The salt-, pH- and oxidant-responsive pervaporation behaviors of weak polyelectrolyte multilayer membranes

Abstract

a b s t r a c tThe layer-by-layer (LbL) assembled polyelectrolyte multilayer has recently been recognized as a new class of promising membrane material for various separation uses. However, there is a lack of understanding about the influences of separation mixtures on the adsorbed polyelectrolytes. Therefore, clear understanding on it would be very important for the design and application of a type of new functional composite membrane. In this paper, the multilayer of weak polyelectrolytes polyethyleneimine and polyacrylic acid was constructed onto a hydrolyzed hollow fiber polyacrylonitrile support membrane under a negative pressure condition. The salt-, pH-and oxidant-responsive pervaporation behaviors of polyelectrolyte multilayer membranes were evaluated by post-treating with sodium chloride, hydrochloric acid, sodium hydroxide and sodium hypochlorite aqueous solutions, respectively. The pervaporation performances for separation of ethanol/water were compared before and after post-treatments. Scanning electron microscopy and atomic force microscopy confirmed the microtopographical changes of membrane surfaces. Optical microscopy was also used to real-time observe surface morphologies of polyelectrolyte multilayers deposited on the quartz substrates. Finally, the comparison of zeta potential values of inner surface before and after post-treatment also demonstrated the changes of surface electrical property.

Dynamic pressure‐driven covalent assembly of inner skin hollow fiber multilayer membrane

“…For example, we have recently reported that the post-treatments of the weak polyelectrolyte multilayer membranes with salt, acid, and alkali offer much opportunity for the formation of loose structure and big defects on multilayers, which would in turn lead to the deterioration of membrane performance. 28 To improve the stability, a metal-ligand-coordinated multilayer membrane has been recently developed for separation applications in our laboratory. 29 In contrast, covalent bonding may yield much more stable structures.…”

“…This type of module may offer advantages such as easy formation of ultrathin selective layer, easy protection of the separation layer, good distribution of feed solution, and low-transport resistance on the permeate side. 20,21,28,29 Recently, a pilot-scale inner skin hollow fiber pervaporation module with a length of 1 m was successfully produced in our laboratory. 21 It suggested that the inner skin hollow fiber pervaporation membranes have great potential for industrial applications.…”

“…However, it is necessary to seek for effective approaches to improve the stability of electrostatically LbL assembled multilayer membrane. 28 Herein, we report on the development of dynamic pressuredriven covalent assembly to construct stable crosslinking multilayers onto the inner surface of hollow fiber substrate membranes. Differing from the rigid substrates, in terms of the unique features of polymeric porous substrates such as wide pore diameter distribution and good permeability, dynamic pressure-driven LbL assembly had been recently developed in our laboratory.…”

“…Differing from the rigid substrates, in terms of the unique features of polymeric porous substrates such as wide pore diameter distribution and good permeability, dynamic pressure-driven LbL assembly had been recently developed in our laboratory. 20,21,28,29 This technique provides a particularly effective approach for fabricating an ultrathin selective layer by dynamically depositing polymer building blocks onto the porous substrates. Figure 1 shows a schematic illustration of the preparation of a GA-crosslinked PEI multilayer on a polyacrylonitrile (PAN) hollow fiber substrate membrane by dynamic pressure-driven LbL assembly.…”

Functionalized assembly of solid membranes for chiral separation using polyelectrolytes and chiral ionic liquid

“…This is because some of the PEI/PAA may have swelled and partly peeled off, due to the b-CD-IL assembly process. [30][31][32] It was clear that although the b-CD-IL can be assembled on to the PEI/PAA due to the electrostatic adsorption force, the b-CD-IL will, to Figure 7. UV-vis spectra of (PAA/IL) n films with n 5 1-6 on quartz substrates.…”