Microfluidic fabrication of novel polymeric core-shell microcapsules for storage of CO₂ solvents and organic chelating agents

Monodispersed polymeric microcapsules loaded with CO2 solvents or chelating agents were produced by capillary microfluidics by photopolymerisation of three different UV curable materials, 1,6-hexanediol diacrylate (HDDA), Norland Optical Adhesive (NOA) 81, and Semicosil® 949 UV A/B (PDMS). Polymerization of HDDA and NOA 81 started after exposure to UVA light for 5 s and was completed within a minute, as confirmed by continuous FT-IR. Corrosive aqueous solutions of tetraethylenepentamine and diisopropyl iminodiacetic acid were encapsulated with 100% efficiency into poly(HDDA) and cured NOA81 shells without any leakage during prolonged storage. Poly(HDDA) shells were mechanically more stable than cured NOA81 and PDMS shells and resistant to drying-induced shell buckling. NOA81 and PDMS capsules underwent morphological changes during freeze drying leading to the formation of dimpled and crescent-moon-shaped particles, respectively. The storage stability in a hypotonic solution and buckling resistance of PDMS shells were significantly improved by embedding carbon-based nanomaterials into PDMS matrix. The incorporation of 0.5 wt% multi-walled carbon nanotubes into PDMS matrix led to an increase in a Shore A hardness from 1.6 to 2.3. A uniform distribution of MWCNTs in the polymer network was confirmed by XRD. All fabricated shells were thermally stable up to the temperature of 300°C.