CERAMICS Unidirectional solution-based freeze cast polymer- derived ceramics: influence of freezing conditions and templating solvent on capillary transport in isothermal wicking Daniel Schumacher 1 , Pedro Henrique da Rosa Braun 1 , Michaela Wilhelm 1, * , and Kurosch Rezwan 1,2 1 Advanced Ceramics, University of Bremen, Am Biologischen Garten 2, IW3, Bremen, Germany 2 MAPEX—Centre for Materials and Processes, University of Bremen, Am Fallturm 1, Bremen, Germany Received: 30 November 2019 Accepted: 14 December 2019 Ó Springer Science+Business Media, LLC, part of Springer Nature 2019 ABSTRACT Porous SiOC monoliths were prepared by solution-based freeze casting of polysiloxane at constant freezing temperature or constant freezing front veloc- ity. Dendritic and prismatic pore structures were obtained by using cyclohexane and tert-butyl alcohol as solvent, respectively. Gradients in freezing velocity lead to gradients in pore window size, whereas a constant freezing velocity (3.3–6.8 lm/s) generates homogeneous pore structures. The water permeability varies from 1.12 9 10 -13 to 1.03 9 10 -11 m 2 and correlates with the pore win- dow diameter (10–59 lm) and the porosity (51–82%). In wicking tests, the gra- dient in pore window size is clearly reflected by a pronounced decrease in the wicking speed. Contrary, a homogeneous pore structure results in wicking curves which are closer to the prediction according to the Lucas–Washburn equation. However, this theoretical approach based on the three parameters, pore window size, porosity and permeability, is insufficient to describe complex three-dimensional pore structures. Besides the porosity, the pore morphology was found to be a major influencing factor on the wicking. The filling of sec- ondary dendrites slows down the wicking into the dendritic structure. Fastest wicking was observed for a prismatic pore structure at low freezing front velocity (6.6 lm/s) and high porosity (78%), whereas slowest wicking occurred into the dendritic structure with high porosity (76%) and constant freezing temperature (- 20 °C). The knowledge of the relationship between structural properties and the resulting wicking behavior can address a variety of pivotal applications in chemical engineering for capillary transport. Address correspondence to E-mail: mwilhelm@uni-bremen.de https://doi.org/10.1007/s10853-019-04310-0 J Mater Sci Ceramics