Surfactants (e.g., fluorosurfactants) for stabilizing aqueous or
hydrocarbon droplets in a fluorophilic continuous phase are presented. In
some embodiments, fluorosurfactants include a fluorophilic tail soluble
in a fluorophilic (e.g., fluorocarbon) continuous phase, and a headgroup
soluble in either an aqueous phase or a lipophilic (e.g., hydrocarbon)
phase. The combination of a fluorophilic tail and a headgroup may be
chosen so as to create a surfactant with a suitable geometry for forming
stabilized reverse emulsion droplets having a disperse aqueous or
lipophilic phase in a continuous, fluorophilic phase. In some
embodiments, the headgroup is preferably non-ionic and can prevent or
limit the adsorption of molecules at the interface between the surfactant
and the discontinuous phase. This configuration can allow the droplet to
serve, for example, as a reaction site for certain chemical and/or
biological reactions. In another embodiment, aqueous droplets are
stabilized in a fluorocarbon phase at least in part by the electrostatic
attraction of two oppositely charged or polar components, one of which is
at least partially soluble in the dispersed phase, the other at least
partially soluble in the continuous phase. One component may provide
collodial stability of the emulsion, and the other may prevent the
adsorption of biomolecules at the interface between a component and the
discontinous phase. Advantageously, surfactants and surfactant
combinations of the invention may provide sufficient stabilization
against coalescence of droplets, without interfering with processes that
can be carried out inside the droplets.