General Background Membrane Types and Structures

A membrane can be described as a semipermeable barrier between two phases which prevents intimate contact. This barrier must be permselective which means that it restricts the movement of molecules in it in a very specific way. The barrier can be solid, liquid or gas. Permselectivity can be obtained by many mechanisms  

Differences in diffusion coefficients (bulk as well as surface) 

Differences in adsorption and/or reactivity on (internal) surfaces With R. R. Bhave. 

The flux of liquids or gases through the membrane is in most cases driven by a pressure gradient and sometimes by an electric field gradient. Membranes can be used for  

Separation of mixtures (liquids, gases or liquid-solid mixtures can be separated). 

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