The structure of cellulose acetate membranes for reverse osmosis. Part 2. Transmission and scanning electron microscopy of membranes cast from an acetone-formamide dope

A study was made of the structure of membranes cast from the Loeb-Manjikian acetone-formamide dope by transmission and scanning electron microscopy, and of the general problem of preparation of specimens and interpretation of electron micrographs of polymer membranes.The formation of the membrane structure during casting of cellulose acetate membranes is discussed in relation to the evaporation time during the casting step. A 3-layer membrane structure is observed similar to that in membranes cast from a dioxan-based dope (1), and it is thought to have similar origins in the casting process. It is concluded that both transmission and scanning microscopy are required for a detailed analysis of all aspects of membrane morphology. Transmission microscopy reveals more information on the “active” surface layer while scanning microscopy is shown to reveal more of the texture of the bulk of the membrane.