A perspective: Is viscosity the key to open the next door for foam templating?

Abstract

Macroporous polymers can be produced by curing liquid foam templates, which consist of air bubbles mechanically beaten into a liquid monomer phase. However, non-aqueous foam templates containing hydrophobic monomers as liquid phase are difficult to produce, as they cannot be stabilised by reducing their surface tension. In this perspective, we reviewed work on whipped foam templates with and without surfactant or particulate foaming agents. Once the liquid monomer phase has a suitable viscosity, froths with promising foam stability and foamability were produced. The average bubble size of the foam templates decreased with increasing viscosity of the liquid monomer phase. These foam templates were sufficiently stable to be polymerised to produce macroporous polymers with a porosity, average pore size and pore size distribution controlled by the viscosity of the monomer phase, rendering the polymer foams suitable for various potential applications. Therefore, it can be anticipated that solely the viscosity of the monomer phase is responsible to kinetically stabilise foam templates allowing for the production of macroporous polymers with well-defined properties. Tailoring the rheology of any monomer system is anticipated to be universally applicable to kinetically stabilise non-aqueous foam templates allowing for the production of useful macroporous polymers beyond the examples shown in this article, such as polyepoxides and polyacrylates. This will allow for further exploring the applicability of the foam templating technology to produce polymerizable liquid froths for printing and other shaping processes.