ABSTRACT
When the permeant molecules are retained in the membrane, they are confined in the space created between polymer molecules. The space should be penetrating from one side of the membrane to the other, since the permeant molecule can permeate through the membrane, under the influence of a driving force. Microscopic technique is one method of physically proving the asymmetric structure of the membrane. Keilin is the first person who attempted to observe the cross-sectional structure of the membrane, by a dyeing method. Scanning electron microscopy offers higher magnification than optical microscopy, extending the resolution down to the nanometer level. The first electron micrographic picture of a cellulose acetate membrane was taken by Riley et al. A cellulose acetate membrane was dried and shadowed in a vacuum deposition chamber with palladium from a 20° angle.
