Stereological-fractal analysis as a tool for a precise description of the morphology of hybrid alginate membranes

A precise description of the morphology of a material is necessary in order to establish structural and functional relationships. Tools for morphological analysis should be quantitative techniques, which would yield objective and reproducible values for any morphological structure and enable statistically defined comparisons. The combination of the stereological analysis and fractal analysis provides the researchers with such a tool. This work investigated hybrid alginate membranes filled with various amount of magnetite (Fe₃O₄) and crosslinked using four different agents, i.e. calcium chloride (AlgCa), phosphoric acid (AlgP), glutaraldehyde (AlgGA) and citric acid (AlgC). Alginate membranes can be used to dehydrate ethanol in the process of pervaporation. The morphology of studied membranes was characterized on the basis of the image analysis of the membrane cross sections obtained from a scanning electron microscope Phenom Pro-X. The quantitative analysis of the structure and morphology of the above-named materials was conducted by using a new tool: stereological-fractal analysis (the so-called SFA method). The SFA method was based on the shape descriptors (elongation factor, surface factor, irregularity parameter and bulkiness), fractal dimension, generalized fractal dimension and lacunarity. In relation to the membranes subjected to the tests, it was possible to identify the correlation between transport properties (pervaporation separation index (PSI)) and morphological parameters. The use of a comprehensive analysis made it possible to determine the morphology of the membrane with the best separation properties.