where D is the crystalline domain size, λ is the wavelength of the radiation (nm), θ is the angle of the considered Bragg reflection, b is the width on a 2θ scale, and k is a dimensionless constant (close to unity). Hence, larger FWHM values indicate a small long-range order. PEI- : The peak position, full width at half maximum (FWHM) and crystallinity degree based on the PXRD patterns of PEI-33%-C16 samples. These evaluations involved removing the amorphous contribution and using the Pearson VII function adjusted in the Origin Lab software package. In addition, coherent length estimation was facilitated by applying the Scherrer equation.