Application of polyelectrolyte multilayer reverse osmosis membrane in seawater desalination

Alternate adsorption of polyanion and polycation onto a substrate through layer by layer (LbL) assembly provides a convenient mean of depositing ultrathin film with controlled thicknesses and compositions. Spin assisted layer by layer (SA-LbL) assembly was introduced to reduce processing time and improve layering quality. This dissertation explores the use of SA-LbL assembly in particular for fabricating reverse osmosis (RO) membrane.;The effect several parameters such as molecular weight of polyelectrolyte, concentration of polyelectrolyte solution, spin speed, and ionic strength of polyelectrolyte solution has been thoroughly investigated. However; the effect of pH for this particular technique has not been investigated yet whereas pH is one of the most important parameter for controlling film properties. This dissertation also investigated the effect of pH coupled with other parameters such as spin speed and concentration.;Four different polyelectrolyte membrane systems such as poly(diallyldiamine ammonium chloride) (PDAC) /poly(vinyl sulfate) (PVS); poly(allylamine hydrochloride) (PAH)/PVS; Poly(ethylene imine) (PEI)/Poly(acrylic acid) (PAA), and PAH/PAA were deposited on polysulfone (PSF) ultrafiltration membrane as a support. Characterization using atomic force microscope (AFM), Fourier transform infra red (FTIR), and contact angle show the existence of the coating on PSF membrane. The membrane performance in terms of salt rejection and water flux was also examined using cross-flow permeation cell for short term testing (7 hours). PAH/PAA was selected and tested for longer period (48 hours) to examine the film stability. Effects of various RO operating conditions such as pressure, temperature and salt concentration of feed water on permeation characteristic of the PAH/PAA membrane were also thoroughly investigated. The testing and characterization shows that PAH/PAA membranes are quite stable and still intact with the PSF support however their performance becomes poorer as the feed water salt concentration is increased.;In this dissertation, hand-made RO polyamide (PA) was also fabricated using interfacial polymerization technique and tested as comparison. Nanoclays were incorporated in PA membrane to enhance membrane performance. The test demonstrates that the performance of PAH/PAA membrane is comparable to that of hand-made RO PA. While clay modified PA performs somewhat better than PAH/PAA and unmodified PA membranes.