Controlled microporosity in reverse osmosis membranes by template molecule inclusion

• Published in: Journal of colloid and interface science 1966-01, Vol.22 (6), p.588-598
• Main Authors: Baddour, R.F., Vieth, W.R., Douglas, A.S.
• Format: Article
• Language: English
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/0021-9797(66)90053-1

The effect of including a template molecule, tellurium tetrabromide, on the structure and reverse osmosis properties of cellulose nitrate membranes was studied. The effect of tellurium tetrabromide content in the range from 0 to 41 vol.% on the reverse osmosis transport of water and salt was determined at an applied pressure of about 1800 p.s.i., using 4 wt.% sodium chloride solutions. The effects of pressure and temperature were also studied, with the use of membranes having template inclusions in the range of 20 to 27.8 vol.%. Below 7.5%, the tellurium tetrabromide probably exists as isolated groups of molecules surrounded by compact polymer. From 7.5% to 26.5%, the tellurium tetrabromide apparently creates pores in the film which permit water to diffuse but which restrain dissolved ions, either because the pores are too small or because they are interrupted by thin films. The water is probably transported by diffusing from hydrogen-bonding site to hydrogen-bonding site along the pore. Calculations indicate that only about 5% of the TeBr 4 which is present is effective in making useful pores. The remainder is in regions which do not contribute to the water flow. Above 26.5% TeBr 4 content, some larger pores are formed which permit the hydrodynamic flow of undiluted brine. These large pores arise from the preparation technique, since above 26.5% TeBr 4 gross structural disruptions of the polymer are required in order to accommodate all the TeBr 4.