The production
of microcapsules by electrospraying two immiscible liquids from oppositely
charged parallel nozzles and the subsequent microcapsule collection constitute
an electroencapsulation process influenced by numerous parameters. The electroencapsulation
parameters include the liquid properties, e.g.
bulk liquid conductivity K, viscosity η, density ρ, and surface tension γ; the electric field, gravity
field, and the electrospraying and collection geometries; and the atmospheric
properties. In the present work, NaI-doped glycerol was used as core liquid,
with an optional payload of dispersed thermally carbonized porous silicon
nanoparticles (PSi). Chloroform with dissolved Eudragit E 100
cationic copolymer and dispersed talc particles as an anti-tacking agent was
used as shell liquid. The influence of varying ten electrospraying parameters
(liquid flow rates Q_i,
electrospraying voltages |U_i|
and polarity, solid concentrations, and temperature T) within the cone-jet mode regime on the structure and yield of
microcapsules produced by parallel nozzle electroencapsulation was investigated
simultaneously using the Taguchi robust design method. Of the investigated
parameters, the most important were found to be NaI concentration and T, both influencing the core liquid
conductivity; and the liquid flow rates. The Taguchi experiment and additional
results suggest that optimally, the parameters affecting liquid conductivities
should be set for a coarse atomization current balance when using a maximal shell
liquid flow rate. Then, the core liquid flow rate can be adjusted for best
process efficiency.