Formation of Ultrathin, Defect-Free Membranes by Grafting of Poly(acrylic acid) onto Layered Polyelectrolyte Films

Abstract

Deposition of hyperbranched poly(acrylic acid) (PAA) films on porous supports is an attractive method for synthesizing derivatizable, ultrathin composite membrane skins. We previously synthesized these films by sputtering a thin gold layer onto a porous alumina support and then grafting several layers of PAA to a self-assembled monolayer of mercaptoundecanoic acid on the gold. This paper demonstrates grafting of PAA onto PAA/poly(allylamine hydrochloride) (PAH) films that were prepared by alternating polyelectrolyte deposition. This procedure overcomes the inconvenience associated with sputtering of gold and allows synthesis of defect-free membranes using only one grafted PAA layer. Membrane skins consisting of 2.5 bilayers of PAA/PAH plus 1 layer of grafted PAA (total thickness of ∼14 nm) effectively cover the underlying pores of porous alumina supports without filling them, as shown by field-emission scanning electron microscopy (FESEM) images. When derivatized with H2NCH2(CF2)6CF3, these composite membranes show an ideal selectivity of 2.4 for O2 over N2, demonstrating the absence of defects in this system. The chemistry developed for the grafting process also allows modest derivatization of PAA/PAH films with H2NCH2(CF2)6CF3 to increase hydrophobicity.

Characterization of pH-induced changes in the morphology of polyelectrolyte multilayers assembled from poly(allylamine) and low molecular weight poly(acrylic acid)

“…These results suggest that the internal structures (e.g., relative compositions, degrees of internal crosslinking, etc.) of PAH/PAA films fabricated using low molecular weight PAA could vary significantly from those fabricated using higher molecular weight PAA [9,10,[21][22][23][24][25]27,[32][33][34][35][36][37][38][39]. These results also suggest that the physical properties and post-fabrication behaviors of these materials could differ in significant ways from those of the PAH/PAA assemblies investigated in past studies.…”

Persistent Multilayer Electrode Adsorption of Polycationic Au Nanoparticles

“…[43][44][45][46][47] This is understood as basically an entropic effect created by release of multiple solvent and small counterions from the polyelectrolyte structures.…”

Charge insertion into hybrid nanoarchitectures: mesoporous manganese oxide coated with ultrathin poly(phenylene oxide)

“…Most studies of electrodeposited polymers are on planar substrates, but these strategies have also been extended to electrodeposition within porous non-electroactive substrates [12][13][14]. As a fabrication method to create hybrid three-dimensional nanoarchitectures, electropolymerization has advantages over both self-assembly in forming thin, pinhole-free films and chemical vapor deposition in coating three-dimensional architectures conformally.…”