A liquid marble is a small liquid droplet with a diameter of several mm, for which the surface is covered by hydrophobic nano- (or micro-) particles. This coverage by hydrophobic particles decreases the apparent surface tension of the liquid, and it allows the liquid to keep a spherical shape on any substrate. Liquid marbles shows many unique characteristics such as smooth movement on any substrate without any leakage of liquid. Many researchers have focused on the understanding of their unique physical properties as well as the demonstration of potential applications. Here we discuss the formation mechanism and physical characterization of this unique colloidal material. From the interpretation based on the surface chemistry and the direct observation using X-ray computed tomography, we shed light on the formation mechanism of liquid marbles, and the design of functional liquid marbles. Additionally, we introduce the wrapping of liquid droplet by using poly(lactic acid) particles, robust liquid marbles using inorganic nanotubes, and monolayer particle coating with monodisperse polymer particles.
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