Janus particles are colloids with two different spatial domains. When these domains are synthesized with a contrast in wettability the particle shows an enhanced interfacial activity in comparison with the corresponding homogeneous particles. There are different synthesis routes to fabricate such particles. One of the most common is to start with a homogeneous particle and functionalize just one hemisphere of the particle or form the particle directly with two compartments, the so-called true Janus particles. Other particles which rely on the phase separation during synthesis are rather considered Janus-like particles. The Langmuir balance and the pendant drop tensiometry are useful to characterize the interfacial activity of the Janus and homogeneous particles at liquid interfaces.

This work was supported by MINECO MAT 2016-78778-R, MAT2014-60615R, MAT 2013-44429-R, and PCIN 2015-051 projects (MINECO and FEDER, Spain), by “Junta de Andalucía” and FEDER (projects P10-FQM-5977 and P12-FQM-1443). M. A. F. R. acknowledges financial support from the Swiss Government Excellence Postdoc Scholarship 2016.0246.