Characterization of asymmetry in microporous membranes by cross-sectional confocal laser scanning microscopy

Oftentimes, membrane morphology studies are done with scanning electron microscopy or transmission electron microscopy. One disadvantage of these techniques is that they retrieve only superficial information. To study the interior of a sample, the sample must be cut, and the integrity of the structure can be destroyed. In this contribution, we present data on membrane morphology characterization by confocal laser scanning microscopy (CLSM), a minimally invasive technique that utilizes optical, rather than mechanical, sectioning to provide three-dimensional imaging. CLSM was used to characterize symmetric and asymmetric membranes with nominal pore sizes in the range 0.22–8.0 μm. A standardized protocol for sample preparation and analysis by CLSM was developed for symmetric membranes to capture high resolution images at different depths. Optical sectioning of the membrane was performed at 0.4 μm intervals from the surface to the depth-of-penetration limit. To characterize the asymmetry in the thickness direction of membranes with thicknesses greater than the observed light penetration depth, we developed a new cross-sectional CLSM method involving membrane cryosectioning that enabled imaging of the entire membrane cross section. Concerns about surface artifacts due to sample preparation were avoided by imaging just below the surface of the membrane cross section. Finally, porosity was quantified as a function of depth for the symmetric and asymmetric membranes.

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► Cross-sectional CLSM imaging overcomes limits of light penetration depth (PD).
► Method enables characterization of asymmetry in membranes with thicknesses >2PD.
► Porosity was quantified versus depth throughout the full membrane thickness.