Janus Particles in a Nonpolar Solvent

Amphiphilic Janus particles are currently receiving great attention as "solid surfactants". Previous studies have introduced such particles with a variety of shapes and functions, but there has so far been a strong emphasis on water-dispersible particles that mimic the molecular surfactants soluble in polar solvents. Here we present an example of lipophilic Janus particles which are selectively dispersible in very nonpolar solvents such as alkanes. Interfacial tension measurements between the alkane dispersions and pure water indicate that these particles do have interfacial activity, and like typical hydrophobic, nonionic surfactants, they do not partition to the aqueous bulk. We also show that the oil-borne particles, by retaining locally polar domains where charges can reside, generate electric conductivity in nonpolar liquids-another feature familiar from molecular surfactants and one commonly exploited to mitigate explosion hazards due to flow electrification during petroleum pumping and in the formulation of electronic inks.