Semipermeable elastic microcapsules for gas capture and sensing

Monodispersed microcapsules for gas capture and sensing were developed consisting of elastic semipermeable polymer shells of tunable size and thickness and pH-sensitive, gas selective liquid cores. The microcapsules were produced using glass capillary microfluidics and continuous on-the-fly photopolymerization. The inner fluid was 5–30 wt % K2CO3 solution with m-cresol purple, the middle fluid was a UV-curable liquid silicon rubber containing 0–2 wt % Dow Corning 749 fluid, and the outer fluid was aqueous solution containing 60–70 wt % glycerol and 0.5–2 wt % stabilizer (poly(vinyl alcohol), Tween 20, or Pluronic F-127). An analytical model was developed and validated for prediction of the morphology of the capsules under osmotic stress based on the shell properties and the osmolarity of the storage and core solutions. The minimum energy density and UV light irradiance needed to achieve complete shell polymerization were 2 J·cm–2 and 13.8 mW·cm–2, respectively. After UV exposure, the curing time for capsules containing 0.5 wt % Dow Corning 749 fluid in the middle phase was 30–40 min. The CO2 capture capacity of 30 wt % K2CO3 capsules was 1.6–2 mmol/g depending on the capsule size and shell thickness. A cavitation bubble was observed in the core when the internal water was abruptly removed by capillary suction, whereas a gradual evaporation of internal water led to buckling of the shell. The shell was characterized using TGA, DSC, and FTIR. The shell degradation temperature was 450–460 °C.