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 active layer membranes, has been investigated using small-angle neutron scattering. These membranes are known to have structural and functional similarity to the surface or "skin" layer in commercial reverse-osmosis (RO) membranes and hence are useful model systems for understanding the structure of the RO membrane skin layer. Active layer membranes were studied after swelling them with either DzO or CD30D. The results in both cases clearly indicated the presence of very small (10-20 A) porous structures in the membrane. The presence of such pores has been a subject of long-standing controversy in this area. The data was analyzed using a modified Debye-Bueche analysis and the resultant membrane structure was seen to agree well with structural information from electron microscopic studies. Finally, a possible explanation for the differences in scattering observed between the DzO swollen membranes and the CD30D swollen membranes has been presented.