Crystallinity, percentage membrane

Hickey and Peppas showed that diffusion of solutes from a PVA cryogel membrane is related to the mesh size, which is roughly related to the percentage crystallinity. Also, there is a size exclusion phenomenon present as a result of the presence of the crystallite network. The solute diffusion coefficient for theophylline and FITC-dextran was determined to be dependent on the mesh size [61]. 

Knowledge of crystalline morphology is essential in understanding the permeability and permselectivity of polymer membranes such as dense membrane, dialysis membrane and gas separation membrane. X-ray is very common to study the crystallinity in polymeric membranes. Crystalline structure of a polymer membrane includes dimensions of unit cell, percentage of crystallinity, crystallite size, and orientation. The most generally applicable technique that provides information is the X-ray diffraction method. 

To increase the percentage of uranium-235 in a sample of uranium (a process called enrichment), one first prepares uranium hexafluoride, UF, a white, crystalline solid that is easily vaporized. Uranium hexafluoride vapor is allowed to pass through a series of porous membranes. Each membrane has many small holes through which the vapor can effuse. Because the UFe molecules with the lighter isotope of uranium travel about 0.4% faster than the UF molecules with the heavier isotope, the gas that passes through first is somewhat richer in uranium-235. When this vapor passes through another membrane, the uranium-235 vapor becomes further concentrated. It takes many effusion stages to reach the necessary enrichment. 

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