Various applications require macroporous materials with high permeability and a significant compressive strength. For instance, the oil servicing industry is interested in utilizing a liquid medium that can be placed within the annulus between the oil bearing natural formation and a screen wrapped perforated pipe, which turns into a macroporous permeable and mechanically stable solid during a curing step. [1] The minimum requirements for the solid macroporous material are a permeability of 1 D (10 -12 m 2 ) and a compressive strength ≥ 3.5 MPa. This challenge could be addressed by employing high internal phase emulsions (HIPE), whose continuous phase consists of monomers, as a template to produce macroporous polymers, commonly known as poly(merized)HIPEs, [2] with a well defined controllable pore structure.However, conventional polyHIPEs synthesized from surfactant stabilized water-in-oil (w/o) HIPEs have poor mechanical properties [3, 4] and low permeabilities [5] due to the rather small pore and pore throat sizes. [2] Here we present a new approach for synthesizing polyHIPEs with much higher permeabilities and sufficient mechanical properties. We utilize the ability of w/o particle-stabilized HIPE templates (Pickering-HIPEs) to produce closed-cell macroporous polymers with large pores as reported recently by us. [6] We demonstrate that small amounts of

High Internal Phase Emulsions (HIPEs) are important for a wide range of applications in the food, cosmetic, pharmaceutical and petroleum industries. [1] If the continuous phase is polymerizable, HIPEs can be used as templates [2] for the synthesis of highly porous polymers with potential applications as low weight structures or scaffolds in tissue engineering. [3] HIPEs are characterized by a minimum internal phase volume ratio of 0.74 [2] but Lissant first defined this minimum as 0.7. [4] HIPEs consisting of a continuous organic phase and an internal aqueous phase (w/o emulsion), are commonly stabilized by large amounts of surfactants. [5] Particle-stabilized emulsions also known as Pickering-emulsions have recently attracted much interest. [6] Unlike surfactants, particles irreversibly adsorb at the interface of emulsions due to their high energy of attachment which makes them good emulsifiers. [7] The ability of particles to adsorb at the interface between the two phases is primarily dependent on the wettability of the particles. [8] Hydrophilic particles such as metal oxides tend to stabilize o/w emulsion while hydrophobic particles such as carbon tend to stabilize w/o emulsions. [9] Nevertheless, it is possible to modify the wettability of particles by adsorbing surfactant molecules onto the particle surfaces [10] or by silanation. [11] All reports on particle-stabilized emulsions deal with emulsions having internal phase levels elow 70 vol.-%. Kralchevsky et al. [12] developed a thermodynamic model, which predicts that * Financial support of the Challenging Engineering Programme (EP/E007538/1) of the UK Engineering and Physical Science Council (EPSRC), Halliburton Energy Services and an ORS Award is greatly acknowledged.2 particle-stabilized emulsions will phase invert above internal phase volume fractions of 0.5 but added that experimentally, phase inversion is observed at volume fractions of 0.7 due to kinetic factors. Binks et al. [11] further stated that particle stabilized emulsions phase invert between volume fractions of 0.65 and 0.7 meaning the majority phase becomes the continuous phase.We report on the stabilization of Pickering-HIPEs with volume fractions up to 0.92, using silica nanoparticles (SP), which have been hydrophobized by adsorption of oleic acid (OA) in order to use them as emulsifier for w/o HIPEs. We studied the influence of the particle concentration on the emulsion stability, the droplet size and the upper limit of the internal phase volume fraction within the emulsion. Furthermore, we polymerized the Pickering-HIPEs to produce highly porous poly-Pickering-HIPEs (PPH).Hydrophilic SP (20-100 nm in diameter) were functionalized by adsorption of OA. The OA content of the functionalized SP was determined by TGA to be 3.5 wt.-%. Binks and

Porous polymer foams (poly-Pickering-HIPEs) have been synthesised from stable high internal phase emulsion templates solely stabilised by low concentrations of functionalised titania nanoparticles.

Particle-stabilized high internal phase emulsions have been used to synthesize tough and very high porosity macroporus polymers with a closed-cell pore structure. In this study, we show that Pickering water-in-oil emulsion templates with up to an 85 vol % internal phase can be stabilized by only 1 wt % of titania particles with their surfaces suitably modified by the adsorption of 3.5 +/- 0.5 wt % oleic acid. The pore structure and mechanical properties of the resulting macroporous polymers were tailored by altering the internal phase volume ratio of the emulsion template and the titania particle concentration used to stabilize the emulsion templates. The pore size and pore size distributions increase with increasing internal phase volume of the emulsion template as well as decreasing titania particle concentration used to stabilize the emulsion template. The mechanical properties, namely, Young's modulus and the crush strength of the macroporous polymers, increased with decreasing porosity and increasing foam density. The toughest macroporous polymer had the lowest porosity but also the smallest pore size and narrowest pore size distribution.

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