X-Ray Diffraction and Differential Scanning Calorimetry Studies of Crystalline and Amorphous Regions in Composite Porous Films

Abstract

A comparative analysis of the structural evolution of MGA-95 and ESPA1 polymer composite porous films is performed by plotting the radial distribution functions of atoms using empirical X-ray scattering intensity curves and the thermophysical parameters of melting are calculated using data from differential scanning calorimetry (DSC). In the case of the water-saturated MGA-95 sample, the atomic density in the first coordination sphere of the cellulose acetate macromolecule is shown to decrease due to the breaking of intramolecular hydrogen bonds. The atomic density of coordination spheres with radii corresponding to the lattice parameters decreased suggesting spatial disorder of the macromolecules. The DSC data for the MGA-95 film (the enthalpies of melting of the dry and water saturated samples are ΔH = 8.57 and 6.55 J/g, respectively) suggests that sorption of water molecules leads to a decrease in the degree of crystallinity due to a change in the crystalline fractions in the polycrystals. In the case of the ESPA1 composite film, a decrease in the radius and an increase in the atomic density of the first coordination sphere are indicative of the orientational disorder of amorphous phase molecules upon the sorption of water. The appearance of additional coordination spheres with R₂ = 3.88 and R₃ = 5.26 Å in the swollen ESPA1 sample suggests the quantitative redistribution of crystal phases in the substrate material. A detailed analysis of endothermic peaks on the DSC curve shows that the ratio of low- and high-temperature phases varies from 64% : 36% in the dry sample up to 51% : 49% in the water saturated sample at almost identical enthalpies of melting of ΔH = 12.18 and 11.66 J/g, respectively.