Langmuir 2011, 27, 7–10 Janus droplets: liquid marbles coated with dielectric/semiconductor particles. Edward Bormashenko 1 , Yelena Bormashenko 1 , Roman Pogreb 1 , Oleg Gendelman 2 1 Ariel University Center of Samaria, The Research Institute, Applied Physics Department, Department of Chemistry and Biotechnology Engineering, POB 3, Ariel, 40700, Israel 2 Faculty of Mechanical Engineering, Technion – Israel Institute of Technology, Haifa, 32000, Israel Abstract Manufacturing of water droplets wrapped by two different powders, carbon black (semiconductor) and polytetrafluoroethylene (dielectric) is presented. Droplets built of two hemispheres (Janus droplets) characterized by various physical and chemical properties are reported first. Watermelon-like striped liquid marbles are reported. Janus droplets remained stable on solid and liquid supports. Janus droplets could be activated with an electric field. 1. Introduction. Janus particles have been subjected to intensive research during the last decade. 1-6 The notion "Janus" is used for the description of particles whose surfaces of both hemispheres are different from a chemical point of view. De Gennes coined the term "Janus" for such particles in his Nobel lecture. 7 By combining a hydrophilic hemisphere with a hydrophobic one, amphiphilic Janus particles could be useful for the stabilization of water-in-oil or oil-in-water emulsions. 8 Janus particles have been used for the development of dual-functionalized optical, electronic, and sensor devices. 9-10 Janus particles are usually nano- or micrometrically scaled solid beads. Our letter introduces Janus droplets coated partially by hydrophobic and partially by hydrophilic particles. The Janus droplets presented here are based on so-called liquid marbles. Liquid marbles are droplets enwrapped by hydrophobic or hydrophilic particles. 11-34 Liquid marbles are characterized by extremely low friction between the droplet and solid support, which is due to air pockets separating the marbles from the substrate. 11-13, 28, 35 Various applications of liquid marbles have been reported including gas sensing, revealing water pollution and micro- and ferrofluidic devices, micro-reactors, micro-pumps, etc. 21, 22, 24, 26, 36 In our letter we introduce marbles built