Macroporous Polymers with Hierarchical Pore Structure from Emulsion Templates Stabilised by Both Particles and Surfactants

Abstract

Inspired by natural porous materials, such as wood, bamboo and spongy bone consisting of individual structural units that are hierarchically arranged to optimise mechanical properties such as strength and toughness, synthetic macroporous polymers with enhanced physical properties were created by emulsion templating. Hierarchical poly(merised) high internal phase emulsions (HIPE) were created from HIPEs stabilised simultaneously by particles and a surfactant. In these HIPEs, surfactant stabilised and particle stabilised water droplets coexist, which upon polymerisation of the minority oil phase gives rise to macroporous polymers with a hierarchical pore structure. An improvement of the mechanical properties of our hierarchically structured macroporous polymers at equal porosity was observed, due to a more efficient packing of pores in a configuration that improves mechanical strength despite the presence of interconnecting pore throats. Moreover, the permeability of the hierarchically structured polyHIPEs are exceeding those measured for conventional polyHIPEs made from surfactant only stabilised HIPEs.

Highly permeable macroporous polymers via controlled agitation of emulsion templates

“…The technique developed and described by Manley et al [4,7,30] was used for measuring the gas permeability of the macroporous polymers. After removal from the 15 ml centrifuge tubes the macroporous polymer cylinders (≈14 mm in diameter) were coated using Araldite® rapid adhesive in order to seal the sides of the monolith against cross flow.…”

“…This would lead to much larger pores than the original droplet size in the emulsion immediately after blending making it much less trivial to predict pore size of macroporous polymers produced by emulsion templating. Ostwald ripening (coarsening) [29] can also occur within the system leading to a hierarchal pore system, in which much larger pores are embedded in between much smaller ones [30,31]. The rate of coalescence in emulsions was observed to increase at elevated temperatures [32] needed to typically initiate a free-radical polymerization.…”

Synthesis and characterization of polyHIPE composites containing halloysite nanotubes

“…This result is highly similar with the morphological properties of polyHIPE composites synthesized with constant 3 vol% surfactant concentration which were discussed in the supplementary material file. The formation of such hierarchical structures could be attributed to usage of nanoparticle and surfactant simultaneously for the stabilization of the HIPE system as reported in the literature (30).…”

Robust macroporous polymers: Using polyurethane diacrylate as property defining crosslinker

“…A number of acrylates for example, butyl acrylate [33], ethylhexyl acrlylate and ethylhexyl methacrylate [34], has been used to improve the mechanical properties of polyHIPEs while reducing their brittleness. In our previous work, we dramatically reduced the brittleness of styrene based polyH(M)IPEs simply by replacing the stiff crosslinker divinylbenzene by the more flexible, long-chain crosslinker polyethylene glycol dimethacrylate (PEGDMA) [15,17,20,35]. Pulko et al [36] prepared bendable poly-HIPE membranes based on glycidyl methacrylate, ethyleneglycol dimethacrylate and ethylhexyl methacrylate.…”

“…In order for polyHIPEs to reach their full potential it became increasingly important to be able to tailor their mechanical performance to the needs of specific applications. We focused on improving the mechanical properties of emulsion templated macroporous polymers by increasing their foam densities, namely making polymerised medium internal phase emulsions (polyMIPEs) [15,16] and by creating hierarchical pore structures [17,18]. Furthermore, the synthesis of polyHIPE nanocomposites provides an alternative to improving their mechanical properties.…”