The behavior of Janus particles fabricated from core silica particles decorated with gold nanoparticles on one hemisphere is studied at the air/water interface. An unexpected reduction in the effective surface tension is observed in the presence of these chemically-modified Janus particles. Experiments on the interfacial behavior of a variety of control particles, including the physically-modified Janus particles made from the same core silica particles coated with a thin gold layer, do not exhibit significant surface tension effects. We hypothesize that the chemical modification of particles in form of a Janus structure is needed to alter the surface tension and attribute the surfactant-like behavior of these particles to the presence of immersion forces. (C) 2019 Elsevier Inc. All rights reserved.