Preparation techniques for composite membranes

Dense homogeneous polymer films can separate various gaseous or liquid mixtures very effectively. However, normal thicknesses (20 - 200 pm) lead to very low permeation rates. Such membranes cannot be made thin enough (of the order of 0.1 to 1 pm) to improve permeation because they are very difficult to handle (no mechanical strength), and also because such thin layers need to be supported. 

Several techniques can be used to apply an (ultra)thin toplayer upon a support  

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