The lifetime of floating liquid marbles: the influence of particle size and effective surface tension

Abstract

In this study, we investigated the factors affecting the lifetime of liquid marbles placed on a glass surface and floating on water. It was found that the particle size, surface free energy and hydrophobicity of the encapsulating microparticles determine the effective surface tension and lifetime of a liquid marble floating on water. We formed liquid marbles using ultra-hydrophobic poly(perfluoroalkyl ethyl acrylate) powder with three different particle sizes (8 ± 1, 20 ± 2 and 60 ± 5 μm) and polytetrafluoroethylene powder (7 ± 2 μm). It was found that both the effective surface tension and lifetime of a floating liquid marble increased considerably with the decrease in the particle size of the ultra-hydrophobic poly(perfluoroalkyl ethyl acrylate) powder. We also determined that a floating liquid marble had a longer lifetime if the water contact angle of the polymer powder was high and its surface free energy was low by comparing the results of two different powders having very close average particle sizes but different hydrophobicities.