INVESTIGATION OF THE PORE STRUCTURE AND MORPHOLOGY OF CELLULOSE-ACETATE MEMBRANES USING SMALL-ANGLE NEUTRON-SCATTERING .1. CELLULOSE-ACETATE ACTIVE LAYER MEMBRANES

The structure of ultrathin cellulose acetate membranes, known as activ e layer membranes, has been investigated using small-angle neutron sca ttering. These membranes are known to have structural and functional s imilarity to the surface or ''skin'' layer in commercial reverse-osmos is (RO) membranes and hence are useful model systems for understanding the structure of the RO membrane skin layer. Active layer membranes w ere studied after swelling them with either D2O or CD3OD. The results in both cases clearly indicated the presence of very small (10-20 Angs trom) porous structures in the membrane. The presence of such pores ha s been a subject of long-standing controversy in this area. The data w as analyzed using a modified Debye-Bueche analysis and the resultant m embrane structure was seen to agree well with structural information f rom electron microscopic studies. Finally, a possible explanation for the differences in scattering observed between the D2O swollen membran es and the CD3OD swollen membranes has been presented.