Imaging of 3D Complex Porous Membrane Structure in Nanoscale-Resolution with Ptychographic x-Ray Computed Tomography

3D imaging of porous materials can be now obtained with resolution in the nanoscale over large sampling volume. This is possible due to the highly coherent x-ray beams available in 4th generation synchrotron sources. New visualization methods can be utilized to resolve structures in resolutions that were previously unachievable. Here, we demonstrate how ptychographic x-ray computed tomography can be applied for the visualization of soft matter with a spatial resolution of 23.1 nm over large fields of view. Thanks to the high-penetration depth of the x-ray beam, we visualized 3D complex porous structure of polyetherimide hollow fibers in a non-destructive manner and obtained quantitative information about pore size distribution and pore network interconnectivity across the whole membrane wall. The reconstruction of the x-ray coherent diffraction patterns overlapping projection angles results in not only visualization of the complex porous morphology across the whole membrane wall volume, but also provides a detailed 3D quantitative model of the porous network with resolutions unprecedented for x-ray techniques and soft-matter samples. Apart from the porosity, we obtained the pore size of every single pore in the membrane within the resolution limits (23.1 nm), to evaluate the pore size distribution and its evolution across the entire membrane wall, from the shell to the lumen side. The presented PXCT method is not limited to the measurements of porous structures but can be used when the nanostructural details in the large sample volumes need to be resolved within the soft matter, without the need for sample modification for contrast enhancement and increasing stability. The non-destructiveness of the method and lack of requirement for high vacuum makes it useful within the fields of porous- and nano-material sciences enabling imaging in different environmental conditions.