Step by step guidance for formation of liquid marbles and hollow granules

Liquid marbles are micro reservoirs with promising technological applications in medicine, biotechnology, chemical and mechanical engineering and are attracting significant research attention. The unique properties of hollow granules made from liquid marbles are ideal for high-value applications in the pharmaceutical, food and cosmetics industries. In this study, liquid marbles were prepared from six mixtures of water and glycerol by releasing a droplet from different heights on a loosely packed powder beds of Aerosil R202 powder and different sizes of hydrophobic glass ballotini and PTFE spheres. Pictures of the liquid marbles were taken with a stereo microscope and the fraction of the surface covered with powder was analysed using image analysis. Selected powder-liquid combinations were also granulated for form liquid marbles and hollow granules in a lab-scale high shear mixer. Based on the experimental results, we propose a framework for liquid marble formation based on a physical flow mechanism for liquid marble formation. The framework presents step by step requirements for liquid marble formation via a preformed droplet template. Separate frameworks for the formation of a liquid marble via mechanical dispersion and for the formation of hollow granules were also developed. These frameworks give a better understanding of the controlling mechanisms during granulation of hydrophobic particles and provide guidance on how to mass produce liquid marbles and hollow granules.