Fabrication and drying of CNC-based microcapsules with PDMS/antimicrobial oil cores via the microcapillary device
Cellulose nanocrystals (CNC) which are the crystalline regions of elementary microfibrils found in cellulose are becoming a promising biocompatible nanoscale building block. We report on the generation, evolution, and drying of CNC capsules with oil cores, obtained from double emulsion drops. Microcapillary devices were used to generate the double emulsion drops with outer diameters ranging from 75 to 225 µm, and shell thicknesses ranging from 5 to 60 µm. 10 wt% aqueous CNC suspensions without and with the addition of PEGDA, a UV-crosslinkable binder, were used as the shell material while 10 cSt PDMS oil was used in the core. Drops were dispersed in 10 cSt PDMS oil. The evolution of the CNCs in the shell was tracked as a function of time in an optical microscope operated in bright field mode and under crossed polarizers. Soon after double emulsion generation, a fraction of the CNCs adhere to the inner and outer oil/water interfaces providing enhanced drop stability and influencing the assembly of the CNCs in the shell. Before drying, an anisotropic chiral nematic phase forms that occupies 30 to 38% of the shell volume. During drying the CNC volume fraction increases forming a shell with a non-uniform thickness due to the difference in densities between the inner and outer drops. The addition of PEGDA increased the strength of the capsules but delayed the anisotropic phase onset. A flowing UV-crosslinking method for the CNC-PEGDA capsules improved their strength and shape when compared to stationary UV-crosslinking. Finally, the encapsulation of antimicrobial oils in CNC-PEGDA capsules was also demonstrated.
Martinez, Purdue University.
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