A quantitative framework for the formation of liquid marbles and hollow granules from hydrophobic powders

Liquid marbles are micro reservoirs of fluid surrounded by a powder shell. Their unique properties show promise for high-value technological applications in the medical, biotechnology, chemical and pharmaceutical industries. In this study, liquid marbles were prepared from six mixtures of water and glycerol by releasing droplets from different heights onto a loosely packed powder bed using a 1. mL syringe. Pictures of the liquid marbles were taken with a stereo microscope (SMZ series) with a 3MP Motic camera. The powders used were Aerosil R202, hydrophobic glass ballotini and PTFE spheres. In this paper, our previous proposed qualitative framework for liquid marble formation via solid spreading coefficient mechanism was updated in light of recent new research and the quantitative criteria for each step was established and validated. The last step of the framework was modified to reflect the physical flow mechanism now understood to be responsible for liquid marble formation. The revised framework presents the step by step process and quantitative criteria for liquid marble formation via a preformed droplet template. In addition, new frameworks for the formation of liquid marbles via the mechanical dispersion regime and for the formation of hollow granules were also developed and validated. These frameworks give a better understanding of the mechanisms controlling the granulation of hydrophobic particles to form liquid marbles and provide guidance on how to mass produce liquid marbles and hollow granules.