Particle stabilized liquid-air mixtures near the phase inversion point: Partial bicontinuity and phase inversion into...

Particle stabilized liquid-air mixtures formed by high-speed mixing can undergo phase inversion from liquid-in-air droplets to air-in-liquid foams as the three-phase contact angle decreases. Here, we show that highly bicontinuous interfacially jammed air-liquid mixtures similar to bijels can form in the transitional range where phase inversion occurs. This range can easily be approached e.g., via addition of a surfactant. The materials also contain coexisting air bubbles and liquid droplets. Upon aeration by shaking, the materials can be converted into stable air-in-liquid-in-air "foam capsules" or simpler liquid-in-air "dry liquid" capsules with sizes controllable from around 1 mm to <100 µm. This partial phase inversion method allows creation of dry liquid capsules with as little as 0.5 wt% fumed silica particles, notably lower than the 2 wt% achievable with conventional preparation method, i.e., high-speed mixing. Furthermore, these capsules exhibit greater sphericity, narrower droplet size distribution, and smaller size compared to those produced by conventional high-speed mixing method.