The Quest for Contrast in Digital Images of Micro/Nano Structured Polymer Blends Before and After CO₂ Foaming: Impact of Block Copolymer Content and Size Upon Acrylic Cellular Structures

This work addresses the structural quantification of multiphase materials, here nanostructured polymer solid precursors and their micro/nano sized foamed counterparts. It is based on a strategy of contrast/edge enhancement, locally adaptive to image data in digital images of materials. The method allows to binarize straightforwardly the structures (the phases) in TEM and SEM images after edge identification, edge choice, and image virtual reconstruction. A detailed insight is brought into one-step batch supercritical CO₂ foaming of acrylic amorphous PMMA (polymethyl methacrylate) polymers, aided by the nanostructuration of block copolymers (BCP), here MAM (butyl acrylate center block methyl acrylate side blocks). The foaming conditions, i.e., pressure drop rate (PDR) and saturation temperature required for an actual one-step procedure are specified and clarified, whereas previous works, dealing with "one-step procedures", are probably incurring in a two-step procedure. The roles of the BCP content (and size) and saturation temperature are carefully analyzed and further clarified, more comprehensively than in previous literature. Thanks to the analysis of size distributions of foams and foam blend precursors (0.25, 0.5, 10 wt% MAM), bi modality of 10 wt% foams is for example revealed. A discussion of kinetics effects, i.e., evolutions of the effective sample temperature T_ef(t), and the effective glass transition temperature T_{g, ef}(t). provides a new insight of "pseudo" one-step VS "real" one-step batch foaming.