Observation of the liquid marble morphology using confocal microscopy

The structure of the hydrophobic powder shell of a liquid marble is investigated in this study. Although the liquid marble morphology has been investigated using various forms of microscopy, the cross-sectional structure and the thickness variation of the shell have not been examined in detail due to the incapacity to view the cross-sectional plane of the liquid marble or low resolution images. In this work we employed a confocal microscopy approach to visually reveal and measure the shell structure of the liquid marble using confocal microscopy. The confocal microscopic imaging allows for the signal from out-of-focus planes to be eliminated and give a more in-depth view of the internal structure of a liquid marble from the in-focus plane. The 2D cross-sectional plane images or/and 3D images provide new visual insights of liquid marble shell morphology. Image reconstruction and analysis enables the measurement of the extent of particle penetration into the liquid core. From the investigation, it was found that the liquid marble shell consists of mainly fine particle multi-layers which facilitate the liquid core in avoiding contact with a surface outside of the shell and increase the resistance of the liquid marble to deformation forces. The encapsulated liquid volume displays a fine balance between the hydrophobic interactions between the liquid and particles and the attractive particle-particle interactions. The particle-liquid core interaction is not the primary attribute to the liquid marble's integrity, rather it is speculated that the hydrophobic effect that forces the hydrophobic particles to aggregate on water surface is the dominating factor in keeping the integrity of the liquid marble. (C) 2010 Elsevier B.V. All rights reserved.