyte backbones to their nano-/micro-superstructures. This Review surveys recent progress in porous polyelectrolytes including membranes, particles, scaffolds, and high surface area powders/resins as well as their derivatives. The focus is the interplay between surface chemistry, Columbic interaction, and pore confinement that defines new chemistry and physics in such materials for applications in energy conversion, molecular separation, water purification, sensing/actuation, catalysis, tissue engineering, and nanomedicine.

Preparation and performance of antibacterial layer-by-layer polyelectrolyte nanofiltration membranes based on metal–ligand coordination interactions

Coordinative nanofiltration membranes with commendable antibacterial property and hydrophilicity are prepared and investigated extensively by alternating LBL assembly of polyethyleneimine and polystyrene sulfonate using Cu²⁺ as coordination agent.

The development of novel Nexar block copolymer/Ultem composite membranes for C2-C4 alcohols dehydration via pervaporation

Novel composite membranes comprising sulfonated styrenic Nexar pentablock copolymers were developed by dip-coating on poly(ether imide) hollow fibers for pervaporation dehydration of C2-C4 alcohols. The advantages of using block copolymers as the selective layer are (1) their effectiveness to synergize the physicochemical properties of different chemical and structural moieties and (2) tunable nanoscale morphology and nanostructure via molecular engineering. To achieve high-performance composite membranes, the effects of coating time, ion exchange capacity (IEC) of the copolymer, and solvent systems for coating were investigated. It is revealed that a minimum coating time of 30 s is needed for the formation of a continuous and less-defective top layer. A higher IEC value results in a membrane with a higher flux and lower separation factor because of enhanced hydrophilicity and stretched chain conformation. Moreover, the composite membranes prepared from hexane/ethanol mixtures show higher separation factors and lower fluxes than those from the hexane solvent owing to microdomain segregation induced by ethanol and a smooth and dense top selective layer. These hypotheses were verified by atomic force microscopy and positron annihilation spectroscopy. The newly developed composite membranes demonstrate impressive separation performance with fluxes exceeding 2 kg/m(2) h and separation factors more than 200 for isopropyl alcohol and n-butanol dehydration from 85/15 wt % alcohol/water feed mixtures at 50 °C.

Highly sensitive and fast responsive fiber-optic modal interferometric pH sensor based on polyelectrolyte complex and polyelectrolyte self-assembled nanocoating

A new fiber-optic pH sensor is demonstrated by coating negatively charged polyelectrolyte complex (PEC(-)) nanoparticles, made of sodium carboxymethyl cellulose and poly(diallyldimethylammonium chloride) (PDDA), and positively charged PDDA on the surface of a thin-core fiber modal interferometer (TCFMI) with a layer-by-layer (LbL) electrostatic self-assembly method. The fabricated TCFMI pH sensor has different transmission dip wavelengths under different pH values and shows high sensitivities of 0.6 nm/pH unit and -0.85 nm/pH unit for acidic and alkaline solutions, respectively, and short response time of 30-50 s. The LbL electrostatic self-assembly process of a PEC(-)/PDDA multilayer is traced by quartz crystal microbalance and shows a fast thickness growth. Atomic force microscopy shows the root mean square (RMS) surface roughness of electrostatic self-assembly nanocoating of polyelectrolyte complex/polyelectrolyte is much higher than that of polyelectrolyte/polyelectrolyte due to the larger size of PEC(-) colloidal nanoparticles. The enhanced RMS surface roughness and thickness of the nanocoating can shorten the response time and raise the sensitivity of the TCFMI pH sensor, respectively. In addition, the TCFMI pH sensor has highly reversible performance and good durability.