X-Ray analysis and other methods

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. 

There are other modern spectroscopic methods such as X-ray photoelectron spectroscopy (XPS), small angle neutron scattering (SANS), Raman spectroscopy (RS), electron spinning resonance (ESR) and nuclear magnetic resonance (NMR). These techniques are well known in the membrane field. Static secondary ion mass spectrometry (SSIMS), energy dispersive X-ray spectroscopy (EDS), laser confocal scanning microscopy (FCSM) and environmental scanning electron microscopy (ESEM) can also be added to new microscopic methods to characterize the membranes [84]. 

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Semicrystalline PVA is characterized by its degree of crystallinity which is defined as the ratio of the volume of PVA crystallites to the total volume of PVA. Density measurements, calorimetric methods, spectroscopic methods. X-ray analysis, and other methods such as NMR spectroscopy have been used to determine degrees of crystallinity of PVA hydrogels [32]. Using such methods, degrees of crystallinity were determined for PVA samples (Mc=4770) that were prepared under varying annealing conditions (Table 1). 

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