Dongyu Cai

Making Non-aqueous High Internal Phase Pickering Emulsions: Influence of Added Polymer and Selective Drying

We report the first example of a non-aqueous (oil-in-oil) Pickering high internal phase emulsion (HIPE) stabilized by chemically modified fumed silica. In this case, a 75 vol % ethylene carbonate (EC)-rich internal phase is emulsified in 25 vol % p-xylene (xylene)-rich continuous phase using interfacial nanoparticles. It is revealed that no phase inversion takes place during the HIPE formation process when using the appropriate wettability of solid particles. Incorporating polystyrene (PS) into xylene enables one-step formation of PS-filled HIPEs in place of a multi-step polymerization of the continuous phase. We observe that the size of droplets changes with the addition of PS, and we associate this with the change in the viscosity of the continuous xylene-rich phase. Drying the pure HIPE results in the selective removal of xylene and coalescence of EC-rich droplets. With the PS in the xylene-rich continuous phase, we show that EC-rich droplets can be retained even though the xylene is evaporated off, and a new semi-solid composite containing both liquid phase and solid phase is formed via this non-aqueous Pickering-HIPE template.

Hybrid electrolytes with 3D bicontinuous ordered ceramic and polymer microchannels for all-solid-state batteries

Hybrid solid electrolytes, composed of 3D ordered bicontinuous conducting ceramic and insulating polymer microchannels are reported. The ceramic channels provide continuous, uninterrupted pathways, maintaining high ionic conductivity between the electrodes, while the polymer channels permit improvement of the mechanical properties from that of the ceramic alone, in particular mitigation of the ceramic brittleness. The conductivity of a ceramic electrolyte is usually limited by resistance at the grain boundaries, necessitating dense ceramics. The conductivity of the 3D ordered hybrid is reduced by only the volume fraction occupied by the ceramic, demonstrating that the ceramic channels can be sintered to high density similar to a dense ceramic disk. The hybrid electrolytes are demonstrated using the ceramic lithium ion conductor Li1.4Al0.4Ge1.6(PO4)3 (LAGP). Structured LAGP 3D scaffolds with empty channels were prepared by negative replication of a 3D printed polymer template. Filling the empty channels with non-conducting polypropylene (PP) or epoxy polymer (epoxy) creates the structured hybrid electrolytes with 3D bicontinuous ceramic and polymer microchannels. Printed templating permits precise control of the ceramic to polymer ratio and the microarchitecture; as demonstrated by the formation of cubic, gyroidal, diamond and spinodal (bijel) structures. The electrical and mechanical properties depend on the microarchitecture, the gyroid filled with epoxy giving the best combination of conductivity and mechanical properties. An ionic conductivity of 1.6 × 10−4 S cm−1 at room temperature was obtained, reduced from the conductivity of a sintered LAGP pellet only by the volume fraction occupied by the ceramic. The mechanical properties of the gyroid LAGP–epoxy electrolyte demonstrate up to 28% higher compressive failure strain and up to five times the flexural failure strain of a LAGP pellet before rupture. Notably, this demonstrates that ordered ceramic and polymer hybrid electrolytes can have superior mechanical properties without significantly compromising ionic conductivity, which addresses one of the key challenges for all-solid-state batteries.

Stabilizing bijels using a mixture of fumed silica nanoparticles

Bijels are typically prepared by arresting the phase separation of two liquids using interfacial particles. The surface treatment of the particles is challenging but can be overcome at a cost (Cui et al., Science, 2013, 342, 460-463). Here, we use mixed commercial fumed-silica nanoparticles, giving a facile route to bijel production.

Direct transformation of bijels into bicontinuous composite electrolytes using a pre-mix containing lithium salt

We report a general strategy for making bicontinuous conducting composite materials in a controllable fashion. Our approach begins with a bicontinuous interfacially jammed emulsion gel (bijel) fabricated from a pre-mix containing a salt, here bis(trifluoromethane)sulfonimide lithium salt (LiTFSI). The resulting structure has interpenetrating ionic conducting and non-conducting domains composed of an ethylene carbonate (EC)-rich phase and a p-xylene (xylene)-rich phase of roughly equal volumes. This is the first time that bijel fabrication has been carried out using a pair of partially miscible liquids whose phase behaviour has been modified due to the addition of salt. Diffusing polystyrene (PS) into the xylene-rich phase enables the facile formation of a PS-filled bijel in place of a multi-step polymerization of added monomers. Drying the bijel results in the selective removal of xylene, reducing the total sample volume without compromising the morphology of the EC domain. Electrochemical impedance spectroscopy of the composite electrolytes confirms the existence of ion conducting pathways.

Erratum: Bijels stabilized using rod-like particles

Correction for Bijels stabilized using rod-like particles by Niek Hijnen et al., Soft Matter, 2015, DOI: .