We present a generic and versatile low-temperature route to produce macroporous bodies with porosity and pore size distribution that are adjustable in a wide range. Capillary suspensions, where the minor fluid is a monomer, are used as precursors. The monomer is preferentially located between the particles, creating capillary bridges, resulting in a strong, percolating network. Thermally induced polymerization of these bridges at temperatures below 100 °C for less than 5 h and subsequent removal of the bulk fluid yields macroscopic, self-supporting solid bodies with high porosity. This process is demonstrated using methyl methacrylate and hydroxyethylmethacrlyate with glass particles as a model system. The produced poly(methyl methacrylate) (PMMA) had a molecular weight of about 500,000 g/mol and dispersity about three. Application specific porous bodies, including PMMA particles connected by PMMA bridges, micron-sized capsules containing phase change material with high inner surface, and porous graphite membranes with high electrical conductivity, are also shown.
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The authors would like to thank Jonas Keller and Christoph Pfeifer for fruitful discussions, as well as Carolyn Benner for contributing of physical properties of Micronal PCM materials and Frank Schultz and Stefanie Stadler from Freudenberg Technology Innovation SE for μ-Tomography images. Furthermore, we would like to thank Volker Zibat from LEM for SEM and 3M for providing glass hollow spheres iM16K, as well as BASF SE for providing the Micronal DS particles and Altuglas International for providing the PMMA particles. Additionally, we would like to acknowledge financial support from the European Research Council under the European Union’s Seventh Framework Program (FP/2007-2013)/ERC Grant Agreement no. 335380.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no competing interests.
Example for SEC analysis of the molecular weight distribution for a bridge sample extracted after polymerization of a capillary suspension with 40 vol % solid fraction and 6 vol % MMA at 84 °C for 5 h with 15 mg/ml BPO. (GIF 29 kb)
The atomic composition of both the neck and the particle surface of porous materials made of hydrophilic glass spheres (Φsolid = 40 vol %) and HEMA as secondary phase (ΦHEMA = 4 vol %) using Energy-dispersive X-ray spectroscopy (EDX) in the ESEM-mode. The samples were polymerized in paraffin oil with 15 mg BPO/ml HEMA at 82 °C for 2.5 h and afterwards extracted with hexane. (GIF 133 kb)
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