Preparation of Composite Reverse Osmosis Membranes by Plasma Polymerization.

摘要

Composite reverse osmosis membranes are formed by plasma polymerization onto a porous substrate. An inductively coupled system is used with the substrate in a fixed position relative to the monomer inlet and to the coil supplying power to the system. Deposition rate is independent of power if one works with the 'full glow'regime. The chemical nature of the polymer is also independent of power over a wide range. A system is described for a study of the effect of the chemical nature of the monomer(s) on the physical and chemical properties of the plasma polymer formed. The chemical nature of the polymer,the concentration of trapped free radicals,its stability,permeability,surface energy and internal stress can be controlled by choice of monomer(s). Composite reverse osmosis membranes are formed using a porous polymeric film substrate in the inductively coupled system using nitrogen containing monomers or a combination of a hydrocarbon plus nitrogen or carbon monoxide. Up to 99.5% salt rejections from 3.5% NaCl at 1500psi have been achieved together with high water fluxes. Good salt rejection accompanied by resistance to chlorine has been found using CO as a comonomer. The effects of pretreatment of the substrate with nonpolymerizing nitrogen followed by coating using nitrogen as a comonomer is to increase salt rejection at the expense of chlorine resistance. A method of measuring porosity in dry membranes was developed and the porosity of composite membranes was measured and related to their salt rejection. The shift from hydraulic to diffusive water permeability with increasing salt rejection has also been demonstrated. Preliminary studies have been carried out using hollow fibers which move through the plasma using both an inductively coupled system and a capacitively coupled system with internal electrodes.