Three-dimensional characterization of polymeric micro- and nanoporous materials using SEM photogrammetry

Understanding the three-dimensional (3D) structure of polymeric porous materials is essential for assessing their functional properties. Traditional imaging methods, such as micro-computed tomography ( μCT ), although effective for microporous materials, often fall short in resolving features at the nanoscale. Furthermore, for open-pore porous materials, conventional 2D scanning electron microscopy (SEM) imaging is limited, as it provides only projected information that does not accurately capture pore connectivity, orientation, and true geometry. SEM photogrammetry emerges as a promising approach for reconstructing the three-dimensional morphology of porous polymers. By capturing multiple SEM images at several angles, it enables quantitative volumetric characterization of microporous structures and provides qualitative nanoscale surface information for materials with pore dimensions in the nanoscale, showing potential for improvement in cryogenic conditions. The technique allows for assessing parameters such as the pore size distribution, anisotropy, porosity of the gaseous phase, or tortuosity and fraction of mass in the struts for the solid phase. This study evaluates the capabilities and limitations of SEM photogrammetry by characterizing the structure of three distinct polymeric materials: low-density polyethylene (LDPE) and polyurethane (PU) as microporous materials, and polymethyl-methacrylate (PMMA) as a nanoporous material. The results of PU are compared with those of μCT . In particular, for open microporous structures, the approach demonstrates a significant improvement over conventional image-based analysis, allowing a more precise and physically meaningful description of the pore network, while keeping a consistency similar to the one obtained from μCT .