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Morphological Properties of Methacrylate-Based Polymer Monoliths: From Gel Porosity to Macroscopic Inhomogeneities

Müllner, Tibor, Zankel, Armin, Höltzel, Alexandra, Svec, Frantisek, Tallarek, Ulrich
Langmuir 2017 v.33 no.9 pp. 2205-2214
adsorption, mass transfer, polymers, porosity, scanning electron microscopy, silica
Shaping chemical interfaces of hard and soft matter materials into physical morphologies that guarantee excellent transport properties is of central importance for technologies relying on adsorption, separation, and reaction at the interface. Polymer monoliths with a hierarchically structured pore space, for example, are widely used in flow-driven processes, whose efficiency depends on the morphology of the support material over several length scales. Compared with alternative support structures, particularly silica monoliths, polymer monoliths yield lower efficiency, which suggests a suboptimal morphology. Based on physical reconstruction by serial block-face scanning electron microscopy we evaluate the structural features of a methacrylate-based polymer monolith from the pore scale to the column scale. The morphological data reveal a homogeneous polymer skeleton with a solute-impenetrable core–porous shell architecture and a heterogeneous macropore space that suffers from inhomogeneities at the short-range and the transcolumn scale. Although the morphology of the polymer phase is favorable to efficient mass transport, the performance of the polymer monolith is limited by severe transcolumn gradients in macroporosity and macropore size. We propose to overcome these morphological limitations by pursuing a preparation strategy that involves active rather than passive shaping of the macropore space, for example, by using silica monoliths as templating structures for polymer monolith preparation.