Preparation of Hierarchically Structured Amorphous Carbon Monoliths with Closed Spherical Mesopores via the Lower Critical Solution Temperature Phase Transition

Some polymer mixture systems become immiscible above a specific temperature, the so‐called lower critical solution temperature (LCST). In this work, the LCST behavior of a mixture of poly(ethylene oxide)‐block‐poly(propylene oxide)‐block‐poly(ethylene oxide) triblock copolymers and phenolic resin oligomers is observed, and the corresponding phase transition is exploited to develop a facile route to hierarchically structured carbon monoliths. Whereas evaporation‐induced self‐assembly generates hexagonal channels in the monoliths, an additional phase transition at the LCST leads to an ordered arrangement of isolated pores. The fabrication method involves annealing the gel‐phased mixture with polymeric microbeads in a 3D‐structured mold at the LCST, followed by thermosetting and a carbonization process. The LCST phase transition behavior is observed experimentally by in situ small‐angle X‐ray scattering, optical transparency measurements, differential scanning calorimetry, and infrared spectroscopy. The fundamental mechanism of the LCST phase transition is further investigated by atomistic molecular dynamics simulations. A fabrication method for hierarchical carbon structures using lower critical solution temperature (LCST) is presented. Combining the colloidal self‐assembly of micro beads and macroscale molding, an additional phase transition at the LCST brings out hierarchically structured porous materials with a complex macrostructure. The fabricated hierarchical carbon monolith shows structures with four distinct length scales from the near‐atomic to the macroscopic level.