Ultrathin self-assembled polyelectrolyte multilayer membranes

The paper is concerned with ultrathin membranes prepared upon alternating layer-by-layer adsorption of cationic and anionic polyelectrolytes on a porous substructure. The formation of the polyelectrolyte multilayer membranes is characterised and the transport of gases, liquid mixtures and ions across the membranes is studied. In particular, the use of the membranes for alcohol/water separation under pervaporation conditions, and for the separation of mono- and divalent ions is described. It is demonstrated that upon a suitable choice of polyelectrolytes and substructures, and a careful optimisation of preparation and operation conditions, membranes can be tailored exhibiting an excellent separation capability

Polyelectrolyte multilayer membranes for desalination of aqueous salt solutions and seawater under reverse osmosis conditions

Ultrathin, multilayered membranes of polyvinylamine (PVA) and polyvinyl sulfate (PVS) were electrostatically adsorbed on a porous polymer (polyacrylonitrile/polyethylene terephthalate) support. Their use for desalination of aqueous salt solutions, diluted and non-diluted artificial seawater was investigated under reverse osmosis conditions. Using 60 layer pairs of PVA/PVS as separating membrane, it was possible to completely reject MgCl2 and MgSO4 from feed solutions of 1 and 10 mM concentration independently from the operative pressure applied. The rejection of NaCl and Na2SO4 increased from 84 and 96 % at 5 bar to 93.5 and 98.5 % at 40 bar, respectively. From diluted seawater (1:10; 1:100; 1:1000), 99 +/- 1 % of Mg2+, 97.0 +/- 1 % of Ca2+ and 92.5 +/- 1 % of Na+ were rejected at 40 bar, and from non-diluted seawater, 98 +/- 1% of Mg2+, 96.4 +/- 1 % of Ca2+, and 74.5 +/- 0.8 % of Na+ were rejected at 40 bar. The permeation flux J increased linearly with the pressure applied. For a membrane of 60 PVA/PVS layer pairs, a flux value of 4 +/- 0.2 L m(-2) h(-1) was found at 40 bar. The influence of the number of deposited layer pairs on R and J was also investigated. (c) 2004 Elsevier B.V. All rights reserved

Tailor-made poly(vinylamine)s via thermal or photochemical organometallic mediated radical polymerization

peer reviewedPoly(vinylamine) is a highly valuable class of polymer used in several applications. Although free radical polymerization has been extensively exploited for its synthesis, the preparation of poly(vinylamine) with low dispersity and controlled molar mass is barely developed. Recently, a great step was made in this direction via organometallic-mediated radical polymerization (OMRP) of N-vinylacetamides followed by hydrolysis of the pendent amide groups. This chapter summarizes, completes and put in perspective the main accomplishments in the OMRP of acyclic N-vinylamides for the controlled synthesis of both primary and secondary poly(vinylamine)s. Thermal and photochemical initiating systems are compared and the controlled thermally initiated radical polymerization of N-vinylacetamide is reported for the first time. The optimal hydrolysis conditions for producing the poly(vinylamine) derivatives as well as their potential as vectors for gene transfection are also presented

Charged micropollutant removal with hollow fiber nanofiltration membranes based on polycation/polyzwitterion/polyanion multilayers

Hollow fiber nanofiltration membranes can withstand much higher foulant concentrations than their spiral wound counterparts and can be used in water purification without pretreatment. Still, the preparation of hollow fiber nanofiltration membranes is much less established. In this work, we demonstrate the design of a hollow fiber nanofiltration membrane with excellent rejection properties by alternatively coating a porous ultrafiltration membrane with a polycation, a polyzwitterion, and a polyanion. On model surfaces, we show, for the first time, that the polyzwitterion poly N-(3-sulfopropyl)-N-(methacryloxyethyl)-N,N-dimethylam-monium betaine (PSBMA) can be incorporated into traditional polyelectrolyte multilayers based on poly(styrenesulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDADMAC). Furthermore, work on model surfaces allows a good characterization of, and insight into, the layer build-up and helps to establish the ptimal membrane coating conditions. Membranes coated with these multilayers have high salt rejection of up to 42% NaCl, 72% CaCl2, and 98% Na2SO4 with permeabilities of 3.7−4.5 l·m−2·h−1·bar−1. In addition to the salt rejections, the rejection of six distinctively different micropollutants, with molecular weights between 215 and 362 g·mol−1, was investigated. Depending on the terminating layer, the incorporation of the polyzwitterion in the multilayer results in nanofiltration membranes that show excellent retentions for both positively and negatively charged micropollutants, a behavior that is attributed to dielectric exclusion of the solutes. Our approach of combining model surfaces with membrane performance measurements provides unique insights into the properties of polyzwitterion-containing multilayers and their applications