It is shown that, in general, when submicrometer hybrid particles of polymer@silica are subjected to thermal treatment, phase-separated hydrophobicity emerges at particles surface; and that the triggering of hydrophobicity results in particles which show amphiphilic behavior, arranging themselves at water interfaces and stabilizing W/O and O/W emulsions. Many polymer@silica particles show this behavior, and the entrapped polymers include polyethylene Engage, poly(dimethylsiloxane), poly-L-lactic acid, poly(ethylene-block-ethyleneglycol), poly(styrene-co-allyl-achohol), and poly(dimethylesiloxane-block-ethyleneoxide-co-propyleneoxide). The concept is attractive because, by doping the particles with functional molecules, one can get various surfactants from the same treated particle; this is demonstrated with fluorescent probes. It is proposed that the amphiphilic activity is due to Janus heterogeneous distribution of the hydrophobic moieties on the surface.