Owing to their immense potential in energy conversion and storage, catalysis, photocatalysis, adsorption, separation and life science applications, significant interest has been devoted to the design and synthesis of hierarchically porous materials. The hierarchy of materials on porosity, structural, morphological, and component levels is key for high performance in all kinds of applications. Synthesis and applications of hierarchically structured porous materials have become a rapidly evolving field of current interest. A large series of synthesis methods have been developed. This review addresses recent advances made in studies of this topic. After identifying the advantages and problems of natural hierarchically porous materials, synthetic hierarchically porous materials are presented. The synthesis strategies used to prepare hierarchically porous materials are first introduced and the features of synthesis and the resulting structures are presented using a series of examples. These involve templating methods (surfactant templating, nanocasting, macroporous polymer templating, colloidal crystal templating and bioinspired process, i.e. biotemplating), conventional techniques (supercritical fluids, emulsion, freeze-drying, breath figures, selective leaching, phase separation, zeolitization process, and replication) and basic methods (sol–gel controlling and post-treatment), as well as self-formation phenomenon of porous hierarchy. A series of detailed examples are given to show methods for the synthesis of hierarchically porous structures with various chemical compositions (dual porosities: micro–micropores, micro–mesopores, micro–macropores, meso–mesopores, meso–macropores, multiple porosities: micro–meso–macropores and meso–meso–macropores). We hope that this review will be helpful for those entering the field and also for those in the field who want quick access to helpful reference information about the synthesis of new hierarchically porous materials and methods to control their structure and morphology.

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Hierarchically porous materials: synthesis strategies and structure design

Nanoporous polystyrene monoliths were prepared from polystyrene−polylactide (PS−PLA) block copolymers that form hexagonally packed nanocylinders of PLA in a PS matrix. A morphology diagram was developed to determine the range in composition and molecular weight over which this morphology existed. Macroscopic alignment of these materials gave anisotropic monoliths that were subjected to mild degradation conditions leading to the chemical etching of the PLA. The resulting nanoporous monoliths consisted of a polystyrene matrix containing hexagonally close-packed, oriented, and continuous nanoscopic channels (pore size was tunable through synthesis or blending) lined with chemically accessible hydroxyl functional groups. Both the precursors and the porous materials were analyzed moleculary (size-exclusion chromatography and proton nuclear magnetic resonance spectroscopy) and structurally (small-angle X-ray scattering, scanning electron microscopy, and differential scanning calorimetry). In addition, the surfa...

Ordered nanoporous polymers from polystyrene-polylactide block copolymers.

https://ris.utwente.nl/ws/files/6817254/medical_applications.pdf

Medical applications of membranes: Drug delivery, artificial organs and tissue engineering

Polymer nano-foams for insulating applications prepared from CO2 foaming

Microcellular and nanocellular solid-state polyetherimide (PEI) foams using sub-critical carbon dioxide II. Tensile and impact properties

We report the formation of open nanoporous polymer films composed of homogeneous polysulfone/polyimide blends. Porosity is introduced by expansion of carbon dioxide-saturated films at elevated temperatures. To interpret details of the porous morphologies in terms of the experimental conditions during expansion, the glass transition temperature and carbon dioxide solubility of the dense film were examined at various blend compositions. We find that above a critical threshold of the carbon dioxide concentration the porous structure obtained changes from microcellular into open nanoporous. This critical carbon dioxide concentration is independent of the blend composition. Remarkably, it resembles the value previously reported on different polymers

K. Diekmann

Papers

Open nanoporous morphologies from polymeric blends by carbon dioxide foaming