| Recent years, the so-called layer-by-layer (LBL) deposition technique of oppositely charged polyelectrolytes can be successfully applied to prepare organic ultrathin films. For their simple fabrication (operation), precisely controlled film thickness and structure, broad range of materials that is available for incorporation into polyelectrolyte multilayers (PEMs), they are applied abroad in many different fields such as drug release, biosensors, photoelectric materials and membrane separation. This paper is concerned with the viscosity behaviour of dilute aqueous solutions of polyelectrolytes (PDDA& PSS) and is a system investigation of the main factor that influenced the buildup of PEMs and its structure. It is valuable to study PEMs as the pervaporation membrane for dehydration of isopropanol.Firstly, the influence of non-eletrostatic force during the alternating electrostatic layer-by-layer (LBL) adsorption of oppositely charged PDDA and PSS was investigated by UV-VIS spectrum. PSS can be adsorbed on clean silica with the same sign charge, the adsorption mass was increased with the increasing roughness of silica surface, PSS concentration, and with decreasing adsorption temperature. These indicated that the driving force of oppositely charged PDDA/PSS isn't only electo-static force, non-coulomb force also play an important role during the buildup of PEMs.Secondly, the adsorption mechanism and main factor that influenced the buildup of PEMs and its structure were studied using UV-VIS spectrum, Contact angle measurement (CA) and viscometry. It was found that the adsorption amount can be constant, increase and decrease as the concentration of polyelectrolyte, salinity, pH, composition of the organic solvent/water mixtures and adsorption temperature varies. The viscosity study of PDDA and PSS at corresponding adsorption conditions indicated that there being a inverse proportion relationship between intrinsic viscosity of the polymer and the adsorption amount. The smaller the coil size contracted, the more mass the polymer adsorbed. PEMs' surface contact angle as a function of layer number showed a serrate state variation. The wetting property of PDDA/PSS PEMsby Contact angle measurement demonstrated that polyelectrolyte multilayers composed of two distinct zones. Zone I is premonitory layer comprised of one or a few polyelectrolyte layers close to the substrate. Zone II is the "bulk" film comprised of regularly alternating deposition of two oppositely charged polyelectrolytes.At last, PDDA/PSS PEMs was successfully prepared on polyamide (PA) reverse osmosis substrate membrane using "single-side" deposition method as pervaporation membrane to separate 95% isopropanol/5%water mixtures. The pervaporation performance of PEMs prepared from salt solution was quite good with less than ten layer pairs. It was found that the separation factor a increased and the flux J decreased as the layer number increased, The adsorption of 6.5 layer pairs of PDDA/PSS at the presence of 0.75mol/L NaCl yielded the maximum flux of 1498g/m2h and the minimum separation factor of 247 when the feed temperature was 55"C. Both separation factor and flux increased with elevating operation temperature.
|
PDF Full Text Request