Millimeter-sized capsules prepared using liquid marbles: Encapsulation of ingredients with high efficiency and preparation of spherical core-shell capsules with highly uniform shell thickness using centrifugal force.

Hypothesis: In our previous study, we prepared millimeter-sized spherical hard capsules by solidifying droplets of liquid monomer or polymer solution placed on superamphiphobic surface. Application of liquid marbles in place of the naked droplets for capsule preparation has a great potential to increase encapsulation efficiency of high volatile ingredients. Further, interfacial thermodynamic prediction of internal configuration of capsules from spreading coefficients may be effective to prepare core/shell capsule.

Experiments: Droplets of liquid monomer containing a volatile ingredient were rolled on superamphiphobic powders to prepare liquid marbles and solidified by photopolymerization. For preparation of core/shell capsules, the liquid marbles injected with an immiscible water droplet were also solidified.

Findings: A volatile ingredient could be encapsulated with higher efficiency than our previous method. Interfacial thermodynamic prediction of internal configuration of capsules from spreading coefficients indicated successful formation of core/shell capsules. However, photopolymerization of the liquid marbles in a static condition resulted in formation of not only core/shell capsules but also acorn-type capsules. Furthermore, the core/shell capsules were distorted and the shell thickness was not uniform. Rolling of the liquid marbles, which generated centrifugal force inside of the liquid marbles, was effective to prepare spherical capsules with highly uniform shell thickness.