ABSTRACT
The effect of LCVD reaction time is depicted in Figure 34.18, which shows the decline of performance after passing the maximum as observed with many LCVDprepared membranes. In reverse osmosis membrane, the increase of flux as salt rejection declines was not observed. Figure 34.18 plots water flux vs. salt rejection for a series of acetylene/CO/H2O discharge polymer membranes on cellulose nitrate/ cellulose acetate (CNCA) porous membrane. The results bear three important observations: First, good reverse osmosis membranes can be produced by CNCA with acetylene/CO/H2O plasma. Second, much shorter deposition times are sufficient for this system, reflecting the fact that carbon monoxide is incorporated with ease. For instance, deposition time of only 2min results in membranes with salt rejection around 94% and with water fluxes of 32 gal/ft2 day (gfd). Lastly, prolonged plasma reaction times have negative effects on the salt rejection properties of the membrane. This trend is generally observed in every kind of application of LCVD.
