Manipulation of the Floating Liquid Marble

Abstract

The liquid marble is a small liquid droplet coated with a thin layer of hydrophobic powder. This seemingly simple object challenges our state-of-the-art knowledge in physics, surface sciences and microfluidics. As such, liquid marbles have been the subject of numerous research works throughout the past two decades. A liquid marble consists of two components, namely the liquid content and the marble coating. The liquid content is usually an aqueous solution, whereas the coating consists of various types of fine hydrophobic powder. The porous powder coating traps air and physically isolates the liquid content from its surroundings. A liquid marble behaves like a soft solid due to the unique combination of a liquid content and a flexible solid shell. These features allow a liquid marble to transport small volumes of liquid with virtually zero loss and even to float on a carrier liquid. Recent advances in liquid marble research have provided various manipulation techniques with a wide range of applications. One of the most prominent recent applications is the three-dimensional (3D) cell culture within a liquid marble. The liquid marble presents a simple, flexible and economic means for culturing 3D tissues such as spheroids. The ability to float increases the effective lifespan and mobility of a liquid marble. On the other hand, the marble coating has been undergoing major improvements thanks to continuous engineering efforts. Recent advances allow for new manipulation techniques and further enhance the application potential of liquid marbles.