Permeabilities and Retention Properties

The pore size of a membrane is manifested in the permeabilities and separation (retention) characteristics of the membrane. For gases, the pore size of the membrane also affects the prevailing transport mechanisms through the pores (see Chapter 6). 

Typically, the liquid permeabilities are obtained with water being the permeate and expressed in terms of L/h-m -bar. The gas permeabilities are often expressed in terms of air or nitrogen permeabilities. The retention characteristics can be generally and generically obtained by using some model molecules. The most commonly used model molecules are polyethylene glycol (PEG) polymers which are linear and flexible in nature, and 

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