Porous materials that have an interconnected network of pores are an interesting class of materials and have drawn attention in the area of separation science. The ability to fabricate robust so-called open cellular materials with control of the porosity remains a scientific challenge. The ability of regulating the interconnected network determines how a fluid (liquid or gas) can flow through the system. Think for example of how water runs through soil, or how water can be taken up through capillary action into a sponge. In addition, one can foresee that matter which flows through the porous material can temporarily be adhered/adsorbed onto the surface of the porous monolithic structure. The ability to easily control the surface functionality of the walls of the pores therefore is important.
In collaborative work with Chris Desire, a talented PhD student from the group of prof. Emily Hilder at the University of South Australia, we in the BonLab describe in Green Chemistry that we can use polymer latex particles as colloidal building blocks to form robust open cellular porous monolithic materials by simply stacking them onto each other. This assembly process is triggered by colloidal instability of a polymer latex dispersed in water which leads to the formation of a colloidal gel. The structure of the gel can then be made permanent by cross-linking through polymerization.
Schematic representation for the formation of crosslinked colloidal gels from oppositely charged latex particles prepared from the soap-free emulsion polymerisation of styrene using different initiators (Strategy 1) or from the addition of electrolyte to a cationic polymer latex (Strategy 2).
The pore size of the resulting monoliths was predictable as this was observed to directly correlate to the particle diameter, with larger pores achieved using particles of increased size. All gels obtained in this work were highly mouldable and retained their shape, which allowed for a range of formats to be easily prepared without the requirement of a mould.
Our innovation is applicable for the preparation of polymer monoliths for a wide variety of applications, including but not limited to, tissue engineering, catalysis, chromatography, extraction, sample preparation, and as absorbents. In particular these monoliths were found to posses relatively high porosities and were capable of rapidly absorbing solvents of varying polarity by capillary action, which suggested their applicability for thin layer chromatography (diagnostics) and extraction.
The original paper is published in Green Chemistry DOI:10.1039/C8GC01055B